transitional fossils

Fossil tracks push back the invasion of land by 18 million years

edyong — Wed, 06 Jan 2010 12:00:37 +0000

Fossil tracks push back the invasion of land by 18 million years

Around 395 million years ago, a group of four-legged animals strode across a Polish coast. These large, amphibious creatures were among the first invaders of the land, the first animals with true legs that could walk across solid ground. With sprawling gaits and tails held high, they took pioneering footsteps. Their tracks eventually fossilised and their recent discovery yields a big surprise that could rewrite what we know about the invasion of land. These animals were walking around 18 million years earlier than expected.

The evolution of four-legged creatures - tetrapods - is one of the most evocative in life's history. It has been illustrated by a series of beautiful fossils that vividly show the transition from swimming with fins to walking on legs. These include Panderichthys, a fish with a large tetrapod-like head and a muscular pair of front fins. Tiktaalik expanded on these themes. Its head could turn about a solid neck. Its limbs had the fin rays of its fishy predecessors but clear wrist bones and basic fingers too. Tiktaalik could support itself on strong shoulder bones, bend its fins at the wrists, and splay out its hand-like bones.

These animals - the elpistostegids - have largely been seen as transitional fossils. Tetrapods supposedly evolved from these intermediate forms and eventually replaced them. You could draw all of their skeletons in the corner of a book and flick the pages to see the move from sea to land happen before your eyes. But the new fossil tracks tell a very different story. As one reviewer writes, they "lob a grenade into that picture".

The earliest true tetrapods so far discovered were around 375 million years old and the earliest elpistostegids hail from around 386 million years ago. But the Polish tracks are 10 million years older still. These dates suggest that the elpistostegids weren't transitional forms at all. They weren't early adopters of new biological technology, but late-surviving relics that stayed in their fish-like state while other species had evolved new bodies and, quite literally, run with them. Per Ahlberg, who led the study, says, "I've been working on the origin of tetrapods for about 25 years, and this is the biggest discovery I have ever been involved in. It is enomously exciting."

It would be tempting to cast animals like Pandericthys or Tiktaalik in the role of biological luddites, outstaying their welcome with outmoded bodies. But that would be an injustice. If these animals co-existed with tetrapods for at least 10 million years, it suggests that their bodies were stable, well-adapted structures in their own right. They weren't just brief flirtations with sturdiness on the way to full-blown walking.

Ahlberg discovered the fossil tracks along with researchers from Warsaw University, led by Grzegorz Niedzwiedzki. The tracks are found in the disused Zachelmie Quarry, nestled among Poland's Holy Cross Mountains. The area used to be part of a tidal plain. Rocks from the site and a few rare fossils allowed the team to confidently date the track-ridden layer to around 395 million years ago, the middle of the Devonian period.

Among this layer, Niedzwiedzki found several tracks of different shapes and sizes. He also found several isolated handprints and footprints that clearly show signs of toes and ankles. Many of these tracks (such as in the diagram at the top) were clearly made by an animal walking with powerful, diagonal strides, powered by sprawling right-angled limbs.

They weren't the work of any elpistostegid, whose straight limbs and backward-pointing shoulders and hips would have created far narrower tracks. Elpistostegids would also have dug long central troughs as they laboriously dragged themselves along. No such troughs exist at the quarry. This tells us that the track-makers strode along using strong hips and shoulders to hold their bodies and tails off the ground.

Niedzwiedzki thinks that they were undoubtedly tetrapods, and big ones too. The animal that created the tracks above was just 40-50 cm long. But some of the footprints were 15cm wide and hinted at creatures that were around 2.5 metres in length. The largest print is 26cm wide and its maker was probably a giant.

The implications of the Polish tracks are so controversial that reactions from other palaeontologists have been, understandably, mixed. Ted Daeschler and Neil Shubin, who discovered Tiktaalik, both find the study intriguing, but not definitive.

For Shubin, the deal-breaker would be identifying the animals that made the trackways and establishing where they sit on the evolutionary tree. He says, "The skeletal anatomy, let alone evolutionary relationships, of a trackmaker is hard to interpret from a track or print." For example, he says that a model of Tiktaalik's skeleton would produce a print much like the one in the paper if it's mushed into sand, and different consistencies or angles would produce an even closer match. He adds, "There is nothing in Tiktaalik's described anatomy that suggests it didn't have a stride."

Daeschler agrees that "trace fossils such as these presumed tracks... are a notoriously difficult class of evidence to interpret with full confidence". Nonetheless, he's keeping an open mind and a keen eye on future developments. "Paleontology is a lively field in which new discoveries constantly refine our knowledge of the history of life on earth," he says.

Jenny Clack, the Cambridge scientist who discovered Acanthostega, has seen the Polish tracks for herself and finds them more convincing. Her only reservation is that the detailed prints don't have any trackways to show how their maker moved, while the trackways themselves consist of blobs. "But so do lots of previously known tracks," she says. "If you'd found those in other deposits in the last part of the Devonian, you wouldn't have any qualms about them." She'd like to see trackways of the detailed prints but she's nonetheless excited. "It's going to change all our ideas about why tetrapods emerged from the water, as well as when and where."

On the question of where, many scientists have suggested that the invasion of land began at the margins of freshwater - at river banks, deltas, lakes or flooded forests. But the Zachelmire quarry wasn't any of these. Most likely, it was a shallow tidal flat or perhaps a saltwater lagoon. The first tetrapods didn't lurk in rivers, but trampled the mud of coral-reef lagoons.

Niedzwiedzki thinks that this revised locale makes a better staging ground for the invasion of land. Twice a day, the zone between high and low tide is awash with stranded marine animals that would provide a feast for marine creatures experimenting with life on land. He argues that life was driven aground by the rich availability of snacks.

This new setting for the rise of the tetrapods also helps to answer a big question raised by the tracks. If tetrapods were walking around 18 million years earlier than we thought, they and the elpistostgids must have large "ghost lineages" - periods when they must have existed but for which no fossils have been found. Actually, very few fossils have been found at Zachelmie Quarry at all. These sites, where tetrapods first marched onto land, may have been good at preserving footprints, but they haven't been equally kind to bones.

But why do the fossils that have been found make it look a lot like the elpistostegids preceded the tetrapods? That's more of a stumper, but Niedzwiedzki has a possible answer. He thinks that elpistostegids may have colonised new environments before their tetrapod peers (or at least those environments that would preserve their bones). It's a nice hypothesis, but for the moment, it's just that. There's no clear answer, although the hunt for new fossils or tracks will hopefully provide one.

Clack is certainly excited by the new doors opened by this discovery. "People are now going to start looking in different places from where they traditionally looked," she says. "The Polish trackways were only discovered by accident. Nobody had ever looked at these Devonian deposits in detail before. Now the same team are starting to look for body fossils and they've started to find some, but no tetrapods yet. I'm expecting stuff to come out from other parts of the world too, like China."

And here, even the sceptics agree. "All scenarios are intruiging, but we simply do not know for sure," says Shubin. "All the more excuse to continue to go out in the field and find skeletons!"

Reference: Niedzwiedzki. 2009. Tetrapod trackways from the early Middle Devonian period of Poland. Nature doi:10.1038/nature08623

All images: copyright of Nature

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edyong Wed, 01/06/2010 - 07:00

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Ed,

You say :

1. "This tells us that the track-makers strode along using strong hips and shoulders to hold their bodies and tails off the ground."

and then later you say...

2. "Niedzwiedzki thinks that this revised locale makes a better staging ground for the invasion of land."

Surely, if the first statement is true then the creature that made these tracks wasn't invading the land - it was already master of it?

Is it sure that these rocks are of terrestrial origin? Also, I am almost certain that the first invaders of the land were bacteria, fungi or algae.

I too found the title of "invasion of land" misleading, thinking instead of animal invasion of land by insects.

As for the fossils, like Shubin, I am not convinced but it's a highly facinating topic and I await more evidence and new fossils.

Every time you see "invasion of the land", the words "by vertebrates" are behind it in small, white letters. Oh okay, I'll take the criticism. I did think about insects and I remember correcting the text to this effect somewhere, but clearly not everywhere or in the headline. Nuts.

The phrase "invasion of the land" always makes me think of this.

Finally, mainstream support for Henderson's hypothesis that Acanthostega and Ichthyostega were the secondarily aquatic descendants of earlier, more terrestrial tetrapods...

Henderson, D. M. 1999. Late Devonian amphibians as secondarily aquatic tetrapods. In Hoch, E. & Brantsen, A. K. (eds) Secondary Adaptation to Life in Water. University of Copenhagen, p. 18.

I wonder if people who work in this area are used to considering rich habitats that existed then but have since been eliminated by seabirds.

I'm not very excited. For some reason it reminds me of the early Triassic "bird" track ways of Santo Domingo formation. Not that it would necessarily be something like that, though.

And, again an analogy with dinosaur-bird evolution, I think it's not quite right to say that the species previously thought as transitional forms are "not transitional forms at all", but, as the text implies, it may be just like the so-called "temporal paradox" for the origin of birds (i.e.: "Deinonychus only appearing much later, 35 million years later, in the fossil record than Archaeopteryx"), which is not a real paradox at all, but the same underlying logic of the answer of "why there are still monkeys".

The only thing they may not be are transitional forms in the most strict sense of a phyletic gradualist fashion, with newer forms appearing and completely replacing some earlier form in the same adaptive "trend", and also neatly disappearing and giving space to the new and more advanced, all pretty and linearly, all the time.

For those of you who haven't already seen it, the Nature webpage has a video about the find:

http://www.nature.com/nature/videoarchive/tetrapods/index.html

Can one name a species from fossil tracks alone?

Species named from fossil tracks or other trace fossils are known as ichnospecies. Similarly genera known only from trace fossils are called ichnogenera, see http://en.wikipedia.org/wiki/Trace_fossil#Common_ichnogenera.

I find the whole business a little unreliable, because for most extant species there is no way congeners could be separated only from tracks. Then again, some paleontologist have weird practices in delimiting species...

Is there a reason for supposing that vertebrates colonized land only once? The idea of Tiktaalik et al being relics implies that they had a common land vertebrate ancestor with the maker of these tracks. Could it be that Tiktaalik and its ilk were simply a later group of land vertebrates? It seems logical to me that many groups of Ray-finned fish would've been preadapted to colonizing land

It would be quite easy for those (and there are few) that are well versed enough in the art and science of tracking to determine species from a track alone. Especially a track that has not been seen before that is fossilized in bedrock.

I second Darren Naish's post. I have never been comfortable with the idea that tetrapod limbs with digits evolved for walking underwater, which is my understanding of the current thinking in the field based on fossils like Acanthostega and Ichthyostega. This earlier fossil of a competently terrestrial tetrapod that predates those species does lend support to the idea that those forms were secondarily aquatic descendants of more terrestrial tetrapods. This may mean that tetrapod limbs did evolve for walking on land, rather than being a preadaptation that originally developed in the water for walking underwater.

The nomenclature of animals is kept strictly separate from that of their tracks. Ichnospecies can be named from tracks â species can't. :-)

I second Darren Naish's post.

On his own blog (click on his name), he said he was not completely serious. After all, why do both Acanthostega and Ichthyostega retain functional internal gills, tail fins (dragging the lower lobe across hard ground would lead to constant bleeding at the very least), the inability to put their feet on the ground and thus to walk (Ichthyostega could have moved on land like a seal, Acanthostega with its thin bonesâ¦ hard to imagine it was more terrestrial than a catfish), and so onâ¦

Is there a reason for supposing that vertebrates colonized land only once?

Yes â all land vertebrates share a common ancestor exclusive of all other vertebrates.

It would be quite easy for those (and there are few) that are well versed enough in the art and science of tracking to determine species from a track alone.

This rock was very soft mud before the limestone hardened between the microscopic grains. No clear footprints can be left in such stuff.

the idea that tetrapod limbs with digits evolved for walking underwater

No, for moving through thick vegetation, and for sneaking up on prey without moving the tail fin and thus moving so much water that the prey notices.

We can't say whether vertebrates colonized land more than once, but we can say that only one lineage left good fossils that we have found. You might take that to mean the other colonists were failures, but luck has a bigger role in evolutionary (as in all) success than we like to think.

Calling the earliest walkers "terrestrial" may be overstating the case. Today, tidal mud flats are a terribly hazardous environment that demands obsessive burrowing, but wouldn't have been at the time.

I should have written "limbed vertebrates" instead of "land vertebrates". It's not clear how terrestrial certain extinct limbed vertebrates were.

David,
Thanks for replying to my post. Perhaps secondarily aquatic was not a good term to use, I was influenced by Darren Naish's sarcasm and my tremendous respect for him influenced my post. I have read Clack's book and understand the theory of limbs evolving for moving through thick vegetation (although some of the frog-fish used as examples don't use their "limbs" for moving through vegetation). My point is that the current thinking is that limbs evolved on animals that were fully aquatic.
I would imagine that the animal that made these tracks would likely have internal gills and tail fin(s)and was amphibious or even primarily aquatic but evolved and used its limbs for walking on land. I think this find opens the door for the possibility that earliest limbed tetrapods did not have the anatomical contraints that Acanthostega et. al. had on terrestrial living. There are fish today ("walking" catfish, "walking" anabantids, and mudskippers) that have internal gills and fins yet still drag themselves around on land. It does not seem hard to believe that Acanthostega and Ichthyostega had ancestors that were more competent on land than they were, and that limbs did evolve for walking on land, and that these later forms resumed a more aquatic lifestyle than their ancestors. A major point made around Tiktaaliks discovery is that it's forelimb anatomy allowed it to do a "push-up." I don't see how that fits into the "limbs evolved for walking underwater (through aquatic vegetation or not) theory."
Damn that Darren, always so sarcastic! Where did he comment on this story in his blog?

Ok David, I found Darren Naish's comment buried in the toad thread. I was hoping for a full post by Darren Naish on the subject but know that it is unlikely since the subject is being covered by so many others.

Is there any way to tell whether the earliest leggy things found lived in fresh or salt water? Those would seem to correspond to very different sorts of origins. I'm presuming the seas were already pretty salty by that point, but maybe they weren't, yet; somebody must know.

Is there any way to tell whether the earliest leggy things found lived in fresh or salt water?

In short, no. I mean, you can tell for a specific fossil (for example, I think these track-makers are the first marine examples of fishapods known), but until we know which fossils are "the earliest" that's not much help. There is no obvious phlogenetic/physiological signal in our current knowledge, if that's what you're asking. They might have even been estuarine or anadronous or something.

Yes â all land vertebrates share a common ancestor exclusive of all other vertebrates.

I understand that, but my question was, couldn't it be possible that the LCA of all current tetrapods was aquatic, but that the only surviving lineages are terrestrial (or secondarily aquatic) That is, that 400 million years ago or so, there was a wide range of shallow-water lobe-finned fish. Several of these lineages could've come on to land and radiated, but the lineages that remained aquatic died out, save for the coelecanths and lungfish. Or that all but one of those terrestrial lineages died out, outcompeted by our clade.

I think I see what Christina is getting at. If "our" common ancestor was obligately aquatic, then its various descendants could have colonized land more than once, each becoming terrestrial in its own way, more or less convergently. My only qualm about this scenario is that definitions of "aquatic" and "terrestrial" get (as it were) muddy at that interface.

Raptorex shows that T.rex body plan evolved at 100th the size

edyong — Thu, 17 Sep 2009 12:00:03 +0000

Raptorex shows that T.rex body plan evolved at 100th the size

Meet Raptorex, the "king of thieves". It's a new species of dinosaur that looks, for all intents and purposesÂ¸ like the mighty Tyrannosaurus rex, complete with large, powerful skull and tiny, comical forearms. But there's one very important difference - it's 100 times smaller. Unlike the ever-shrinking world of music players and phones, it seems that evolution crafted tyrannosaur technology with much smaller specifications before enlarging the design into the giant predators of the late Cretaceous.

Raptorex is a new species of meat-eating dinosaur, discovered in northwest China by Paul Sereno from the University of Chicago. The specimen is a young adult, but it wouldn't have grown to more than 3 metres in length. It stood about as tall as a human, and wouldn't have weighed much more. And yet Raptorex looked very much like a scaled-down version of its giant future relatives. All the features that made tyrannosaurs so recognisable and such efficient killers (except their enormous size) were present in this animal.

It really is a beautiful transitional fossil. As Sereno says, "Raptorex really is a pivotal moment in the history of the group where most of the biologically meaningful features of tyrannosaurs came into being, and the surprising thing is that they came into being in such a small animal." Raptorex clearly shows that natural selection initially honed the distinct body shape of these giant predators at a 1/100^th scale. This design was then scaled up with remarkably few modifications.

It had a skull that had clearly been developed into the animal's primary weapon. It was unusually big for its body size (40% of its torso length), it was structurally reinforced against the stresses of heavy bites, it had large places where powerful jaw-closing muscles attached and it was armed with sharp teeth.

Its limbs also had classic T.rex proportions - strong hind legs that that were fit for running, but miniscule forearms. In contrast, other early tyrannosaurids, such as Guanlong, Dilong, Eotyrannus and Stokesosaurus, looked very different with arms that were long and useful, and proportionally smaller heads (just 30% of its torso length). Only a few distinctive parts of their skeleton mark them out as early tyrannosaurids.

Raptorex brain was also large for its size. For comparison, the Jurassic predator Allosaurus had a brain that was just 60% bigger, despite having a body that was 10 times heavier! Raptorex's sense of smell was particularly well-developed, just as Tyrannosaurus's was. A scan of its skull showed a large area for its olfactory bulbs - the parts of its brain devoted to smell. These bulbs take up a full 20% of the brain's total volume, a proportion that exceeds that of all meat-eating dinosaurs except the giant tyrannosaurs.

Despite what many newspapers will assuredly tell you, Raptorex isn't the ancestor of Tyrannosaurus although it probably looked very much like what this hypothetical animal would have done. It's more like an early cousin, but one that's clearly more closely related to T.rex and its giant kin than any of the other smaller species so far discovered.

Based on his new fossil, Sereno tells a three-act story of tyrannosaur evolution. Act One was set in the Jurassic and early Cretaceous periods, with a cast that included Eotyrannus and Dilong. Their snouts had become stronger and their jaws more powerful, but they were typical of other predators of the time. It was only during Act Two, around 125 million years ago, that this dynasty of predators started to become truly specialised, enhancing the skull, lengthening the legs, and shrinking the forearms.

All of these features were present in Raptorex, setting the stage of the final act in tyrannosaur evolution - getting really big. The lineage grew in bulk by around 100 times. By the end of the Cretaceous, the meat-eating scene in the northern continents was dominated by tyrannosaurids - predators such as Albertasaurus, Gorgosaurus, Daspletosaurus and Tarvosaurus, each weighing in at 2.5 tons or more.

It would be fascinating to see if the same story could be told for other lineages of predators, if the abelisaurids, carcharodontosaurids and spinosaurids all had their own mini-prototypes.

Reference: Science 10.1126/science.1177428

Images: Reconstruction by Todd Marshall; other images from Science/AAAS

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edyong Thu, 09/17/2009 - 08:00

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Very nice work, Ed! This is the kind of thing that reminds me why I love paleontology.

Just one minor quibble. You wrote that Raptorex was "discovered in northwest China by Paul Sereno from the University of Chicago." As Sereno says in the video interview, though, the fossil was dug up by a local person and sold to a private collector. That collector then contacted Sereno, who was able to convince the owner to donate the skeleton to science. Scary as it is to think about, Raptorex could have remained in private hands for a long time had its owner not felt as generous.

I'm having trouble seeing where this "100 times smaller" figure comes from. For most comparisons, we use length. This might be comparing volume or mass, which exaggerates such differences by a power of three.

1 picogram hummingbird genome, 100 picogram salamander genome weight.

To answer Nathan's question: yes, we are using mass as a comparison. Raptorex was about 60 kg, some estimates of Tyrannosaurus mass are 6000 kg. In terms of length, Raptorex is about 1/4 or 1/5 the length of T. rex. Mass is the most important comparison here, since we are talking about the evolution of various skeletal features in relation to colossal body size.

Steve Brusatte

Nitpick: If mass is what's being referred to by "size", why not just change the title to say "100th the mass"? And instead of "100 times smaller", "100 times less massive"?

-- A humble pedant for clarity and precision in scientific language

Steve: I'm sorry to say that smacks of special pleading. You could say the same of almost any comparison of the size of taxa, except where you were comparing reach. By my lights, all such comparisons should be by mass, but that's not the way it's done, which makes it misleading in this case.

Could you be more explicit, Nathan?

Thanks!

"That's not the way its done"? Hah? That IS the way its done. See this nice refereed paper in one of the biggest journals. After searching on "Size differences animals" and looking at the books in the results shows that mass is often used as the criterion.

Can you visualize Jesus playing with one of these killing machines?

Land shark comes to mind.

Bill Parker and Nick Gardner sent me the paper. Wonderful animal, and a real surprise, too. I'm surprised that there's such a large morphological gap between Raptorex and Dilong/Guanlong. I wish the paper included photos of the fossil in situ, though. This was a 3D fossil, right?

"Raptorex"???
are you joking?

I wonder which/how many dino fossils have been used to identify these shared derived (ancestral modified) characters in the 3 act story of ryrannosaur evolution.
franÃ§oise

I wonder which/how many reptile fossils have been used as a comparison to identify these shared derived (ancestral modified) characters in the 3 act story of tyrannosaurus evolution
franÃ§oise

I wonder which/how many fossil(s) have been used as an external comparison to identify these shared derived (ancestral modified) characters in the 3 act story of tyrannosaur evolution.
franÃ§oise

So... what's up with the ridiculous hairdo? (Of the Raptorex, not Serano :))

So what does this do to the arguement that TREX was a scavenger ? Part of the arguement was the huge olfactory bulbs and also the size of trex made him able to drive on other predators. So we now have this small one that must have hunted ?

The weight of T rex is greatly exaggerated - depends on its skull, it weighed some - tonnes.
What is more important from an evolutionary point of view is that tyrannosaurs are quite primitive theropods, they still have amphicoelous dorsals. The thing is, once opisthocoely is evolved, it never turns back to amphicoely. Something that cladistics is impossible to solve. So Torvosaurus et al were more derived theropods.
I do not understand why people bother with questions whether T rex was a scavenger or not when it is impossible to answer...

Peter Mihalda

Some error appeared - I meant 1,5 - 2 tonnes.

Peter Mihalda

Darwinius changes everything

edyong — Wed, 20 May 2009 06:00:43 +0000

Darwinius changes everything

Yesterday, the entire world changed noticeably as the media, accompanied by some scientists, unveiled a stunning fossilised primate. The creature has been named Darwinius masillae, but also goes by Ida, the Link, the Chosen One and She Who Will Save Us All.

The new fossil is remarkably complete and well-preserved, although the media glossed over these facts in favour of the creature's ability to cure swine flu. Ida was hailed as a "missing link" in human evolution, beautifully illustrating our transition from leaping about in trees to rampant mass-media sensationalism.

Speaking to a group of international reporters, the scientists who discovered Ida described the animal in painstaking detail to the sound of Wagner's Ride of the Valkyries played from 50-foot speakers. As a barrage of fireworks launched in the background, one journalist said, "The release of 30 doves just at the right moment really helped to drive home the unique paleoecological perspective that Ida provides."

Evolutionary biologist Stephen Wilton added, "Ida has been waiting for us for 47 million years so I'm grateful that the publication of the paper wasn't rushed and that the whole thing didn't turn into some sort of media circus. You never know when that might happen."

Businesses around the world are also hoping that demand for Ida merchandise will stimulate an ailing global economy out of recession. Retailer Bud Hornblower said, "We're seeing a massive spike in demand for fainting couches as ordinary lay people fail to cope with the total change brought on by this small, weird-lookin' monkey thing."

Scientists and people who actually know a thing or two about evolution warned of hype and exaggeration but were forced to abandon their reason and critical analysis in the face of incontrovertible speculation that Ida could convert base metals into gold and has already led to the invention of flying cars.

"I didn't believe it at first," said Professor Adam Templesmith from the University of Slough. "When I read the press release about a fossil that would change everything, I naturally assumed that it was some sort of poorly conceived and overly exaggerated PR claim. But now that the total reversal of climate change is underway, I'm forced to reconsider my prejudices."

Already the star of her own website, book and documentary, little Ida will soon have her own action figure, underwear range, three-album deal and seat in Parliament. "Ida's brand is a hot as Obama's right now," said Don Chumleigh, market analyst. "I'm just sad that her fossilised hand isn't doing that fist-bump thing."

Recreated through CGI, Ida is also set to play a pivotal role in the climax of the new Harry Potter film, where she will be voiced by Keira Knightley and wield a powerful 'Changus Totalus' spell. Special effects will also be used to insert Ida into previous seasons of the Wire and past G8 summits.

Around the world, signs that everything has changed have already begun to appear. Jeanette Gould from Stoke-on-Trent was shocked to discover the outline of Darwinius emblazoned on her morning toast. "Well, it ruined breakfast," said Ms Gould, failing to appreciate the detail of the creature's stomach contents outlined in bread crumbs. "I couldn't very well spread raspberry jam over the direct ancestor of my children, could I?"

For actual details about Ida, look no further than excellent takes from Brian Switek, PZ and Carl Zimmer. Brian in particular has serious reservations about the paper itself. I'm too weary to tackle it.

edyong Wed, 05/20/2009 - 02:00

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Not Exactly Rocket Satire

You failed to mention that it is the Primate Who Lived.

Thanks, Ed! This is quite a thorough send-up.

That was utterly awesome. You've just got yourself a new reader.

It's that damn Ida! She's so hot right now!

I just can't make up my mind: Should Ida toast be served with Jesus toast or Blessed Virgin Toast? (One doesn't want to make a mistake with holy breakfast manifestations.)

Nicely written - but what would newspapers and journalists do if they didn't sensationalize everything?

One Darwinius masillae to rule them all,
One Darwinius to find them.
One Darwinius to bring them all
And in the P.R. bind them.

"Well, it ruined breakfast," said Ms Gould, failing to appreciate the detail of the creature's stomach contents outlined in bread crumbs. "I couldn't very well spread raspberry jam over the direct ancestor of my children, could I?"

Ms Gould is mistaken; Ida died much too young to have borne offspring, so there can be no possible direct line from Ida to Ms Gould's sprogs.
Oh, and John... isn't it rather the Primate Who Died?
Martin

Lucky I wasn't drinking anything. ;p

"incontrovertible speculation"

Brilliant!

As an astrophysicist, I am furious that you forgot to mention that Ida also proves (finally! for the 20th time) the existence of black holes.

Mr Yong, this was the first time I've heard of you (thanks to link from PZ Myers).

That piece ranks up there with Mark Twain and H. L. Mencken. Thank you!

I think I'll name my daughter Ida. Heck, I'll rename all my kids Ida!

LOL

Excellent, with this post you'll be the toast of the science blogging commenity!

OK, you can shoot me now:-(

#1 and #8: Considering what happened, it should be The Primate Who Couldn't.

Awesome write-up. and... notice Google's image today!!

Ida cured my herpes and regrew my amputated leg! She's a miracle, and clearly beyond the scope of mere science. She's a veritable sphinx, the gatekeeper of another realm, bigger and more fantastic than this life, where people live forever in bliss and children frolic in butterscotch waterfalls.

Ok, I want my Ida underwear!! Awesome stuff, Ed. :)

Look at me way down here!

You wouldn't be auditioning for your favourite news source would you?

Great post Ed, from someone who didn't just get here from a PZ link. And you Myerites don't mess the place up while you're here.

Amen Dennis. They are, for the most part, with one or two notable exceptions, a foul bunch.

Last night, Ida came to me in a dream. She told me to go forth into the woods and eat leaves and fruits, and to pick bugs off my spouse and eat them.

Great post. A complete skeleton with soft tissue remains from a 47 million year old mamal... naw, that would never sell. Better call it the Salvation of Darwin Kind.

Great post Ed, from someone who did just get here from a PZ link. I can assure you that this "Myerite" will not mess up the place. Despite Pete the well meaning fool/king of bizarre analogies Rooke's characterization, most of us are well behaved.

Pure gold, Ed! I came over as a visitor from PZ's, but the bookmark's duly installed, and I'll be a regular in future.

Oh thanks heaven I can finally sleep know.

Hah that was made of awesome Ed!

On All Hallows' Eve, when you look into a mirror and say Darwinius three times you gain a random superpower from a hero of the X-Man series.

Brilliant stuff Ed. The Ida on toast image is the icing on the cake!

I want my Ida action figure!

Hmmm, lots of new readers. See? Everything HAS changed!

/memo to self: write more satire...

/silently clapping in my seat

The ailing American auto industry has plans to unveil a revolutionary new vehicle dubbed the Ida, which they hope will reverse the slump in sales. The all-terrain Ida will be larger than the Hummer, get 15 miles per gallon, and will cost a mere $72,000. But it will have all-new "evolutionary" cupholders, "Hard Rock" suspension, "Raptor Claw" wheel covers, plus sporty feral-looking "Predator" headlights. It will also come in three "Thunder Lizard" color schemes originated by an award-winning Parisian designer.

PZ's blog sent me over here, and I was thinking, "oh probably someone warning us about Creationists or something." Funniest thing I've read in weeks. Now I can laugh whenever I see the History Channel adverts.

How long do you think it will take before nude pictures of Ida start showing up on USENET newsgroups? And is it true that Ida has been signed to appear on "Dancing with the Stars" next season?

She's dating Brad Pitt now, so I hear. Compared with her curing swine flu and changing planetary orbits, that really matters.

Glen D
http://tinyurl.com/6mb592

It's that damn Ida! She's so hot right now!

Ida...so hot right now...Ida.

This was Stephen Fry worthy drumming!!!
I can barely write through my tears of laughter.

I can't eve pick a quote it is ALL so inspired.

This text has my vote to be included in the next unmanned spaceship to go beyound the solar system.

I was going to blockquote some of my favourite bits of your blog post here, and then write things like '*snorts*' and '*chortle*' after each one, but then I realised I was going to end up blockquoting every single paragraph so I gave up.

OK, now you owe me a new keyboard.

Well done! Very enjoyable read.

Oh, before I forget: Pete Rooke, get stuffed.

Ida layed her fossilized hands on me and BAM I was cured of cystic fibrosis. Science bless Ida!

All in all an insightful, fact-filled post, putting the recent discovery into its proper perspective, but I'm afraid I must pick a small nit.

I was shocked to see that Ida's cameo appearance in the recent Star Trek movie passed completely unremarked.

Now, off to Pharyngula. I promise to take my mess with me. (Howdy, Pete.)

Amen Dennis. They are, for the most part, with one or two notable exceptions, a foul bunch.

Rooke, obviously, has never proven to be one of the exceptions.

Glen D
http://tinyurl.com/6mb592

I don't usually comment, but I'm so indescribably delighted that I have to express gratitude.

So... thank you! The influence this piece has had on me, is second only to Ida.

Lastly, I assume everyone has seen the homage paid by google?

Giggle. Nice one.

Another via PZ, but this time only because I hadn't reached your feed in my reader yet.

Oh and re: Pete cRooke, I echo Patricia's sentiment.

Awesome, Ed. Just frackin awesome.

That was hilarious. Thanks.

That post was made of Awesome. The Ida toast was just the icing on the cake.

Bravo Ed!! A post for posterity! Chuckling away here. --dan

Ahh..the Rapture is at hand and the Idites cometh.

Cheers Ed

Ida turned me into a newt!

I got better...

Brilliant! It made my day.

Hilarious! Do you, by any chance, also write for The Onion?

Muahahahaha.

So when will they discover the remains of Hera Agathon? Surely that will presage some truly miraculous shit (like, possibly, the mainstream media doing some decent science reporting for a change).

Oh, and I share the sentiments of Patricia @ #41 regarding both Ed's post and Mr Rooke.

Yes, but will Ida solve the economic crisis? Of course! As an evolutionary missing link she can travel through time and alter the course of human history so that it never happened.

(deep American movie voice)
"Ida IS the Creator!"

Does this mean that Fox will bring back Firefly?

(Bravo!)

Is it true that Jenny McCarthy complained today that remnants of Ida have been discovered in vaccines?

To say that Ida "Lived" is a little presumptive. Presumably with its Lemurical appearance it most likely had an arborial existence. So come on, would you like to have to eat berries and insects and sleep in a tree? What kind of life is that, you can hardly call that "Living"
Ida the missing link? She missed the bloody point i think!

Ida has even forced the ICZN to change their rules on nomenclature.

I wonder if I can get "revealing the link" to enter common parlance as the sci-comms equivalent of "jumping the shark" or "nuking the fridge". Hmmm...

Anyway, welcome all, loyal readers and incoming Pharyngulites alike. Everyone make yourselves comfy.

Looks like a plain old run-of-the-mill monkey to me.

I stumbled through the news today and this article came up. At the end of the first paragraph, you had me. I totally believed it. Why? Because it made sense that, after watching Ida's unveiling that I must have been listening too hard, cause I missed the real significance of the find?

But that caused me to read the entire article and I loved it. Now, after countless failed attempts, I was able to take a snake, put it in a roller coaster, and expected it to bake me a cake. Thanks Ida!

Best. Post. Ever.

AndyD, it's quite the opposite. Jenny McCarthy is claiming that Ida can CURE autism.

Pithy satire clad in stylish writing. This blog will certainly make my top ten.

About as good as it gets, fantastic find, bizarre story, hyperhype, smackdown, real science and hilarious satire.

This was great, Ed. You expressed what was annoying me with razzmatazz.

You got yourself a new reader.

If I may be so bold as to coin a new term: Paradolida.

"She Who Will Save Us All." Hmm. Was she found lying in the shadow of the statue on a time-traveling island with strange electromagnetic properties?

Puijila, the walking seal - a beautiful transitional fossil

edyong — Wed, 22 Apr 2009 11:00:10 +0000

Puijila, the walking seal - a beautiful transitional fossil

Seals and sea-lions gracefully careen through today's oceans with the help of legs that have become wide, flat flippers. But it was not always this way. Seals evolved from carnivorous ancestors that walked on land with sturdy legs; only later did these evolve into the flippers that the family is known for. Now, a beautifully new fossil called Puijila illustrates just what such early steps in seal evolution looked like. With four legs and a long tail, it must have resembled a large otter but it was, in fact, a walking seal.

Natalia Rybczynski unearthed the new animal at Devon Island, Canada and worked out that it must have swam through the waters of the Arctic circle around 20-24 million years ago. She named it Puijila darwini after an Inuit word referring to a young seal, and some obscure biologist. The skeleton has been beautifully preserved, with over 65% of the animal intact, including its limbs and most of its skull.

Puijila is a massive boon for biologists trying to understand the evolution of pinnipeds, the group that includes seals, sea lions and walruses. It's not itself a direct ancestor, having branched off the evolutionary path that led to modern pinnipeds. It did, however, retain many of the same features that a direct ancestor would have had. "Puijila is a transitional fossil," Rybczynski explains. "It gives us a glimpse of what the earliest stages of pinniped evolution looked like, before pinnipeds had flippers. And it suggests that in the land-to-sea transition, pinnipeds went through a freshwater phase."

This familiar group evolved from land-dwelling carnivores and their closest living relatives are the bears and the mustelids (otters, weasels, skunks and badgers). For other marine mammals like whales and dolphins, the fossil record has given us dramatic visuals for the gradual transformation from land-dweller to full-time swimmer. But for pinnipeds, that transition is much murkier because until now, the earliest known seal Enaliarctos already had a full set of true flippers. Puijila changes all of that.

In the Origin of ~~the~~ Species, the ever-prescient Darwin wrote, "A strictly terrestrial animal, by occasionally hunting for food in shallow water, then in streams or lakes, might at last be converted into an animal so thoroughly aquatic as to brave the open ocean''. This year, on the 150th anniversary of the book's publication, the walking seal that bears his name pays a fitting tribute to Darwin's insight.

Puijila was just over a metre in length and had a long tail. Its four legs were short but strong, and would have been attached to its trunk by powerful muscles. The bones of its toes were somewhat flattened, which strongly suggests that they were webbed. In many ways, its skeleton was very similar to a modern otter's but the shape of its skull and teeth mark it out as a seal.

As examples, its bottom jaw had four incisors rather than the standard six of other carnivores. And it had a large "infraorbital foramen" - a hole beneath each eye through which whisker nerves would have passed. The wide hole suggests that, like modern seals, this animal had sensitive whiskers.

Based on these features, Rybczynski built a new family tree that included Puijila and other prehistoric carnivores, which rewrote some of their relationships. According to Rybczynski's analysis, Puijila and Enaliarctos belong to a small family of early pinnipeds that also includes Potamotherium (formerly thought to group with the weasel-like mustelids) and Amphicitceps (previously classified with the bears).

Compared to all other pinnipeds, it was the least specialised for life in the water, but it lived at the same time as the distinctly seal-like Enaliarctos. "In its time, Puijila would have been a 'living fossil'," says Rybczynski. It was a relict of a previous body plan that had since been refined for superior swimming.

Rybczynski thinks that Puijila swam using all four of its feet and it wouldn't have been anywhere as graceful as its modern cousins. Most otters swim by thrusting simultaneously with their hind legs and using their long tails. Seals also use their hind flippers by waving them from side-to-side, while sea lions rely on their front pair to fly through the water. Puijila's four-legged swimming stroke represented a style that could easily have given rise to either of the techniques used by today's pinnipeds.

Puijila's discovery also tells us about where the earliest seals may have evolved. It wouldn't have been suited to life at sea and probably lived and hunted in freshwater, suggesting that seals made the transition from land to sea via rivers and lakes. It lived in the Arctic and 23 million years ago, this region was cool and temperate, with freshwater lakes that would have frozen over in winter. Rybczynski speculates that these conditions may have driven the ancestors of seals to experiment with coastal environments. Free of ice, these would have provided them with opportunities to hunt even in the depths of winter.

Update: The Canadian Museum of Nature have developed an entire microsite dedicated to the new find! I'm really impressed - it's got some fantastic detail, great use of Flash and 3D animations. Go over and see Puijila up close.

Also have a look at Brian's excellent take at Laelaps.

Reference: Nature doi:10.1038/nature07985

Images: Painting by Mark Klingler; 3D reconstruction by Alex Tirabasso; skeleton laid out by Martin Lipman;

More on transitional fossils:

PS: I guarantee that someone, somewhere will get these details wrong, so two points are worth clarifying:

Puijila is not the "ancestor of seals"
This does not mean that seals "evolved from otters/bears" or other such nonsense

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edyong Wed, 04/22/2009 - 07:00

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Wow! I was just reading my marine mammal book the other day, specifically the section about pinnipeds, and I thought, "when are they going to find a pinniped version of Ambulocetus?" Turns out I didn't have to wait long!

but wait! if seals evolved from otters, then WHY are there still otters around? answer me that, silly evolutionist person...

Yay! Two more gaps for the DI and ID Creationists to get confused about! Hilarity will ensue. Thanks for the post - it was great.

Great stuff. Small suggestion....Insert words to this effect:

"that shares an ancestor with modern seals, and since it retains many features of that ancestor we can infer what that ancestor may have looked like"

approximately here at the ^

Rybczynski unearthed the new animal ^ at Devon Island

And then the next nine or ten references that strongly imply that this is an ancestor to the seals will not have to be undone in the last half of the writeup!!!!! :)

It is a great write-up, though. Nice fossil as well.

Done, after a fashion. Fair point Greg.

http://en.wikipedia.org/wiki/Puijila

The lead author of the discovery is a personal friend. Great work.

That's exciting and for no logical reason but partisanship, I'm glad the fossil was found by a fellow Canadian!

Can we also give a shout out to one of the co-authors, Mary Dawson (Carnegie Museum paleomammalogist), who is a pioneer for women in paleontology and a true scientific hero? I consider it a great privilege in my life to have gotten to know her, and you won't regret having a chat with her at the next SVP, for those of you that attend! She was asked recently, prior to the lifting of the press embargo, about this new paper coming out and slyly looked at the questioner while replying: "All I can say is, my lips are sealed."

This is so cool.

Awesome. The 3D reconstruction of skull makes it seem like this animal had some pretty heavy hardware on the front end.

Oh and I just checked out the CMN site; it is fantastic.

On CBC radio today it was suggested that the first piece of the skeleton was found because one of the researchers (a grad student i think) was kicking around (literally) after her group's ATVs had run out of gas. One of those fortuitous things I suppose. Wasn't there a story like that about the Burgess Shale (someone fell off a horse or something??) that turned out to be false? It's been awhile since I read Wonderful Life.

Actually, now I see that the CMN site has the running-out-of-gas story too. It was Liz Ross (a field tech) who found it.

She named it Puijila darwini after an Inuit word referring to a young seal, and some obscure biologist.

Heh, nice. :D

Nit, but one that can confuse: Origin of Species, not Origin of the Species.

I just finished the book, btw. Thanks for both that and this blog; I've mined it several times when putting together lectures for my behavioural neuro class this semester :-).

Awesome. The 3D reconstruction of skull makes it seem like this animal had some pretty heavy hardware on the front end.

Don't underestimate the hardware that modern seals and sea lions have. Check out Paul Nicklen's leopard seal pics - here's a taster from the Wildlife Photographer of the Year competition. I once interviewed this man about whether swimming with these animals was a scary experience. He said, "Their threat display, when they take your head in their jaws, is a bit nerve-wracking, but you just have to stay calm..."

Update: I should probably mention that one of Nicklen's photos is really very graphic (and could very well be used as the main image for the F*ck You Penguin blog. If you're squeamish, don't click on that link.

Wow. Those photos were killer.

Thanks for the science even a History major can understand...

Welcome Fark readers. The person who posted "This doesn't explain bananas, does it? No, I didn't think so." made me snort coffee through my nose.

reply to tbell
but wait! if seals evolved from otters, then WHY are there still otters around? answer me that, silly evolutionist person

my answer
location, location, location thats the answer. different locations have different needs and dangers.
same reason why humans dont look the same. location,location, location

Great writeup! I'm sharing it with my students since this has been a topic of discussion recently.

reply to tbell
Why are otters still around?

There is still a place in nature where the otter can survive. Just because a species changes doesn't mean the original line dies off.
Imagine if one of your children moved to China. In three or four generations that part of your lineage would begine to look diffrent than the part of your family that stayed here. Both branches of your family continue to survive. One branch will evolve into somthing a little diffrent because of its location.

Er folks, I think tbell was joking?

Obviously good on you for the defence, but the satire filter probably needs ratcheting one notch up ;-)

All hail the holy FARK for he is the bringer of amusement and truth.

Bananas were bred selectively to look like that. Just like poodles and pomeranean punt doggies. The imaginary level 80 sky wizard did not touch a wolf and say 'be thy meek, tiny, domesticated, and the general mass of a football.'

Or perhaps since your religion based off of a jewish zombie that is his own father that gets nailed to a giant tree that you telepathically tell him that he is your savior that you are saved. And also that the world whose recorded civilization goes back more than forty thousand years suddenly gets cut down to 6000.

It seems to be a recurring theme that major groups of marine animals got their start in freshwater. Jawless fish, bony fish, whales and now seals...are rivers like training grounds for the more demanding environment of the sea?

Are rivers like training grounds for the more demanding environment of the sea?

That sounds about right to me. In freshwater, you have to adapt to moving about in water, perceiving prey, holding your breath and so on. The sea has all of that plus the additional challenge of high concentrations of salt, and a much larger scale.

"Answers" in Genesis has replied. It seems that some newspapers have called the fossil "otter-like" thus combined with some more quote mining of newspaper accounts this evidence for evolution has been disproved. Yeah, that the ticket.

Thank you Ed for writing such a nice article on Puijila! This crater carnivore still has alot more to tell us about the evolution of our flippered friends. Back to work...

Wow A Lurker, your lack of intelligence just made me spit up my drink that I just took a sip of. Its not wonder you are a religious person because you believe "newspaper accounts" of everything you read, do you also believe in everything in the National Inquirer?

Disprove evolution Lurker, when you do i'll break the reality to you that believing in god, and a fictional book is the same as believing in Clifford... Show me Clifford Lurker..

Dave, I think the use of words like "quote mining" and the final statement should make it clear that A lurker did not agree with the link he posted.

Um, yeah... I too am quite confident that A lurker's comment was tongue-in-cheek. I would also note the use of quotes - "Answers" in Genesis XD And not all religious people are creationist nutbars... Clifford is cool though. Well anyway. Thanks to the author for this great article. This is really exciting!

I'm definitely not a creationist but neither do I believe the evolution stuff. The handy thing about creationists is the excellent ways they show the fallacy of the evolutionists. If macro evolution exist, we would see the process today with animals that transverse to other types of animals. I'm still waiting on a much better theory.

SteveF, I suggest that you hold your breath while you wait. I hear that it helps.

SteveF, here's how quickly the process can happen. Now, granted, it's still a lizards (as PZ laments), but if a carnivorous lizard can become not only herbivorous but develop specific gut adaptations to deal with heavy herbivory in 30-odd years, I mean...it happens pretty quickly.

New theory on why there are no transitional fossils

gregladen — Sun, 29 Mar 2009 20:39:11 +0000

New theory on why there are no transitional fossils

This was mysteriously sent to me. I think maybe by god.

gregladen Sun, 03/29/2009 - 16:39

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awesome, but old. don't remember where i've seen it first though...

One of my favs like this is I believe a Far Side. Two whale looking creatures with feet are sitting on a beach watching an ark sail away, and one of the whales says "He said to figure something out." :)

That's just brilliant!

Fossil foetus shows that early whales gave birth on land

edyong — Tue, 03 Feb 2009 18:42:43 +0000

Fossil foetus shows that early whales gave birth on land

Nine years ago, a team of fossil-hunters led by Philip Gingerich from the University of Michigan uncovered something amazing - the petrified remains of an ancient whale, but one unlike any that had been found before. Within the creature's abdomen lay a collection of similar but much smaller bones. They were the fossilised remains of a foetal whale, perfectly preserved within the belly of its mother. Gingerich says, "This is the 'Lucy' of whale evolution."

The creatures are new to science and Gingerich have called them Maiacetus inuus. The genus name is an amalgamation of the Greek words "maia" meaning "mother" and "ketos" meaning "whale", while Inuus, the Roman god of fertility, gave his name to the species.

The foetus's teeth were the first to be uncovered and only as the surrounding (and much larger) bones were revealed, did Gingerich realise what his team had found - the first ever foetal skeleton of an ~~ancestral~~ ancient whale (see video). Alongside the mother and calf, the group also discovered another fossil of the same species in even better condition. Its larger size and bigger teeth identified it as a male.

This trio of skeletons is so complete and well-preserved that Gingerich likens them to the Rosetta Stone. They provide an unparalleled glimpse at the lifestyle of an ancient whale before the group had made the permanent transition to the seas. How it gave birth, where it lived, how it competed for mates - all these aspects of its life are revealed by these beautiful new finds.

Maiacetuswasn't quite like the whales we know and love. It was an intermediate form between the group's earliest ancestors and the fully marine versions that swim about today. For a start, still had sturdy hind legs that were good for swimming but would have allowed it to walk on land.

Another piece of evidence tells us that Maiacetus was definitely amphibious - its foetus was facing backwards in the womb. If the mother had lived long enough to give birth (and judging by the foetus's size, that wasn't far off), the infant would have greeted the world face-first. No living whale or dolphin does that - all of their young emerge backwards, leading with their tails, to minimise the risk of drowning in the event of a prolonged labour. A head-first delivery means that Maiacetus gave birth as a landlubber.

Whales are so beautifully adapted to life in the water that their relationships to other mammals aren't immediately clear. Thankfully, their evolution has been beautifully charted by a series of "transitional fossils" documenting the change in their bodies over massive gulfs of time.

They evolved from deer-like ancestors, hoofed mammals that lived on land and occasionally ventured into the water. Early members of the family included Pakicetus, a meat-eater with long, hooved legs, a dog-like snout, and a distinctive inner ear that only whales and their kin possess. From there, the family became gradually more comfortable in the water, with later species like Ambulocetus having powerful tails and back legs that were clearly adapted for swimming.

These adaptations became even more extreme in the protocetids, a group that included species like Rodhocetus. They had seal-like bodies and possibly tail flukes like modern whale, but they still kept powerful hind legs to support their weight on land. Later whales like Basilosaurus or Dorudon were very different. Their hind legs were tiny - larger than those of modern whales, but useless for walking. Their hip bones were also disconnected from their spines. They were fully marine animals.

The newly discovered Maiacetus was a protocetid - several changes away from its original hooved ancestors, but not as thoroughly adapted of ocean life as Basilosaurus. Gingerich believes that it fed in the sea before coming ashore to rest, mate and give birth. Its teeth are suited for eating fish. Its legs were built to power swimming and support its weight on land, but they wouldn't have let it swim very far, or granted it with much terrestrial agility. These legs constrained the animal to the boundary between land and sea - jack-of-all-trades, but master of none.

The foetus was alone in the womb, which suggests that Maiacetus (like modern whales) devoted its energy to rearing a single infant during every found of breeding. As I've mentioned, the baby would have been delivered head-first while mum was safe on land. The foetus as large and its teeth were well-developed, with the growth of its permanent teeth already underway. Among mammals, advanced chompers like these are a sign that the calf would have emerged from the womb as a mobile and capable youngster - just as deer fawns can run soon after they're born.

The male skeleton was about 12% larger than the female and in the flesh, the animal would have weighed about 39% more. Compared to other marine mammals, this size difference between the two genders is actually relatively small. It suggests that males didn't have to compete too brutally for mates for those that do (like elephant seals) grow to enormous proportions that dwarf the fairer sex. These fighters hoard females in harems, and the fact that Maiacetus didn't suggests that it couldn't. Perhaps food and shelter were widely spread out commodities that were impossible to hoard and defend.

All in all, Gingerich's latest finds are among his most alluring yet. The remains of these three individuals have lasted through 48 million years of compression and today, they paint an incredibly vivid picture of the life of an ancient species. The fact that they are whales is the icing on the cake. This group's story is one of the most beautifully illustrated in the field evolution and every new discovery is a welcome one.

Reference: PLoS ONE Gingerich PD, ul-Haq M, von Koenigswald W, Sanders WJ, Smith BH, et al. (2009) New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism. PLoS ONE 4(2): e4366. doi:10.1371/journal.pone.0004366

Update: For other accounts of this story, I'd highly recommend reading what Carl Zimmer (Loom) and Brian Switek (Laelaps) have to say on it. Both bloggers have written extensively on whale evolution before and I used their pieces as a lot of background reading for this story.

More on transitional fossils:

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edyong Tue, 02/03/2009 - 13:42

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Damn it! You and Switek both posted this before me, as I thought there was an embargo present. Curses! Beautiful fossil though!

Amazing!

This is lovely and timely. I've been looking at the evolution of the whale with my dtrs. I'm going to show this to them tomorrow. They'll be fascinated by the foetus. (When they were pre-schoolers they had me pretend to go into labour complete with sound effects while they slid down the twisty slide in the playground, ie the birth canal. But I draw the line at being the ancestral whale mother).

It's an exciting discovery Ed, though I can't help thinking that your comment "Its teeth are suited for eating fish. Its legs were built to power swimming and support its weight on land, but they wouldn't have let it swim very far, or granted it with much terrestrial agility. These legs constrained the animal to the boundary between land and sea - jack-of-all-trades, but master of none. " does Maiacetus a disservice. The description isn't far off how you'd describe a seal or (stretching it a little) otter, so Maiacetus may have been very well adapted to its coastal environment, perhaps even the "master" of it.

Paul - Fair point. Perhaps a bit of hyperbolic prose on my part. Will change later.

Lilian - I love that you show the blogposts to your kids ;-)

Zach - Bora tells us that the PLoS embargoes lift automatically if the paper is published slightly ahead of schedule. We only posted by 90 mins tops.

Ed,

Might I recommend linking this as a Trackback?

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004…

Thanks for the links, Ed! I'm glad you find some of my other posts helpful. I should have just sent you the chapter on whales I'm working on (which now needs to be updated, of course).

I am a HS physics teacher, and I was amazed by this reporting. Thank you for the good service you provide to me who loves knowledge.

Wow! Great story. Thank your for such excellent writing and use of hypertext.

If you tried to send a trackback - don't worry. TOPAZ upgrade saved them elsewhere and will automatically put them on the paper once the process is over.

When you're talking about mammals, it's apparently considered OK to describe any old transitional fossil as "ancestral", even though (a) it's almost certainly not an ancestor of anything living, and (b) if it was, you would have no way to demonstrate it. I see that as a convenient shorthand, but it seems that if you step back to the Mesozoic and say "ancestor", or even "possible ancestor", you will assuredly be scalped.

Yeah it's meant to be a shorthand. But you're right - it could be misinterpreted. Tell you what - let's take a poll. Anyone else think that "ancestral" in this context is a misfire. Is this one of the things that science writers do that pisses off scientists? Let me know so I can continue/refrain as appropriate.

Actually sod it - I've mulled it over and Nathan's right. "Ancestral" is ambiguous verging on wrong. Out it goes.

Me, I think the interesting distinction is between "might have been ancestral" and "was not ancestral because...". Invariably (unless the intermediate form is just a damn tooth or something) there's some collection of derived features not present in the next taxon up (shovelwise). Exactly what those features are makes an interesting sidelight: "they fused some wrist bones, but it didn't save them!"

I have read that mammalogists are particularly sloppy about this sort of thing. Is that your impression? (I think it was one of the Zachs who mentioned the phenomenon.)

Dave Hone hosted an interesting, if slightly apoplectic, exploration of the issues at http://archosaurmusings.wordpress.com/2008/12/23/anchiornis-a-new-basal… . You're mentioned there, by the way, entirely non-ironically.

Heh. Interesting discussion over there. On balance, I think David's right though and I value accuracy in science writing above all else. What's interesting to me is that I specifically avoided this mistake in an earlier post on Indohyus, another key fossil in the whale evolution story.

Disappointing, then, that it's cropped up here. All I can really say is that I, just like any other science writer/journalist, will inevitably make mistakes. Even with the best will in the world, it's going to happen.

I will, however, always correct stuff here if the right reasons are given. It's part of the ethics of blogging and part of what I think makes the medium strong. You get feedback from much more learned and informed people than yourself, which can only help people like us to be better at our jobs. Only an idiot would turn a deaf ear to that.

So thanks Nathan. And for the compliment over at Archosaur Musings too. Appreciated.

It's hard to know what you're agreeing with Dave about.

You feel it's better to splash a bucket of facts on ignorant reporters, and let them try to put together a coherent story, and then complain when they fail, than to give them an engaging story, including some background and context, that they can run as is?

I meant specifically that I think he's right about the incorrect use of the word "ancestral".

OK, everybody agrees on that. Apologies for misunderstanding.

Great story. Thanks for the interesting read.

Beipaiosaurus was covered in the simplest known feathers

edyong — Mon, 12 Jan 2009 16:00:25 +0000

Beipaiosaurus was covered in the simplest known feathers

Beipaiosaurus was among the strangest of dinosaurs. It looked like a fusion of body parts taken from several other species and united in the unlikeliest of proportions. It had a stocky body, long arms adorned with massive claws, a long neck topped by an incongruously small head, and a beaked mouth. Bizarre as this cocktail of features is, it's the animal skin that has currently warrants attention.

Fossils of Beipaiosaurus include impressions of its skin and these clearly show long, broad filaments clumped around its head, neck, rump and tail. They are feathers, but most unusual ones. Traces of feathers have been found on other dinosaurs (including the infamous Velociraptor) and they come in a variety of shapes and forms. But all are composite structures consisting of several slender filaments that either sprout from a single base or branch off a central stem.

Beipaiosaurus was also covered in some of these complex feathers, but it had other plumes that were far simpler. Each of these was a single, unbranched, hollow filament - exactly the sort of structure that palaeontologists had predicted as the first step in the evolution of feathers.

Until now, their existence was merely hypothetical - this is the first time that any have actually been found in a fossil. Other, more advanced stages in feather evolution have been described, so Beipaiosaurus provides the final piece in a series of structures that takes us from simple filaments to the more advanced feathers of other dinosaurs to the complex quills that keep modern birds aloft.

The simple feathers were discovered by Xu Xing, the famous Chinese palaeontologist who discovered such species as Microraptor and Dilong, among many others. The filaments are longer and broader than those possessed by other dinosaurs and Xu calls them "elongated, broad, filamentous feathers" or EBFFs.

Each is about 10-15cm long and 2mm wide - not exactly thick, but still 10-20 times broader than the simple feathers of Sinosauropteryx. They are also unusually stiff, for despite the rigours of death and fossilisation, very few of them are curved or bent.

In other species of extinct dinosaur, simple feathers probably helped to insulate their bodies. But Beipaiosaurus's feathers were too patchily distributed to have provided much in the way of insulation and they certainly weren't complex enough for flight.

Instead, Xu thinks that the animal used them for display - their length and stiffness are well-suited for such a purpose, and they're only found on parts of the body that bear display feathers in modern birds. They provide strong evidence that feathers were used for display long before they were co-opted for flight.

Beipaiosaurus's feathers provides yet more evidence that these structures, so characteristic of modern birds, actually evolved and diversified well before this group flew on the scene. For the moment, it's unclear how widespread these simple feathers were, whether they existed in other dinosaur species or even if they were found on other therizinosaurs - the bizarre group of dinosaurs that Beipaiosaurus belongs to. Is this species the exception, or just one of a wider group of (proto-)feathered friends?

Xu notes, perhaps controversially, that some species do bear long filaments that are remarkably similar to EBFFs. The primitive horned dinosaur Psittacosaurus had a row of long, hollow bristles at the base of its tail, which it probably used for display. And some pterosaurs (flying reptiles that aren't dinosaurs) are covered in similar "hairs" on their neck, body and tail.

With similar filaments turning up in such disparate groups, it's possible that the sorts of filaments that eventually became feathers were not just restricted to small, predatory dinosaurs. They may have turned up very early on in the evolution of the archosaurs - a diverse group of reptiles that includes dinosaurs, pterosaurs, crocodiles and the crurotarsans.

Image: Beipaiosaurus by Pavel Riha; fossil images from PNAS

Reference: X. Xu, X. Zheng, H. You (2009). A new feather type in a nonavian theropod and the early evolution of feathers Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0810055106

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edyong Mon, 01/12/2009 - 11:00

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That a really beautiful specimen. I'm more interested in the skull morphology, honestly. It's no surprise that therizinosaurs had feathers. They are consistently placed within Maniraptora. The only real debate is whether or not they are a sister group to oviraptorosaurs or not. Zanno's SVP presentation last year suggests that they do NOT, but instead form the most basal branch of the Maniraptora.

Awesome find, though. Now I need to get my grubby hands on a copy of the paper. Is there, perchance, a link?

"They are feathers, but most unusual ones..." ? Maybe no feathers at all:
see:
http://www.ncsce.org/PDF_files/feathers/Lingham%20paper.pdf
or try to google:
http://www.google.com/search?hl=en&q=Theagarten+Lingham-Soliar+collagen…

Yeah, I'm aware of those. But I don't buy it. See Brian's take on the Psittacosaurus paper and Scott Hartman's views on the Sinosauropteryx one.

Wait a minute, I thought crocodiles were crurotarsans!

It would be helpful to know when these things lived, and what happened before and after.

Crocodiles are crurotarsans. Actually, by definition, crocodiles are like the only thing that are definitely crurotarsans. ;)

Well how was I supposed to know? It's not like I actually ever wrote an entire article on the crurotars... oh bollocks. ;-)

Heroes in a half-shell show how turtles evolved

edyong — Wed, 26 Nov 2008 12:55:58 +0000

Heroes in a half-shell show how turtles evolved

Clad in hard, armoured shells, turtles have a unique body plan unlike that of any other animal. Their shells have clearly served them well and the basic structure has gone largely unchanged since the time of the dinosaurs. But this unchanging nature poses a problem for anyone trying to understand how they evolved and until now, fossil turtles haven't provided any clues. All of them, just like their living descendants, have fully formed two-part shells.

But three stunning new fossils are very different. They belong to the oldest turtle ever discovered, which lived about 220 million years ago in the area that would become China. Unlike today's species, its mouth had a full complement of small, peg-like teeth but even more amazingly, it had a feature that distinguishes it from any other turtle, either living or extinct - it only had half a shell.

The ancient turtle was unearthed by Chun Li (no, not that one) from the Chinese Academy of Sciences, who called it Odontochelys semitestacea, a name that literally means "toothed turtle in a half-shell". It was a small animal, just 35 cm from snout to tail, and its shell consisted of just a plastron (the bottom half) and not a carapace (the top half).

Li's team believes that this incomplete shell represents an intermediate step along the evolutionary path to the modern version. To them, Odontochelys's anatomy settles debates about how the group's distinctive shell evolved, which animals they were most closely related to and what sort of lifestyles the earliest members had. It's a true hero in a half-shell.

For a start, Odontochelys suggests that the shell was a two-step innovation, with the plastron evolving first and the carapace coming later. In a way, modern turtles replay the evolutionary history of their ancestors as their embryos mature, for the plates of their plastron harden before those of their carapace. Some scientists have used this sequence to argue that the turtles evolved a lower shell before an upper one, and Odontochelys provides strong support for this theory.

The animal also has structures that look like the very earliest stages of carapace evolution. Its upper body may have been uncovered but its upper ribs had started to expand, and its backbone had bony outgrowths at its flanks called neural plates. Li thinks that the widening ribs would eventually merge with each other, and the neural plates, to complete the second half of the distinctive shell. Again, turtle embryos do the same thing as they grow, accomplishing in mere months what their entire lineage took millions of years to do.

Scientists have put forward other theories for the evolution of the carapace. According to one alternative, it evolved from bony scales called osteoderms, which lie just beneath the skin. They are found in many reptiles and are responsible for both the distinctive plated look of crocodiles and the formidable armour of the ankylosaurian dinosaurs. Some say that turtle shells are merely very large osteoderms that fused together over the course of evolution, but Odontochelys consigns that theory to the shredder. Its remains show no signs of any osteoderms.

In this way, the new find settles debates that no previous turtle fossil could. Proganochelys, the animal formerly known as the world's earliest turtle, lived 10 million years after Odontochelys. It, however, did have a fully-formed shell and a massive, spiky one at that. In this way, it was of no use in piecing together the shell's origins and may actually have led scientists down some wrong alleys.

Proganochelys does have possible osteoderms in its legs and some camps used these, along with other features, to suggest that the turtle lineage splintered off from a group of extinct armoured reptiles called pareiasaurs. But according to Li, Odontochelys's bones suggest that turtles were more closely related to another reptile group - the diapsids, which include modern snakes, lizards and crocodiles.

The bones of its foot also suggest that it had reached a stage in development that only adult turtles get to, ruling out the possibility that the three Odontochelys fossils were teenage specimens whose shells simply hadn't finished growing. But whether it truly represented the ancestral turtle body is a more open question.

Li certainly thinks so, but others are less convinced. In a related editorial, Robert Reisz and Jason Head from the University of Toronto argue that the fossil could equally represent a turtle that did have a carapace, but one that hadn't hardened into bone yet. Their view is that Odontochelys is a more advanced species than Li suggests and its carapace had been reduced into an incomplete, softer version, in the style of modern soft-shelled turtles. That would make it an adaptation rather than a primitive state.

Both sides agree that Odontochelys's protected underside, and the size of its front legs, suggest that it spent a lot of time in water (although probably not in sewers). After all, land reptiles would have a greater need to protect their backs than their ground-hugging bellies. But in Li's view, this means that turtles probably evolved from an aquatic ancestor, while to Reisz and Head, it means that Odontochelys evolved from a land-lubbing ancestor and was one of the first turtles to adapt to a watery life.

For now, it's an open question, but either way, Odontochelys is a wonderful example of a 'transitional fossil'. I've blogged about similar discoveries before and they are always great cause for excitement, providing vivid illustrations of the evolutionary past of today's species. What they can't do of course if tell us if Odontochelys led, did machines, was cool but crude, or was, in fact, a party dude.

Reference: Chun Li, Xiao-Chun Wu, Olivier Rieppel, Li-Ting Wang, Li-Jun Zhao (2008). An ancestral turtle from the Late Triassic of southwestern China Nature, 456 (7221), 497-501 DOI: 10.1038/nature07533

Image: from Nature; fossil altered by me

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edyong Wed, 11/26/2008 - 07:55

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164ma Skye turtle in the news too. http://www.sciencedaily.com/releases/2008/11/081119093227.htm

Call me a skeptic but it looks to me as though each fore appendage is holding a dagger-like weapon. Is this a hoax?

I photoshopped it for a joke. I was feeling whimsical.

Maybe the 1/2 shells were simply mineralized ballast? If they were semi-aquatics floating and sculling along the surface of shallow waters, the dense plastron keeping them upright and a bit of protection against submerged crocs, and a long neck would allow for quick fishing jabs beneath the water surface, while the upper carapace came later in the partial-return to terrestrial living, where protection from above/behind became more significant?

Of course the most interesting question is to find an intermediate form that shows how the scapulae got inside the ribs. Any guesses?

Most excellent photoshopping, Ed. It made me giggle on this sad day (watching Mumbai news on CNN).

TMNT was very popular in Brazil when I was a kid. "Odontochelys consigns that theory to the shredder"
"the turtle lineage splintered off"
ahahahahahahaah very funny :-)

LOL good joke Ed. Good Photoshop job too! Was it Michaelangelo who used the sai?

Y'know, I was really hoping that someone would notice that before I felt obliged to point it out ;-). Congratulations Igor.

(Oh and it was Raphael who used the sai. Mikey used nunchucka (except in Britain, where he used bugger all).

Minor point: (yeah, nobody is reading posts this old) At SVP, a couple of researchers demonstrated that the turtle scapula is not actually inside the ribcage, but in fact sit just in front of the first thoracic vertebra. The plates of the SHELL grow over the scapula, but NOT the ribs.

So, as the authors continually pointed out, the scapula is within the shell, but not the ribs.

Microraptor - the dinosaur that flew like a biplane

edyong — Wed, 08 Oct 2008 08:00:50 +0000

Microraptor - the dinosaur that flew like a biplane

Many of us believe dinosaurs to be extinct but in truth, they surround us every day. All the world's birds, from the pigeons of our cities to the gulls of our seasides, are descended from dinosaurs, and modern science now classifies the birds with their long-dead kin. The gulf between dinosaurs and modern birds may seem huge, but the discovery of several feathered dinosaurs are seriously blurring the line between the two. And now, new research on the feathered dinosaur Microraptor reveals that birds may have evolved from dinosaur ancestors that flew not on two wings, but on four.

The link between dinosaur and bird was cemented in the last two decades, when palaeontologists unearthed hundreds of beautifully preserved fossils in the Liaoning province of China. Many of the newcomers were small predators, belonging to the same group as the famous Velociraptor (and indeed, most scientists believe that this Hollywood star was also covered in primitive feathers).

The new species run the full evolutionary gamut from flightless dinosaurs to flying birds. They range from Sinosauropteryx with its primitive, downy, proto-feathers to Caudipteryx, a dinosaur with proper flight-capable feathers, to Confuciusornis, a true bird. Together, these species provide a tantalising snapshot of how small prehistoric predators transformed into the familiar fliers of today's skies.

One of these species, Microraptor, stood out among the rest, for it had winged legs as well as arms. The animal's metatarsal bones were covered in long, asymmetric flight feathers. Their shape is clearly designed to produce lift during flight, but how Microraptor used its four wings has puzzled scientists. The species' discoverers believed that by splaying its legs out sideways from its body, it held its wings in tandem like a dragonfly. But for Sankar Chatterjee and R. Jack Templin of Texas Tech University, the facts didn't add up.

For a start, no bird or dinosaur has shown the ability to splay its legs out sideways and doing so would probably have dislocated the hip. Microraptor must have tucked its legs vertically beneath its body, like modern birds of prey do when they pounce. Its leg flight feathers would only produce lift if the leading edge faced forward, against the flow of air. The leg feathers must therefore have protruded horizontally from the tucked legs. Chatterjee's revised pose makes Microraptor look like a feathered biplane, with the leg wings sitting below and just behind the main pair.

This new posture may also answer a long-standing debate about the origin of flight. Some scientists believe that bird flight evolved when ground-dwelling dinosaurs began to take to the skies. In contrast to this 'ground-up' theory, the 'trees-down' camp believes that tree-dwelling dinosaurs evolved flight to glide from tree to tree.

And this is exactly what Microraptor did. It lacked the muscles for a ground take-off and couldn't get a running start for fear of damaging its leg feathers. But a computer simulation showed that Microraptor could successfully fly between treetops, covering over forty metres in an undulating glide.

It is unclear if Microraptor could truly fly or was just an exceptional glider. Certainly, its body plan shows many features that would make its avian descendants such great aeronauts. It had a large sternum for attaching powerful flight muscles and strengthened ribs to withstand the heavy pressures of a flight stroke. Its long, feathered tail acted a stabiliser and rudder and its tibia (shin bone) was covered in smaller, backwards-facing feathers. Modern birds of prey carry similar feather 'trousers' and Chatterjee believes that they helped to reduce drag by breaking up turbulent airflow behind the animal's leg.

It could be that Microraptor's biplane design was just a failed evolutionary experiment. But Chatterjee thinks otherwise. He believes that the biplane model was a stepping stone to the two-wing flight of modern birds. As the front pair of wings grew larger and produced more lift, they eventually took over the responsibilities formerly shared with the hind pair. This series of events stunningly mirrors the evolution of man-made aircraft. When the Wright brothers unveiled their new plane in 1903, little did they no that dinosaurs had got there first 125 million years ago.

Reference: S. Chatterjee, R. J. Templin (2007). Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui Proceedings of the National Academy of Sciences, 104 (5), 1576-1580 DOI: 10.1073/pnas.0609975104

edyong Wed, 10/08/2008 - 04:00

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Excellent article except for one thing - you spelled "know" as "no" down by where you discussed the Wright brothers.

The Mysterious Origin of the Wandering Eye

grrlscientist — Wed, 09 Jul 2008 19:13:22 +0000

The Mysterious Origin of the Wandering Eye

tags: researchblogging.org, evolution, flatfish, Amphistium, Heteronectes, transitional fossils, missing link, Matt Friedman

During the development of extant flatfishes, such as this plaice, Pleuronectes platessa, one eye has migrated round the head to lie on the same side as the other. So these fishes have an 'eyed' (up) side and a 'blind' (down) side suitable for their bottom-dwelling lifestyle.

Image: KÃ¥re Telnes.

Flounder, turbot, sole, halibut and plaice (pictured above) are more than just a tasty slab of flesh on your plate. They are flatfishes that spend their adult life lying with one side flat on the seabed, while the other side faces up and is camoflaged, so the fish can lie motionless for hours, waiting for a tasty morsel to swim by. When this happens, the flatfish lunges upwards and suddenly opens its mouth to vacuum the hapless fish inside. Since flatfish spend all their adult lives with one side up and the other side facing the seafloor, they have evolved several morphological adaptations, such as having both eyes located on one side of their head, giving them a sighted (up) side and a blind (down) side. But flatfish are not born with both eyes on one side of their heads, so how do they end up that way? How did this asymmetrical character first evolve? Even Charles Darwin, one of the co-discoverers of the theory of evolution by natural selection, was baffled by what he referred to as this "remarkable peculiarity" of flatfish morphology.

Flatfishes are born with one eye on each side of their head, but undergo larval metamorphosis where one eye migrates to the other side of the fish's head late in larval development, producing asymmetrical juvenile fishes. By the time the skull is fully ossified, the eyes are permanently fixed in place.

But there are no known transitional fossils with only partially displaced eyes that would link these asymmetrical flatfishes with their symmetrically shaped relatives. This lack of transitional fossils has been the source of tremendous scientific controversy regarding whether this asymmetry evolved gradually or through a sudden evolutionary leap that produced "hopeful monsters," as originally described by geneticist Robert Goldschmidt in the 1930s.

Of course, creationists have entered the fray as well; seizing upon this curious morphological feature as part of their argument against evolution, they insist that the flatfishes' wandering eye could not have evolved gradually through natural selection because there is no apparent evolutionary advantage to a fish with a slightly asymmetrical skull that still retained eyes on opposite sides of its head. Further, they say that no fish fossils have ever been discovered with a wandering eye that had gotten "stuck" in an intermediate position on the fish's head.

Until now, that is.

Graduate student Matt Friedman, who is on the Committee on Evolutionary Biology at the University of Chicago and who is also a member of the Department of Geology at the Field Museum, was describing and naming a new genus of fossilized fish, Heteronectes. He was comparing this new genus to another similar primitive fish fossil, Amphistium, that had first been described two centuries ago, and made a startling discovery.

He noticed that adults from both fossil genera possessed features that are intermediate between modern flatfishes and their primitive symmetrical relatives, particularly the partial displacement of one eye -- an intermediate condition predicted by evolutionary biologists for a transitional flatfish fossil, or "missing link".

"What we found was an intermediate stage between living flatfishes and the arrangement found in other fishes," said Friedman, adding that these two fossil fishes "indicate that the evolution of the profound cranial asymmetry of extant flatfishes was gradual in nature."

How did Amphistium and Heteronectes see? As modern flatfishes so often do today, these transitional forms probably lifted their bodies partially off the seafloor with their elongated dorsal and pectoral fins, which would provide a greater range of vision for their lower eye.

Curious to learn whether this misplaced eye was a freak accident in a few specimens or was a common feature of these groups, Friedman traveled to many of the great natural history museums of the world to carefully examine the fossilized remains of Heteronectes and Amphistium. In every situation, he noticed the halfway misplaced eye in all the fossils he sudied. Additionally, these asymmetrically placed eyes were present in fossils of adult and larval specimens.

"Most remarkably, orbital migration, the movement of one eye from one side of the skull to the other during the larval stage, was present but incomplete in both of these primitive flatfishes," reports Friedman. In both fossils, one eye had begun its migratory journey but had not crossed the midline from one side of the fish to the other (figure 1);

Figure 1: Skulls of primitive pleuronectiforms showing incomplete orbital migration intermediate between generalized fishes and living flatfishes. a, Heteronectes chaneti gen. et sp. nov., holotype, NHMW 1974.1639.25 (dextral morph); transfer preparation dusted with ammonium chloride and presented in right-lateral view. b, Counterpart, NHMW 1974.1639.24; transfer preparation dusted with ammonium chloride and presented in left-lateral view, showing migrated orbit. c, Amphistium paradoxum, MusÃ©um national d'Histoire naturelle, Paris (MNHN), MNHN 10878b/Bol87 (sinistral morph); specimen presented in left-lateral view (photo credit: C. Lemzaouda, MNHN). d, Interpretive drawing. Solid grey shading indicates impression; diagonal hatching indicates damaged bone. e, Amphistium altum, Natural History Museum, London (BMNH), BMNH P. 3940 (dextral morph); silicone peel dusted with ammonium chloride and presented in left-lateral view, showing migrated orbit. f, Interpretive drawing. bsp, basisphenoid; ent, entopterygoid; f, frontal; hym, hyomandibular; la, lacrimal; le, lateral ethmoid; m.o, dorsal margin of migrated orbit; mes, mesethmoid; pmx, premaxilla; psp, parasphenoid; ri.par, parietal/epioccipital ridge; ri.pto, pterotic ridge; scl, sclerotic ring; sn, supraneural; soc, supraoccipital; names followed by 'r' or 'l' indicate right or left feature, respectively; '?' indicates uncertain identification. Scale bars, 10 mm. DOI: 10.1038/nature07108 [larger view].

Friedman's studies differed from previous work because he performed Computed Tomography scans (CT or CAT Scan) on the fossils instead of relying on traditional methodologies and this new technique revealed that both genera of fishes "unequivocally" had the cranial asymmetry.

When Friedman compared Amphistium and Heteronectes to modern flatfishes, he found they possess some characters in common with each other that are not present in modern flatfishes, while they share other characters with modern flatfishes, thereby allowing him to place them on the evolutionary tree as transitional fossils, or evolutionary "missing links" (figure 2);

Figure 2: Phylogenetic placement of Heteronectes and Amphistium and implications for the origin of cranial asymmetry in flatfishes. a, Topology arising from the analysis of a matrix comprising 19 taxa coded for 58 morphological characters (8 ordered) (number of cladograms = 1; cladogram length = 135; consistency index = 0.50; retention index = 0.74; rescaled consistency index = 0.37). Heteronectes and Amphistium are placed as successively more crownward plesions on the flatfish stem. Unordered analyses reconstruct these taxa in the same position. Numbers at nodes indicate Bremer decay index, bootstrap support and jackknife support, from top to bottom, respectively. Extinct taxa are marked (â ) and '-' indicates that bipartition occurs in fewer than half of cladograms arising from bootstrap or jackknife analysis. Previous placements of Amphistium outside Pleuronectiformes are rejected. See Supplementary Information for full details of the analysis. b, Reconstruction of Amphistium, showing sinistral (front) and dextral (back) individuals in the left lateral view (modified from ref. 20). c, Simplified cladogram adapted from a showing the progression of orbital migration across flatfish phylogeny. Neurocrania are depicted in left lateral (top), dorsal (middle) and right lateral (bottom) views. DOI: 10.1038/nature07108 [larger view].

Interestingly, there is another peculiar extant flatfish genus, Psettodes, that contains three species of flatfishes that range throughout the Indian and Pacific Oceans. As you can see in the above diagram, Psettodes has an eye that is placed near its midline, near the top of its head. These fishes swim vertically like other fishes, although they do spend some of their lives laying on the seafloor, waiting for lunch to arrive. The asymmetrical placement of their eyes provides a greater range of vision while they are prone, thereby enhancing their own ability to escape becoming another fish's lunch.

But the relationship of this genus to other modern flatfishes was mysterious, so
Friedman included Psettodes in his analysis and found that this genus is the basalmost living flatfish, while the extinct Amphistium and Heteronectes form a lineage that is paraphyletic with respect to modern flatfish.

According to Friedman, his findings "refutes these claims of radical sudden change" -- Goldschmidt's "hopeful monster" hypothesis -- "and demonstrates that the assembly of the flatfish body plan occurred in a gradual, stepwise fashion."

So once again, scientists have discovered another transitional fossil that, like Tiktaalik, provides creationists with yet another gap to demand that scientists fill with yet more fossils -- thus ensuring plenty of scientific research for centuries to come.

Sources

Friedman, M. (2008). The evolutionary origin of flatfish asymmetry. Nature, 454(7201), 209-212. DOI: 10.1038/nature07108.

University of Chicago Medical Center press release (quotes).

grrlscientist Wed, 07/09/2008 - 15:13

Friedman included Psettodes in his analysis and found that this genus is a true "living fossil" because it diverged away from the ancestral flatfish lineage before even the extinct Amphistium and Heteronectes did.

That's not what the analysis shows. Psettodes is the basalmost living flatfish, Amphistium and Heteronectes form a paraphyletic stem to living flatfish.

Thanks for this! Coincidentally, I was just the other day trying to explain the fun-ness and funny-ness of flatfish to my six-year-olds, and I misinformed them about the timing of the eye migration. Now, I can not only give them correct information, but I can also show them your super-cool plaice photo and tell them even more fun stuff about these fish and their forebears.