When I first met Hans Thewissen, he spending an afternoon standing on a table, pointing a camera at a fossil between his feet. He asked me to hold a clip light to get rid of some shadows. I felt like I was at a paleontological fashion shoot.
Thewissen was taking pictures of bones from a whale that walked. As I later wrote in my book At the Water's Edge, Thewissen has discovered some crucial clues to the transitions that the ancestors of whales made from land to sea. In Pakistan, he discovered a 47-million-year-old fossil called Ambulocetus natans, that had an otter-like body. It was the first whale fossil ever found with functional legs. New fossils of other ancient whales have since surfaced. The bones Thewissen was photographing, for example, belonged to an even older, even more terrestrial relative of today's whales, called Pakicetus.
When Thewissen and other have compared these fossils to those of other mammals, they've found that whales either evolved from even-toed ungulates (known as artiodactyls) or a close relative of artiodactyls. Meanwhile, other scientists have been comparing the genes of whales to other mammals, and they've found that one kind of artiodactyl--hippos--is the closest living relative to whales. But the fossil record of hippos is pretty sketchy. The oldest member of the family is only 15 million years old.
So I was pretty excited to read the newest paper from Thewissen and his colleagues, published in tomorrow's issue of Nature. They've identified what they believe is the closest fossil relative of whales. It's a raccoon-sized beast named Indohyus that lived 48 million years ago in Kashmir. Analyzing the bones of Indohyus, the scientists discovered that it shares some--but not all--of the traits previously considered unique to cetaceans from Pakicetus to today's whales and dolphins.
Even more intriguing is the evidence suggesting that Indohyus was fairly aquatic. The evidence comes from isotopes in the fossils, as well as from the structure of the bones. Living mammals that spend a lot of time underwater tend to have heavy bones that they use to keep them from floating up to the surface of the water. So does Indohyus. Its teeth appear adapted for eating vegetation. It might have eaten underwater, like muskrats do today, or on land, as hippos do. Its adaptations to water may have helped it find refuge from predators on land. (The inimitable Carl Buell, who illustrated walking whales for me in At the Water's Edge, has painted this portrait of Indohyus.)
If Thewissen's right, then a key step in the origin of whales was the transition from eating plants to eating meat. (Pakicetus and other early whales show signs of having been meat-eaters.) But that transition came after the ancestors of whales had already started to take the plunge.
For more, watch Thewissen talks about Indohyus and whales on this video
Source: Thewissen et al, "Whales originated from aquatic artiodactyls in the Eocene epoch of India," Nature, http://www.nature.com/doifinder/10.1038/nature06343
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Great post. Great Picture. I love this stuff.
I love this stuff too. I'm not sure I understand how the transition from herbivorous to carnivorous diet takes place. Wouldn't there need to be significant metabolic changes? I guess change is not hard to do evolutionally, but still! Giant pandas seem to have recently undergone the opposite transition and I often wonder how they did that.
"Wouldn't there need to be significant metabolic changes? "
I don't think so. I don't think cows changed significantly when we started grinding up meat-by-products and put it into their feed.
I mean, other than getting mad cow disease because of the brain/spinal cord matter.
I look at the change this way... SLOWLY changing the diet over many, many generations. Look at the little guy in the picture. He's happily grazing on duckweed from the bottom of the pond. One day he eats a worm too, and doesn't spit it out--mmm... high protein, maybe a little tough to digest, but not so bad. After a number of generations, these guys are duckweed and worm-eaters. Some guys develop a taste for those worms, and get good at finding them, and maybe a small fish every now and then... or just the fish eggs on the bottom of the roots of the duckweed.
Anyway.... slow changes in the proportion of veggies to meat every generation. Give it a thousand generations, or ten thousand or so... no big deal.
Re metabolic changes--along the lines of Siamang's comment, think of the living omnivores out there that eat lots of different kinds of food.
Actually, I think the transition from herbivore to carnivore would be easier than the reverse. Plants are full of indigestible cellulose; that's why extant artiodactyls rely on intestinal symbionts for digestion and have a long intestine (and is some cases, specialized "fermentation vats"). Plants also typically produce toxic defensive chemicals, which must be tolerated or detoxified (or bred out of the population, as humans have accomplished).
As for Homie Bear's question on Pandas, I recall that pandas are very inefficient herbivores in that they digest only cell contents and leave the cellulose undigested (as do humans).
All this wicked cool sciencey stuff, and a Carl Buell picture into the bargain! You really should be charging admission.
I think anatomical adaptations to the aquatic environment are more interesting...like the nostrils and air passages shifting from the front of the face to the top of the head. Is anyone aware of transitional forms showing this migration?
Wonderful post, thank you! Keep it coming.
All Eocene whales together.
Aren't the oldest anthracotheres much older? Because the hippos are anthracotheres (and the whole group is closest to the whales -- Tabuce et al. 2005 in PNAS -- or rather to the whales + raoellids).
Herbivore to carnivore isn't what makes me wonder -- it's transitioning from fresh water to salt water. Mammals eat anything that sits still or moves slowly enough for us to catch up with it and pop it in our mouths so when push comes to shove, we can chow down on almost anything, but no matter what, we can't drink salt water any of us. It's as good as poisonous.
If whales DO drink salt water (and I can't see how they could avoid it), then this is a mammal that had to carry out the more daunting transition from drinking fresh water to somehow living on water that's saltier than it is. I'd love to know more about how that happened.
"Anyway.... slow changes in the proportion of veggies to meat every generation. Give it a thousand generations, or ten thousand or so... no big deal."
Sounds so simple! *eyes rolling*
The credulity of evolutionists is mind boggling.
A bit OT, but with the amazing progression of whale evolution that now seems likely, I offer a music video of Ogden Nash's epic 'What a queer bird the frog are.'
http://www.youtube.com/watch?v=FhhbOw_qdK4
It's really good. I am a fellow Guilfordite, and am proud to have you as a neighbor.
There are a lot of examples of omnivores becoming herbivores--look at people who decide to become vegetarians.
FWIW, deer have been known to eat live birds.
Maybe now we can convince the Japanese to hunt, er do scientific research, on Muskrats instead of Humpback whales?
One question related to the illustration: The air bubbles seem to suggest that the creature is breathing out. Wouldn't it be more typical for such creatures to hold their breath untill they surface again?
Concerning Indohyus purposefully altering its genetic coding to simulate the appearance and flesh of a whale:
"Without contradiction, all flesh is not the same flesh. There is one kind of flesh for fish, another kind of flesh for reptiles, another flesh for birds, another for beasts of the field, and yet another for preternatural creatures. Man, incorrectly classified as a mammal ("beast of the field"), is mandated with a unique type of flesh which differs from all other species. This includes the family of apes which obstructionists theorize to be man's closest ancestors.
It is an indisputable, biological fact that flesh of different types cannot mate and produce a hybrid or intermediate species. A fish cannot mate with a chicken, a cow with a serpent, or a monkey with a whale. More on scale, but equally ridiculous, a bull cannot mate with a mare, a deer with a buffalo, a goat with a pig, or man with any of the preceding; besides which, there are intermediate categories or variances between species of any one order (except man) which precludes crossbreeding between species closely related. For instance, a chicken may only mate with another of the same flesh; it cannot mate with a duck,
turkey, or any other bird.
The fundamental truth that all flesh is not the same flesh and that species of varying flesh cannot crossbreed is one of the most misrepresented facts in biology. A familiar corruption of the truth is the nonsensical clatter promoted by some biologists, who should know better, that the great dinosaurs did not just die out but may have degraded to birds. Abiding by the prospect, a little wren sitting on a branch may have in its ancestral tree a dinosaur or two. The theory, hyped by the media, often with tongue-in-cheek (poking fun at the biologists), may be dismissed entirely: preternatural creatures were and are of one flesh and birds of another. Any suggested crossover, great dinosaurs mating with wrens, or down pattern; that is, hapless dinosaurs purposefully altering their genetic coding to simulate the
appearance and flesh of birds, borders on the bizarre
and should be held with disdain.
The realized truth, downplayed by biologists, has been recognized by most every man, woman, and child throughout the ages. The law of procreation has not been compromised even though learned men of great patience have tried for years to violate it. The rule is even recorded in the Bible for all to see, perhaps, for such a time as this:
38. But God giveth it a body as it hath pleased him, and to every seed his own body.
39. All flesh is not the same flesh: but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds.
40. There are also celestial bodies, and bodies terrestrial: but the glory of the celestial is one, and
the glory of the terrestrial is another.
41. There isis one glory of the sun, and another glory of the moon,and another glory of the stars:for one star differeth from another star in glory.--I Corinthians 15
The 2000 year old statement of truth remains unchallenged and reveals the great wisdom of the writer, surpassing that of obstructionist leagues, even in the assertion that "one star differeth from another in glory"; indeed, all stars are not the same as the investigation will bear out."
The text was taken from The Quest for Right, a new series of 7 textbooks created for the public schools. The several volumes are based on physical science, the old science of cause and effect. The Quest for Right levels the playing field between those who teach physical science and those who preach evolution. Volume 1 is currently available at http://tatepublishing.com Or visit the http://QuestForRight.com website for more information.
Plants are full of indigestible cellulose; that's why extant artiodactyls rely on intestinal symbionts for digestion and have a long intestine (and is some cases, specialized "fermentation vats"). Plants also typically produce toxic defensive chemicals, which must be tolerated or detoxified
I'm glad I checked back on this discussion. Here's a good paleoartist whose work I dig if anyone is interested:
http://ntamura.deviantart.com/
I don't understand how Indohyus and Ambulocetus, both dated to around 47 mya, can both be the ancestors of today's whales. You say carnivory was an important transition for whales. Then Indohyus would have had to split off before Pakicetus, before whales became carnivorous.
Parsons, explain mules and ligers.
Noumenon--good question. See my latest post for an answer: http://scienceblogs.com/loom/2007/12/27/return_to_the_dawn_of_whales_c…
I suppose Indohyus probably already ate animals on occasion. A lot of hoofed animals do actually comparably often eat meat, not only carion, but also small animals. Deers are known to eat young birds, reindeers eat lemmings, hippos eat carrion and sometimes even self-killed big animals and wild pigs eat everything, to make only some examples. Besides the occasional carnivorous behavior of hippos the small duikers and chevrotains are probably most interesting in the relation of Indohyus, as they were of comparable size and had a similar habitat. Most duikers are comparably small, and as forest-dwelling herbivores they have to eat comparably energy-rich things, as their short digestive-system is not effective enough to consume big amounts of low-energy-plant-material. But they do not only eat fruits, buds and fresh foiles, but consume also a lot of animals from ants and other insects to amphibians, reptiles, small mammals and birds, as well as carrion. The bird-hunting behavior of duikers is well-documented from zoos. Interestingly their dentition shows no indication for this behavior, but they are very eager to hunt and kill smaller animals.
The chevrotain is even more interesting, as it dives often in small jungle-streams. It is really amazing to see how this little beasts jump into the water and walk on the ground. But they do not only submerge to flee from enemies, but also to collect fruits which has fallen in the water, and sometimes they even catch small fish.
I can well imagine that occasional carnivory was already present at a very early stage.
BTW, here´s a nice video of a diving chevrotain: http://youtube.com/watch?v=13GQbT2ljxs
"Parsons, explain mules and tigers."
Please know that it is not possible to publish the entire book in this forum.
For more information, purchase Volumes 1 and 2 at your favorite online bookstore. Or go to http://tatepublishing.com or http://questforright.com