Lysorophians and aïstopods

:-) :-) :-)
*happy happy joy joy*

Aquatic sidewinders? Why would an aquatic animal sidewind?

I don't remember which paper it is that debunks the hypothesis of the kinetic phlegethontiid skull, but it looked very convincing. In general, I suspect most non-mammal tetrapod palaeontologists started out by learning extant squamate anatomy and are therefore accustomed to see lots of mobile joints in every skull, leading to streptostylic gorgonopsians, mesokinetic Archaeopteryx, sort of pleurokinetic anthracosaurs, and of course pleurokinetic ornithopods...

As for aïstopods, these are also long-bodied Carboniferous and Permian animals, imagined by some to be eel-like swimmers, and by others to be terrestrial and fossorial (the slide above says that they included both aquatic and terrestrial forms, but I'm not sure where I got that from. Has this issue been resolved yet?).

Based on things like the circular cross-section of the body, Germain (2008a, b) argues for a terrestrial lifestyle for all aïstopods and even suggests that Lethiscus could be the oldest known terrestrial tetrapod, complete with the pun "the first step on land -- without legs".

BTW, you remember how Ruta & Coates (2007) found the adelogyrinids next to the colosteids and far, far away from the other "lepospondyls"? Looks completely crazy at first glance, but it's apparently correct. At least two papers on this are in the works.

Germain D (2008a): Anatomie des Lépospondyles et origine des Lissamphibiens [PhD thesis, partially in English]. Paris: Muséum National d'Histoire Naturelle. 351 pp.
Germain D (2008a): A new phlegethontiid specimen (Lepospondyli, Aistopoda) from the Late Carboniferous of Montceau-les-Mines (Saône-et-Loire, France). Geodiversitas 30: 669 -- 680.
Ruta M, Coates MI (2007): Dates, nodes and character conflict: addressing the lissamphibian origin problem. Journal of Systematic Palaeontology 5: 69 -- 122.

I'm sorry, I' not familiarised with these groups... but if they were fossorials.... shouldnt they at least retain, if not reinforse, their skull bone (particulary the skull roof and the postorbital bar)??

It is impossible to have too many posts about pre-Permian tetrapods.

It is also impossible to have too many pre-Permian tetrapod fossils.

It is also impossible to form a consensus on the relationships between many of the various groups. The morphological gaps are impressive. E.g. whence aïstopods?
Heck, whence "lepospondyls"? [And my personal favorite: whence Acherontiscus?] Lotsa luck forming an authoritative answer. If the creationists ever bothered to read the literature, they would have a field day with the gaps.

I harmonize with Davids sentiments, thanks for the post Darren.

Many thanks for comments, David in particular (I was unaware of Germain's work).

For those who've been following, Tet Zoo did not make it into the top 3 in the 3 Quarks Daily competition. Oh well. Making it into the top seven was an achievement in itself, thanks to all who voted.

WHAT???!!!???!!! Tet Zoo didn't make it into the top 3? That's disgusting. It should have won! BTW, I love those little eely-fishy-amphibiany critters. There so cute! (And, I must admit, I'd never even heard of most of them before. Shocking, I know.) When will you write a full-length article about them?

Derren: I refuse to turn this discussion into one on dinosaurs (I personally can't get enough dinosaurs, but we also can't forget about all the other cool creatures out there, including these little things in the current post. After all, this is Tet Zoo, not Dinosaur Zoo, and one major reason I come here is for the variety). However, there is something I would like to know. As you outlined in Troodontids and Owls - Oh the Irony!, trodontids are very owl-like. Thus my question: Could troodonts turn their heads nearly all the way around, like owls can? I know it's a very idiotic question, but please answer it if you can. Thank you!

I'm really glad to see this post, aïstopods are really interesting, especially from an evo-devo perspective. The trunk vertebral count is pretty well known to be genetically controlled and strict in some amniote groups, and it's interesting to see where it is flexible in other.

I'm also glad this is a non-dinosaur post.... the number of comments to this one, in comparison to comments on dinosaur posts, it noticeable. I understand the enthusiasm for dinosaurs, but what about all the other tetrapods readers? Dinosaurs are even more interesting in the context of how they fit as tetrapods, but one cannot see that if they ignore the rest.

It reminds me of marine mammal work - I could publish a million papers about Sirenia and Desmostylia, but the only time anyone notices marine mammals is when they are whales or pinnipeds. It almost makes we want to avoid working on whales, except that being so diverse they are great for exploring in a comparative way.

I wonder if that's a subject for another post or blog, the question of what motivates people's interest in specific fossil groups?

I hate to sound overly speculative, but I'd hazard a guess ... er.. opinion... that these beauties did NOT have feathers. Anyone care to challenge me on that? ~

BTW, Darren, more marine/aquatics always appreciated; I note that your 'clustermaps' shows red like crazy but still lots of blue showing! Oh, and, do you think any of these ancient slitherers were electroshocking predators?

I've got a question for Darren (Comment 6). Does anybody know when he usually checks the comments on his articles?

Interesting creatures! Me too, never heard of them before.

BTW - did extinct amphibians have tadpoles (I know, some were neotenic). Do tadoples fossilize? Does a tadpole have a cartillage skeleton - and what happens to it when it metamorphoses?

Jerzy: Yes, tadpoles fossilize, but only rarely. Tadpoles do, indeed, have a cartillage skeleton, which is then replaced with a bony one when they metamorphose.

We find snakes and snake like animals among the reptiles and amphibians and their ancestors, but no snake like animals among the mammals and their ancestors. What is this telling us?

What it tells me is that the ophidiform body plan was lost among the ancestors of mammals fairly soon after reptiles and mammals split, and thus the reptilian and mammalian lines go back a lot further than we think.

Now consider the difference in the placement of the pineal gland in mammals and reptiles.

I'd never heard of any sidewinding trace fossils, amazing to see. But there's absolutely no way they were made underwater; any animal able to sidewind would more easily swim by simple lateral undulation, with no twisting required. The lifting of the body loops in sidewinding is a way of concentrating contact forces at a small proportion of belly area, increasing friction to prevent sliding, so it would be totally pointless where body weight is supported (and locomotion facilitated) by water. Even with a very thin water layer over the mud there'd probably be a lot more lateral and posterior sliding, not such clear straight tracks, so I guess the mud was drained enough to be sticky rather than slippery. I'll go look up the paper now...

Oh, and Michael Erickson, some of your comments on the preceding post reminded me of this. You Americans!

Alan Kellogg: What is this telling us? That for small endothermic animals, surface area / volume ratios matter? But what it tells you is... very strange. The ophidiform body plan was lost among ancestors of mammals (lost? - but they never had it!) - maybe you mean potential for the ophidiform body plan? (BTW, we'd usually say serpentiform, so as not to mix Latin and Greek roots). But what has this got to do with divergence dates or pineal organs?

John Scanlon, #13

No snake like mammals: Exactly? And how long ago was the shape lost? How far back does one have to go until one finds an ancestor of mammals that was snake like?

On pineal glands: Two questions;

One. Where is the pineal gland located in reptiles?

Two; Where is the pineal gland located in mammals?

Yes, it's located in the brain in both cases, but where exactly in the brain?

Re: "underwater" sidewinding.
The trace fossil sure LOOKS like a trace of sidewinding, and it may be (I wouldn't know) that there are good sedimentological reasons to think the substrate was wet when the sidewinder wound it, but how deep: perhaps sidewinding was used for essentially above-water progression (hence obviating the "why didn't they just SWIM?" objection) when there was only a millimeter of water over the substrate?

Ancestor of mammals that was snakelike?

Well, that would not be any synapsid, amniote, tetrapod, osteichthyan or gnathostome. Basically, some kind of chordate 'worm', say the last common ancestor of mammals and lancelets or conodonts. Precambrian or early Cambrian, say.

@Darren: I dunno if this entry has anything to do with my recent begging for entries on aïstopods, but either way you have my gratitude.

@Alan: The mammal-"reptile" split is currently thought to have occured in the Carboniferous, 6/7 or so the way back to Acanthostega. How much earlier would you have it?

Of course, depending on how you define "ophidiform", Basilosaurus may qualify.

Jerzy:

Do tadpoles fossilize?

Sometimes, yes. See here, for example.

I'm here, just very busy (so much so that I've again been unable to complete anything new for the blog). Assorted responses...

-- troodontid neck flexibility (comment 6). I don't think anyone has published any comments on deinonychosaur neck flexibility, but given the anatomy of the cervical vertebrae and length of the neck, I'd expect that these animals could turn their heads well round to the side. However, their cervicals were long, and low in number compared to neornithines like owls (where the cervicals are far shorter and apparently with a greater degree of rotational ability). In other words, no reason to imagine owl-like neck flexibility.

-- Brian (comment 7): I love dinosaurs, but I get frustrated by the fact that they sometimes seem to be the only animals that draw in a huge readership. Note how few comments appear when I post about certain groups of living animals: very frustrating, but nothing I can do about it. Also of great interest is the fact that the super-sexy animals â dinosaurs (including birds), hominids â are the only ones that draw in huge amounts of vocal controversy and 'fringe' interest. This is really ironic, as the greatest controversies and areas of uncertainty in evolutionary biology do NOT concern such things as bird origins, or the environmental preferences of early humans, but such things as microsaurs and lissamphibian origins, and the position of snakes and turtles.

-- Did any Palaeozoic/Mesozoic non-amniote tetrapods have aquatic larvae (comment 10)? Note for starters that the term 'tadpoles' is restricted to anurans: the larvae of other animals (including other lissamphibians) should not be called tadpoles (or so I'm reliably informed). We know that some temnospondyls and perhaps some microsaurs, at least, had aquatic larvae and underwent metamorphosis, but the transformations involved may have been less radical than that associated with anurans, and it may be that 'advanced' temnospondyls â like eryopoids, dissorophoids and zatrachydids â and just a few microsaurs (like Pantylus) were the only ones that did this (Schoch 2001). How widespread were larval phases and metamorphosis among tetrapods in general? Though some authors have opined that loss of the larval stage was unique to amniotes (Robert Carroll said this in a few papers from the 1970s and 80s), I get the impression that those tetrapods more basal than temnospondyls and microsaurs (Ichthyostega and similar forms, baphetids, anthracosaurs, nectrideans, lysorophians etc.) did not undergo a profound ontogenetic transformation. A few people who work on these groups are Tet Zoo regulars: they may know more!

-- Sidewinding tracks preserved underwater (comments 13): obviously, you need to read Braddy et al. (2003), the relevant section is on pp. 678-680. They argue that the tracks were indeed produced underwater, and they conclude that the long-bodied animal that made the tracks was indeed undergoing a sort of subaqueous sidewinding. There is another reason to be slightly sceptical: the diagrams (p. 679) show the foot impressions much more clearly than do the trace fossils themselves (p. 678), and the foot impressions are the important bit, as they indicate that these traces were not made by fish (fish often leave S-shaped traces on submerged substrates). However, the authors are pretty convinced about the foot impressions, and are therefore pretty confident that the tracks were made by a long-bodied tetrapod. One of the authors on the paper is also a Tet Zoo regular: does he have comments?

And, Andreas, yes, you were inspirational :)

Right, back to work (TV research)...

Ref - -

Schoch, R. R. 2001. Can metamorphosis be recognised in Palaeozoic amphibians? Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 220, 335-367.

Thanks, fascinating.

Even more interesting are developmental/genetic implications of tadpole. Vertebrate which radically alters its body plan, huge areas of bones, muscles and nerve structures disappear and develop. I wonder why half of genetic papers on cancer, hox genes etc. don't draw heavily from amphibian development.

PS. snakelike mammals? Look at weasels and ground squirrels at land, and otters and whales underwater.

> BTW - did extinct amphibians have tadpoles (I know, some
> were neotenic).

Jerzy,
some non-amniote tetrapods had distinct juvenile and adult forms. Others dropped the adult form and became neotenic. Others dropped the juvenile forms and became peramorphic.
This is one of the reasons why non-amniote tetrapod systematics are such a mess. To quote Palaeos: "Like some peculiar non-Euclidian fold in the universe of physics, this is a region in which the fundamental laws of cladistics may not hold.(...) How can we do good cladistics on animals which may have more than one morph?" Or, even worse, with animals that are known from only one of the two potential morphs? The microsaurs, for example, had effectively jettisoned the adult form. If an adult form of, let's say, *Pantylus*, had existed, it might have looked exactly like an early amniote, and the phylogenetic position of this beast may change entirely. This is, btw, one of the reason why stem tetrapods shouldn´t be called "amphibians", we don't know for sure if temnospondyls or lepospondyls were actually closer related to modern lissamphibians than they are to amniotes.

> Do tadpoles fossilize?

We have fossils of juvenile seymouriamorphs, and some neotenic temnospondyls are so abundant that the remains of their armour are used as index fossils, but those aren't "tadpoles" in the strictest sense.

Darren:

Note for starters that the term 'tadpoles' is restricted to anurans: the larvae of other animals (including other lissamphibians) should not be called tadpoles

That I didn't know. What should the larvae of salamanders and newts be called, then? Just 'larvae'?

Note how few comments appear when I post about certain groups of living animals: very frustrating, but nothing I can do about it. Also of great interest is the fact that the super-sexy animals â dinosaurs (including birds), hominids â are the only ones that draw in huge amounts of vocal controversy and 'fringe' interest.

Cryptozoology also attracts the crowds, no? (Personally, though, I rather prefer the more favourable signal-to-noise ratios in the less 'sexy' subject threads.)

if they were fossorials.... shouldnt they at least retain, if not reinforse, their skull bone (particulary the skull roof and the postorbital bar)??

Sure, but the lysorophians only burrowed into soft mud at the bottom of bodies of water (like lungfish), and the aïstopods burrowed, if at all, in leaf litter. And while Phlegethontia has indeed lost the parietals, it has a complete ossified braincase roof.

It is also impossible to form a consensus on the relationships between many of the various groups.

Naaah. We're close to having one. :-)

The morphological gaps are impressive. E.g. whence aïstopods?

Probably from the nectrideans (which are paraphyletic in this case) or right next to them.

Heck, whence "lepospondyls"?

Lepospondyls, amniotes + diadectomorphs, seymouriamorphs, and Solenodonsaurus are all very similar. Westlothiana, the basalmost lepospondyl, was originally thought to be an amniote or very close to them.

And my personal favorite: whence Acherontiscus?

It goes right between colosteids and adelogyrinids, where Ruta & Coates (2007) found it.

Yes, it's located in the brain in both cases, but where exactly in the brain?

In the exact same place. What you're talking about is the fact that the mammalian cerebral hemispheres are so bloated they've overgrown the pineal gland.

Tadpoles: later. I have to go. (Translation: I should have gone 1/4 h ago...)

What should the larvae of salamanders and newts be called, then? Just 'larvae'?

Yes. "Tadpole" is reserved for the stage before the extremely compressed metamorphosis of frogs.

How could I be so rude as to ignore a personal request for comment?
My involvement in the project came about when I was at Bristol and Simon Braddy asked me if there were any long-bodied limb-reduced tetrapods in the Permian. I then told him of Lysorophians. When he showed me pictures of the tracks I immediately said - 'they look like sidewinding tracks'. That was pretty much my input into the paper. To be sure I'd never been quite convinced that they really were footprints on those tracks but they certainly do contain are a series of repeating en-echelon marks that look like sidewinding. If they weren't sidewinding I don't know what the hell those trackmakes were up to.
As an interesting aside, similar marks have since been found in the Clarens Formation by Francois Durand of the University of Johannesburg. Now this is a nice aeolian unit - a perfect environment for sidewinding as we know it but of course being Early Jurassic - no snakes to sidewind. Francois thinks that snakes are an older clade than their body fossil record would suggest, he actually goes so far as to ascribe the Clarens traces to the activities of advanced viperids. Needless to say that idea is not terribly popular but the question still remains what long bodied animal was around to make those tracks? - none that I know of.
Which then begs the question 'Is there some other action that we are not thinking of that can produce a sidewinder like trace?' I really don't know.

I was thinking about the "no mammalian snakes" post. I don't know a whole lot about the details of the vertebrate skeleton, but it seems to me that mammalian backbones are better able to bend vertically, while snakes, amphisbeanians, caecelians, and all these other things have vertebral columns which bend horizontally. Just compare the up and down tailstrokes of a whale with the side to side strokes of everything else. So a mammal just wouldn't be able to slither effectively-it just wouldn't bend well in the right way. Or at least that's my theory. This is supported by the fact that there is a fairly snakelike fossil whale (the name escapes me at the moment). In the water the direction of undulation doesn't really matter.

@Adam: You're presumably thinking of Basilosaurus which I mentioned above.

I did a double-take when I saw Adam Yates say...

I don't know a whole lot about the details of the vertebrate skeleton

Let me note that the Adam in comment 26 is not the same as the Adam in comment 25. The latter is Adam Yates, author of Dracovenator (both the blog and the taxon :)).

Oh, and, as David said, salamander larvae should indeed just be called larvae. However, the name 'eft' is also available (though little used).

Darren:

'Note how few comments appear when I post about certain groups of living animals: very frustrating, but nothing I can do about it.'

Well, sometimes we just read with amazement! It's not that these topics are uninteresting. Topics which generate most comments are usualy not the most interesting - there are some troll topics which generate vomitingly repetitive arguments. Please keep the unusual animals coming!

Thanks!

So, how a skeleton of a larval non-anuran looks like? Is it carillage? Does it have all the bones of an adult + gill arches?

To all, check the article anew: have just added an update.

For those who are interested I've put up a post on the poorly known Clarens side-winding trace up on Dracovenator.

"I don't know a whole lot about the details of the vertebrate skeleton"

After a slew of rejections from journals I'm wondering whether or not that might be true.

230-250 vertebrae? Amazing! I'm guessing the skeletons in the first picture are not to scale with each other? How large did these guys get?

Quick question, which will lay my ignorance bare: how exactly would such a large number of vertebrae have formed? I am guessing that these guys are in some way descended from tetrapods possessing fewer vertebrae; thus, how do you add a vertebra to the vertebral column? I know in humans, at least, extra vertebrae can be present as a result of genetic mutations: is the situation in these amazing lysorophians and aïstopods just the result of selective pressures favouring such mutations over time, or is there some other way for vertebrae to be "added"?

I'm back (at home now) and I'm looking at the Braddy, Morrissey and Yates paper. There are a couple of issues to comment on: (1) subaqueous vs. terrestrial, and (2) direction of motion. This leads to (3) questioning taxonomic affinity of the trackmaker. Disclaimer: IANA ichnologist, but I do see plenty of reptile tracks about these parts of northern Australia, and I've done a small study of sidewinding in elapids.

(1) I gave reasons above (comment 13) why sidewinding underwater would make no sense. Numerous aquatic snakes sidewind on wet mud or sand, but as far as I'm aware nobody ever reported seeing it done underwater. After a closer look at the figure of Serpentichnus robledoensis (fig. 4, reproduced by Darren above) I now see more evidence of lateral sliding, and the sediment is apparently a very fine-grained mud because those things are tiny, each body impression of the bigger trackway about 88 mm long. So I still think they're subaerial, but the top layer of the substrate was wet and very soft and slippery, not 'sticky' as I judged when guessing a larger body size (30 cm or more). The authors infer that the trackways were "produced in a subaqueous freshwater environment, with intermittent subaerial exposure"; the parallel lineations attributed to a water current are much fainter than the animal tracks but seem to overlie them, and I don't see why they couldn't all have been formed as water rose to very gently cover the tracks.

(2) When a snake sidewinds, waves are initiated by lateral (and posterior) motion of the (usually raised) head end, and travel from front to back (caudad) as in normal lateral undulation. Supposing a starting position with the body at rest, stretched out straight on a nearly frictionless surface: the only possible motions involve pulling one or both the extremities towards the centre of mass. That's what happens: the head (or most anterior part touching the ground) is lifted, pulled back and to one side, and replaced on the substrate. The lateral component causes compression ridges along the side the snake is travelling away from, as it pushes loops in the opposite direction. The rest of the body follows, naturally, and by the time the tail is lifting off the head may already be two full steps away, or more.

But what Braddy et al. depict in fig. 5 requires loops to form at the tail and travel craniad (each lifting cycle moving body segments forward and to the left). This arse-about progress is biomechanically possible, but seems behaviourally unlikely as a normal means of locomotion. However, it does seem consistent with the sliding traces being mainly on the left side (especially in the posterior trunk), with compression ridges to the right... UNLESS
(3) the 'forward-facing pes prints' are actually marks of backward-facing pectoral fins. The supposed drag-marks of 'ventral scales' could also be from fins - they look more like they were produced by a row of spines than scale-margins.

So that's my version: a sidewinder indeed, but not a subaqueous serpentiform tetrapod moving head-forward and to the left (up-slab in Braddy et al's fig 4), rather a subaerial anguilliform fish moving back and to the right (still up-slab, but head-down). Arguments, any?

BTW Darren, what's that coiled skeleton in the photo next to the trackways in the slide? Was that from Carroll '88? (looks familiar but I don't have a copy)

Is there a difference between serpentiform and anguilliform, or is it just the later seems more natural when applied to fish?

Braddy et al. (2003) is a strange paper. What are xiphosurans doing in a freshwater environment, there are nectrideans with just four fingers per hand, I can't see the pes prints of Serpentichnus, what sense does it make to assume sauropsid scales on a lysorophianâ¦

As an interesting aside, similar marks have since been found in the Clarens Formation by Francois Durand of the University of Johannesburg. Now this is a nice aeolian unit - a perfect environment for sidewinding as we know it but of course being Early Jurassic - no snakes to sidewind.

Hm. All I can suggest is Eocaecilia, but of course a sidewinding caecilian would be bizarre enough in itself⦠Eocaecilia does come from an aeolian deposit, though.

I get the impression that those tetrapods more basal than temnospondyls and microsaurs (Ichthyostega and similar forms, baphetids, anthracosaurs, nectrideans, lysorophians etc.) did not undergo a profound ontogenetic transformation.

Apparently all those animals, and most temnospondyls, underwent a very slow transformation. You could define metamorphosis by the point at which the gills disappear* and/or the gill slits close** (and that's done in the seymouriamorph literature), but none of the other changes happen at the same time: one bone ossifies after another, and the body proportions change gradually.

The dissorophoid temnospondyls, as well as the zatrachydid (â¦zatracheid?) ones, concentrated many of these changes, and many new ones, in a shorter period that can be called metamorphosis. (In addition to Schoch 2001, see Schoch 2002, ref below.) This involves the delay of some changes (like the ossification of quadrate and articular) until metamorphosis, a condition that reaches an extreme in the micromelerpetontids and the branchiosaurids (some species of which, perhaps most, were neotenic).

Salamanders and caecilians have an even more clearly defined metamorphosis (which, in salamanders, involves major restructurings of the bones of the palate, like the complete loss of the palatine for example, as well as general bone remodelling), and the frogs show the extreme condition by making sexual maturity, loss of the tail, lots of ossification, and other events part of the package (so much so that even completely aquatic frogs like pipids undergo a complete metamorphosis with the loss of tail, gills, and gill slits).

Lepospondyl ontogeny is completely unknown, except for partial growth series in the neotenic "microsaurs" Microbrachis and Hyloplesion (where even the smallest known specimens have a completely ossified skull and even a completely ossified vertebral column), eight specimens of Phlegethontia which can be grouped into three stages of a growth series (Anderson 2002), and traces of what appears, by comparison to lissamphibians and/or temnospondyls but not Phlegethontia, to be neoteny in lysorophians (lack of certain skull bones, lack of interpterygoid vacuities, retention of sutures between centrum and neural arches and even between left and right neural arches). That's it. To add insult to injury, the skull ossification sequence (as far as it can be reconstructed from those three stages) is utterly unlike those of temnospondyls, lissamphibians, or anything else.

Schoch (2001) says the lepospondyl Pantylus had a slow ontogeny not condensed into a metamorphosis. Neither I nor Michel Laurin (pers. comm. -- he's sitting at the other side of the desk) are aware of any kind of known growth series for Pantylus, and Schoch doesn't cite anything for this. ~:-| I'll write to him.

* There's evidence for gills in apparent adults of the temnospondyls Trimerorhachis, Dvinosaurus, and Gerrothorax, BTW. But these have long been considered completely aquatic and even neotenic.
** In salamanders with incomplete metamorphosis, like cryptobranchids and Amphiuma, the gills disappear, but the gill slits never close -- they're useful for feeding.

On to tadpoles. Tadpoles are basically pharyngula-stage embryos elaborated into a feeding stage; that's why they're so similar to tunicate larvae. The entire skeleton is cartilaginous for a long time (some dermal skull bones appear a bit before metamorphosis); there are no real jaws and no teeth; the tail never ossifies at all. Many tadpoles are herbivorous, while no adult frog is.

Jason S. Anderson (2002): Revision of the aïstopod genus Phlegethontia (Tetrapoda: Lepospondyli). Journal of Paleontology 76: 1029 -- 1046.
Rainer R. Schoch (2002): The evolution of metamorphosis in temnospondyls, Lethaia 35: 309 -- 327.

Many neat comments and questions here - I don't have time to address them though.

What is the coiled skeleton shown on the slide (comment 34)? It's a skeleton of Brachydectes elongatus (originally described by Olson (1971) as Lysoropus tricarinatus), apparently aestivating at the bottom of a burrow (taxonomic revision provided by Wellstead (1991)).

Refs - -

Olson, E. C. 1971. A skeleton of Lysorophus tricarinatus (Amphibia: Lepospondyli) from the Hennessey Formation (Permian) of Oklahoma. Journal of Paleontology 45, 443-449.

Wellstead, C. F. 1991. Taxonomic revision of the Lysorophia, Permo-Carboniferous lepospondyl amphibians. Bulletin of the American Museum of Natural History 209, 1-90.

Failed to close a <b> tag somewhere near the end of comment 36.

So that's my version: a sidewinder indeed, but not a subaqueous serpentiform tetrapod moving head-forward and to the left (up-slab in Braddy et al's fig 4), rather a subaerial anguilliform fish moving back and to the right (still up-slab, but head-down). Arguments, any?

<would lift one eyebrow if I could>

Fascinating.

What could such a "fish" be? Acanthodes? A baby of one of the more elongate chondrichthyans like Thrinacoselache?

some non-amniote tetrapods had distinct juvenile and adult forms. Others dropped the adult form and became neotenic. Others dropped the juvenile forms and became peramorphic.

Lack of a terrestrial adult morph appears to be plesiomorphic for limbed vertebrates (Schoch 2001).

This is one of the reasons why non-amniote tetrapod systematics are such a mess.

A mess? The only real problem is where the lissamphibians fit. (This particular problem is connected to ontogeny discombobulating phylogeny, though.)

To quote Palaeos: "Like some peculiar non-Euclidian fold in the universe of physics, this is a region in which the fundamental laws of cladistics may not hold.(...)

At least one of the authors of Palaeos.com loves his scenario-based phylogenies so much that he spent a lot of time and webspace on saying "Haaa! I found a hole in cladistics!!!1!" It gets annoying after a while.

How can we do good cladistics on animals which may have more than one morph?" Or, even worse, with animals that are known from only one of the two potential morphs?

Easy: score only adults as known for ontogeny-related characters. See Wiens et al. (2005).

The microsaurs, for example, had effectively jettisoned the adult form.

What??? Do you mean Microbrachis, or do you maybe mean the branchiosaurid and micromelerpetontid temnospondyls?

If an adult form of, let's say, *Pantylus*, had existed,

Pantylus is only known from terrestrial adults (unless Schoch's unsourced claim cited above is right -- as mentioned, I'll write to him).

it might have looked exactly like an early amniote, and the phylogenetic position of this beast may change entirely.

Yeah, right. It might have grown a fifth finger on the already fully ossified hand, a transverse flange on the pterygoid, a fucking supratemporal in the skull, a drastically more plesiomorphic skull-atlas joint, an axis intercentrum⦠Look, this is nonsense. I mean, I can't disprove it, but it fails epically at resisting Ockham's Chainsaw.

Wiens JJ, Bonett RM, Chippindale PT (2005): Ontogeny discombobulates phylogeny: paedomorphosis and higher-level salamander relationships, Systematic Biology 54: 91 -- 110.

I always see microsaurs and eel-amphibians briefly described in every "encyclopedia of prehistoric life" type book I read, but there's never enough information on them. Good to read this post, and the ensuing comments.

Steve P @ #33 asked a good question (from the perspective of a developmental biologist at least):

how exactly would such a large number of vertebrae have formed?

Vertebrae develop from embryonic cell populations called somites (the sclerotome part, to be specific), or chunks/balls of mesoderm on either side of the neural tube. The somites themselves are periodically segregated (in pairs) from masses of presomitic mesoderm through a "clock and wavefront" mechanism, driven by a molecular oscillator.

There's an interesting paper by Gomez et al. in Nature, from 2007 (doi:10.1038/nature07020) on somitogenesis in the corn snake embryo, which concludes that the segmentation "clock" in the mesoderm runs faster in this animal, with respect to overall developmental rate. They propose that this leads to the formation of more somite pairs (and hence more vertebrae) in the snake, but the individual somites are much smaller. The corn snake embryo has 315 somite pairs, and the images in the Gomez paper are absolutely fascinating. The paper includes comparisons with somitogenesis in zebrafish, mouse, and chick embryos, and I guess one could extrapolate to the lysorophians and aistopods discussed here.

I just saw the add-on. Yes, I, for one, LOVE Palaeozoic non-amniote tetrapods! Keep 'em coming Darren!

Only one who has never been in thrall to crosswords would say that the word "eft" is rarely used. It's such a pleasing word that it's disappointing that most people rarely find occasion to use it in conversation. I try, I try.

I hate crosswords. Also soduku, sport, cookery programmes and reality TV.

Cheers Barn Owl, I will read that paper (and another associated one I found whilst searching for Gomez et al.) on my lunch break!
#43: Darren, I whole-heartedly agree with you about cooking programs and (especially) "reality" TV shows, though I love soccer (sorry, football; force of habit)...

[aïstopods] Probably from the nectrideans...

How "probably"? Skulls are kinda quite different. Same for caudals. From stem to stern.

Lepospondyls, amniotes + diadectomorphs, seymouriamorphs, and Solenodonsaurus are all very similar.

Mmm, yes, aïstopods, Diadectes, easily confused. :-)

[Acherontiscus]...goes right between colosteids and adelogyrinids, where Ruta & Coates (2007) found it.

*fnort*

I haven't seen Ruta & Coates (2007), does it differ much from Ruta et al. (2003)?

The only real problem is where the lissamphibians fit.

Assuming monophyly for the group. Could be two or three problems. Besides, lissamphibian placement is the only problem? I have pointed out the existence of the morphological gaps earlier, and I am far from alone on this. Sure cladists can load up their PAUPs and get their results and be darn sure that they have a definitive answer. But when you have these huge morphological gaps obscured by the problems of pedomorphosis [a problem elaborated on by Schoch (1986), and AFAIK has not been adequately dealt with since]. IMHO cladists should be reminded that it is perfectly respectable to use the phrase incertae sedis.

Ruta M, Coates MI, Quicke DL. 2003. Early tetrapod relationships revisited. Biol Rev Camb Philos Soc. 78(2):251-345.

Schoch, RM. 1986. Phylogeny Reconstruction in Paleontology. Van Nostrand Reinhold.

While we are on the subject of non-dinosaurs, does anybody know of a good diagram of the superficial musculature of a modern crocidilian (any species will do)? I have searched ABSOLUTLEY EVERYWHERE and can't find a single one. (The exception, of course, being a diagram of very questionable accuracy in a kids' book: Zoobooks Crocodiles & Alligators. But even if it is accurate, the animal in the diagram is twisted in such a way that I can't see most of the neck and forelimb musculature.) I am in desperate need of help. If a kind soul out there somewhere could lend me a hand, it would be WILDLY apprectiated. Thank you.

Were'd everybody go? I certainly hope I'm not being pushy, but it's really important that some kind soul answer my question (comment 46). Maybe I should start begging. Here we go... PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE PLEASE

> Lack of a terrestrial adult morph appears to be
> plesiomorphic for limbed vertebrates (Schoch 2001).

Yep. But in some cases, the terrestrial adult morph was lost secondarily.

> A mess? The only real problem is where the lissamphibians
> fit.

A rather big problem, especially if you consider the fact that the broad public still calls ALL stem tetrapods "amphibians".

> At least one of the authors of Palaeos.com loves his
> scenario-based phylogenies so much that he spent a lot of
> time and webspace on saying "Haaa! I found a hole in
> cladistics!!!1!" It gets annoying after a while.

Palaeos is full of rants and side-stories, dealing with everything from classical mythology to lovecraftian lore. Some of it is quite enlightening, some of it is entertaining, and some of it is plain weird. As a rule of the thumb, I consider this amusing rather than annoying. I know that they have a strong bias against molecular-based clades in general and afrotheres in peculiar; I haven't recognized an anti-cladistic bias yet, the sheer humungous size of Palaeos means that I haven't read all of it.

> What??? Do you mean Microbrachis, or do you maybe mean
> the branchiosaurid and micromelerpetontid temnospondyls?

*Microbrachis*.

> Pantylus is only known from terrestrial adults (unless
> Schoch's unsourced claim cited above is right -- as
> mentioned, I'll write to him).

This will be helpful :-)

> Yeah, right. It might have grown a fifth finger on the
> already fully ossified hand, a transverse flange on the
> pterygoid, a fucking supratemporal in the skull, a
> drastically more plesiomorphic skull-atlas joint, an axis
> intercentrum⦠Look, this is nonsense. I mean, I can't
> disprove it, but it fails epically at resisting Ockham's > Chainsaw.

Oops, I shouldn't have used *Pantylus* as a standard or model microsaur. This was a brainfart - when I hear microsaur, I think *Pantylus*, probably because it is the only member of this otherwise emo-like clade that has some charisma, sort of. *Microbrachis* would have been a better example of a pedomorphic microsaur.

I know that they have a strong bias against molecular-based clades in general and afrotheres in peculiar

Mr White had a change of heart regarding molecular trees some years ago; Palaeos being Palaeos, plenty of anti-molecular rants are still left scattered on the site, but newer pages are much more accepting of them.

(No idea what he thinks of Afrotheria specifically these days.)

Rainer Schoch has, admirably, already replied: He does not remember why he included Pantylus in that list, because he's not aware of any juveniles/larvae either; maybe it was just because he (like everyone else) thinks it was terrestrial (as an adult anyway). He told me to write to Andrew Milner; I'll tryâ¦

How "probably"?

It's the most parsimonious option.

The idea isn't new, either: the name "Holospondyli" for both goes back several decades.

Skulls are kinda quite different.

Forget Phlegethontia and Diplocaulus. Check out Sauropleura, Ptyonius and Lethiscus.

Same for caudals. From stem to stern.

"Nectrideans" and aïstopods share a fairly long list of pretty weird vertebral synapomorphies.

Mmm, yes, aïstopods, Diadectes, easily confused. :-)

Look at Hylonomus, Westlothiana and Tuditanus, and tell me that again. :-) Limnoscelis and Tseajaia differ from those mostly by sizeâ¦

I haven't seen Ruta & Coates (2007), does it differ much from Ruta et al. (2003)?

Not as much as it should (they added taxa, added characters, and removed a few correlated characters without properly fusing them; not a single mistake in the matrix was corrected!), but it does differ. You should get it one way or another, because it replaces the 2003 versionâ¦

Test to see if I can write a tree here or if that only works on Pharyngula:

--+--A
`--+--B
`--C

Anyway, Ruta & Coates (2007) find (Scincosaurus (Diplocaulidae (Urocordylidae, Aïstopoda))), of which the first three are "nectrideans", next to Brachydectes (the lysorophian) and nested inside the "microsaurs".

The only real problem is where the lissamphibians fit.

Assuming monophyly for the group. Could be two or three problems.

Yes, but lissamphibian monophyly is by far the most parsimonious assumption from several independent lines of evidence (MarjanoviÄ & Laurin 2007, 2008a, 2008b, in press, and references therein).

Besides, lissamphibian placement is the only problem?

I wrote "the only real problem". It's the only major-league problem in here. There are of course minor-league ones -- "nectridean" monophyly or lack thereof, "microsaur" phylogeny, the position of Solenodonsaurus, the position of anthracosaurs and temnospondyls with respect to each other, the position and monophyly of the "gephyrostegids", the positions of Silvanerpeton and Caerorachis, the position of Casineria (but I repeat myself⦠wait for the papers, or read chapter 8 of this thesis), the exact positions of "whatcheeriids" (probable but questionable monophyly), baphetids, colosteids, and Crassigyrinus with respect to each other, the already mentioned adelogyrinids and Acherontiscus, the exact positions of Acanthostega and Ichthyostega with respect to each other⦠oh, and, temnospondyl phylogeny is a greater mess than one might think. :-) But the general shape of the tree has practically not changed at all since Carroll (1995).

Sure cladists can load up their PAUPs and get their results and be darn sure that they have a definitive answer.

LOL. Guess what I'm working on right now. Or just read our 2008b paper -- I'll post a link later; it's free-access.

Phylogenetics is hard work⦠:-)

But when you have these huge morphological gaps obscured by the problems of pedomorphosis (a problem elaborated on by Schoch (1986), and AFAIK has not been adequately dealt with since).

I cited Wiens et al. (2005) above; check it out. Its findings are applied in our 2008b paper and the in-press one.

IMHO cladists should be reminded that it is perfectly respectable to use the phrase incertae sedis.

Nope. Phylogenetics is a science now; you have to quantify your uncertainty. That's what all those bootstrap, jackknife and Bremer values and the Bayesian posterior probabilities are for, as well as all those winning-sites tests and whatnot.

Were'd everybody go? I certainly hope I'm not being pushy, but it's really important that some kind soul answer my question (comment 46).

Where in the world are you? Maybe everyone else was sleeping?

I for one have little idea about myology; I can't help you.

Palaeos is full of rants and side-stories, dealing with everything from classical mythology to lovecraftian lore. Some of it is quite enlightening, some of it is entertaining, and some of it is plain weird. As a rule of the thumb, I consider this amusing rather than annoying.

Oh, I agree: many of them are interesting and/or amusing. I especially enjoy the Jarvik saga: so true, so trueâ¦

this otherwise emo-like clade

:-D :-D :-D

Yes, Microbrachis was clearly paedomorphic (though much less so than any pre-/non-metamorphic branchiosaur).

Test to see if I can write a tree here or if that only works on Pharyngula:

Wow. What an epic fail.

@David: The link to that thesis doesn't work.

Hi,

Did any amphibian clade reversed from neoteny back to metamorphosis, or it is one way track?

"Yes. "Tadpole" is reserved for the stage before the extremely compressed metamorphosis of frogs."
wrote D. MarjanoviÄ

..and male children in the South eastern United States.

I've long been a bit...disappointed that mammals never
came up with the snake body plan, especially after being
razzed about 'Snow snakes' during my youth in North Dakota.
I wonder if isn't simply that the mammels simply haven't
gotten around to it yet...Weasels, minks, and the like
( Mustelids, I think? ) would seem to be good candidates
for an excercise in Spec. Zoology...

Will somebody PLEASE answer my question (comment 46)?

Sorry, I just saw that David had adressed my question, but couldn't help. Thanks anyway, David!

The link to that thesis doesn't work.

It does. Try again.

I wonder if isn't simply that the mammels simply haven't gotten around to it yet...Weasels, minks, and the like ( Mustelids, I think? ) would seem to be good candidates for an excercise in Spec. Zoology...

They already have a doubled resting metabolic rate to compensate for their disadvantageous surface-to-volume ratio. The maximum for endotherms can't be far away.

BTW, this is a computer, not a typewriter. You don't need to hit "Enter" at the end of a line. Line breaks are made automatically. :-)

Regarding mammalian snakes: The star nosed mole is probably the best candidate, it burrows through soft wetland soils and can smell underwater, eats superfast, amazing tentacles, etc.
http://en.wikipedia.org/wiki/Star-nosed_mole

Sort of related to topic..
Question: Sauropods have large pneumantic vertebrae, manatees have big super dense ribs, bony fish have many thin bones; so did early vertebrates (way before dinos) swim upside down with dense vertebrae as part-ossified ballast (like early turtle plastron), making them inverted invertebrates, then after developing an air sac, flip back right side up, then sauropods further lightened the vertebrae due to occasional (upright) shallow water wading and swimming? (I know 'semi-aquatic dinos' are old school, but I figure more primitive dinos were more water dependent, later ones much less so.)

IOW was the backbone & bony rib cage initially a ballast & armor trait? Is a notocord lighter than a vertebral column?

Do sharks have a (buoyant) myelin segmented sheath around the spine, while bony fish and tetrapods have a mineralised segmented sheath around the spine? (comment posted to tetzoo, pharyngula, SVPOW, AAT) Anyone know?

On the mammalian snake issue, has anyone mentioned the possibly legless fossorial hedgehog?

did early vertebrates (way before dinos) swim upside down with dense vertebrae as part-ossified ballast

Nope. Really early vertebrates did not have ossified vertebrae in the first place. They only had dermal bone.

making them inverted invertebrates

The evidence for the inversion hypothesis is a lot weaker than many people think. It looks obvious when you just compare chordates and arthropods, but add mollusks and flatworms, and it all breaks down.

then after developing an air sac, flip back right side up

Why wouldn't they develop it on the side that was up?

then sauropods further lightened the vertebrae due to occasional (upright) shallow water wading and swimming?

So you haven't been able to get Henderson's paper on how at least the most famous sauropods were basically too light to swim? They floated like corks and may have had their center of gravity above the waterline -- don't try this at home.

I figure more primitive dinos were more water dependent

Because of which evidence? Surely you've taken the dinosaur-filled Early Jurassic desert sediments of North America and southern Africa into account...?

was the backbone & bony rib cage initially a ballast & armor trait?

Would really surprise me. The armor was in the skin, and additional ballast wasn't needed.

Is a notocord lighter than a vertebral column?

I think so.

Do sharks have a (buoyant) myelin segmented sheath around the spine

What? Myelin is the isolation sheath around certain nerves. It doesn't occur anywhere else. And there's never enough of it to convey buoyancy -- the heaviest part of your body is the head, which is chock full of myelin.

On the mammalian snake issue, has anyone mentioned the possibly legless fossorial hedgehog?

The longer people look at it, the more probable it appears that it did have legs... we've been through that on the DML-KT...

David: Some people have hardly nothing but myelin in there.

Oh yeah, what was the name of that hedgehog? Googling "legless fossorial hedgehog" didn't get me an instant answer, so... David, still up? I vaguely recall having an online discussion and looking up the paper, but that was several years ago.

John, go here for starters. I asked Dougal Dixon about it; he's not sure where he got the idea of limblessness from, and it doesn't seem to be in the literature. Weird.

Thanks Darren! Should have searched the blog I was on, instead of the whole known universe. Of course!

It happens that several (but I'm not sure exactly how many) Proterix specimens are known, and NONE of them shows legs, and there's not a hint of a pectoral girdle or pelvic girdle to be seen. Either the hedgehog had crap luck preserving its limbs, or it had no limbs at all. I think Occam's Razor favors the latter.

That kind of preservation appears to be fairly common. Keep in mind that the mammalian pelvis-sacrum connection is just laughable (except in xenarthrans) -- in humans, it actually functions as a hinge joint during giving birth!!! --, and that it took people decades to figure out whether Diplocaulus had limbs.

"...it took people decades to figure out whether Diplocaulus had limbs."

Wow, I didn't know that. Thanks!

ARGH! Why didn't I read the text in the first picture more attentively? No known aïstopod has lost the postorbital bar. Instead, there's a temporal fenestra behind it. The triradiate bone in Phlegethontia is the squamosal, and the thing that looks like an antorbital fenestra is the orbit. The jugal is there (rostral to the squamosal), and dorsal to it is what appears to be a postfrontal-postorbital fusion product (judging from limited ontogenetic data) and contacts the frontal, which extends far caudally (just reaching the pineal foramen).

Well, I reckon I was looking at Anderson et al. (2003) when I wrote this: they state that the postorbital was lost between Ophiderpeton and Phlegethontia. I don't have Anderson's more recent papers to hand - Anderson (2002) is the one that smacks down the notion of cranial kineticism - but I guess I was fooled by the fact that (in Phlegethontia) the dorsal ramus of the jugal appears to lie adjacent to the lateral wall of the braincase.

Ref - -

Anderson, J. S. 2002. Revision of the aïstopod genus Phlegethontia (Tetrapoda: Lepospondyli). Journal of Paleontology 76, 1029-1046.

- ., Carroll, J. S. & Rowe, T. B. 2003. New information on Lethiscus stocki (Tetrapoda: Lepospondyli: Aistopoda) from high-resolution computed tomography and a phylogenetic analysis of Aistopoda. Journal of Paleontology 40, 1071-1093.

Oh - did you know that Bob Carroll has a new book coming out entitled The Rise of Amphibians: 365 Million Years of Evolution? It's due out this month, apparently.

they state that the postorbital was lost between Ophiderpeton and Phlegethontia.

Oh. Yes, they call the fusion product the postfrontal; Anderson (2002) goes on to show his ontogenetic mini-series, which has two tiny bones in place of the "postfrontal", one in the rostrodorsal corner, the other in the ventral one. Anyway, the bar is not lost.

did you know that Bob Carroll has a new book coming out

No, I had no idea.

Let's just hope he doesn't label the braincase of Phlegethontia "parietal" again. He's done that at least twice now.

Raise your hand if you love Palaeozoic non-amniote tetrapods. :)

I thought that, at least in American usage, "eft" referred to a terrestrial stage in the critter's life-style: the Red Eft, which after a while goes back to the water (and I think regrows a fin around its tail, and maybe changes color?) to breed. The relevant crittr being some species of newt. ("Eft" and "Newt" being, of course, etymologically connected.)

The relevant crittr being some species of newt.

Yes, the salamandrid Notophthalmus viridescens, which has a greenish aquatic adult morph. It's especially noteworthy for keeping its lateral-line organ throughout life: it's normal and functional in the aquatic larva, then sinks deep into the skin in the juvenile "red eft" stage, and then comes back out and works again in the adult (Schoch 2001).

Besides, it has been pointed out to me that I promised a link to my & Michel Laurin's 2008b paper in comment 50 but still haven't coughed it up. Here goes.

David, just a little question.
Do you know where to find info about family Ostodolepididae?
Or if you have something to say me about those microsaurs.
:)

Thanks.

DM Thank you.