Odontochelys, a transitional turtle

| 33 Comments

Blogging on Peer-Reviewed Research

Now this is an interesting beast. It’s a 220 million year old fossil from China of an animal that is distinctly turtle-like. Here’s a look at its dorsal side:

odontochelys_fossil.jpeg

a, Skeleton in dorsal view. b, Skull in dorsal view. c, Skull in ventral view. d, Body in dorsal view. Teeth on the upper jaw and palatal elements were scratched out during excavation. Abbreviations: ar, articular; as, astragalus; ca, calcaneum; d, dentary; dep, dorsal process of epiplastron; dsc, dorsal process of scapula; ep, epiplastron; fe, femur; fi, fibula; gpep, gular projection of epiplastron; hu, humerus; hyo, hyoplastron; hyp, hypoplastron; il, ilium; ipt, interpterygoid vacuity; j, jugal; ldv, last dorsal vertebra; m, maxilla; n, nasal; na, naris; op, opisthotic; p, parietal; phyis, posterolateral process of hypoischium; pm, premaxilla; po, postorbital; prf, prefrontal; q, quadrate; sq, squamosal; st, supratemporal; sv1, 1st sacral vertebra; ti, tibia; ul, ulna; vot, vomerine teeth; I, V, 1st and 5th metatarsals.

Notice in the skull: it’s got teeth, not just a beak like modern turtles. The back is also odd, for a turtle. The ribs are flattened and broadened, but…no shell! It’s a turtle without a shell!

Flip it over. There’s another specimen, and we can look down on its ventral side, and there it is — a plastron, or the belly armor.

odontochelys_belly.jpeg

a, Skeleton in ventral view. b, Body in ventral view. c, d, Skull in ventral and slightly lateral views. Abbreviations as in Fig. 1, plus: ao, anal opening; bo, basioccipital; bs, basisphenoid; cav, caudal vertebrae; che, chevron; ent, entoplastron; hyis, hypoischium; is, ischium; meso I and II, mesoplastra 1 and 2; pr, prootic; prq, pterygoid ramus of quadrate; pt, pterygoid; pu, pubis; qj, quadratojugal; qrp, quadrate ramus of pterygoid; ra, radius; trpt, transverse process of pterygoid; xi, xiphiplastron; I, IV and V, 1st, 4th and 5th digits.

So, what we have here is a long-legged, toothed reptile with an elongate body, and it also has a plastron like a turtle, and hints in the bony structure of the spine of the carapace-to-be. It also fits perfectly with the embryology: modern turtles form the plastron first, and the carapace second. This is a beautiful transitional form. I’d love to have some swimming in the streams near me. And here’s a reconstruction of what they would have looked like, way back in the Triassic.

odontochelys.jpeg

Li C, Wu X-C, Rieppel O, Wang L-T, Zhao L-J (2008) An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.

33 Comments

yeah, well then why are there still turtles?

better yet WHY AER THAR PYGYMY TURTLES????/?

Makes me wonder what the advantage of the plastron would have been… armor against attacks from beneath? Protection from sharp coral? What? What?

… or a variation that just wasn’t a disadvantage…

I suppose turtles will pose a difficult problem for phylogeny and cladograms. You see, when you start looking at the ancestry, .…

.

.

.

.

…drum roll please …

.

.

.

… it is turtles all the way

bang!

dash!!

[Ducks and runs for cover before rotten tomatoes and eggs could be hurled]

Poor things - homeless until they learn how to grow the roof of their shells! :p

Ah, but they don’t have wings.

Dear Ravilyn:

Alas your comment is far more serious than you can imagine:

Ravilyn Sanders said:

I suppose turtles will pose a difficult problem for phylogeny and cladograms. You see, when you start looking at the ancestry, .…

.

.

.

.

…drum roll please …

.

.

.

… it is turtles all the way

bang!

dash!!

[Ducks and runs for cover before rotten tomatoes and eggs could be hurled]

I think turtles are among the main reasons why “Reptilia” is regarded as a paraphyletic group by any respectable vertebrate cladistic systematist.

Cheers,

John

That ainno turtle. ‘Sjussa lizard with a six-pack. When you guys gunna learn, there ainno such thing as transitional forms? Every time you come up with one, all you get is two gaps in the fossil record where you only had one before. What use is half a shell, anyway, except to eat it off? Prolly that’s why it died out.

I hope someone will post updates here as creationists explain why this isn’t a transitional form.

NPR ran a longish segment on this fossil find today. Wed Nov 26th. Thanksgiving eve.

Helena Constantine said: I hope someone will post updates here as creationists explain why this isn’t a transitional form.

Dont have the patience to dig through the references, but last time the creotards tried to explain away tiktaalik it was something like, “the author (Shubin?) gave the names of the bones in the fossil (like ulna) but did not give the name of the corresponding bone in the descendant species, thus the whole claim of transitional form could not be verified independently”.

Of course bones like ulna, radius, tarsals have exactly the same name on so many species all the way to the modern extant species including H sapiens. That creotard did not even know that. It shows how shallow that creotard’s understanding of biology/zoology/anatomy etc than any real deficiency in declaring tiktaalik as a transitional form.

That is the level of scholarship in the creationists’ side. But they will declare that Darwinism is in its last legs and they will predict an imminent death of evilution very very soon.

Ravilyn Sanders said:

Dont have the patience to dig through the references

Found the link. Here is the thread I was talking about. Read and laugh at the pathetic level of scholarship and standards of the creotards.

The tree of life website tentatively put turtles with the anapsida, outside the the lizard, crocodile, bird group.

http://tolweb.org/Amniota/14990

Lenny said they belong in the diapsida, closer to crocodilians than to lizards and snakes.

I thought it was birds that caused the reptile class to be paraphyletic, since they’re inside the clade of living reptiles; turtles would seem closer to them than anything else even if they are outside the diapsida clade.

Henry

Maybe there was a soft shell that didn’t fossilize. In any case the turtle shell, like the eye, couldn’t have evolved in one pop. If it did, it would be evidence of creation. Score another one for Darwin.

fnxtr said:

Makes me wonder what the advantage of the plastron would have been… armor against attacks from beneath? Protection from sharp coral? What? What?

Possibly an example of exaptation??

Ventral plates may have been a genetic by-blow of the development of the dorsal shell? Once in use further development of it would have been an advantageous adaptation - hence exaptation?

Of course that’s just speculation.

Anyone know for sure??

proof of transitions? hardly. what good is half a plastron? your argument defeats itself

It’s worth looking at Gish’s “The Fossils Say No” and the following AiG article, in which they specifically state that such fossils should not be found.

http://www.answersingenesis.org/cre[…]/turtles.asp

I’ll quote the relevant bit in case the creationists get all revisionist about this:

The biblical account of Creation in Genesis 1—animals created to reproduce after their kinds—would mean that turtles should be instantly recognizable as turtles, with the shell and other unique features fully formed from the start,7 and no series of ‘pre-turtle ancestors’ should be found. It is obvious that the fossil record of turtles gives powerful support to biblical Creation, and stands opposed to the idea of evolution.

So I suppose they’ll just say “This isn’t a turtle?”

Wheels said: “So I suppose they’ll just say “This isn’t a turtle?”

Well, of course. If Gish said that there is no series of “pre-turtle ancestors’ then this cannot be a pre-turtle ancestor because Gish said there are no pre-turtle ancestors.

Q.E.D.

I used to have two pet turtles. One of the things I noticed about them was, when they were sunning themselves, they were able to appear perfectly relaxed, yet were grasshopper quick in leaping off the rock and into the water whenever I walked by. It occurred to me this morning that leaping is not what they do. They don’t have to stand up first before they go, they save time (one motion instead of two) by snapping all four legs back and sliding forward using the plastron like a toboggan. After all, it takes less energy to slide a weight along a surface than it does to pick it up and carry it. So the plastron would have a defensive purpose, just not in the sense of armour. That would be an exaptation.

Henry J said:

The tree of life website tentatively put turtles with the anapsida, outside the the lizard, crocodile, bird group.

http://tolweb.org/Amniota/14990

Lenny said they belong in the diapsida, closer to crocodilians than to lizards and snakes.

I thought it was birds that caused the reptile class to be paraphyletic, since they’re inside the clade of living reptiles; turtles would seem closer to them than anything else even if they are outside the diapsida clade.

Henry

Exactly, it is birds that cause Reptiles to be paraphyletic, not turtles.

Kevin Alexander said:

(snip) They don’t have to stand up first before they go, they save time (one motion instead of two) by snapping all four legs back and sliding forward using the plastron like a toboggan. (snip)

cool.

Dear Henry J:

You’ve made a good point here:

Henry J said:

I thought it was birds that caused the reptile class to be paraphyletic, since they’re inside the clade of living reptiles; turtles would seem closer to them than anything else even if they are outside the diapsida clade.

Henry

However, I believe that it is the lineage leading to mammals which is one of the reasons why Reptilia should be regarded as a paraphyletic group (I’m not someone with a background in vertebrate systematics, so will defer to others who may have such a background.).

Regards,

John

Dear Henry J:

As a postscript I will note that of the living reptiles, crocodiles and their kin would be most closely related to birds, as the sole surviving branches of the great archosaur lineage which emerged during the early Triassic. Turtles are more “primitive” than crocodilians, so therefore, they aren’t the closest “reptilian” relatives of birds.

Regards,

John

Also, a plastron as toboggan would be useful in that sense at every stage in a slow evolution. Begin with somewhat tougher ventral skin with fewer and then fewer scales.

A plastron with no shell could be very useful in outcompeting other species for food, if for example the food was all nestled in amongst sharp coral. Just bear down on your protected belly for stability while grazing with your long neck.

It doesn’t have to be advantageous for the same reason in all times and places. “What good would that adaptation be?” is an important and fun question to ask. Lack of an answer is a silly reason to discount a transitional form. As little as we know about creatures that left bones for us to find, we know far less about what their complex daily life was like. Just my novice opinion.

I was also impressed by the thick ribs. Very thick,dense bones are an aquatic adaptation for an air breathing animal. Think of ballast countering buoyant lungs. A massive body also stabilizes an animal that hunts with its neck. I lightweight head on a lithe neck attached to a massive body is very good at grabbing fast prey. Maybe this is why turtles lost their teeth, the same reason that birds did, to save weight.

Of course there’s a penalty with mass. Where the ground is very soft as it is around water, feet would sink into the ooze. Then you would have to evolve something like, say, a plastron to slide around on.

Speaking as a fisherman and not as a biologist, it is my observation that species that feed in the water column as opposed to bottom feeders tend to attack their prey from below, so a ventral plastron might provide some protection from predation.

It the predator were large enough to swallow you whole, of course, the plastron would provide no advantage. However, if prototurtles evolved in a shallow water/transitional zone environment, piscene predators of that size would likely be rare to non-existent.

Hello. I have a new book that answers the question–can an Atheist be elected president? It is available on Amazon or the createspace site and is a social/political/thriller about a presidential election after the Obama era. The createspace site has more info. The book also says that we do not say “and to the DEMOCRACY” when we say the Pledge. This is one of the recurring themes in the story line. The book is $15.95 for anyone who likes a political thriller and also wants to find out if it is possible to elect an Atheist to major offices in the U.S. government. My email is in the book for anyone to write me a comment, and I hope some of you will read it. You will be surprised.

Oh…

You evilutionist just have all the answers to life & the purpose there of.

You must be God. For than you’d have all the infinite knowledge of the universe. To say what happened verses what didn’t happen or what exist as to what does not exist.

Just cause there’s a turtle with half a shell does not mean its a transitional fossil. That’s like saying a possum is one evolutionary step down from an armadillo. Stick to your theory that doesn’t hold water. Remain in your ignorance of circular reasoning (dating the fossils by the rocks & the rocks by the fossils they contain). Grabbing at straws to keep your lifestyle of no accountability intact.

Tell me something evilutionist..? WHY ARE THERE MALES & FEMALES..? Would that have been a smart move by a cell that could reproduce itself by splitting in 2..? Why would a species ever (not including almost every species alive) split into 2 different parts. 1 needing to hook up with the other… just to continue the furtherance of the species evolutionary process. That would be survival of the fittest suicide. & to add insult to injury. Homosexuality just adds fuel to that fire. Cause if a species turned homosexual… That would be the end of that species.

Who knows… maybe all the dinosaurs turned gay & quit producing dinosaurs. & that’s why they’re not around these days. There’s a theory you guys should put in your pipes & smoke.

frog turns into a person quickly: F-A-I-R-Y T-A-L-E frog turns into a person over zillions & zillions of years: E-V-I-L-U-T-I-O-N

www.fool4given.com/books/301proofs.pdf www.eternal-productions.org/101science.html www.discovery.org/articleFiles/PDFs/survivalOfTheFakest.pdf

Poe?

Possibly, but only possibly. Poe’s Law does state that it is impossible to know whether a given creationist rant is satirical in intent or not, because no satire could ever be more demented than the most extreme of real ones.

That one is pretty far out there, though, and, speaking as a writer of fiction, I think it would be difficult to simulate an extreme creationist this well. The arrogance, ignorance, pride in stupidity and aggressive luddism leap off the page, despite what appears to be a level of English literacy that would shame a Panamanian pimp. Nevertheless, I lean slightly towards believing that this is a satire, on the grounds that somebody this stupid, ignorant and illiterate wouldn’t be making puns that really only work in print. That’s only a very tentative hypothesis, though. Perhaps another sample will turn up and provide more evidence.

Oh, and one other observation: the idiotic remark about possums and armadillos, which have the apparent effect of placing the writer in the rural south. It’s just a little too stereotyped. On balance, I vote Poe. It’s a satire.

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This page contains a single entry by PZ Myers published on November 26, 2008 2:08 PM.

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