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Re: What are the biggest highlights of modern paleontology?
Now, Reisz is definitely something of an authority on turtle origins.
"[..] For years, however, biologists dismissed Eunotosaurus on the
> grounds that turtle ribs are not expanded, but fused to plates of
> dermal bone. A careful study of Eunotosaurus showed that in almost
> every feature it was nothing like a turtle. Eunotosaurus was
> accordingly dropped from the list of suspects until the discovery of
> Odontochelys, which has expanded ribs of its own, created a brief
> flurry of renewed interest in it. The ribs of Eunotosaurus are,
> however, not really like those of Odontochelys (their shape is
> different, and they wrap around the chest cavity in non-turtle
*Odontochelys* doesn't have expanded ribs either, it has ribs fused to
bone plates of unknown origin (their histology hasn't been studied).
Besides, Eunotosaurus lived a very long time ago—some 45 million
> years before even Odontochelys, more than the distance separating
> turtles from another candidate group, the pareiasaurs. Its role in
> turtle evolution seems, despite superficial similarities, unlikely."
The time gap is of course real, but that's the fossil record for you.
*Triadobatrachus* and *Czatkobatrachus*, both of them obvious
stem-frogs, lived some 60 Ma before the next two described
lissamphibians, *Prosalirus* (stem-frog) and *Eocaecilia* (stem-caecilian).
I'm surprised Reisz brings up the pareiasaurs. Has he ever supported
that hypothesis in print? I thought his latest publications on the topic
are the ones that propose the procolophonoids as the turtle
sister-group? Anyway, the pareiasaurs are quite tempting, but they come
with their own problems: off the top of my head, they have sutures
between the parasphenoid and the pterygoids in the palate, making the
basipterygoid articulations immobile, and so do post-Triassic turtles --
but both *Progano-* and *Odontochelys* retain actual synovial joints
there. Also, now that we know what turtle teeth look like, they're
plesiomorphic, not elaborated with a long row of extra denticles for
cutting leaves like in pareiasaurs... unless *O.* has undergone a reversal.