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Re: What are the biggest highlights of modern paleontology?



I won't claim that this is my area of expertise, but I know that Robert Reisz 
told me that he is unconvinced of the similarities.  Here (FWIW) is what I had 
to say in my recent book "Turtles, Tortoises and Terrapins: A Natural History", 
based on a conversation with Dr Reisz (the responsibility for it, though, is 
mine, not his!):

"One long-shot candidate [for a turtle ancestor], a little reptile called 
Eunotosaurus that lived in South Africa during the Permian, had a very peculiar 
rib cage. Instead of being a thin bow of bone, each rib was a broad, flattened 
paddle. It did not take much imagination to visualize the paddles growing even 
broader, fusing together, and forming the turtle shell. 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 fashion).
 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."  

Ronald Orenstein
1825 Shady Creek Court
Mississauga, ON L5L 3W2
Canada
ronorenstein.blogspot.com


________________________________
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu> 
Sent: Sunday, February 3, 2013 6:55:45 PM
Subject: Re: What are the biggest highlights of modern paleontology?

Rescued from truncation:

> Well, the Eunotosaurus  "comeback" is highly questionable to some (if
> you mean as a turtle ancestor).

I know all molecular phylogenies continue to be against it (though the latest 
study I've seen is surprisingly inconclusive on this topic* and on 
Lissamphibia). But has the anatomy of *Eunotosaurus* been questioned? The trunk 
ribs are pointed (indicating loss of the sternum), have the same number as in 
turtles, and are fused to plates of dermal bone that immobilize the trunk... 
and on the other side, there's still no trace of a cleithrum in any crown-group 
diapsid.

* The reason may be that, as usual, there's no tuatara in the data matrix.