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Eunotosaurus and turtles
I do not know if there are features that indicate Eunotosaurus is less
related to turtles than to procolophonids, parieasaurs,
sauropterygians or archosaurs, but I found some derived similarities
(I do not know if these were proposed):
1- The widened ribs. Something also striked me as similar is that
there are 8 expanded ribs in each side in Eunotosaurus, while in
turtles the carapace is formed by 8 pleural plates/ribs!!! Although
this counts as just a similar apomorphy, the fact that there is the
same number of expanded ribs seems as much coincidential!!
2- These dorsal ribs are said in Romer 56' to articulate with the
vertebra via a single attachment, as in turtles (I suppose it would be
the capitulum, as it seems to be low in the centrum).
3- Finally, the dorsals of Eunotosaurus are quite elongate, just as in
It may be that the elongation of the vertebrae is just related to the
increase in the distance between the capitular articulations due to
the antero-posterior widening of the ribs. Eunotosaurus also has
osteoderms, but these seem to be present in most of the taxa
considered as related to turtles (parieasaurs, placodonts).