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Re: On the subject of mysterious absences...The Answer

Hi All

Speaking of pareiasaurs, what's the current opinion on their affinities with chelonians? Years ago, when I was reading every news bite on amniotes evolution in *paper* magazines, I read a discussion of how pareiasaurs, at least in one lineage, showed a "progression" towards more turtle-like morphology. This quite excited my imagination, but not so long after I read that turtles were actually more akin to some thecodont lineage, maybe aetosaurs or some such. What's the current opinion?

BTW Is "thecodont" still a useful term? Or is it too inclusive?


Tim Williams wrote:

Nick Pharris wrote:

_Pseudocetorhinus_ is even older (Triassic). It was an elasmobranch
(maybe a synechodontiform).

What about _Mesosaurus_ (Permian)?

The idea of filter-feeding mesosaurs was recently shot down I'm afraid...

Modesto, S.P. (2006) The cranial skeleton of the Early Permian aquatic reptile _Mesosaurus tenuidens_: implications for relationships and palaeobiology Zool. J. Linn. Soc. 146: 345-368.

Abstract: "The cranial osteology of the aquatic reptile _Mesosaurus tenuidens_ is redescribed on the basis of new and previously examined materials from the Lower Permian of both southern Africa and South America. _Mesosaurus_ is distinguished from other mesosaurs in exhibiting an absolutely larger skull and possessing relatively longer marginal teeth. The teeth gradually angle outwards as one progresses anteriorly in the tooth row and become conspicuously procumbent at the tip of the snout. The suggestion that mesosaurs used their conspicuous dental apparatus as a straining device for filter feeding is based upon erroneous reconstruction of a high number of teeth in this mesosaur. Reinterpretation of the morphology and the organization of the marginal teeth of _Mesosaurus_ suggests that they were used to capture individually small, nektonic prey. General morphological aspects of the skull support the idea that _Mesosaurus_ was an aquatic predator and that the skull was well adapted for feeding in an aqueous environment. The anatomical review permits critical reappraisal of several cranial characters that have appeared in recent phylogenetic analyses of early amniotes. Emendation of problematic characters and reanalysis of amniote phylogeny using a slightly modified data matrix from the literature strengthens the hypothesis that mesosaurs form a clade with millerettids, procolophonoids and pareiasaurs within Reptilia."


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