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Re: On the subject of mysterious absences...The Answer
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
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 elasmobranchWhat about _Mesosaurus_ (Permian)?
(maybe a synechodontiform).
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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