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

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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