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Phytosaurs: Paleorhinus status and new Machaeroprosopus species

From: Ben Creisler

New online papers about phytosaurs:

Michelle R. Stocker (2013)
A new taxonomic arrangement for Paleorhinus scurriensis.
Earth and Environmental Science Transactions of the Royal Society of
Edinburgh (advance online publication)
DOI: http://dx.doi.org/10.1017/S1755691013000340

The paraphyletic genus ‘Paleorhinus’ is understood currently as a
cosmopolitan phytosaur taxon from the Late Triassic. There is no
consensus regarding the number of species of ‘Paleorhinus,’ with
multiple species and genera synonymised into a single genus or even a
single species at various points in its published history. The
taxonomy is confounded by historical descriptions without the benefit
of comparisons to more recently collected specimens, emphasis on
plesiomorphic cranial morphology as diagnostic features of the genus,
and lack of cladistic analyses. When included in a recent explicitly
cladistic phylogenetic analysis, the holotype of ‘Paleorhinus’
scurriensis (TTU P-00539) was found to be the earliest-branching
phytosaur with respect to other North American specimens previously
referred to ‘Paleorhinus,’ and is generically distinct from
Paleorhinus. ‘Paleorhinus’ scurriensis differs from all known
phytosaurs in five unambiguous characters: basitubera widely separated
mediolaterally; ridge present on lateral surface of jugal; thickened
shelf present along posteroventral edge of expanded pterygoid-quadrate
wing; ‘septomaxillae’ separated and excluded from internarial septum;
and nasal swelling present posterior to posterior borders of nares.
This detailed morphological description of an early-branching
phytosaur taxon is a first step towards resolving long-standing issues
surrounding specific anatomical features and relationships among early
members of the clade.


Axel Hungerbühler, Bill Mueller, Sankar Chatterjee and Douglas P.
Cunningham (2013)
Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with
the description of a new species from West Texas.
Earth and Environmental Science Transactions of the Royal Society of
Edinburgh (advance online publication)
DOI: http://dx.doi.org/10.1017/S1755691013000364

The skull anatomy of a new species of the phytosaur Machaeroprosopus
is described for the first time on the basis of two specimens from the
Upper Triassic Cooper Canyon Formation of Texas. Additional
information is provided by a third specimen referred to
Machaeroprosopus sp. A paranasal bone, an additional paired element of
the narial region, is identified. Important new data are presented for
the braincase, including the morphology of the epipterygoid and
presphenoid, an anterior process of the prootic, an anteroventral
process of the laterosphenoid, and a parasphenoid process.
Machaeroprosopus lottorum n. sp. is characterised by four apomorphies:
a supratemporal fenestra closed on the skull roof with bevelled
anterior rim, a comparatively short squamosal, a flat and rugose
narial rim, and medially extended palatines that come close to form an
ossified secondary palate. With respect to the supratemporal fenestra,
the supraoccipital–parietal complex and several features of the
squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological
gap between species previously referred to the genera Pseudopalatus
and Redondasaurus. A parsimony analysis of known species of
Machaeroprosopus supports the hypothesis that the development of the
rostral crest in Machaeroprosopus is a sexually dimorphic feature, and
questions the validity of the genus Redondasaurus. Consequently,
Redondasaurus is here considered a junior synonym of Machaeroprosopus.