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Trialestes (was Re: PDF-request: Original description of Lagosuchus and/or Marasuchus)
David Peters <firstname.lastname@example.org> wrote:
> What three to five genera preceded Marasuchus in the
> lineage of the Dinosauria?
What David M. said. The terms "ancestor" and "sister taxon" are not
> Testing indicates Turfanosuchus and Trialestes are in there
> for starters.
Ah yes. _Trialestes romeri_...
What specimen(s) are you using for _T. romeri_? Aside from the holotype (PVL
2561), two specimens (PVL 2559 and PVL 3889) have been referred to _T.
romeri_. The holotype (an incomplete skeleton that includes cranial elements)
and PVL 3889 (an incomplete postcranium) have been assigned to the same taxon
(_T. romeri_) based on the striking similarity of the forelimb elements. PVL
2559 is a partial pes. All three specimens were found in the same horizon.
However, PVL 3889 appears to come from a dinosaur, based on features such as a
perforated acetabulum, inturned femoral head, and mesotarsal ankle. It is
therefore possible that the holotype comes from a dinosaur too. Alternatively,
the _T. romeri_ holotype is a sphenosuchian-grade crocodylomorph, and PVL 3889
is a dinosaur, and the two just happen to have uncannily similar forelimb
morphology & proportions (e.g., antebrachium longer than humerus).
So _T. romeri_ must be treated with caution when putting together an OTU. The
hypodigm is currently uncertain.