Re: [dinosaur] Gnathovorax, new herrerasaurid (open access)

Eucoelophysis as a neotheropod was based on the misconception that the
femoral head was badly weathered. Of course we didn't know about
silesaurids in 1999 so the assumption by the original researchers is
reasonable, although they missed an opportunity there regarding early
ornithodiran phylogeny. However, Rinehart et al., (2009) raised that
same argument again when assigning a neotheropod specimen from the
Royal Tyrrell Museum Ghost Ranch block to Eucoelophysis, insisting
that E. baldwini was indeed a neotheropod. This is not supported
because 1) the femoral head for the type specimen of E. baldwini has
all of the key silesaurid synapomorphies and is not convergent based
on preservation, and 2) the Royal Tyrrell specimen has none of the
apomorphies of E. baldwini. So, despite the unfortunate name,
essentially there is not much to specifically support the position of
Eucoelophysis as any closer to neotheropods than most other
silesaurids.

On Sun, Nov 10, 2019 at 8:26 PM Brad McFeeters
<[email protected]> wrote:
>
> The "compromise" hypothesis, of course, which I don't believe has ever been supported quantitatively, would be that (Ornithischia + Silesauridae) is the sister group of Theropoda within Ornithoscelida. I don't know is this is at all plausible, but the silesaurid *Eucoelophysis* was initially described as a neotheropod... Notably, Pacheco et al. (2019) seem to be the first study to recover *Pisanosaurus* closer to Ornithischia than to Silesauridae, after taking into account the studies that find it as a silesaurid.
>
> Etymologically, is *Gnathovorx* the "devouring jaw," or the "devourer of jaws"?
>
> Brad
>
> Sent from Outlook
>
> ________________________________
> From: [email protected] <[email protected]> on behalf of Tim Williams <[email protected]>
> Sent: November 10, 2019 9:04 PM
> To: [email protected] <[email protected]>
> Subject: Re: [dinosaur] Gnathovorax, new herrerasaurid (open access)
>
> David Marjanovic <[email protected]> wrote:
>
> > ...and the silesaurids come out as the basal grade of ornithischians, which will be very familiar to a few of us. Herrerasauridae is found as the sister-group of all other
> > saurischians.
>
> The phylogeny retains a rump clade of "core" silesaurids, comprising
> _Silesaurus_ and its closest kin.  Meanwhile,
> _Lewisuchus_/_Pseudolagosuchus_ remain(s) outside the Ornithischia
> (and Dinosauria) entirely.
>
> If silesaurids are ornithischians, then they fill in the gap of
> missing ornithischians from the Triassic.  The apparent absence of
> ornithischians from the Triassic (assuming _Eocursor_ is Jurassic) has
> been perplexing.  It could be an artifact of an imperfect fossil
> record.  Or, Triassic ornithischians have already been discovered -
> such as silesaurids (e.g., Pacheco &c), or as weird theropods (such as
> _Daemonosaurus_).  The latter raises the prospect that all
> ornithischians are 'weird' theropods, having originated from among
> basal theropods.  I quite liked the idea of a
> _Daemonosaurus_-heterodontosaurid nexus.  However, in this analysis,
> _Daemonosaurus_ falls out as a saurischian, in between herrerasaurids
> and eusaurischians (theropods + sauropodomorphs), and the traditional
> Saurischia-Ornithischia dichotomy is preserved.