Eucoelophysis (was Alamosaurus as biggest North American sauropod)

[Tim Williams <tijawi@gmail.com>]

David Marjanovic <david.marjanovic@gmx.at> wrote:

> The story of the silesaurid *Eucoelophysis* is more complicated than that,
> but I'm not sure I remember the details and can't look them up now.


The holotype material for _Eucoelophysis baldwini_ (NMMNH P-22298)
consists of a partial postcranium that was discovered in the Orphan
Mesa locality in New Mexico.  This locality is believed to be the same
as the Arroyo Seco locality that yielded the original type material of
_Coelophysis bauri_ (Sullivan et al., 1996).  _E. baldwini_ was
originally thought to be a coelophysoid theropod by Sullivan & Lucas
(1999), based on NMMNH P-22298 and a referred pubis (AMNH 2706).  This
study also speculated that the original _Coelophysis_ syntypes might
also belong to _E. baldwini_, but this couldn't be demonstrated due to
its non-diagnostic nature.  However, Eczurra (2006) subsequently
showed that NMMNH P-22298 belongs to a non-dinosaur dinosauriform
similar to _Silesaurus_, and AMNH 2706 comes from a coelophysoid.
Subsequent phylogenetic analyses have recovered _Eucoleophysis_ as a
silesaurid (e.g., Nesbitt et al., 2010).


The locality that yielded _Eucoelophysis_ and the original
_Coelophysis_ syntypes represents the Petrified Forest Formation of
the Chinle Group, whereas the abundant skeletons of _Coelophysis_
(including the neotype, AMNH 7224) from Whitaker Quarry at Ghost Ranch
represents the stratigraphically higher (i.e., younger) Rock Point
Formation.






Cheers

Tim