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Re: Eucoelophysis (was Alamosaurus as biggest North American sauropod)

Thanks for the correction/update.  The possibility that the Siltstone
Member is late Rhaetian / early Hettangian in age is also mentioned in
the "Triassic Life on Land: The Great Transition." (Sues, H.-D. &
Fraser, N.C.) http://www.bioone.org/doi/pdf/10.1525/bio.2011.61.7.14

On Tue, Dec 13, 2011 at 4:56 AM, William Parker <saurian55@gmail.com> wrote:
> On Sun, Dec 11, 2011 at 9:58 PM, Tim Williams <tijawi@gmail.com> wrote:
>> 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).
> We (Randy Irmis, Sterling Nesbitt, and I) noted this at the 2005 SVP
> meeting and in our subsequent 2007 paper we discuss the affinities of
> much of Cope's Coelophysis material. Subsequent work has also
> recognized that Dromomeron material is also present in the sample (see
> Irmis et al, 2007, and Nesbitt et al. 2009).
>> 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.
> Although it is certain that the Coelophysis Quarry is in strata (the
> siltstone member of the Chinle Formation) higher than the Petrified
> Forest Member and thus older than the Hayden and Snyder Quarries as
> well as David Baldwin's original collecting sites, the exact
> correlations of this unit are still debated. Recent paleomagnetic work
> by Kate Zeigler and John Geissman have shown that the siltstone member
> has a different magnetic polarity signal than the type Rock Point
> Member and thus the units are not correlable (i.e., the Coelophysis
> Quarry is not in the Rock Point). I just gave a presentation at SVP
> this year demonstrating that based on vertebrate biochronology the
> siltstone member could be equivalent to the Owl Rock Member (which is
> between the Petrified Forest and Raock Point Members in Arizona, but
> purportedly absent in the Ghost Ranch area); however, Zeigler and
> Geissman suggested that based on paleopole position it could be a
> Moenave Formation equivalent, and thus latest Triassic or even early
> Jurassic!
>> Cheers
>> Tim