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Re: Bajo Barreal Formation

Mickey Mortimer wrote:

> Does anyone know when the Bajo Barreal Formation was laid down?  My
> resources say everything from Cenomanian to Maastrichtian.
> Mickey Mortimer

the following is an abstract that we published in JVP in September.  The
age of the Bajo Barreal (presumed Cenomanian) has been based largely on
the phylogenetic relationships of the dinosaurs to other Cenomanian taxa
(which the debacle over the age of the Yixian Formation in China should
give us all pause as to ever using phylogenetic relationships as age
determiners again...).  The age is thus fairly weak right now.  Give us
some time, though...

Some additional, informal information about this work can be found
through the Bajo Barreal Dinosaurs link off of

MART´INEZ, Rubén D., Universidad de la Patagonia "San Juan Bosco,"
Comodoro Rivadavia,
LAMANNA, Matthew C.; SMITH, Joshua B., University of Pennsylvania,
Department of Earth
   and Environmental Science, 240 South 33rd Street, Philadelphia, PA
   lamanna@sas.upenn.edu; smithjb@sas.upenn.edu 
CASAL, Gabriel; LUNA, Marcelo, Universidad de la Patagonia "San Juan
Bosco," Comodoro
      Rivadavia, Argentina
   Published in the Journal of Vertebrate Paleontology, 19(3):62A.

Associated remains of an amazing theropod have been recovered from the
Bajo Barreal Formation (?Cenomanian) of Chubut, Argentina, in cluding
much of a large ungual phalanx of digit II of the left pes and an
incomplete right metatarsal II. The ungual is similar to that of the
enigmatic theropod Megaraptor from slightly younger deposits in NeuquÈn.
It is transversely compressed with grooved lateral and medial surfaces,
with the medial groove more dorsal than the lateral. The flexor tubercle
is dorsoventrally low, and the articular surface is keeled. The
metatarsal is distally robust. It is much more massive than metatarsal
III of Megaraptor, suggesting heavier construction of the pes.
A second, smaller theropod specimen was previously discovered from the
Bajo Barreal, consisting of a dorsal vertebra, three caudal centra, a
complete rib, a partial metatarsal II, and manual and pedal unguals. The
pedal elements have the same basic morphology in both of the Bajo
Barreal predators, suggesting that they pertain to the same taxon. The
dorsal vertebra shares features with that of Deinonychus, such as a high
neural arch, widely spaces, suboval articular facets, a low neural
spine, a marked hapidocoel, and a short, low-angled centrum with a small
pleurocoel. The neural arch has three large and deep caudal pneumatic
fossae. However, metatarsal II does not have the distal, deep grove
present in dromaeosaurids. the phylogenetic relationships of the Bajo
Barreal theropod must thus remain uncertain pending the recovery of
additional material.

Josh Smith
Department of Earth and Environmental Science
University of Pennsylvania
471 Hayden Hall
240 South 33rd Street
Philadelphia, PA  19104-6316
(215) 898-5630 (Office)
(215) 898-0964 (FAX)