[dinosaur] Poposaurus (Late Triassic bipedal archosaur) osteology

Ben Creisler
[email protected]

A new paper:

Emma R. Schachner, Randall B. Irmis,  Adam K. Huttenlocke,r  Kent Sanders,
Robert L. Cieri  & Sterling J. Nesbitt (2019)
Osteology of the Late Triassic Bipedal Archosaur Poposaurus gracilis
(Archosauria: Pseudosuchia) from Western North America.
The Anatomical Record (advance online publication)
doi:  https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1002_ar.24298&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=MUAZ7ohZQmRM6qMdGl4R26q-n_aJOdQhUxQm6tKMhhw&s=aU6lYHW0n48IPN5dVBYh4Gs3-6BnH9kp0_yavDbBNDI&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__anatomypubs.onlinelibrary.wiley.com_doi_abs_10.1002_ar.24298&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=MUAZ7ohZQmRM6qMdGl4R26q-n_aJOdQhUxQm6tKMhhw&s=az3ABaxxM89WP3319SlWTsckg38bO_b_2wv_b2GqY9I&e= 


Poposaurus gracilis is a bipedal pseudosuchian archosaur that has been
poorly understood since the discovery of the holotype fragmentary partial
postcranial skeleton in 1915. Poposaurus. gracilis is a member of
Poposauroidea, an unusually morphologically divergent clade of
pseudosuchians containing taxa that are bipedal, quadrupedal, toothed,
edentulous, and some individuals with elongated thoracic neural spines
(i.e., sails). In 2003, a well preserved, fully articulated, and nearly
complete postcranial skeleton of P. gracilis was discovered with some
fragmentary cranial elements from the Upper Triassic Chinle Formation of
Grand Staircase‐Escalante National Monument of southern Utah, USA. The aim
of this work is to describe the osteology of this specimen in detail and
compare P. gracilis to other closely related pseudosuchian archosaurs. The
open neurocentral sutures throughout the majority of the vertebral column,
the small size of this individual, and the presence of seven evenly spaced
cyclic growth marks in the histologically sectioned femur indicate that
this specimen was a skeletally immature juvenile, or subadult when it died.
The pes of P. gracilis contains multiple skeletal adaptations and
osteological correlates for soft tissue structures that support a
hypothesis of digitigrady for this taxon. When coupled with the numerous
postcranial characters associated with cursoriality, and the many
anatomical traits convergent with theropod dinosaurs, this animal likely
occupied a similar ecological niche with contemporaneous theropods during
the Late Triassic Period.