[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Azendohsaurus (Triassic archosauropmorph from Madagascar) postcranial osteology (free pdf)



Ben Creisler
bcreisler@gmail.com


A new paper:

Sterling J. Nesbitt, John J. Flynn, Adam C. Pritchard, J. Michael
Parrish, Lovasoa Ranivoharimanana and André R. Wyss (2015)
Postcranial Osteology of Azendohsaurus madagaskarensis (?Middle to
Upper Triassic, Isalo Group, Madagascar) and its Systematic Position
Among Stem Archosaur Reptiles.
Bulletin of the American Museum of Natural History 398: 1–126
URI: http://hdl.handle.net/2246/6624
Free pdf link:
http://digitallibrary.amnh.org/handle/2246/6624

Also:
http://www.bioone.org/doi/abs/10.1206/amnb-899-00-1-126.1

During the Triassic, archosauromorphs became one of the first groups
of diapsid reptiles to diversify in terms of body size and
morphological disparity in both terrestrial and marine ecosystems
across Pangaea. This seemingly rapid divergence, and the numerous
unique body plans stemming from it, concomitantly has confounded
reconstructions of archosauromorph relationships. Teasing apart
homology from homoplasy of anatomical characters in this broad suite
of body types remains an enormous challenge with the current sample of
taxa. Here, we present the postcranial anatomy of Azendohsaurus
madagaskarensis, an early archosauromorph from ?Middle to Upper
Triassic strata of Madagascar. Azendohsaurus madagaskarensis is known
from nearly the entire skeleton in an ontogenetically variable sample.
The holotype locality consists of a monotypic bone bed; preservation
ranges from complete but disarticulated bones to articulated sections
of the skeleton. Azendohsaurus madagaskarensis embodies an aberrant
constellation of archosauromorph features, including an elongated
neck, a short, stocky tail, robust limbs, and unexpectedly short
digits terminating in large recurved unguals on the manus and pes.
Together with the cranium, the postcrania reveal A. madagaskarensis to
be another representative of a growing coterie of highly apomorphic
and bizarre Triassic archosauromorphs. At the same time, recovery and
description of the full anatomy of A. madagaskarensis helps to
identify a monophyletic grouping of specialized taxa that includes the
North American Late Triassic–aged archosauromorphs Trilophosaurus,
Spinosuchus, and Teraterpeton, Indian Pamelaria, and Moroccan
Azendohsaurus laaroussii. Moreover, information derived from the
skeleton of A. madagaskarensis solidifies the systematic position of
these taxa among other archosauromorphs. Using the most
comprehensively sampled phylogenetic analysis of early
archosauromorphs, we found the clade encompassing the aforementioned
taxa as the nearest outgroup of Prolacerta broomi + Archosauriformes.
The newly recognized clade containing Azendohsaurus, Trilophosaurus,
Spinosuchus, Pamelaria, and Teraterpeton demonstrates high
morphological disparity even within a closely related group of
archosauromorphs, underscores the polyphyly of protorosaurs ( =
prolacertiforms), and suggests that most major divergences within this
group occurred in the Triassic. Furthermore, our results indicate that
craniodental character states ascribed to a herbivorous diet were much
more pervasive across Triassic Archosauromorpha than previously
conjectured.