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Dinosauromorphs, Postosuchus, and Decuriasuchus papers



From: Ben Creisler
bcreisler@gmail.com

Some additional advance papers from the Lyell Collection Special
Publication on early archosaurs:

http://sp.lyellcollection.org/online-first/379

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Max C. Langer, Sterling J. Nesbitt, Jonathas S. Bittencourt and
Randall B. Irmis (2013)
Non-dinosaurian Dinosauromorpha.
Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin SP379
doi: 10.1144/SP379.9
http://sp.lyellcollection.org/content/early/2013/02/12/SP379.9


Ichnological evidence suggests that dinosauromorphs originated by the
Early Triassic, and skeletal remains of non-dinosaur representatives
of the clade occur from the Anisian to the end of the Triassic. These
taxa are small- to medium-sized, vary in feeding and locomotor
features, and occurred over most of western Pangaea. They include the
small lagerpetids from the Mid–Late Triassic of Argentina and the
United States, and the larger, quadrupedal Silesauridae, with records
in the Middle Triassic of Africa and Argentina, and in the Late
Triassic of Europe, the Americas and northern Africa. The former group
represents the earliest diverging dinosauromorphs, whereas silesaurids
are more closely related to Dinosauria. Other dinosauromorphs include
the archetypal early dinosauriform Marasuchus lilloensis (Middle
Triassic of Argentina) and poorly known/controversial taxa such as
Lewisuchus admixtus and Saltopus elginensis. The earliest diverging
dinosauromorphs may have preyed on small animals (including insects),
but cranio-dental remains are rare; by contrast, most silesaurids
probably included plant material in their diet, as indicated by their
modified jaw apparatus and teeth. Our knowledge of the anatomy and
thus relationships of non-dinosaurian Dinosauromorpha is still
deficient, and we suspect that future discoveries will continue to
reveal novel patterns and hypotheses of palaeobiology and
biogeography.


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Jonathan C. Weinbaum (2013)
Postcranial skeleton of Postosuchus kirkpatricki (Archosauria:
Paracrocodylomorpha), from the upper Triassic of the United States.
Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin SP379
doi: 10.1144/SP379.7
http://sp.lyellcollection.org/content/early/2013/02/13/SP379.7.abstract

Postosuchus kirkpatricki is a Late Triassic (Norian) ‘rauisuchid’
archosaur from North America. The initial description of the
Postosuchus type material included elements from two poposaurids. This
confusion has prevented adequate description of the material. Recent
examination of the type material and other specimens of Postosuchus,
and of related taxa, has helped clarify the osteology of Postosuchus.
The type specimens represent c. 75% of the skeleton. Together with
other referred material, Postosuchus remains one of the most
completely known rauisuchids. The paratype skeleton, which is
relatively complete, would have been c. 3.5–4 m in length, and the
holotype would have been closer to 5–6 m.

Analysis of the postcranial skeleton of Postosuchus suggests that it
may have been an obligate biped (based in part on limb proportions,
which are similar to some theropod dinosaurs, the size of the manus
(30% of the size of the pes) and the highly reduced nature of the
digits and vertebral measurements). Possible postcranial
autapomorphies of Postosuchus include a large, rugose triangular
supra-acetabular buttress confluent with the dorsal margin of the
iliac blade, and a symmetrical pes with digits two and three being
roughly equal in length.

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Marco A. G. De França, Max C. Langer and Jorge Ferigolo (2013)
The skull anatomy of Decuriasuchus quartacolonia (Pseudosuchia:
Suchia: Loricata) from the middle Triassic of Brazil.
Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin SP379
doi: 10.1144/SP379.8
http://sp.lyellcollection.org/content/early/2013/02/12/SP379.8.abstract



Unlike most rauisuchians, which are known based on partially preserved
specimens, fossils attributed to Decuriasuchus quartacolonia include a
monotaxonomic assemblage composed of nine associated individuals
(MCN-PV10.105a–i), three with almost complete skulls
(MCN-PV10.105a,c,d), and a partial disarticulated skull (MCN-PV10.004)
collected in the Middle Triassic (Ladinian, Dinodontosaurus Biozone)
beds of the Santa Maria Formation, in south Brazil. Because of its
completeness and possible phylogenetic position, as one of the most
basal loricatans, D. quartacolonia is a key taxon for anatomic,
evolutionary and biomechanical studies of rauisuchians. The
comparative description of its osteology reveals that the skull and
mandible of D. quartacolonia are very similar to those of cf.
Prestosuchus chiniquensis and Saurosuchus galilei, sharing a
drop-shaped subnarial fenestra, a subtriangular antorbital fenestra
with an elongated and narrow anterior point, a ‘roman nosed’ nasal,
and a posteroventrally oriented ridge on the lateral surface of the
ventral ramus of the squamosal. Among the differences are the
autapomorphies of D. quartacolonia: numerous maxillary teeth (17),
lateral expansion of the nasal/lacrimal covering the antorbital
fenestra dorsally, and squamosal and quadratojugal forming a
subtriangular projection that invades the lower temporal fenestra.