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Triassic archosaurs: Nundasuchus (new taxon) from Tanzania, Venaticosuchus phylogeny, Silesaurus ontogeny

Ben Creisler

In the new issue of JVP:


Sterling J. Nesbitt, Christian A. Sidor, Kenneth D. Angielczyk, Roger
M. H. Smith & Linda A. Tsuji (2014)
A new archosaur from the Manda beds (Anisian, Middle Triassic) of
southern Tanzania and its implications for character state
optimizations at Archosauria and Pseudosuchia.
Journal of Vertebrate Paleontology 34(6):  1357-1382

The presence of early pseudosuchians and avemetatarsalians in Anisian
beds of Africa demonstrates that the archosaur radiation was well
underway by the beginning of the Middle Triassic. The rapid radiation
produced a variety of forms, but many of the unique, well-diagnosed
Late Triassic clades (e.g., Aetosauria, Ornithosuchidae) lack
diagnosable members from the Middle Triassic. Here, we introduce a new
Middle Triassic archosaur, Nundasuchus songeaensis, gen. et sp. nov.,
with an unusual mix of apomorphic character states found within
Pseudosuchia and just outside Archosauria. The holotype consists of
partial skeleton, including representative postcranial elements and
parts of the skull. We added Nundasuchus songeaensis, gen. et sp.
nov., into the two most comprehensive early archosaur phylogenetic
data sets available, and in both analyses the new taxon falls within
Pseudosuchia. However, a number of plesiomorphic archosaurian
character states (e.g., posterolaterally directed tuber of the
calcaneum) optimize as local autapomorphies of the new taxon within
Pseudosuchia in our analyses. Therefore, we tested alternative
hypotheses of relationships for the new taxon by utilizing constraint
trees. The analyses resulted in little change in the relationships and
structure of other Triassic archosaur clades, but changed
optimizations of certain character states and character support at the
base of Pseudosuchia and Archosauria. Our analyses suggest that the
complex evolution of character-state changes at the base of
Archosauria is inhibiting our understanding of the relationships of
early Pseudosuchia and, in turn, Archosauria.


M. Belén Von Baczko, Julia B. Desojo & Diego Pol (2014)
Anatomy and phylogenetic position of Venaticosuchus rusconii
Bonaparte, 1970 (Archosauria, Pseudosuchia), from the Ischigualasto
Formation (Late Triassic), La Rioja, Argentina.
Journal of Vertebrate Paleontology 34(6): 1342-1356

Ornithosuchidae is a group of Late Triassic pseudosuchian archosaurs
of controversial phylogenetic affinities. This clade currently
comprises three taxa: Venaticosuchus rusconii and Riojasuchus
tenuisceps, both from Argentina, and Ornithosuchus longidens, from
Scotland. V. rusconii was erected on the basis of an incomplete skull
with articulated lower jaws and some elements of the postcranium that
are currently lost. Venaticosuchus rusconii is redescribed here and
included for the first time in a phylogenetic analysis to test its
affinities with ornithosuchids. The bizarre morphology of V. rusconii
has a unique combination of traits that distinguishes it from the
other ornithosuchids, such as basipterygoid processes directed
ventrally, dentary with the dorsal margin of the anterior end dorsally
expanded, articular without a foramen on its medial side, and the
absence of a surangular foramen, corroborating the validity of this
taxon. V. rusconii is recovered as an ornithosuchid more closely
related to R. tenuisceps than to O. longidens, based on the presence
of a nearly pointed anterior margin of the antorbital fenestra, and a
vertical bony strut of the jugal that separates the antorbital
fenestra from the infratemporal fenestra.


Rafał Piechowski, Mateusz Tałanda & Jerzy Dzik (2014)
Skeletal variation and ontogeny of the Late Triassic Dinosauriform
Silesaurus opolensis.
Journal of Vertebrate Paleontology 34(6): 1383-1393

A principal component analysis (PCA) performed for a set of 24
measurements on 33 femora and 15 measurements on 20 ilia of Silesaurus
opolensis from the early Late Triassic of Krasiejów, southern Poland,
shows that this sample is highly variable but probably monospecific.
Most of the morphological variation is concentrated in the muscle
attachments and proportions of bones, which significantly change in
both size and position during ontogeny. Despite the small sample size,
femora of smaller individuals have less flattened shafts and a more
sinusoidal appearance. In many large specimens, proximal parts of
muscle tendons are ossified at their attachment site on femora and
remain attached to the bone in the largest specimens. The specimens
with attached ossifications are interpreted as mature females that
were statistically larger than proposed males. It is suggested that
ossifications developed in females under calcitonin control. The
intrapopulation variability of ilia is high, but less dependant on
ontogeny. The population represented by a few specimens from the lower
level at Krasiejów may represent a different stage in the evolution of
the species than that from the upper horizon.