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Therapsid papers: Sinophoneus (Permian) + Thrinaxodon (Triassic)



From: Ben Creisler
bcreisler@gmail.com

In the new JVP:


Jun Liu (2013)
Osteology, ontogeny, and phylogenetic position of Sinophoneus
yumenensis (Therapsida, Dinocephalia) from the Middle Permian
Dashankou Fauna of China.
Journal of Vertebrate Paleontology 33 (6): 1394-1407
DOI: 10.1080/02724634.2013.781505
http://www.tandfonline.com/doi/full/10.1080/02724634.2013.781505#.UoJOB_k_sbk

Sinophoneus yumenensis and Stenocybus acidentatus are the only
dinocephalians from China, and the latter taxon has been proposed to
be a junior synonym of the former. Here I confirm this synonymy on the
grounds that the differences between the two putative taxa are due to
ontogenetic variation. The osteology of Sinophoneus yumenensis is
described in detail based on both previously described specimens and
several new ones from the same locality. Sinophoneus yumenensis
differs from all other anteosaurs in having premaxillary dorsal
processes that are separated by relatively long nasal anteromedial
processes, and vomers without raised, elongated edges; from all other
anteosaurs except Archaeosyodon praeventor in having distinct frontal
posterolateral processes, and a wide intertemporal region formed
partly by long posterior processes of the postfrontals that approach
the posterior edge of the skull roof; and from Archaeosyodon
praeventor in having a well-developed midline ridge on skull roof. A
revised phylogenetic analysis including the new material recovers
Sinophoneus as the most basal known anteosaurid.
==


Fernando Abdala, Sandra C. Jasinoski & Vincent Fernandez (2013)
Ontogeny of the Early Triassic cynodont Thrinaxodon liorhinus
(Therapsida): dental morphology and replacement.
Journal of Vertebrate Paleontology 33 (6): 1408-1431
DOI: 10.1080/02724634.2013.775140
http://www.tandfonline.com/doi/full/10.1080/02724634.2013.775140#.UoJOIvk_sbk

Here for the first time we use micro-computed tomography (μCT)
scanning techniques to study dental replacement in the Early Triassic
cynodont Thrinaxodon liorhinus. We analyzed five specimens ranging
37–87 mm in skull length using μCT scanning, which were supplemented
by detailed anatomical analysis of 48 specimens with a basal skull
length of 30–96 mm. Our results indicate that lower postcanines are
more numerous and present a more complex morphology than the upper
postcanines, even in the same individual; only the lower postcanines
have more than three sectorial cusps and a cingular collar on the
lingual margin. Complexity of the postcanines increases from the
smallest individual to specimens with a skull length of 75 mm, but
complexity decreases in larger specimens. Our results confirm the
alternate replacement of the postcanines and the posterior migration
of the postcanine series (including the loss without replacement of
the anterior-most postcanines). Observations point to a
posterior-to-anterior replacement wave in lower postcanines, but the
evidence is not clear-cut for the upper series. The virtual extraction
of functional and replacement teeth permitted us to conclude that in
most of the cases the upper canines were replaced anteriorly, whereas
lower canines were replaced posteriorly. The presence of two
simultaneous replacements of the upper canine tooth was observed in
two small juveniles, suggesting a higher rate of canine replacement at
a younger age. Incisors also had a sequential replacement pattern, and
more replacement teeth were present in medium-sized individuals.