[dinosaur] Analysis of skull shape in Triassic dicynodonts (Therapsida) from South America

Ben Creisler
[email protected]

A new paper:


Maria de los Angeles Ordonez,  Guillermo H. Cassini,  Sergio F. Vizcaíno
& Claudia A. Marsicano (2019)
A geometric morphometric approach to the analysis of skull shape in
Triassic dicynodonts (Therapsida, Anomodontia) from South America.
Journal of Morphology (advance online publication)
doi:  https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1002_jmor.21066&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=CUf1QF8c2ZDSVEbYr_3eT7v4NT49Ptoh2xl4KoQRY44&s=IlhyJIzdyGfqdv8pU7osxO9me3Qu75r0YbSzOPoJJxw&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__onlinelibrary.wiley.com_doi_10.1002_jmor.21066&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=CUf1QF8c2ZDSVEbYr_3eT7v4NT49Ptoh2xl4KoQRY44&s=JTG5Co3-kkHPZOq_36aZ4kLq1XGKaoqVw5fb5EGOAFo&e= 


Dicynodont therapsids were a major component of the Permo‐Triassic
terrestrial ecosystems across Pangea and have been regarded as specialized
herbivores. In South America, the group was represented by several taxa of
the clade Kannemeyeriiformes spanning from the Middle to the Late Triassic.
In order to evaluate if cranial differences among taxa are potentially
related to differences in feeding function, we performed a geometric
morphometric analysis on 28 South American dicynodont crania. We digitized
19 cranial landmarks and conducted generalized Procrustes analysis,
principal component analysis (PCA), principal component analysis between
groups (bg‐PCA), and a branch weighted squared‐change parsimony approach.
Phylogenetic inertia was not a significant driver of cranial shape
evolution in the group, whereas PCA and bg‐PCA support that major
morphological shape differences are concentrated in the preorbital region
(relative length of the snout and width of the caniniform process), in the
position of quadrate condyle in relation to the caniniform process, and in
the increase in the intertemporal surface area. In this context, tusked
Dinodontosaurus, "Kannemeyeria," and Vinceria have relatively smaller
adductor attachment areas and input moment arm than younger taxa lacking
tusks, such as Ischigualastia, Stahleckeria, and Jachaleria. Differences in
cranial morphology in later dicynodonts reflect modifications in feeding
mechanics, probably due to changes in food resources (vegetation) in their
habitats toward the end of the Triassic.

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