Field of Science

New Cynodont from the Upper Triassic of Brazil

This is a sizeable monograph containing a description of a new taxon of cynodont, Trucidocynodon riograndensis, from the Upper Triassic Santa Maria Formation of Brazil.  This paper includes a detailed phylogenetic analysis of the Cynodontia with 145 characters, and a detailed atlas depicting various character states used in the analysis.  The resulting tree does appear to be significantly different than the one recently published by Liu and Olsen (2010).  I don't study cynodonts so I cannot evaluate the phylogenetic, taxonomic, and descriptive work; however, it is maddening to see that the straigraphic section still considers the Ischigualasto Formation to be entirely Carnian in age ignoring much of the recent Triassic timescale revisions and studies showing good evidence that much of the Ischigulasto is actually Norian in age (Furin et al. 2006; Irmis and Mundil, 2008; Currie et al. 2009). Despite this, however, this still appears to be an impressive piece of work pending resolution of the differences with the Liu and Olsen study.

Oliveira, T. V., Soares, M. B. and C. L. Schultz. 2010. Trucidocynodon riograndensis gen. nov. et sp. nov. (Eucynodontia), a new cynodont from the Brazilian Upper Triassic (Santa Maria Formation). Zootaxa 2382:1–71.

Abstract - An almost complete skeleton of a new carnivorous cynodont from the Upper Triassic of Southern Brazil, Trucidocynodon riograndensis gen. nov. et sp. nov., is described. The new taxon is very similar to Ecteninion lunensis Martinez et al. 1996 from Upper Triassic of Argentina (Ischigualasto Formation). Both have an elongated skull, large pterygoid flanges, a well developed orbitosphenoid, a relatively short osseous secondary palate, greatly developed canines and sectorial postcanines with posteriorly directed cusps. However, the new taxon shows some differences relative to E. lunensis such as an open pterygoparoccipital foramen, the posterior opening of the post-temporal foramen enclosed by tabular and squamosal, and upper incisors with serrated cutting edges. The more remarkable features of the postcranium of T. riograndensis are the presence of 32 presacral vertebrae, a greater number than in most of non-mammaliaform cynodonts, the accentuated lumbarisation of the posterior trunk vertebrae and a remarkable morphological gradient in the caudal vertebrae; the femur and humerus show some interesting adaptations suggesting a more upright limb posture. The overall morphology of the astragalocalcaneal complex is similar to that of Diademodon and of the therocephalian Bauria.

REFERENCES

Currie, B. S., Colombi, C. E., Tabor, N. J., Shipman, T. C., and I. P. Montañez. 2009. Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation, Ischigualasto Provincial Park, San Juan, Argentina, Journal of South American Earth Sciences 27:74-87. doi: 10.1016/j.jsames.2008.10.004

Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J.L., and Bowring, S.A., 2006, High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs: Geology, v. 34, p. 1009–1012, doi:10.1130/G22967A.1.


Irmis, R. B., and R. Mundil. 2008. New age constraints from the Chinle Formation resolve global comparisons of Late Triassic vertebrate assemblages. Journal of Vertebrate Paleontology 28:95A.

Liu, J., and P. Olsen. 2010. The Phylogenetic Relationships of Eucynodontia (Amniota: Synapsida). Journal of Mammalian Evolution. Published online April 13 2010. doi: 10.1007/s10914-010-9136-8

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