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Article: A primitive Late Triassic 'ictidosaur' from Rio Grande do Sul, Brazil

Publication: Palaeontology
Volume: 44
Part: 4
Publication Date: July 2001
Page(s): 623 635
Author(s): José F. Bonaparte, Jorge Ferigolo and Ana Maria Ribeiro
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How to Cite

BONAPARTE, J. F., FERIGOLO, J., RIBEIRO, A. 2001. A primitive Late Triassic 'ictidosaur' from Rio Grande do Sul, Brazil. Palaeontology44, 4, 623–635.

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A primitive 'ictidosaur' from lower Norian beds of southern Brazil, Riograndia guaibensis gen. et sp. nov., represented by a fragmentary skull and a lower jaw bearing a complete dentition, shows a more generalized morphology than Chaliminia from the Upper Triassic of Argentina and PachygenelusDiarthrognathus from the Lower Jurassic of South Africa, Canada and Greenland. The frontal bone borders the orbit, and ventrally contacts the dorsal process of the palatine. The secondary bony palate extends back to the last postcanine. I1 and i2 are reduced, whereas I2-3 and i1 are hypertrophied. Both PC 1-7 and pc 1-7 have blade-like crowns without cingula and with 5-9 small sharp cuspules. The upper postcanine crowns are semicircular in labial view with the cuspules around their margins. The lower postcanine crowns are asymmetrical with most of the cuspules dorsodistally distributed. The possible origin of this peculiar dentition is interpreted as the retention of the juvenile dentition of ancestors. The hypothesis that Riograndia guaibensis and the so-called 'ictidosaurs' might have been derived from gomphodont cynodonts is presented.
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