ABSTRACT. 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 Pachygenelus and Diarthrognathus 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.

-New discoveries of articulated skulls and lower jaws of Brasilodon and Brasilitherium from the Late Triassic of Brazil provide additional information on these small cynodonts, allowing us to establish the family Brasilodontidae nov. The basicranium, lateral wall of the braincase, primary and secondary palates and the quadrate of Brasilitherium are described, as well as the basicranium, primary palate and lower jaw of Brasilodon. Brasilitherium exhibits more derived characters than Brasilodon in the periotic, the promontorium, and the articular process of the dentary. Brasilodon is more derived in the lower dentition, the mode of tooth replacement, and the vascular features in the "stapedial recess". Both genera have interpterygoid vacuities that are considered here as possibly derived or reversed characters of the mammalian primary palate. The new phylogenetic analysis presented here corroborates the position of both genera as sister-group of mammals as previously proposed.Keywords: Cynodontia, Probainognathia, Brasilodon, Brasilitherium, Late Triassic, southern Brazil.RESUMO -Novos achados, incluindo crânios com mandíbulas articuladas, de Brasilodon e Brasilitherium do Neotriássico do Brasil fornecem informações adicionais sobre estes pequenos cinodontes, permitindo a proposição de uma nova família, Brasilodontidae. São descritos o basicrânio, a parede lateral da caixa craniana, o palato primário e o secundário e ainda o quadrado de Brasilitherium, bem como o basicrânio, o palato primário e a mandíbula de Brasilodon. Brasilitherium apresenta caracteres mais derivados em relação a Brasilodon no periótico, promontório e processo articular do dentário. Brasilodon apresenta uma dentição mandibular mais derivada, bem como o padrão de substituição dentária e ainda o sistema vascular relacionado ao recesso estapedial. Ambos apresentam vacuidades interpterigóides, que são aqui interpretadas como uma característica derivada ou uma reversão, diretamente relacionada à organização do palato primário mamaliano. A nova análise filogenética aqui apresentada confirma a proposição deste dois gêneros constituírem o grupo-irmão dos mamíferos, como já foi proposto em trabalhos prévios.Palavras-chave: Cynodontia, Probainognathia, Brasilodon, Brasilitherium, Triássico superior, sul do Brasil.

Well-preserved cranial remains of a small sphenodontian lepidosaur from the Upper Triassic Caturrita Formation of Rio Grande do Sul, Brazil, are the first record of the genus Clevosaurus Swinton, 1939 from South America. They represent a new species, Clevosaurus brasiliensis, which is distinguished by a very short antorbital region of the skull (corresponding to about 20 per cent of skull length) and the presence of teeth in addition to two longitudinal rows on the pterygoid. C. brasiliensis most closely resembles C. bairdi from the Lower Jurassic of Nova Scotia (Canada) and C. mcgilli from the Lower Jurassic of Yunnan (China). The discovery of Clevosaurus in the Upper Triassic of southern Brazil provides a significant range extension of this widely distributed sphenodontian genus. Along with other recent finds, it also suggests that there may have been less biotic provincialism among terrestrial vertebrates during the Late Triassic than has previously been assumed.

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