Tuesday, December 8, 2020

[Paleontology • 2020] Agudotherium gassenae • A New Prozostrodontian Cynodont (Eucynodontia, Probainognathia) from the Upper Triassic of Southern Brazil

Agudotherium gassenae   
Stefanello, Kerber, Martinelli & Dias-Da-Silva, 2020

Probainognathian cynodonts are well represented in the fossil record from the Middle and Upper Triassic of South America, especially in Brazil and Argentina. In this contribution, we describe a new genus and species of non-mammaliaform prozostrodontian cynodont from southern Brazil. The new taxon comes from the Niemeyer Site, a locality in which the traversodontid cynodont Siriusgnathus niemeyerorum is numerically dominant, whereas probainognathians and other tetrapods are comparatively scarce. The fauna from the Niemeyer Site was putatively assigned to the Riograndia Assemblage Zone (Norian age) recently, although none of the index fossils for that biozone (e.g., Riograndia, Clevosaurus, Jachaleria) have so far been discovered at this locality. The new cynodont taxon is based on a left lower jaw with the canine and six (pc2–pc7) well-preserved postcanines (CAPPA/UFSM 0262, holotype), and a second referred specimen (CAPPA/UFSM 0208, paratype), which includes a right lower jaw with incisors, canine, and seven (pc1–pc7) postcanines, with pc6–pc7 being the best preserved. These specimens have a robust dentary, a long and dorsoventrally tall Meckelian groove, unserrated canines, and unserrated, sectorial postcanine teeth with posteriorly inclined cusps and a poorly developed lingual cingulum. This combination of features is unknown in other Carnian and Norian non-mammaliaform cynodonts. The new taxon contributes to our knowledge of the evolutionary radiation of small prozostrodonts that occurred in western Gondwana during the Late Triassic and led to the emergence of several important cynodont groups, including Mammaliaformes.


THERAPSIDA Broom, 1905 
CYNODONTIA Owen, 1861 

PROZOSTRODONTIA Liu and Olsen, 2010 

Agudotherium gassenae, gen. et sp. nov.

Etymology—Agudo,’ in reference to the municipality of Agudo (state of Rio Grande do Sul, Brazil) where the specimens were found. The suffix ‘therium’ (from the Greek ‘thērion’) means ‘beast,’ and is often used for mammals and closely related forms. The specific epithet honors Mrs. Valserina Maria Bulegon Gassen, former mayor of the city of São João do Polesine (State of Rio Grande do Sul, Brazil), for her valuable contribution in the creation of CAPPA/UFSM.

Micheli Stefanello, Leonardo Kerber, Agustin G. Martinelli and Sérgio Dias-Da-Silva. 2020. A New Prozostrodontian Cynodont (Eucynodontia, Probainognathia) from the Upper Triassic of Southern Brazil. Journal of Vertebrate Paleontology. 40(3)e1782415. DOI: 10.1080/02724634.2020.1782415