Ontogeny and tooth replacement in the brazilian cynodonts Brasilodon quadrangularis, Brasilitherium riograndensis and Minicynodon maieri.

MARTINELLI, AGUSTÍN G.; GILL, PAMELA; CORFE, IAN J.; RODRIGUES, PABLO; FONSECA, PEDRO H. M.; SCHULTZ, CESAR L.; MARINA BENTO SOARES; RAYFIELD, EMILY J.

Simposio; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2019

Brasilodon quadrangularis Bonaparte et al., 2003, Brasilitherium riograndensis Bonaparte et al.,2003, and Minicynodon maieri Bonaparte et al., 2010 are probainognathian cynodonts from theLate Triassic (Norian) of southern Brazil phylogenetically positioned close to Mammaliaformes. Thefirst two taxa are based on several skulls ranging from 25 to 40 mm (anteroposterior length) andisolated upper/lower jaws of different sizes (~10 to ~29mm), whereas M. maieri is solelyrepresented by a skull with lower jaws (27 mm). The taxonomic separation of these species wasbased on features that are now shown to be related to ontogenetic stages and/or incompletenessof the hototypes (e.g., fused prootic/opisthotic, incipient promontorium, interpterygoid vacuities).These genera differ mainly in: the number of upper/lower incisor+canine teeth, length ofupper/lower postcanine diastema, morphology of the lower postcanines, and size of interpterygoidvacuity. Based on new microCT data and re-examination of external features we conclude: smallerindividuals have 4I+2-3C/3i+2c whereas larger individuals have 4I+1C/3i+1c; diastemaenlargement is a result of the loss of incisor-like canines and the anteriormost postcanine teeth.Larger individuals have variable postcanine morphology, whereas smaller individuals do not.Additionally, microCT data reveals evidence of more than one tooth replacement at loci, loss ofanterior postcanines, and addition of new postcanines at the posterior part of the dental series.This evidence supports the hypothesis that the three species represent an ontogenetic series of asingle taxon. It has several mammaliaform apomorphies (e.g., petrosal with promontorium);nonetheless, it lacks the diphyodont tooth replacement pattern of mammaliaforms and a dentarycondyle.