IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Massetognathus pascuali and Santacruzodon hopsoni (Cynodontia, Traversodontidae) from the late Middle−early Late Triassic of South America: new insights on their premaxillary dentition
Autor/es:
MARTINELLI, A.; EZCURRA, M. D.; MELO, T. P.; GAETANO, L. C.; SOARES, M. B.; FIORELLI, L. E.; DESOJO, J. B.
Lugar:
Vitoria
Reunión:
Simposio; IX Simpósio Brasileiro de Paleontologia de Vertebrados; 2014
Institución organizadora:
Sociedade Brasileira de Paleontologia
Resumen:
Massetognathus pascuali and Santacruzodon hopsoniare the commonest recovered vertebrates from thelate Ladinian-early Carnian Chañares Formation(Villa Unión-Ischigualasto Basin, Argentina) andearly Carnian Santacruzodon Assemblage Zone ofthe Santa Maria Sequence 1 (Paraná Basin, Brazil),respectively. Both species are based on well-preservedspecimens; nonetheless, some details of theirdentition are still poorly documented, such as featuresregarding incisors morphology. The discoveryof new specimens (CRILAR-PV-192, 193, and 194;UFRGS-PV-576) of these species allows us the observationof the incisor morphology and the replacementprocess. M. pascuali and S. hopsoni have fourupper and three lower incisors. They are strongly labio-lingually compressed and leaf-shaped, with denticulatemesial and distal margins. Adjacent to themain cusp, there are up to five cuspules mesially andup to six distally. Upper incisors are close, but notin contact with each other, forming a semi-circularcutting edge. In M. pascuali, upper and lower incisorsare similar in size, whereas in S. hopsoni lowerincisors are larger and more procumbent than theupper ones. In both taxa, leaf-shaped incisors arereplaced by the same kind of teeth but particularlyin S. hopsoni, the new incisors have larger, morediscrete accessory cuspules. This may suggest somechanges in the food reduction strategy during ontogeny.Incisor morphology is rather variable in traversodontids.Basal forms, such as Andescynodonand Pascualgnathus, have simple chisel-like incisors,usually subequal in size. Generally, large-sizedforms, such as Exaeretodon and Scalenodontoides,have procumbent and large incisors, with only anenamel layer on the labial surface. The incisor morphologyof M. pascuali and S. hopsoni is one of themost bizarre among traversodontids, also sharedby Arctotraversodon pelmmyridon from the Carnianof Nova Scotia. Dadadon isaloi (Carnian, Madagascar)has an accessory distal cusp on the I4 and thelower incisors have small accessory distal cusps, butthey are rather different from the leaf-shaped conditionof the aforementioned traversodontids. Thedetailed analysis of the incisor morphology amongtraversodontids will permit the character-states refinement,given that the latest phylogenetic analysesonly consider three characters dealing withincisor anatomy (procumbency, cutting margin,and size). Finally, it is worth mentioning that denticulatedleaf-shaped incisors were acquired convergentlyin some archosauromorph lineages (e.g.,Azendohsaurus, Revueltosaurus, basal ornithischians,and sauropodomorphs) during the Triassic, suggestinga partially similar ecological strategy amongthem. Nonetheless, the basic functional differenceis that in traversodontids this morphology is limitedto anterior teeth (incisors) whereas posteriorlythe food was processed by gomphodont postcanines.