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ABSTRACT
New material of the traversodontid cynodont Dadadon isaloi from the Triassic of southwestern Madagascar is described. The new material consists of a complete, well-preserved skull (FMNH PR 2232) and an unassociated, partial lower jaw (UA 10608). The new material reveals several novel aspects of Dadadon's morphology. Newly recognized autapomorphies that diagnose Dadadon include a fourth upper incisor with posterior accessory cusp, deep interorbital depressions confined to the frontals, and a very tall, robust mid-frontal ridge. Dadadon can further be distinguished from the similar traversodontids Massetognathus and Santacruzodon by the presence of shorter, broader prefrontals with prominent dorsal depressions, robust anterolateral processes overhanging the orbits, a single cusp in the anterior cingulum of the upper postcanines, and relatively elongate, striated, conical upper incisors. In a revised phylogenetic analysis incorporating data from the new specimens, Dadadon is recovered in a clade with Massetognathus and Santacruzodon. This clade is the sister taxon to the well-supported traversodontid subclade Gomphodontosuchinae. The ‘basal Isalo II’ cynodont fauna from Madagascar is more similar in composition to that of South America than to mainland Africa, although this is probably attributable to the lack of Ladinian–Carnian therapsid fossils on the mainland rather than an actual biogeographic pattern.
ACKNOWLEDGMENTS
Support was provided by our home institutions, The Field Museum, and the WWF (Worldwide Fund for Nature, Madagascar). Specimen preparation was done at the Field Museum and American Museum of Natural History. Photographs were taken by Frank Ippolito. Drawings by Marlene Hill Donnelly (). We acknowledge the Ministère de L'Enérgie et des Mines for authorizing field efforts and for continuing to facilitate our joint U.S.-Madagascar exploration, research, and education program.
Handling editor: Bruce Rubidge