Describing a New Cryptodont Dicynodont from the Permian of Tanzania

2013 REU Intern Ben Otoo


Junior Geology major at Amherst College

REU Mentor: Dr. Kenneth D. Angielczyk (Assistant Curator of Paleomammalogy, Geology)

Symposium Presentation Title: Describing a New Cryptodont Dicynodont from the Permian of Tanzania

Symposium Presentation Abstract: Dicynodonts (Therapsida, Anomodontia) are a group of non-mammalian synapsids that lived during the Permian and Triassic periods of Earth history (roughly 270-210 million years ago.) They were the first widely successful group of terrestrial herbivores, ranging from marmot-sized to hippo-sized, and were key parts of their ecosystems. A thorough understanding of dicynodont diversity and phylogeny is crucial to understanding terrestrial faunas and ecosystems during the Permo-Triassic interval, which included the largest mass extinction in the history of life at the end of the Permian, 252 million years ago. Here we present a new dicynodont from the early Late Permian (Wuchiapingian Stage, about 257-255 million years ago) of the Ruhuhu Basin of southwestern Tanzania, Batagonda trilovops, gen. et sp. nov. We described the morphology of the holotype specimen, NMT RB156, noting its mixture of characteristics. For example, the morphology of the temporal bar and shape of the snout resemble those of dicynodonts of the clade Cryptodontia; however, the morphology of the secondary palate and the preserved portions of the jaw symphysis are unique. Of particular interest is the fact that the holotype is a juvenile. We included the specimen in a recent phylogenetic data matrix for dicynodonts, and analysis of this dataset recovered Batagonda as the most basal member of the large clade Bidentalia. In addition, we also ran several experiments in recoding phylogenetic characters to gain more insight into this unexpected placement. These experiments show that certain alternative placements of Batagonda on the cladogram are only slightly longer, and that the placement of the species has important implications for the optimization of particular characters. This new species represents a rarely sampled group of dicynodonts from a time and locality that have just recently become subject to sustained, rigorous study. Aside from adding to the diversity of the Permian Ruhuhu fauna Batagonda has interesting implications for dicynodont evolution and biogeography.

Original Project Description: Dicynodonts are an extinct group of ancient mammal relatives, and during the Permian and Triassic periods of Earth history they were the most diverse and abundant terrestrial vertebrate herbivores. The best fossil record of Permian dicynodonts comes from the Karoo Basin of South Africa, but recently I have conducted fieldwork with collaborators in the Permian rocks preserved in the Ruhuhu Basin of southwestern Tanzania.

Research methods and techniques: We will describe a new species of dicynodont from the Permian of Tanzania. The species is represented by the skull, jaw, and partial postcranial skeleton of a subadult individual, and a skull fragment of a second larger individual. We will describe the morphology of the specimen, compare it to other dicynodonts to firmly establish that it is a distinct species, discuss the reasons why the primary specimen seems to be a subadult, examine how it is related to other dicynodonts, and investigate its biogeographic implications. The project will provide the opportunity to learn about vertebrate anatomy and morphology-based taxonomic and phylogenetic methods.