PRELIMINARY ANALYSIS OF BONE AND DENTAL HISTOLOGY OF LATE TRIASSIC DICYNODONTS (SYNAPSIDA, THERAPSIDA) FROM THE NEWARK SUPERGROUP (PEKIN FORMATION) OF NORTH CAROLINA

Because the formation of biomineralized elements (bones, teeth) in life reflects growth and physiologic processes, histological (microstructural) analysis is useful for elucidating aspects of paleobiology (growth strategy, biomechanics, and possibly metabolism) of extinct vertebrates. Dicynodonts were the dominant therapsids (mammal-like reptiles) that ranged temporally from the Mid-Permian, until the Late Triassic. These animals dominated the terrestrial herbivorous ecological niche and enjoyed a global distribution. Although they survived the Permo-Triassic extinction event, they experienced a dramatic decrease in taxonomic diversity, but significantly increased body size in surviving taxa. Previous studies have examined the bone histology of Permian and Early Triassic forms, but none have examined bone microstructure of Late Triassic taxa or addressed how the latest forms may have attained large (hippo) size. Additionally, dicynodonts are enigmatic in the lack of incisor and postcanine teeth (replaced by a keratinous beak), while retaining maxillary caniniform tusks. These tusks lost enamel in maturity and were ever-growing, similar to those of modern elephants. Although growth lines are reported in the dentine of dicynodont tusks, the present study is the first to test the biological significance of the growth line periodicity reflected in dicynodont dentine microstructure.

Selected skeletal elements from a Late Triassic (Carnian) brick quarry in North Carolina (Newark Supergroup; Deep River Basin; Sanford Sub-Basin; Pekin Formation) were sampled, including a femur and tibia from a semi-articulated, non-Placerias (sp. indet.) dicynodont, as well as two isolated, non-associated tusks. This talk discusses dicynodont bone and tusk microstructure, comparing specimens from the Late Triassic of the Newark Supergroup with previous histological studies of earlier taxa (Diictodon, Lystrosaurus), and elements of another Late Triassic dicynodont, Placerias hesternus, from the Chinle Group. These results will be used to identify any temporal fluctuations in growth strategy and rate, as well as to hypothesize biological adaptations of dicynodonts in the continually changing environment of the Triassic.