Postdoctoral Fellowship: EAR-PF: Geochemical taphonomy of a rare dicynodont bonebed and its paleobiological implications of social behavior in the stem-mammalian lineage

Kulik, Zoe, Seattle WA

Investigators

Abstract

Zoe T. Kulik has been awarded an NSF EAR Postdoctoral Fellowship to investigate the depositional history of a rare fossil-rich bonebed that preserves over 100 fossils of a dicynodont species allied with the mammalian lineage called Dolichuranus. Insights from this bonebed can provide a potential snapshot of what life was like for these extinct mammal-relatives from ~240 million years ago. For example, using the geology of the surrounding host rock, interpretations can be made to confirm or refute if this fossil assemblage represents a single population. Furthermore, insights from the microscopic details of fossilized bone tissue composition can be used to reconstruct the skeletal and histological changes that this species (and perhaps population) experienced during growth and development to large body size. Indeed, hard tissue histology- the study of dental and bone tissue microstructure and composition- provide the only insights to understand growth rates in the fossil record. To this end, the project goals are to characterize the depositional history of the bonebed in order to contextualize palaeobiological interpretations that can be understood from the fossilized remains that were recovered there, which can provide new information on social behavior, evolution of large body size, and population age structures in the deep evolutionary history of mammals. Broader impacts of this work include (1) working with the Field Museum of Natural History to disseminate results to a broad audience through a temporary exhibit in the Grainger Science Hub, (2) mentoring undergraduate and graduate students at Loyola University Chicago, and (3) developing a curriculum for college students focused on geochemical taphonomy and bone histology at Macalester College. This project aims to investigate the depositional history of a dicynodont-dominated bonebed using traditional and geochemical taphonomic approaches. This bonebed is the lowermost occurrence in a stratigraphic succession of fossil localities in the Lifua Member of Tanzania that will be used to assess the degree of temporal and spatial reworking of vertebrate remains in fluvial and floodplain deposits. In addition, this project aims to test whether morphology, size, and age are correlated in the large dicynodont species, novel work that has not yet been done due to the scarcity of mix-aged dicynodont assemblages. Preliminary geochemical and traditional taphonomic results suggest that the dicynodont bonebed preserves a homogenous taphonomic history reflective of a single, rapid burial, but a larger sample is needed to validate that this bonebed is a snapshot of a single population. Through independent lines of evidence including sedimentology, petrography, bioclast preservation, trace-element analysis, and size-age assessment through hard tissue histology, this project will reconstruct the life history and preservational history of dicynodonts from this bonebed from microstructural to assemblage-wide scales. This novel combination of methods will establish a new line of inquiry in the long- studied question of mammalian social behavior and will also fill critical gaps in our understanding of growth and development in the most abundant group of Permo-Triassic stem-mammals to provide valuable comparative data to identify ontogenetic stages in dicynodonts more broadly. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.