Trophic Diversity in the Santa Cruz Formation Herbivore Guild

Case Western Reserve University, Cleveland OH

Investigators

Abstract

Trophic Diversity in the Santa Cruz Formation Herbivore Guild Darin Croft, Case Western Reserve The Santa Cruz Formation of Argentina (16-17.5 million years old; early Miocene Epoch) has produced a spectacular array of well-preserved fossils that are highly suitable for studying the biology of extinct mammals. Our project will use these specimens to produce the first detailed dietary reconstructions for two of the most diverse and abundant groups of Santa Cruz mammals: caviomorph rodents (the group that includes guinea pigs, chinchillas, capybaras, porcupines, and their extinct relatives) and endemic ungulates (various extinct groups of hoofed mammals that lived exclusively in South America and that left no living descendants). Because many Santa Cruz species are the best known fossil representatives of extinct families, these dietary data will be valuable for anyone investigating the evolution of plant-eating mammals or the ecology of ancient South American mammal communities. Nearly all prior dietary studies in these groups have relied on relative tooth crown height (hypsodonty), a variable correlated with diet and behavioral ecology (e.g., feeding height) in extant mammals but whose correlates are unclear in many extinct groups (especially those with ever-growing teeth such as notoungulates, a very diverse group of extinct hoofed mammals). Building on our preliminary investigations, we will use two alternative methods of dietary reconstruction: low-magnification enamel microwear (examining small pits and scratches on a tooth?s surface) and mesowear (assessing macroscopic wear and tooth cusp shape). By gathering data that are essentially hypsodonty-independent, this study will test the reliability of hypsodonty for inferring diet in extinct South American mammals and, by extension, other extinct groups. Our study will be the first direct analysis of diet for many of the extinct families under consideration, and will include the first investigation of microwear in living caviomorph rodents. We will also investigate the relationship between incisor morphology and diet in living caviomorph rodents to test whether incisor morphology can give clues to diet in extinct rodent species. Other studies have correlated aspects of incisor morphology with diet in other rodent groups, but none has yet examined variation in this particular group in relation to diet. Caviomorphs are quite are unlike ?typical? rats and mice and have been hypothesized to fill the ecological roles occupied by rabbits and various hoofed mammals on other continents. Results of our project will be incorporated into exhibits at the Cleveland Museum of Natural History and will be highlighted in a new mammal diversity and evolution course at Case Western Reserve University. This project will promote the careers of two young investigators, and will increase participation of underrepresented groups in the scientific process through a one-day museum-based teacher training program for public high school teachers in the Cleveland area; this training program will use our research on South American mammals to create lesson plans for teaching fundamentals of paleontology research to 10th grade students. We will broadly disseminate results of this research through publication in scientific journals, public lectures at universities and museums and presentations at scientific meetings, and also through innovative internet resources such a new public internet archive of microwear and mesowear images.