Meeting Abstract
The Multituberculata were the most abundant and species-rich mammalian clade in many Late Cretaceous terrestrial ecosystems; however, their fossil record consists largely of isolated teeth and jaws, which makes it difficult to understand life history traits of these extinct animals. Osteohistological proxies can provide insights into the growth strategies of fossil taxa; therefore, in order to develop a more comprehensive view of multituberculate biology, we report on the osteohistology of five multituberculate specimens from northeastern Montana. All specimens are isolated proximal femora, which are assigned to two separate morphotypes: Mu1, represented by one specimen from the uppermost Cretaceous Hell Creek Formation, one from the lowermost Paleogene Tullock Formation, and two from the Bug Creek Anthills locality (which yields a mixed assemblage of Cretaceous and Paleogene taxa) and Mu2, represented by one Hell Creek specimen. The bone microstructure is consistent across all Mu1 specimens and suggests a period of rapid bone deposition early in ontogeny followed by slower bone deposition, whereas the Mu2 bone microstructure suggests a continued slow rate of bone deposition. Although our sample is small, these preliminary data suggest that Mu1 taxa had a fast rate of growth early in ontogeny which later slowed, and that Mu2 taxa had a consistently slow rate of growth. Mu1 is found across the Cretaceous-Paleogene (K-Pg) boundary, whereas Mu2 is only found in the Cretaceous, which may suggest a selective advantage for fast growing taxa during the K-Pg mass extinction. Further sampling is in progress to better understand the role of growth rates in the survival of multituberculates across the K-Pg boundary.
