Meeting Abstract

P1-70   -   Fossilized Bones and Ancient Genomes: Preserved Osteocyte Lacunae Predict Genome Size in Vertebrates from the Cretaceous Maevarano Formation, Madagascar Vischer, S*; Curry Rogers, K; Organ, C/L; Anderson, M; Macalester College, St. Paul, MN; Macalester College, St. Paul, MN; University of Reading - Whiteknights, Reading, Berkshire, UK; Macalester College, St. Paul, MN svischer@macalester.edu

In extant organisms, genome size varies by several orders of magnitude, from <0.001 picograms in some bacteria to hundreds of picograms in some unicellular eukaryotes. Amniotes also show substantial variation. The marbled lungfish has a genome size two orders of magnitude larger than hummingbirds, which exhibit one of the smallest genomes. Osteocyte lacunae are well-preserved in fossil bone tissue and are strongly correlated with genome size. Here we present new data on osteocyte lacuna volume and predicted genome size for a diverse group of reptiles from the Upper Cretaceous Maevarano Formation of Northwestern Madagascar. Our sample includes more than 80 paleohistological thin-sections from the abelisaurid theropod Majungasaurus, the titanosaurian sauropod Rapetosaurus, the pelomedusid turtle Sahonachelys, and a diverse array of crocodilians, including the large-bodied Mahajangasuchus, the smaller terrestrial Araripesuchus, the notosuchian Simosuchus, and an unnamed longirostrine. We measured over 4000 osteocyte lacunae and calculated osteocyte volumes. These data were then combined with cell volume and haploid genome size data from more than 40 extant and extinct vertebrates. A Bayesian phylogenetic model was used to generate genome size predictions for the extinct taxa. Our data support the hypothesis that osteocyte lacunae are an abundant resource for studying cellular- and genome-scale biology in long extinct species. Osteocyte lacunae in our sample vary in density, shape, and volume within single thin-sections, between primary and secondary bone tissues, and throughout ontogeny. Our data are, however, consistent with previous studies regarding small predicted genome sizes in theropod dinosaurs and a lack of correlation between genome size and body mass. Our preliminary results also suggest that genome diversity may have underlain the biodiversity of early crocodylomorphs and turtles.