Meeting Abstract
P3.197 Sunday, Jan. 6 Bone Histology and Primary Growth Rates in Hatchling Titanosaurs from Madagascar: New Insights from Micro-Computed Tomography WHITNEY, M*; CURRY ROGERS, K; BAGLEY, B; Macalester College; Macalester College; University of MInnesota rogersk@macalester.edu
The smallest post-hatching juvenile sauropods are only a little less than half of known adult size and leave details of the earliest stages of sauropod ontogeny poorly understood. Here we report on two partial skeletons of hatchling Rapetosaurus krausei, a titanosaur from the Upper Cretaceous Maevarano Formation of Madagascar, that provide new data on primary early stage growth rates in sauropods. The skeletons come from two localities and greatest length ratios for appendicular elements confirm that there are only two individuals present, that there is no significant allometry in Rapetosaurus postcranial ontogeny, and that each individual is less than 15% adult size. The smaller specimen includes sacral and caudal vertebrae, pubis, femur, tibia (12.7 cm long), fibulae, metatarsal I, humeri, metacarpal III, and a phalanx. The larger specimen includes caudal vertebrae, tibia (17.9 cm long), and metacarpals I and IV. We employed an X5000 high-resolution dual-head 225kV microfocus X-ray CT system located in the Department of Earth Sciences, University of Minnesota to garner bone histological data on earliest stage growth rates in these juveniles. We achieved an effective pixel pitch of 36 – 48 microns for the larger samples and 14 – 28 microns for sub-volumes. We collected 2-D radiographs and reconstructed these data to produce a 3-D volume for visual analysis and slices of the 3-D volume for quantitative analysis. Primary bone growth in Rapetosaurus is highly vascularized woven and fibrolamellar bone with mid-diaphyseal remodeling. These results support the hypothesis that intensive remodeling observed in the bones of older juvenile Rapetosaurus may be dictated, at least in part, by resource limitations during periods of drought/ecological stress recorded in the Maevarano Formation.
