Bone histology of the sauropod dinosaur Alamosaurus sanjuanensis from the Javelina Formation, Big Bend National Park, Texas
Woodward, Holly Noelle
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Bone samples of the sauropod dinosaur Alamosaurus sanjuanensis were collected from the Upper Cretaceous Javelina Formation in Big Bend National Park, Texas, for use in a histological analysis. Alamosaurus is a member of the Titanosauridae, the most derived sauropod group. This is the first extensive histological study performed on a member of the Titanosauridae, although previous studies indicated that the vertebral structure in this group is unlike that of any other sauropod family. Parts of twelve ribs; two tibiae; three humeri; one scapula; two fibulae; three femora; one pubis; one ulna; one metacarpal II(?); one metatarsal II(?); two dorsal vertebrae; and two distal caudal vertebrae were examined. The specimens were sectioned and imaged digitally using a flatbed scanner as well as prepared for thin section analysis. The ribs and vertebrae are highly cavernous. The vertebrae possess “camellate” cavities unique to titanosaurids. The ribs are also highly cavernous throughout their length, a feature previously unreported in other sauropods. Several distal rib specimens possess calcified cartilage, suggesting a connection to cartilagenous sternal ribs. The pubis and scapula were the first skeletal elements to be completely remodeled by, 50 percent adult length. Primary tissue, where present, is typically of the woven to fibro-lamellar type. Lamellar-zonal tissue with annuli was only found in the peripheral cortex of a tibia 74 percent adult length, a humerus 78 percent adult length, and in several rib fragments. Several appendicular elements exhibit growth rings, or “cycles”. By estimating body mass from the percent adult length at each cycle, and applying the von Bertalanffy growth rate equation, a growth curve is produced. Using a humerus sample possessing the best preserved cycles, Alamosaurus is estimated to have attained adult mass in 60 years. This method is also used to provide age estimates for previous sauropod growth rate studies.