Dentition and histology in titanosaurian dinosaur embryos from Upper Cretaceous of Patagonia, Argentina

Abstract

Exceptionally preserved sauropod embryos from the Late Cretaceous Anacleto Formation in Auca Mahuevo (Neuquén Province, Argentina), have provided fundamental information on titanosaurian ontogeny. This paper describes the dental composition and disposition as well as bone microstructure of the specimens. Embryonic teeth show size disparity, with lengths that vary from 1 to 3 mm, and diameters ranging from 0.15 to 0.26 mm, the most frequent length values between 2.5 and 3 mm. Seemingly, a typical “pencil–like” teeth morphology, and a dental formula Pm 4, M 7-8 / D10? remained constant during titanosaurian ontogeny, whereas their arrangement in the skull shows notable ontogenetic changes. Absence of wear facet on teeth would indicate absence of pre–natal chewing movements. The enamel proportion is significantly higher in embryos than in mature titanosaurs, which suggests that this relation varies during ontogeny. Embryonic bony tissue is composed by a highly vascularized and cellular woven bone. Absence of osteonal tissue, high degree of vascularization, presence of numerous osteocytes and low development of periosteal bone reveal that the Auca Mahuevo titanosaurs would have had a high early growth rate, and they were not entombed in an advanced embryonic stage.