Reg. Charity No. 1168330
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, disposition and 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, with the most frequent length values between 2.5 and 3 mm. Apparently, a typical 'pencil-like' tooth morphology and a dental formula of Pm 4, M 7–8/D10? remained constant during titanosaurian ontogeny, whereas the arrangement of teeth in the skull shows notable ontogenetic changes. Absence of wear facets on teeth suggests a lack of prenatal chewing movements. The enamel proportion is significantly higher in embryos than in mature titanosaurs, which suggests that this relationship varies during ontogeny. Embryonic bony tissue is composed of highly vascularized, cellular woven bone. The absence of osteonal tissue, the high degree of vascularization, the presence of numerous osteocytes and poor development of periosteal bone reveals that the Auca Mahuevo titanosaurs would have had a high early growth rate and that they were buried at a relatively advanced embryonic stage.