Abstract
BackgroundTooth morphology within theropod dinosaurs has been extensively investigated and shows high disparity throughout the Cretaceous. Changes or diversification in feeding ecology, i.e., adoption of an herbivorous diet (e.g., granivorous), is proposed as a major driver of tooth evolution in Paraves (e.g., Microraptor, troodontids and avialans). Here, we studied the microscopic features of paravian non-avian theropod and avialan teeth using high-spatial-resolution synchrotron transmission X-ray microscopy and scanning electron microscopy.ResultsWe show that avialan teeth are characterized by the presence of simple enamel structures and a lack of porous mantle dentin between the enamel and orthodentin. Reduced internal structures of teeth took place independently in Early Cretaceous birds and a Microraptor specimen, implying that shifts in diet in avialans from that of closely related dinosaurs may correlate with a shift in feeding ecology during the transition from non-avian dinosaurs to birds.ConclusionDifferent lines of evidence all suggest a large reduction in biting force affecting the evolution of teeth in the dinosaur-bird transition. Changes in teeth microstructure and associated dietary shift may have contributed to the early evolutionary success of stemward birds in the shadow of other non-avian theropods.
Highlights
Tooth morphology within theropod dinosaurs has been extensively investigated and shows high disparity throughout the Cretaceous
Tooth shape and enamel microstructure The presence of enamel in all five bird species in this study was confirmed using scanning electron microscopy (SEM) and transmission X-ray microscopy (TXM) imaging of thin sections prepared from the tooth samples (Figs. 1, 2)
Enamel thickness and ultramicroscopic structures vary among ornithuromorphs, enantiornithines, and the nonornithothoracines Sapeornis chaoyangensis and Jeholornis prima (Fig. 1e–h), all of which suggest Mesozoic avian clade had great tooth microstructure diversity
Summary
Tooth morphology within theropod dinosaurs has been extensively investigated and shows high disparity throughout the Cretaceous. Changes or diversification in feeding ecology, i.e., adoption of an herbivorous diet (e.g., granivorous), is proposed as a major driver of tooth evolution in Paraves (e.g., Microraptor, troodontids and avialans). Morphological variation in non-avian theropod teeth is largely reflected in the different number and density of denticles on the mesial and distal carinae of teeth. This is potentially associated with a carnivorous or hyper-. Li et al BMC Evolutionary Biology (2020) 20:46 major reason for the extinction of non-avian dinosaur and stem bird species, including all enantiornithines, at the end of Cretaceous [7]. The survival of avian lineages may have benefited from diversified feeding ecologies, for those taxa with adoption of a granivorous diet
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