Abstract
Among the characters of caenagnathid oviraptorosaurians, the lateral occlusal grooves and ridges on the occlusal surface of the jaw bones often receive special attention. Recent studies demonstrated that ontogenetic edentulism is present in caenagnathids, and therefore the lateral occlusal grooves and ridges are vestigial alveoli and interdental septa, respectively. In the present paper, the dentary structures of caenagnathids were reevaluated based on CT images of Caenagnathiasia sp. IVPP V20377. Several previously unknown features including crateriform vestigial alveoli, the morphology of the dentary interior hollow space, and the paired blind tubes beneath the dentary symphyseal shelf are recognized. Current lines of evidence suggest different jaw bone morphologies are likely produced by various tooth reduction patterns, which indicates ontogenetic dietary shift, if once presented in caenagnathids and Sapeornis, may have been different from the condition seen in Limusaurus. The 3D images of dentary interior spaces suggest that while tooth reduction progresses, the empty alveoli are partially modified into structures accommodating blood vessels that nourish the rhamphotheca, probably representing a functional compensation for the insufficient blood supply in toothed jaw bones.
Highlights
Figure 1. 3D reconstruction of Caenagnathasia sp
Referred specimen described in this study- IVPP V20377, fused dentary preserved the symphyseal region and the anteriormost part of the rami[3]
The contact of the dentaries is strengthened by the distinct symphyseal shelf and there is no trace of an intervening suture (Fig. 1)
Summary
Figure 1. 3D reconstruction of Caenagnathasia sp. IVPP V20377. (a) Right lateral view; (b) anterior view; (c) posterior view showing the alveolar canal (dark blue), mandibular canal (red), and the blind tubes open on the posterior surface of the symphyseal shelf (light blue); (d) dorsal view; (e) ventral view; (f) dorsal view showing the blind tubes (light blue) probably accommodating the anterior extension of Mecklian cartilage; (g) right posterolateral view; (h) horizontal section of the dentary showing the internal wall of the vestigial alveoli; (i) coronal section of the left dentary. (a) Right lateral view; (b) anterior view; (c) posterior view showing the alveolar canal (dark blue), mandibular canal (red), and the blind tubes open on the posterior surface of the symphyseal shelf (light blue); (d) dorsal view; (e) ventral view; (f) dorsal view showing the blind tubes (light blue) probably accommodating the anterior extension of Mecklian cartilage; (g) right posterolateral view; (h) horizontal section of the dentary showing the internal wall of the vestigial alveoli; (i) coronal section of the left dentary. The available evidence suggests the vestigial alveoli have been partially modified into structures accommodating blood vessels that nourished the keratinized rhamphotheca after tooth loss, which broadens our understanding of the peramorphic development of the beaks in theropod dinosaurs[17,18]
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