Meeting Abstract
In heterodont mammals, the alveolus mechanically shapes and adds complexity to the developing crown (e.g. rodents). In crocodylians, which are also thecodont but with pseudoheterodont crown shapes (i.e. two broad categories: caniniform, molariform) it is unclear if alveolar form similarly determines crown morphologies. Here we examine alveolar shape alongside crown type to test for a relationship between sockets and crowns in Alligator mississippiensis for the first time. From CT data, we digitally reconstructed alveoli of the most procumbent caniniform and molariform teeth, as well as ambiguously shaped intermediate teeth. Alveolus outlines were quantified using elliptical Fourier transformation, standardizing for location, orientation, and size. Principal components analysis (PCA) ordinated patterns in the Fourier coefficients, and linear discriminant analysis (LDA) was run on the PC scores to determine consistency of crown categories: caniniform, molariform, and intermediate. The first two PCA axes captured ~87% of shape variance (PC1 = relative mesio-distal alveolar length, PC2 = alveolar curvature). Crown-shape categories fell into largely separate convex hulls. The LDA had high classification rates for caniniform (80%) and molariform (90%) teeth, but middle teeth were less well-defined (60% accurate identification, with the remaining 40% mis-classified as caniniform). These preliminary results suggest a significant relationship exists between alveolar and crown morphologies in crocodylians. Intriguingly, each new tooth in these polyphydont reptiles contributes tissue to the socket wall (e.g. interalveolar bone), thus potentially shaping subsequent crown generations and resulting in a mechanism inverted from the mammalian pattern (e.g. crown-first vs. alveolus-first).
