Function of pretribosphenic and tribosphenic mammalian molars inferred from 3D animation

Abstract

Appearance of the tribosphenic molar in the Late Jurassic (160 Ma) is a crucial innovation for food processing in mammalian evolution. This molar type is characterized by a protocone, a talonid basin and a two-phased chewing cycle, all of which are apomorphic. In this functional study on the teeth of Late Jurassic Dryolestes leiriensis and the living marsupial Monodelphis domestica, we demonstrate that pretribosphenic and tribosphenic molars show fundamental differences of food reduction strategies, representing a shift in dental function during the transition of tribosphenic mammals. By using the Occlusal Fingerprint Analyser (OFA), we simulated the chewing motions of the pretribosphenic Dryolestes that represents an evolutionary precursor condition to such tribosphenic mammals as Monodelphis. Animation of chewing path and detection of collisional contacts between virtual models of teeth suggests that Dryolestes differs from the classical two-phased chewing movement of tribosphenidans, due to the narrowing of the interdental space in cervical (crown-root transition) direction, the inclination angle of the hypoflexid groove, and the unicuspid talonid. The pretribosphenic chewing cycle is equivalent to phase I of the tribosphenic chewing cycle, but the former lacks phase II of the tribosphenic chewing. The new approach can analyze the chewing cycle of the jaw by using polygonal 3D models of tooth surfaces, in a way that is complementary to the electromyography and strain gauge studies of muscle function of living animals. The technique allows alignment and scaling of isolated fossil teeth and utilizes the wear facet orientation and striation of the teeth to reconstruct the chewing path of extinct mammals.

Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution

“…This alignment of the opposing molars differs by an entire cusp row from the reconstructions for Haramiyavia by Jenkins et al (1) and for all haramiyids by other studies (2,6). These alternative interpretations can now be tested by SEM studies on wear facets, by manipulation of scaled 3D models from CT scans (SI Appendix, Methods), and by kinematic simulation using Occlusal Fingerprint Analyzer (OFA) software (SI Appendix, Methods) (37,38).…”

“…More details are given in SI Appendix. Using the OFA kinematic simulation tool (37,38), we further tested the orthal and palinal occlusal movements (2) and the alternative bucco-lingual cusp row alignments (ref. 36 vs. other studies) for the goodness of fit of the molar contact surfaces (Movie S1).…”

Gene networks, occlusal clocks, and functional patches: new understanding of pattern and process in the evolution of the dentition

“…Three-dimensional scans allow skulls and dentitions to be Odontology manipulated in silico to explore hypotheses about how patterns of mandibular movements, occlusal surfaces of teeth, and muscular moment arms contributed to masticatory patterns, even in long extinct species [37,38,100,112,113]. New tools developed for the analysis of 3D data, like occlusal fingerprint analysis (OFA), have been adapted from methods used to study human occlusion to understand ancient fossil dentitions [114][115][116]. Extensions of OFA using applications from engineering, like finite element analysis (FEA), have allowed not only dynamic occlusal patterns, but also masticatory stresses and strains to be modeled [117].…”

Quantitative genetics provides predictive power for paleontological studies of morphological evolution

“…For mammals, compact, dense, and durable teeth are the most commonly preserved objects in the fossil record (8,9), and because they have complex, quickly evolving phenotypes, even an isolated mammal tooth can usually be identified at the level of species (10). Tooth traits provide a rich source of evidence for genetic differentiation and dietary function in the geological past (11)(12)(13). Teeth are frequently used to measure rates and modes of evolution (14,15) and to study which selective factors were important in the evolutionary history of clades such as our own (16,17).…”