TOOTH MORPHOLOGY AND NICHE REPLACEMENT: ANALYSIS OF CRETACEOUS SHARKS, MESOZOIC MARINE REPTILES AND TERTIARY MARINE MAMMALS

The idea of faunal niche replacement has been discussed for nearly a century. While mechanisms of niche replacement have been thoroughly discussed (i.e., extinctions, competition, evolution of new adaptive morphologies), actual studies involving quantitative analyses have been lacking. In this study, morphological features of dentition in Late Cretaceous and Tertiary marine vertebrate predators were analyzed. The analysis included 119 species of Late Cretaceous and Tertiary sharks, 20 species of Late Cretaceous marine reptiles, and 29 species of Tertiary marine mammals. Dental characters utilized in the study included tooth length, width, cross-sectional outline, and longitudinal outline, the presence of serrations, number of lateral cusps, the presence of curvature and/or the presence of re-curvature. Species included in the analysis were originally collected from Late Cretaceous and Tertiary Formations located in the South-Central, South-Eastern, and the Mid-Atlantic US, as well as Europe and the Pacific Rim .

A morphometric “tooth space” was constructed using the eigenvectors generated from Principal Coordinate Analysis of the dental character data. The results of the analysis show that Mesozoic marine reptiles occupied a small, discrete region of the tooth morphospace, while Cretaceous sharks occupied a much larger, diffuse region of the morphospace. During the Early Tertiary a profusion of shark tooth morphologies occurred, and subsequently expansion into new areas of tooth morphospace. Yet, no overlap with the morphospace previously occupied by Mesozoic marine reptiles occurred. With the evolution of marine mammals during the Tertiary a profusion of tooth morphologies evolved. Remarkably, many of the tooth forms converged on the Mesozoic marine reptile designs, and hence a major overlap of marine mammal tooth morphospace with the previously occupied Mesozoic marine reptile morphospace took place.

Based on dental morphology, this study indicates that following the extinction of the Mesozoic marine reptiles during the Late Cretaceous, Tertiary sharks failed to occupy the vacated niches, while Tertiary marine mammal dentition converged on the previous Mesozoic marine reptile tooth designs. Thus, Tertiary marine mammals likely occupied the vacated Mesozoic marine reptile dietary niches.