HIERARCHICAL ONTOGENETIC PATTERNS AND TOOTH LOSS IN TYRANNOSAURUS REX

Tyrannosaurus rex experienced an ontogenetic loss of tooth positions, where the maxilla decreased from 15 to 11 teeth, and the dentary decreased from 17 to 12 teeth. One problem with this hypothesis was the absence of specimens showing an intermediate tooth count between the juveniles and adults. Two new specimens (CM 79057, MOR 1125) fill this gap in the growth series, and a numerical cladistic analysis of ontogenetic characters in T. rex, including tooth data, results in a reconstruction of ontogeny that supports the hypothesis of ontogenetic tooth loss. Several other trends reflect related changes in the feeding apparatus of this dinosaur, including an increased depth of the head, increased size of the teeth, coarsened joint surfaces between bones of the skull and jaws, and prominent muscle scars and fossae. These changes are consistent with the high bite force estimates for adult T. rex. In comparison with growth curve reconstructions for T. rex, it appears that these specializations for high bite forces occurred during interval of rapid growth, where the entire skull was transformed from a lightly built skull with many narrow teeth to a deep skull with fewer enlarged teeth.