Meeting Abstract
2.5 Tuesday, Jan. 4 What’s so great about jaws?: Functional disparity of the early gnathostome radiation ANDERSON, P.*; FRIEDMAN, M.; BRAZEAU, M.; RAYFIELD, E. J.; Univ. of Bristol, UK; Oxford Univ, UK; Museum fur Naturkunde, Berlin; Univ. of Bristol, UK phil.anderson@bristol.ac.uk
In the earliest Devonian (ca. 420 Mya), gnathostomes (jawed vertebrates) shared ecological space with a wide range of jawless fishes (agnathans). However, by the end of the Devonian 100 My later, gnathostomes were the dominant vertebrate group in faunal assemblages in terms of relative richness. Although often cited, the radiation of Devonian gnathostomes has remained unexplored from a functional or ecological standpoint. Here we apply a biomechanical approach in order to examine trends in the functional disparity of gnathostomes during this important interval of their evolutionary history. A series of biomechanically relevant metrics were collected from lower jaws of 182 Devonian gnathostome genera and were used to create a functionally informed morphospace. Disparity metrics were calculated across stratigraphic bins. Resulting profiles of morphospace occupancy were compared with richness data documenting the relative contribution of gnathostomes and agnathans to faunal assemblages throughout the Devonian. Functional disparity among Early Devonian gnathostomes is comparable with that seen in the Late Devonian even as the taxonomic richness of the clade increases substantially over the period. As much as half of jaw morphopace is occupied by stem gnathostomes, specifically placoderms. Much of early gnathostome functional innovation therefore occurred on the stem, suggesting that ecological proliferation is not coincident with the initial radiation of living jawed vertebrates. Steady levels of gnathostome functional diversity in the face of the plummeting relative richness of agnathans raises questions about the role of active displacement in driving the compositional shift in faunas between the beginning and close of the Devonian.
