Paper No. 257-12
Presentation Time: 4:15 PM
FUNCTIONAL DIVERSIFICATION PATTERNS IN THE EARLY MESOZOIC
Escalation has had an important role in determining the distribution and activity of interacting species. Tests of escalation in geological time have generated much controversy and still some patterns are not entirely clear. We measured ecological and functional diversification using Bambach’s ecospace model that classifies taxa according to their motility, feeding and tiering, in order to identify patterns in functional diversity and to evaluate the strength of interactions between ecological groups during the early Mesozoic. A total of 168,604 occurrences of 7389 genera that span the Permian-Jurassic (298.9 to 145.0 Ma) were downloaded from the Paleobiology Database (PBDB). Each genus was classified according to autecological information from the PBDB and literature. Rarefaction was used to standardize the number of genera analyzed per bin. Patterns of functional diversity were assessed using functional richness (FR), evenness (FE), and specialization (FS) indexes. Dynamic Factor Analysis (DFA) was performed in order to observe changes in the structure of ecospace through the time. Finally, in order to test hypotheses related to escalation, we performed cross-correlations of subcategories associated with tiering, predation and motility.
The number of modes of life, FR, and FE increased significantly from the Permian to Jurassic, and FS increased after the Late Permian extinction as a result of new adaptations. DFA identified three latent curves that appear poorly correlated with Sepkoski's faunas, contrary to expectations. Lastly, for the study interval, there are significant positive correlations between the abundance of predatory genera and both infaunalisation and prey motility. These results indicate that both ecological complexity and packing of particular modes of life increased from the Permian through Jurassic, but especially after the Late Permian extinction event. The appearance of marine reptiles, intensification of benthic predation (gastropods, neoasteriods, ophiuroids), and adaptations in the ichthyofauna to new trophic niches presumably increased predation pressure and drove observed increases in infaunalisation. These results support the hypothesis of escalation and suggest that the Triassic was an important episode of ecological change.