Kevin Velez Dissertation Defense

Join us for Kevin Velez’s upcoming dissertation defense!

Title: New paleontological record provides insights into the early evolution and biogeography of gavialoids (Crocodylia: Gavialoidea)

Abstract:
Today, crocodylians are separated into three groups, Alligatoridae (Alligator, Caiman, Melanosuchus, Paleosuchus), Crocodylidae (Crocodylus, Mecistops, Osteolaemus), and Gavialidae (Gavialis). The latter group, Gavialidae, is represented by one species that is restricted to the fluvial habitats of northern India and Nepal. However, the gavialid fossil record shows that the group was more diverse and geographically widespread, with specimens occurring in most landmasses. In this dissertation, I explore the paleontological record of gavialids using new fossil material and test historical biogeographical hypotheses. The abundant fossil record of gavialids, coupled with their occurrences in multiple localities around the world make this group ideal for testing complex biogeographical hypotheses under a paleontological perspective.

In the first part of this dissertation, I explore the evolutionary relationships of three gavialid groups in a phylogenetic context that have been considered the oldest members, all of which are Late Cretaceous in age. These putative early gavialids include Dolichochampsa minima from South America, Ocepesuchus eoafricanus from Africa, and the ‘thoracosaurs’ from North America and Europe. Phylogenetic analyses show Ocepesuchus placed within Alligatoridae, ‘thoracosaurs’ as basal eusuchians, and Dolichochampsa nested within Gavialidae. The placement of Dolichochampsa within Gavialidae brings evidence of a possible South American origin for the clade that can be traced back to the Late Cretaceous. In the following section of this dissertation, I describe a new fossil gavialid from the Eocene (42 Ma) of Pakistan. This new specimen extends the temporal range of gavialids in Indo-Pakistan, indicating that the group possibly arrived in this region before the closure of the Tethys Sea. The results of the morphological analyses demonstrate that the new specimen has strong affinities to Gryposuchinae, a gavialid lineage from the Miocene–Pliocene of South America. Thus, bringing more evidence of an Asian origin for gryposuchines, as has been proposed.

I finally integrate the new paleontological record to reconstruct the historical biogeography of Gavialidae under a model that incorporates geographic and phylogenetic data. I then test the proposed biogeographic hypothesis of dispersals from Africa, Asia, and Europe to the Americas during the Paleocene–Oligocene against a model that does not include such dispersals. The results of this study show strong support for a model that includes the dispersals from Africa, Asia, and Europe to the Americas. Moreover, the best-fitting model shows multiple dispersal events: from Asia to the Americas during the Eocene; from Africa to the Caribbean during the Eocene; and from the Caribbean to South America in the Oligocene. This study highlights the importance of incorporating fossils in biogeographic models to understand the complex history of groups that are represented today by a few taxa. This dissertation offers valuable evidence for the early history, divergence time, and paleobiogeography of gavialids, and demonstrates the use of Gavialidae as a study case to understand complex evolutionary and biogeographic hypotheses when using the paleontological record.