OCGC Seminar - Dr. Hillary Maddin


Challenges in palaeontology: resolving the lissamphibian origins debate

Dr. Hillary Maddin
Department of Earth Sciences, Carleton University

Dr. Hillary Maddin looking at the CT data of a baby alligator skull. This research aims to understand the evolution of the skull by examining its embryonic development.

Thursday, April 2nd, 2015
11:30 a.m.  

3120 HP
Carleton University



There remains debate amongst paleontologists as to how the three groups of living amphibians (lissamphibians: frogs, salamanders, and caecilians) are related to one another and to the various lineages of fossil amphibians. This lack of consensus hinders our ability to test evolutionary hypotheses since no single, widely agreed upon pattern of relationships currently exists. To address this problem, several key fossil taxa were studied with the goal of obtaining new data from the previously unexplored braincase region of the skull. Microsaurs, a group of Permian-aged amphibians, were recently hypothesized as the closest relatives of caecilians, separating them from frogs and salamanders. The use of 3D micro-computed tomography to examine details of braincase in the microsaur Carrolla reveals the traits linking caecilians and microsaurs are more likely shared due to convergence on a similar habit (burrowing) than evolutionary relatedness, as they are also found in distantly related reptile species. The controversial fossil Eocaecilia was also reexamined to test for indication of its affinity to living caecilians. Several new, definitively caecilian characteristics were identified in the braincase of Eocaecilia, thus firmly placing this fossil in the gap between putative relatives and the living forms. A number of traits additionally shared with frogs and salamanders lend support for uniting the living amphibians with one another. Reanalysis of evolutionary relationships of both extinct and extant amphibians incorporating these new data results in a common origin of Lissamphibia derived from the fossil group Temnospondyli. This hypothesis is consistent with broad scale transformations in the braincase that manifests as stepwise simplification towards the condition seen in the living forms. This improved framework of relationships forms the foundation of ongoing studies into the mechanistic basis of this transformation and others in the evolution of frogs, salamanders, and caecilians.