Biology Series Seminar: Dr. Hillary Maddin

"The origin of lissamphibians and implications for tetrapod cranial evolution"

Date: January 31, 2014

Time: 3:30- 4:30 PM

Location: CTTC 4440Q, Carleton University 

The fossil record documents major transitions in the evolution of vertebrates and captures events critical to understanding the origin and maintenance of diversity through time. Analysis of such transitions requires the establishment of a stable pattern of relationships, and this remains lacking for several groups of vertebrates, including lissamphibians–frogs, salamanders, and caecilians. In an attempt to resolve the lack of consensus regarding how lissamphibians are related to one another and to the various groups of fossils, the morphology of caecilians –the most poorly understood group of lissamphibian–was examined in detail. Reanalysis of lissamphibian relationships yielded support for a monophyletic Lissamphia derived from within Permian-aged temnospondyl vertebrates. The morphology-based dataset permitted the inclusion of a controversial fossil taxon, considered by some to be a stem caecilian, Eocaecilia micropodia. Recovery of E. micropodia on the stem of the caecilian crown group supports this hypothesis and provides insight into the nature of morphological transitions that took place during the evolution of the lissamphibian cranium. Additionally this robust phylogenetic framework permits the exploration of events in the evolution of the tetrapod cranium in general. One aspect, the occipital region, is explored from an evolutionary developmental perspective. Perturbation of axial patterning genes in the salamander axolotl mimics events in the evolution of the tetrapod occiput.