Morphology and Phylogenetics

Patterns of morphological change during an evolutionary radiation can yield important information on mechanisms of speciation and the nature of radiations.  A classic case of an adaptive radiation in the fossil record involving Devonian calmoniid trilobites of the Malvinokaffric Realm is examined using geometric morphometrics to quantify morphological change within the clade.  Using an existing phylogeny of the Metacryphaeus group calmoniid trilobites as a species-level framework, morphological change within a lineage can be determined. Determining morphological change through time during an evolutionary radiation can yield important information on the processes causing the radiation. A key innovation and subsequent spreading into disparate adaptive niches (sensu Simpson) would have caused a pattern similar to the tree in b) and the process of radiation could be adaptive in nature. However, my research supports a more uniform change in morphology, as in a), and through biogeography, I examine other possible causes for the radiation.

Geometric Morphometrics

One challenge to any student of morphology is to objectively quantify form and changes in shape.  Morphometrics, coupled with phylogenetics, has been the main tool used to quantify rate of disparity change during the exceptional radiation times.  Geometric morphometrics examines shape variation using landmark-based analysis and multivariate statistics. There are a few different philosophical and methodological approaches in the literature. In my research, I've used geometric morphometrics as approximation of disparity, morphological change, and as assessment of character quality in phylogenetic analyses.