Vertebrate Disparity over Mass Extinctions

  • Tom Trapman

Student thesis: Masters ThesisMPhil


Mass extinctions have had a great impact on life on Earth. The fossil record shows that lineages are terminated, or taxonomic diversity can be greatly reduced in surviving clades. Morphological diversity, disparity, does not follow the same trends as taxonomic diversity. The diversity of body plans throughout the evolutionary history of a clade can be highly variable, especially for clades that survive mass extinctions and (re)populate vacated (eco)morphospace in their wake. Assessing and understanding disparity trends of these surviving clades prior to, and after, a mass extinction can therefore be a complex task. I use the Centre of Gravity (CG) metric to summarise one aspect of the shape of disparity trajectories through time: the temporal mean of the disparity through time profile. In particular, I employ this metric to distinguish top- and bottom-heavy total clade, pre-, and post-extinction disparity profiles. Analysing 76 discrete morphological character matrices for vertebrates, I demonstrate that Phanerozoic vertebrate clades that survived extinctions have a dominant top-heavy (CG > 0.5) pre-extinction and bottom-heavy (CG < 0.5) post-extinction tendency. These same dominant trends are recovered comparing marine to non-marine clades, and amniotes to non-amniotes. Surprisingly, I found that there are no significant differences between the CG of clades surviving an extinction and those that do not. This study demonstrates these trends in clade shape, as indexed by the CG, are common throughout the entire Phanerozoic in both clades that survived a mass extinction and those that do not. These results contribute to a better understanding of the manner in which disparity changes throughout the evolution of clades, and especially demonstrates wider macroevolutionary trends in vertebrates. By extension to other disparity metrics (e.g. sum of ranges, pairwise distance) and data types (e.g. continuous, morphometric), these methods will help to improve our understanding of the impact of mass extinctions and other macroevolutionary patterns further. Ultimately, this can be fundamental to our insight in how taxa or clades may be affected by the current biodiversity crisis.
Date of Award26 Jul 2023
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorMatthew Wills (Supervisor) & Natalie Cooper (Supervisor)


  • Disparity
  • Mass extinction

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