Size matters

Size matters: the effects of ontogenetic disparity on the phylogeny of Trematopidae (Amphibia: Temnospondyli) (Zoological Journal of the Linnean Society, 2020)

https://doi.org/10.1093/zoolinnean/zlz170

Phylogenetic inference in long-extinct taxa is fundamentally limited by the fact that we can only access phenotypic data from fossil remains. This can in turn lead to additional complications when there are biases and gaps in the fossil record - examples include a poor understanding of development (and in turn which features might be both taxonomically and ontogenetically influenced) and preservation of a very specific age class and no other classes (e.g., tweens). For phylogenies based on phenotypic data, disparity in representation between sampled taxa can be a major confounding factor. For example, you may have two taxa that are represented by very different sizes of specimens in the fossil record. However, this often reflects gaps in the fossil record, not marked size diminution/expansion within a clade, and comparing these very disparate taxa is an apples and oranges situation, so to speak. There are many conceptual hypotheses regarding what effects this "apples and oranges" analysis will produce, but they are rarely tested explicitly for fossil taxa in spite of the numerous gaps in the fossil record.

   In this study, I examined a clade of terrestrial amphibians called trematopids that are an ideal case study for examining the effects of ontogenetic disparity on phylogenetic inference. Many trematopids are represented only by one specimen (zero ontogenetic information), and there is a large size range among trematopids - the smallest species is less than 25% the size of the largest species (see attached figure) - even though there is good evidence that all trematopids reached similar adult sizes. Through a series of phylogenetic analyses, I provided a detailed analysis showing how this disparity in relative maturity badly confounds phylogenetic inference and that taxonomic resolution can only be recovered by pruning of taxa (i.e. data removal). This is the first study to do this for temnospondyls, which are widely regarded as the ancestors of modern amphibians, and provides both a major impetus and a cautionary tale for future work.

Read more: https://bit.ly/38IPy8h

March 9, 2020