Development and the Early Animal Fossil Record: Evolution and Phylogenetic Applications

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Although evolutionary developmental biology and paleontology are linked by the study of morphology, the application of development to paleontological questions has only recently become more prominent. The growth of a robust developmental genetic framework for studying the origin and evolution of morphological features, however, holds great promise for understanding ancient animal life. As paleontology provides the historical record as well as the temporal and environmental context of past morphological evolution, uniting knowledge of developmental genetic systems with this historical record will form a key synthetic approach to understanding the early evolution of developmental processes.

Ultimately unraveling the sequence of ancient animal developmental evolution will require combining analysis of comparative developmental data, critical assessment of fossil morphology within a developmental framework, and the targeted exploration of specific geologic periods to fill in the missing record of key times in animal developmental evolution. This study addresses each of these three approaches.

First, I provide a new compilation and evaluation of recent comparative and experimental developmental biology data to review the nature of developmental ‘toolkits’ at the origin of the most basal animal clades. I reconstruct early animal developmental capacities and integrate these data within a temporal framework to better understand the context of earliest animal development. Second, I assess longstanding evolutionary hypotheses about the origin of the panarthropod clade and the phylogenetic position of Cambrian ‘lobopod’ fossils by examining signal present within current morphological datasets. I apply new methods to fossil panarthropod phylogeny estimation and suggest strategies for developmentally-informed phylogenetic coding of morphological data. Third, I present the discovery of the oldest spicule-bearing fossil sponges in the rock record, which co-occur in latest Ediacaran strata with classic enigmatic Ediacaran fauna. I provide a formal systematic description of fossil material from localities in both Nevada and southern Namibia.

The combined approaches presented herein are a first step towards a deeper integration of developmental principles in the study and discovery of ancient animal life, and contribute to our understanding of the evolution of ancient animal developmental processes.