When did animal life first appear? What did these early animals look like? What environmental changes allowed for the evolution and radiation of animal life?
The early fossil record is full of extinct life forms that might be animals. For example, see the picture of Dickinsonia to the left. Unfortunately, scientists have had a hard time reaching consensus about what these fossils are, partially because they are so simple. In my research I study the fossil record using phylogenetic tools, meaning I build trees that represent the evolutionary relationships of between animals. These trees are made by comparing the DNA between species to determine how closely related they are to each other. A simple animal tree (phylogeny) is presented below:
I map genetic and physical traits onto these trees to study how animals have evolved over time. This work helps clarify what types of life forms ancient fossils could or could not represent.
For some relevant publications, check out these papers in the Reprints section:
Gold D.A., Grabenstatter J., de Mendoza A., Riesgo A., Ruiz-Trillo I., and Summons R.E. (2016) Sterol and genomic analyses validate the sponge biomarker hypothesis. Proceedings of the National Academy of Sciences of the United States of America. 113(10 ): 2684–2689.
Gold D.A., Gehling J.G., Runnegar B., and Jacobs D.K. (2015) Ancestral state reconstruction of ontogeny supports a bilaterian affinity for Dickinsonia. Evolution and Development. 17(6): 315-397.