CDB Seminar - Professor Philip Donoghue

Talk abstract: Unequivocal animal fossils are confined to the Phanerozoic but molecular clock analyses invariably infer a prehistory extending deep into the Neoproterozoic, only some of which can be rationalised by invoking a crown-metazoan interpretation of the Ediacaran macrobiota. The c.580 Ma Weng’an biota of South China provides a means of testing molecular timescales since it preserves, with subcellular resolution, a soft bodied fauna and flora, largely limited to developmental stages. These have a long and complex history of interpretation, including claims of embryos and larvae from bilaterian phyla. With colleagues, we have characterised the developmental biology of thousands of these fossil organisms using synchrotron radiation X-radiation tomographic microscopy, testing hypotheses of association, development and affinity. Our results to date indicate that while many of the best known taxa exhibit patterns of cell division compatible with an animal embryo-interpretation, the similarity ends there. Some Weng’an taxa demonstrably undergo cell disaggregation and dispersal, incompatible with an animal-embryo interpretation, but compatible with their interpretation as non-metazoan holozoans. As such, the Weng’an biota may be composed largely of representatives of the holozoan grade from which animals emerged, living alongside archaeplastid relatives. This census of early Ediacaran eukaryote diversity may also evidence an absence of animals and a basis for recalibrating molecular clock analyses of animal diversification.

Suggested references:

• dos Reis, M., Thawornwattana, Y., Angelis, K., Telford, M. J., Donoghue, P. C. J., and Yang, Z., 2015, Uncertainty in the timing of origin of animals and the limits of precision in molecular timescales: Current Biology, v. 25, no. 22, p. 2939-2950.
• Yin, Z., Sun, W., Liu, P., Zhu, M., and Donoghue, P. C. J., 2020, Developmental biology of Helicoforamina reveals holozoan affinity, cryptic diversity, and adaptation to heterogeneous environments in the early Ediacaran Weng’an biota (Doushantuo Formation, South China): Sciences Advances, v. 6, no. eabb0083, p. 1-10.
• Yin, Z., Vargas, K., Cunningham, J. A., Bengtson, S., Zhu, M., Marone, F., and Donoghue, P. C. J., 2019, The early Ediacaran Caveasphaera foreshadows the evolutionary origin of animal-like embryology: Current Biology, v. 29, p. 4307-4314.

Zoom: https://ucl.zoom.us/j/97089923659

Host: Laura Porro