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Fossilised Fish Embryos: Insights into Evolution

Talk, 7-8pm. Great North Museum:Hancock.

Placoderms are a fossil group of primitive jawed vertebrates critical to understanding how characters evolve in vertebrates such as sharks and bony fishes. Along with colleagues from Australia, Zerina Johanson is studying exquisitely preserved early growth stages of placoderms from the Gogo Formation of Western Australia, including embryonic material. These embryos have only recently been discovered in newly prepared specimens and by careful study of existing museum collections; new non-destructive methods such as CT- and synchrotron scanning show great promise for future discoveries. Gogo placoderm embryos provide information about the early development of skeletal elements such as head and trunkshield bony plates, dentitions, and vertebral elements, but also about reproduction. With respect to the latter, new discoveries include multiple embryos in pregnant females, embryos of differing sizes, and of different sexes. By comparison to well-studied sharks, we can make inferences as to the nature of vertebrate reproduction at the evolutionary transition from jawless to jawed vertebrates.

Zerina Johanson is a Researcher at the Department of Earth Sciences, Natural History Museum, London. Her research focuses on the evolution and development of early vertebrates, and she is currently working on projects involving the evolution of dentition, evolution of the vertebrate backbone, and parts of the vertebrate skeleton involved in reproduction. She is particularly interested in groups such as the placoderms and sharks, and has done extensive fieldwork in Australia, where she obtained her Ph.D.