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SUMMARY:Decoding the fossil record of the earliest animals and their embry
 ology - Professor Phil Donoghue\, University of Bristol
DTSTART:20130129T163000Z
DTEND:20130129T173000Z
UID:TALK41470@talks.cam.ac.uk
CONTACT:Dr. Alex Liu
DESCRIPTION:The c.570 Ma Doushantuo biota of South China has yielded impor
 tant fossils that include the oldest widely accepted record for the establ
 ishment of the animal evolutionary lineage\, as well as a suite of specime
 ns with alleged bilaterian affinity. However\, the interpretations of all 
 of these fossils have been criticized on the basis that interpretations of
  affinity are contingent on the presence of key biological structures that
  may be more readily interpreted as artefacts of diagenetic mineralization
 . Furthermore\, these fossils are limited to the earliest stages of embryo
 nic development and the absence of equivalent adults has led to the sugges
 tion that these simple clusters of cells may rather represent clusters of 
 vegetatively dividing bacterial cells. We attempted to discriminate among 
 these competing hypotheses by first characterizing the mineral phases that
  replicate original biological structure versus later diagenetic void fill
 ing using BSE\, EPMA\, EBSD\, SRXTM\, demonstrating that those structures 
 interpreted hitherto as evidence for derived animals are characteristic of
  void filling mineralization long after the original biological structures
  have decayed away. \n\nTo discriminate between animal versus bacterial in
 terpretative models we undertook decay experiments on modern animal embryo
 s and giant bacteria. The taphonomy of the Doushantuo fossils is compatibl
 e with animal embryos\, but not bacteria. Furthermore\, the fossilised rem
 ains of nuclei within the Doushantuo allow us to reject the bacterial mode
 l. It does not follow\, however\, that the animal model is correct\, and n
 ew developmental stages in the Doushantuo assemblage provide compelling ev
 idence against their interpretation as animal embryos. Thus\, while these 
 fossils may no longer be considered direct evidence of Ediacaran animals\,
  they may represent a stage in the deep evolutionary origins of animal gra
 de multicellularity. 
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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