- Fossil embryos
Many
fossil s of the Ma|580|million year oldDoushantuo formation have been interpreted as fossil embryos;embryos are also common throughout theCambrian fossil record.Preservation
Taphonomic studies indicate that embryos are preserved for longest in reducing, anoxic conditions - a length of time similar to that required for bacteria to mineralise the cells and permit their preservation.However, phosphatisation was very rapid in the Doushantuo, so it's possible that earlier preservation allowed embryos in different regimes to be preserved.
Currently, only fossils representing very early stages in embryonic development have been preserved - no embryos have been interpreted as having undergone a large number cleavage stages.cite journal
author = Gostling, N.J.; Donoghue, P.C.J.; Bengtson, S
year = 2007
title = The Earliest Fossil Embryos Begin to Mature
journal = Evolution & Development
volume = 9
issue = 3
pages = 206–7
doi = 10.1111/j.1525-142X.2007.00152.x]Alternative explanations
Some embryos have been interpreted as colonies of sulfur-reducing bacteria, a claim that cannot be upheld in all cases.
Affinities
Most fossil embryos are considered to belong to cnidarians and ecdysozoans, if they even fall into the metazoan crown group. No deuterostome or lophotrochozoan embryos have yet been reported, despite their similar preservation potential; this may be a result of different egg laying behaviour, as ecdysozoans lay eggs in the sediment rather than releasing them into the open - enhancing the chance of them becoming mineralised.cite journal
author = Gostling, Neil J.; Thomas, Ceri-Wyn; Greenwood, Jenny M.; Dong, Xiping; Bengtson, Stefan; Raff, Elizabeth C.; Raff, Rudolf A.; Degnan, Bernard M.; Stampanoni, Marco; Donoghue, Philip C. J.
year = 2008
title = Deciphering the fossil record of early bilaterian embryonic development in light of experimental taphonomy
journal = Evolution & Development
volume = 3
issue = 11
pages = 339–349
doi = 10.1111/j.1525-142X.2008.00242.x
month = June]References
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