Editing Bilateria (section)

=== Fossil record ===

[[File:Ikaria wariootia.jpg|thumb|upright|''[[Ikaria wariootia]]'', living 571–539 million years ago, is one of the oldest bilaterians identified.<ref>{{cite journal |last1=Evans |first1=Scott D. |last2=Hughes |first2=Ian V. |last3=Gehling |first3=James G. |last4=Droser |first4=Mary L. |title=Discovery of the oldest bilaterian from the Ediacaran of South Australia |journal=Proceedings of the National Academy of Sciences |date=7 April 2020 |volume=117 |issue=14 |pages=7845–7850 |doi=10.1073/pnas.2001045117 |pmid=32205432 |pmc=7149385 |bibcode=2020PNAS..117.7845E |doi-access=free }}</ref>]]

The first evidence of Bilateria in the fossil record comes from trace fossils in [[Ediacaran]] sediments, and the first ''bona fide'' bilaterian fossil is ''[[Kimberella]]'', dating to {{Ma|555}}.<ref name=Fedonkin1997>{{Cite journal |last1=Fedonkin |first1=M. A. |last2=Waggoner |first2=B. M. |date=November 1997 |title=The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism |journal=Nature |volume=388 |issue=6645 |pages=868–871 |doi=10.1038/42242 |bibcode=1997Natur.388..868F|s2cid=4395089 |doi-access=free }}</ref> Earlier fossils are controversial; the fossil ''[[Vernanimalcula]]'' may be the earliest known bilaterian, but may also represent an infilled bubble.<ref name=Bengtson2004>{{cite journal |last1=Bengtson |first1=S. |last2=Budd |first2=G. |date=19 November 2004 |title=Comment on 'small bilaterian fossils from 40 to 55 million years before the Cambrian'. |journal=Science |volume=306 |pages=1291a |doi=10.1126/science.1101338 |pmid=15550644 |issue=5700 |doi-access=free }}</ref><ref name=VernAcritarch>{{cite journal |last1=Bengtson |first1=S. |last2=Donoghue |first2=P. C. J. |last3=Cunningham |first3=J. A. |author4=Yin, C. |year=2012 |title=A merciful death for the 'earliest bilaterian,' Vernanimalcula |journal=Evolution & Development |volume=14 |issue=5 |pages=421–427 |doi=10.1111/j.1525-142X.2012.00562.x |pmid=22947315 |s2cid=205675058 |url=http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-597 }}</ref> [[Fossil embryos]] are known from around the time of ''Vernanimalcula'' ({{Ma|580}}), but none of these have bilaterian affinities.<ref name=Hagadorn2006>{{Cite journal |last1=Hagadorn |first1=J. W. |last2=Xiao |first2=S. |last3=Donoghue |first3=P. C. J. |last4=Bengtson |first4=S. |last5=Gostling |first5=N. J. |last6=Pawlowska |first6=M. |last7=Raff |first7=E. C. |last8=Raff |first8=R. A. |last9=Turner |first9=F. R. |last10=Chongyu |doi=10.1126/science.1133129 |first10=Y. |last11=Zhou |first11=C. |last12=Yuan |first12=X. |last13=McFeely |first13=M. B. |last14=Stampanoni |first14=M. |last15=Nealson |first15=K. H. |s2cid=25112751 |title=Cellular and Subcellular Structure of Neoproterozoic Animal Embryos |journal=Science |volume=314 |issue=5797 |pages=291–294 |date=13 October 2006 |pmid= 17038620|bibcode=2006Sci...314..291H }}</ref> Burrows believed to have been created by bilaterian life forms have been found in the [[Tacuarí Formation]] of Uruguay, and were believed to be at least 585 million years old.<ref name="sci">{{cite journal |title=Bilaterian burrows and grazing behavior at >585 million years ago |last1=Pecoits |first1=E. |last2=Konhauser |first2=K. O. |last3=Aubet |first3=N. R. |last4=Heaman |first4=L. M. |last5=Veroslavsky |first5=G. |last6=Stern |first6=R. A. |last7=Gingras |first7=M. K. |s2cid=27970523 |journal=Science |volume=336 |issue=6089 |pages=1693–1696 |doi=10.1126/science.1216295 |pmid=22745427 |date=June 29, 2012 |bibcode=2012Sci...336.1693P}}</ref> However, more recent evidence shows these fossils are actually late Paleozoic, not Ediacaran.<ref>{{cite journal |last1=Verde |first1=Mariano |title=Revisiting the supposed oldest bilaterian trace fossils from Uruguay: Late Paleozoic, not Ediacaran |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=15 September 2022 |volume=602 |doi=10.1016/j.palaeo.2022.111158 |bibcode=2022PPP...60211158V |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018222003285}}</ref>