Evans Scott D, Droser Mary L, Gehling James G
Department of Earth Sciences, University of California at Riverside, Riverside, California, United States of America.
South Australia Museum, Adelaide, South Australia, Australia.
PLoS One. 2017 May 17;12(5):e0176874. doi: 10.1371/journal.pone.0176874. eCollection 2017.
The Ediacara Biota represents the oldest fossil evidence for the appearance of animals but linking these taxa to specific clades has proved challenging. Dickinsonia is an abundant, apparently bilaterally symmetrical Ediacara fossil with uncertain affinities. We identified and measured key morphological features of over 900 specimens of Dickinsonia costata from the Ediacara Member, South Australia to characterize patterns in growth and morphology. Here we show that development in Dickinsonia costata was surprisingly highly regulated to maintain an ovoid shape via terminal addition and the predictable expansion of modules. This result, along with other characters found in Dickinsonia suggests that it does not belong within known animal groups, but that it utilized some of the developmental gene networks of bilaterians, a result predicted by gene sequencing of basal metazoans but previously unidentified in the fossil record. Dickinsonia thus represents an extinct clade located between sponges and the last common ancestor of Protostomes and Deuterostomes, and likely belongs within the Eumetazoa.
埃迪卡拉生物群代表了动物出现的最古老化石证据，但将这些分类群与特定的进化枝联系起来已被证明具有挑战性。狄更逊水母是一种丰富的、明显两侧对称的埃迪卡拉化石，其亲缘关系尚不明确。我们识别并测量了来自南澳大利亚埃迪卡拉组的900多个肋状狄更逊水母标本的关键形态特征，以描述其生长和形态模式。我们在此表明，肋状狄更逊水母的发育受到惊人的高度调控，通过末端添加和模块的可预测扩展来维持卵形形状。这一结果，以及在狄更逊水母中发现的其他特征表明，它不属于已知的动物类群，但它利用了一些两侧对称动物的发育基因网络，这一结果是通过基础后生动物的基因测序预测出来的，但此前在化石记录中尚未得到确认。因此，狄更逊水母代表了一个已灭绝的进化枝，位于海绵动物和原口动物与后口动物的最后共同祖先之间，并且可能属于真后生动物。
