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Sci Rep 2015 Oct 21;5:15541. doi: 10.1038/srep15541.
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Reorganization of sea urchin gene regulatory networks at least 268 million years ago as revealed by oldest fossil cidaroid echinoid.

Thompson JR , Petsios E , Davidson EH , Erkenbrack EM , Gao F , Bottjer DJ .

Echinoids, or sea urchins, are rare in the Palaeozoic fossil record, and thus the details regarding the early diversification of crown group echinoids are unclear. Here we report on the earliest probable crown group echinoid from the fossil record, recovered from Permian (Roadian-Capitanian) rocks of west Texas, which has important implications for the timing of the divergence of crown group echinoids. The presence of apophyses and rigidly sutured interambulacral areas with two columns of plates indicates this species is a cidaroid echinoid. The species, Eotiaris guadalupensis, n. sp. is therefore the earliest stem group cidaroid. The occurrence of this species in Roadian strata pushes back the divergence of cidaroids and euechinoids, the clades that comprise all living echinoids, to at least 268.8 Ma, ten million years older than the previously oldest known cidaroid. Furthermore, the genomic regulation of development in echinoids is amongst the best known, and this new species informs the timing of large-scale reorganization in echinoid gene regulatory networks that occurred at the cidaroid-euechinoid divergence, indicating that these changes took place by the Roadian stage of the Permian.

PubMed ID: 26486232
PMC ID: PMC4614444
Article link: Sci Rep

Genes referenced: ago1b LOC100887844 LOC100893907 LOC115925415

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References [+] :
Amemiya, The Development and Larval Form of an Echinothurioid Echinoid, Asthenosoma ijimai, Revisited. 1992, Pubmed, Echinobase