Citation: Erkenbrack, E. M., Thompson, J. R.(2019).Cell type phylogenetics informs the evolutionary origin of echinoderm larval skeletogenic cell identity. Communications Biology (2): 160.
Reorganization of sea urchin gene regulatory networks at least 268 million years ago as revealed by oldest fossil cidaroid echinoid
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.
Placental invasion into the maternal endometrium of the uterus shows substantial similarities to early cancer dissemination into stroma1,2,3,4. These similarities have inspired the hypothesis of antagonistic pleiotropy5,6. According to this hypothesis, trophoblasts evolved the capacity to invade the endometrium, leading to invasive placentation. These mechanisms can become reactivated in cancer cells, leading to a predisposition to metastasis. This implies that cancer malignancy should be limited to placental mammals where invasive placentation first evolved. This prediction, however, is inconsistent with the fact that opossums, with ancestrally non-invasive placenta7,8, get invasive skin cancers9. Here, we explore an alternative scenario in which stromal cells of the uterus evolved to either resist or permit invasion, determining the outcome of placental invasiveness9.
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