Laurentian origin of solutan echinoderms: new evidence from the Guzhangian (Cambrian Series 3) Weeks Formation of Utah, USA

Abstract

AbstractA new solutan echinoderm,Pahvanticystis utahensis gen. et sp. nov. is described from the upper part of the Weeks Formation (Guzhangian). The Cambrian (Series 3) succession of the central House Range in western Utah documents the early diversification of the class Soluta, which is characterized by a major ecological transition from sessile, ‘pelmatozoan’ primitive taxa (Coleicarpus, Wheeler Formation), to more and more vagile, temporarily attached (Castericystis, Marjum Formation), to mostly unattached, ‘homalozoan’ derived forms (Pahvanticystis, Weeks Formation). The morphology ofPahvanticystisis remarkably intermediate between those ofCastericystisandMinervaecystis. Its twisted, flattened dististele possibly represents an adaptation for a more efficient crawling atop soft substrates. This morphological feature also questions the phylogenetic relationships between syringocrinid and dendrocystitid solutans, and the possible evolution of the latter from basal,Pahvanticystis- orMinervaecystis-like syringocrinids by paedomorphosis.