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

Abstract

A 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.

<p class="HeadingRunIn"><strong>Reinterpretation of the enigmatic Ordovician genus <em>Bolboporites </em>(Echinodermata)</strong></p>

“…The reduction of the number of feeding appendages is relatively common in Palaeozoic echinoderms. It was documented both in some crinoids (e.g., Monobrachiocrinus granulatus Wanner, 1920;Ausich et al 1999) and also in various groups of vagile, epibenthic taxa, such as pleurocystitid rhombiferans (Paul 1967;Kesling 1968;Parsley 1970), solutans (Ubaghs 1981;David et al 2000;Lefebvre & Lerosey-Aubril 2018) and stylophorans (Ubaghs 1968a;David et al 2000;Lefebvre 2003).…”

Solutan echinoderms from the Fezouata Shale Lagerstätte (Lower Ordovician, Morocco): diversity, exceptional preservation, and palaeoecological implications

“…In this expanded definition, the family Minervaecystidae includes the four genera Minervaecystis Ubaghs, 1970, Nimchacystis gen. nov., Pahvanticystis Lefebvre and Lerosey-Aubril, 2018, and Plasiacystis Prokop and Petr, 2003 The morphology of the earliest known member of the family, Pahvanticystis utahensis (Weeks Formation, Guzhangian, Utah, USA), suggests that minervaecystids probably originated from a Castericystis-like ancestor. Pahvanticystis differs from other minervaecystids in the more anterior insertion of its feeding appendage along the antanal thecal side (Lefebvre and Lerosey-Aubril, 2018). The morphology of the isolated minervaecystid homoiosteles from the late Cambrian of Utah is very close to that of Minervaecystis (i.e., similar proxistele consisting of over 20, regular tetramerous rings; Ubaghs, 1963;Sumrall et al, 1997).…”

“…Phylum Echinodermata Klein, 1778Class Soluta Jaekel, 1901 Remarks: The systematic subdivision of solutans into two main orders (Dendrocystitida and Syringocrinida) based on the morphology of their homoiostele follows Noailles et al (2014). Similarly, descriptive morphological terms used below are those used in all recent descriptions of solutans (e.g., Lefebvre et al, 2012;Rahman and Lintz, 2012;Noailles et al, 2014;Lefebvre and Lerosey-Aubril, 2018;Dupichaud and Lefebvre, 2022;Rozhnov, 2022;Dupichaud et al, 2023;Zamora and Gutieŕrez-Marco, 2023). Discussion of the phylogenetic position of solutans within the phylum Echinodermata is beyond the scope of this paper.…”

“…Exceptionally preserved soft parts can be particularly important in the case of extinct classes, such as solutans, whose anatomy and phylogenetic positions within the phylum Echinodermata are debated (see, e.g., David et al, 2000;Smith, 2005;Zamora and Rahman, 2014;Lefebvre et al, 2019). Solutans are considered either basal, pre-radial echinoderms (Smith, 2005;Rahman and Lintz, 2012;Zamora and Rahman, 2014) or regular blastozoans, closely related to gogiid eocrinoids (e.g., David et al, 2000;Lefebvre and Lerosey-Aubril, 2018;.…”

“…The class Soluta is a small, long-lived clade of echinoderms (Drumian-Emsian) characterised by a single feeding appendage, a more or less flattened theca, and a stem-like appendage (homoiostele) used for permanent attachment to the sea floor in plesiomorphic forms (e.g., Coleicarpus; Ubaghs and Robison, 1988;Daley, 1996) but generally modified into a locomotory device in most taxa (e.g., Sprinkle and Guensburg, 1997;Rahman and Lintz, 2012;Noailles et al, 2014). The fossil record suggests a Laurentian origin for solutans, with all their earliest occurrences so far documented exclusively in North America (Lefebvre and Lerosey-Aubril, 2018). During the Furongian-Tremadocian interval, solutans expanded to South China (Zamora et al, 2013) and high-latitude Gondwanan regions, such as the Anti-Atlas (Lefebvre et al, 2016;Dupichaud and Lefebvre, 2022) and the Montagne Noire (Thoral, 1935;Ubaghs, 1970;Dupichaud et al, 2023).…”