A Laurentian Iocrinus Hall (Crinoidea, Disparida) in the Dapingian or Darriwilian (Middle Ordovician, Arenig) of Oman

Abstract

Early and early Middle Ordovician crinoids are rare globally, and are best known from North America and the British Isles. The first Arenig crinoid from the Arabian Peninsula is Iocrinus sp. cf. I. subcrassus (Meek and Worthen), known from two near-complete individuals, and numerous fragmentary specimens and ossicles. These are the stratigraphically oldest Iocrinus specimens, and provide an unexpected extension of the palaeogeographical range of a genus known otherwise from slightly younger deposits in Laurentia (North America) and Avalonia (Wales). The Oman specimens differ from Gondwanan Heviacrinus melendezi Gil Cid et al., currently classified as a maennilicrinid, but morphologically close to Iocrinus, in having arms that branch at least seven times instead of four and in having columnals typical of Iocrinus. Three species from Wales and the Welsh Borders, previously placed in Iocrinus, but differing in having smooth, conical dorsal cups, are reclassified as Margoiocrinus Donovan gen. nov., type species Iocrinus shelvensis Ramsbottom.

The Bohemo‐Iberian regional chronostratigraphical scale for the Ordovician System and palaeontological correlations within South Gondwana

“…() and Donovan et al . (), and the assemblage probably represents upper Oretanian strata, based on the lowest occurrence of N. tristani in Ibero‐Armorica.…”

“…For instance, the disparid crinoid Iocrinus was usually regarded as a Laurentian genus, but due to its first chronostratigraphical occurrences in Oman, Morocco, Spain and Great Britain (Donovan et al . ; Zamora et al . ) it should be regarded as a Gondwanan genus that later migrated into lower palaeolatitudes.…”

“…These terms usually derive from places where certain genera or species are abundant and were first described in the palaeontological literature, yet do not coincide with their area of origination. For instance, the disparid crinoid Iocrinus was usually regarded as a Laurentian genus, but due to its first chronostratigraphical occurrences in Oman, Morocco, Spain and Great Britain (Donovan et al 2011;Zamora et al 2015) it should be regarded as a Gondwanan genus that later migrated into lower palaeolatitudes. Guti errez-Marco et al (1999a) added examples of echinoderm and trilobite species of Ibero-Armorican origin that later migrated to Bohemia, where they received their first description.…”

Filling the Gondwanan gap: paleobiogeographic implications of new crinoids from the Castillejo and Fombuena formations (Middle and Upper Ordovician, Iberian Chains, Spain)

“…Since 1988, several new faunas have been reported, including crinoids from Argentina (Guensburg and Waisfeld, 2015), France (Lefebvre et al, 2015), Morocco (Donovan and Savill, 1988;Le Menn and Spjeldnaes, 1996;Zamora et al, 2015b), Oman (Donovan et al, 2011), Portugal (Ausich et al, 2007;Correia and Loureiro, 2009), and Spain (Gil Cid et al, 1996, 1998Ausich et al, 2002Ausich et al, , 2007. Of these Ordovician Gondwanan faunas, two are Katian in age.…”

Fossil crinoids from the basal West Point Formation (Silurian), southeast Gaspé Peninsula, Québec, eastern Canada

“…The material is morphologically very close to the form figured by Stukalina (1988, particularly pl. 7, figs 14-16) Donovan et al 2011).…”