The first Middle Ordovician and Gondwanan record of the cincinnaticrinid crinoidOhiocrinus byeongseonin. sp. from South Korea: biostratigraphy, paleobiogeography, and taphonomy

Abstract

Ohiocrinus byeongseoni n. sp. from the Middle Ordovician (Darriwilian) Jigunsan Formation of South Korea in the Sino-Korean (North China) block is the oldest species of Ohiocrinus of the Cincinnaticrinidae and the first record outside Laurentia. O. byeongseoni is characterized by a loosely clockwise-coiled anal sac, isotomous branching throughout arms, long, slender xenomorphic column, and small lichenocrinid-type holdfast. The new species occurs in association with a deep-water siliciclastic environment, unlike the Laurentian species with a shallow-water carbonate environment. The monospecific crinoid assemblage is interpreted as parautochthonous, considering that the crinoids were reworked by relatively weak down-current probably caused by storm but preserved within the environment where they lived. The occurrence of O. byeongseoni presents a considerable spatiotemporal gap and ecologic disparity in evolution of Ohiocrinus and the Cincinnaticrinidae. UUID: http://zoobank.org/240417a4-8d33-4f45-aedb-afcc07f1ecbb

Goryeocrinus pentagrammos n. gen. n. sp. (Rhodocrinitidae; Diplobathrida), the first record of camerate crinoid from the Middle Ordovician (Darriwilian) of South Korea (East Gondwana)

“…The slab was found in an exposure along a stream in the Gumunso section of the Jigunsan Formation (Park et al, 2022, fig. 1.2).…”

“…1.2). It is possible that the slab was derived from the Jangseong section located 2.5 km upstream where a disparid, Ohiocrinus byeongseoni Park et al, 2022, occurs. A specimen with calyx and six arms is present along with four fragmentary arms and a stem (probably mesistele); a poorly preserved brittle star specimen, which has not been reported from the formation, also occurs on the slab (Fig.…”

“…The slab containing Goryeocrinus pentagrammos n. gen. n. sp. was found in an outcrop of the Middle Ordovician Jigunsan Formation, part of the Cambro-Ordovician Joseon Supergroup (Lee et al, 2022; Park et al, 2022). The formation mainly consists of mudstone with limestone layers in the upper part.…”

“…The Jigunsan Formation is the most fossiliferous Ordovician unit of the Joseon Supergroup, yielding various invertebrate fossils including trilobites, brachiopods, and cephalopods as major components (Lee et al, 2022). Minor components, such as echinoderms including Ohiocrinus (Park et al, 2022) and Goryeocrinus n. gen. described in this study, machaeridians, and possible soft-bodied fossils suggest that the Jigunsan fauna may have significant potential for understanding the East Gondwanan and Darriwilian aspect of the Great Ordovician Biodiversification Event, including early crinoid diversification.…”

“…This study reports a new diplobathrid genus, Goryeocrinus n. gen., from the Middle Ordovician (middle Darriwilian) Jigunsan Formation of South Korea, which was part of the Sino-Korean (North China) Block, an eastern peri-Gondwanan terrane almost antipodal to Laurentia (Park et al, 2022, fig. 6).…”