Seirocrinus

Seirocrinus
Giant (18 x 6 m) colony over an Agathoxylon log
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Echinodermata
Class: Crinoidea
Superorder: Articulata
Order: Isocrinida
Family: †Pentacrinitidae
Genus: †Seirocrinus
Gislén, 1924
Type species
Pentacrinites subangularis
Miller, 1821
Species
  • S. subangularis (Miller, 1821) (type)
  • S. acutipelvis (Quenstedt, 1876)
  • S. alaskae (Springer, 1925)
  • S. klikushini (Simms, 1989)
  • S. laevisutus (Pompeckj, 1897)

Seirocrinus is an extinct genus of stalked crinoids (sea lilies) belonging to the family Pentacrinitidae. It lived from the Late Triassic (Norian) to the Middle Jurassic (Bathonian) and is best known as a pseudo-planktonic form that attached to floating driftwood. It represents the largest known crinoid and echinoderm overall, with specimens close to 30 m (98 ft).

Description

Seirocrinus subangularis from the Posidonia Shale

Members of the genus possessed long, flexible stems that could reach lengths of 20 to 26 m (66 to 85 ft) in exceptional specimens. Columnal segments range from pentagonal or subpentagonal in proximal regions[clarification needed] to rounded or nearly circular distally. Articular facets display characteristic narrow, pyriform petal floors bordered by numerous fine crenulae, with triangular rugose areas separating the petals. The cirri are short, slender and compressed; they arise from small sockets on the nodals and served as the attachment structures to the substrate, such as wood. The arms branch endotomously, producing a dense filtration fan to capture food particles.

Taxonomy

The genus was established by Gislén in 1924, with Pentacrinites subangularis Miller, 1821 as the type species. It is placed in the suborder Pentacrinitina within the order Isocrinida. Several species have been recognised, although some authors have synonymised certain forms with the widespread type species S. subangularis.

Ecology

Fossils have previously been recorded from Asia, Europe, and North America. North African specimens from Morocco and Algeria were described in 2024; this locale conforms to the southern margin of the Tethys Ocean.

Seirocrinus is thought to have lived as a pseudoplankton, with massive colonies attaching to the undersides of drifting logs by means of dense clusters of cirri. It was an open ocean organism that lived on rafting wood, probably filtering food and serving as a refuge for other animals, such as various ammonite species, as well early pelagic cirripeds. This lifestyle allowed them to inhabit surface waters far from the seafloor. Individuals grew rapidly and colonies could persist for 15–20 years on a single piece of wood before the increasing weight caused the log to sink, which eventually kills the crinoid. The crinoids had a large colonization process, based on their fossils in the wood. It has been estimated that without the presence of modern raft wood predators (that appeared in the Bathonian) these rafts could have lasted floating +5 years, allowing the crinoids to reach such huge sizes. In the same way they supported this crinoids, other animals may have traveled in the large rafts along the Early Jurassic seas.

References

  1. 1 2 3 4 Salamon, Mariusz A.; Benyoucef, Madani; Benzaggah, Mohamed; Brachaniec, Tomasz; Hoşgör, İ̇zzet; Jain, Sreepat; Płachno, Bartosz J.; Rahmonov, Oimahmad (2024-10-02). "Unlocking the secrets of the Early Jurassic of North Africa: first record of pseudoplanktonic crinoid Seirocrinus (Crinoidea, Pentacrinidae) from Morocco and Algeria". Historical Biology. 36 (10). Taylor & Francis: 2174–2186. Bibcode:2024HBio...36.2174S. doi:10.1080/08912963.2023.2243471. ISSN 0891-2963.
  2. 1 2 Gorzelak, Przemysław; Janiszewska, Katarzyna; Hoşgör, İzzet; Salamon, Mariusz A. (2025-08-26). "Microstructural design of the stalk in the crinoid Seirocrinus supports its pseudoplanktonic lifestyle". Scientific Reports. 15 (1). Nature Publishing Group: 31418. doi:10.1038/s41598-025-16412-8. ISSN 2045-2322. PMC 12381209. PMID 40858656.
  3. 1 2 Matzke, A. T.; Maisch, M. W. (2019). "Palaeoecology and taphonomy of a Seirocrinus (Echinodermata: Crinoidea) colony from the Early Jurassic Posidonienschiefer Formation (Early Toarcian) of Dotternhausen (SW Germany)". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 291 (1): 89–107. Bibcode:2019NJGPA.291...89M. doi:10.1127/njgpa/2019/0791. S2CID 134199163. Retrieved 3 March 2022.
  4. 1 2 3 4 Seilacher, A.; Drozdzewski, G.; Haude, R. (1968). "Form and function in the stem in a pseudoplanktonic crinoid (Seirocrinus)" (PDF). Palaeontology. 11 (2): 275–282. Retrieved 20 February 2022.
  5. ↑ Gale, A.; Schweigert, G. (2016). "A new phosphatic-shelled cirripede (Crustacea, Thoracica) from the Lower Jurassic (Toarcian) of Germany–the oldest epiplanktonic barnacle". Palaeontology. 59 (1): 59–70. Bibcode:2016Palgy..59...59G. doi:10.1111/pala.12207. S2CID 128383968. Retrieved 2 March 2022.
  6. ↑ Simms (1989). "Contrasting lifestyles in lower Jurassic crinoids: A comparison in benthic and pseudopelagic Isocrinida". Palaeontology. 29 (2): 475–493. Retrieved 20 February 2022.
  7. 1 2 Haude, R.; Jangoux, M. (1980). "Constructional morphology of the stems of Pentacrinitidae, and mode of life of Seirocrinus". Echinoderms: Present and Past. Vol. 1. pp. 17–23. doi:10.1201/9781003078913-3. ISBN 978-1-003-07891-3. S2CID 225515238. Retrieved 20 February 2022.
  8. ↑ Hunter, A. W.; Mitchell, E. G.; Casenove, D.; Mayers, C. (2019). "Reconstructing the ecology of a Jurassic pseudoplanktonic megaraft colony". Royal Society Open Science. 7 (7): 12–31. doi:10.1098/rsos.200142. PMC 7428219. PMID 32874621.