The isocrinine crinoid Isselicrinus Rovereto from the Paleogene of the Americas
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REGULAR RESEARCH ARTICLE
The isocrinine crinoid Isselicrinus Rovereto from the Paleogene of the Americas Stephen K. Donovan1 • Sven N. Nielsen2 • J. Velez-Juarbe3 • Roger W. Portell4 Received: 8 May 2019 / Accepted: 30 May 2019 Akademie der Naturwissenschaften Schweiz (SCNAT) 2019
Abstract Crinoids are uncommon fossils in the Cenozoic. This scarcity means that even disarticulated elements are of note. Two species of the isocrinine Isselicrinus Rovereto are described from their disarticulated columns. Isselicrinus sp. A is from the upper Eocene Moritzian Stage of Tierra del Fuego. These crinoids have a robust column, varying from pentalobate (proximal?) to rounded pentagonal (distal?) in section and with consistently depressed areola petals. Isselicrinus sp. B is from the Lower Oligocene Juana Diaz Formation of Puerto Rico. This species is typified by slender pluricolumnals, always rounded pentagonal in section, and long noditaxes. Proximal and distal pluricolumnal morphologies are not distinguishable. Keywords Tierra del Fuego Puerto Rico Oligocene Systematics Taphonomy
Introduction ‘‘As a result of the distribution of sea and land during the Tertiary, which was similar to that of today, most marine sediments were deposited in shallow water close to present coastlines. Therefore, there are only a few chances to collect from deposits in which crinoids might be well preserved … the extreme rarity of well-preserved crinoids in such [shallow water] sediments, is therefore no surprise’’ (Hess 1999, p. 233). Hess rightly emphasized the poor fossil record of Cenozoic crinoids, highlighting the remains of well-preserved specimens. The only common crinoids in shallowEditorial Handling: D. Marty. & Stephen K. Donovan [email protected] 1
Taxonomy and Systematics Group, Naturalis Biodiversity Center, Postbus 9517, 2300 RA Leiden, The Netherlands
2
Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
3
Natural History Museum of Los Angeles County, 900 West Exposition Boulevard, Los Angeles, CA 90007, USA
4
Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA
water deposits from this interval were the comatulids, whose fossil record remains patchy because of their low preservation potential and the small size of their component parts. The tiny ossicles of comatulids rarely occur in concentrations, so it takes a keen eye to spot them. For example, from the upper Oligocene shelf limestones of Jamaica, the late Hal Dixon collected over a thousand echinoids and echinoid fragments (Dixon and Donovan 1998), and the first asteroid (Blake et al. 2015) and ophiuroid ossicles from the island, yet the entire crinoid diversity is a single (presumed comatulid) brachial ossicle (Dixon et al. 1994). Yet, in contrast and also from Jamaica, the deep water fore-reef limestones of the Manchioneal Formation (lower Pleistocene) have yielded a moderate diversity of stem ossicles from isocrinine and bourgueticrinid c
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