Urchins on the edge: an echinoid fauna with a mixed environmental signal from the Eocene of Jamaica
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Urchins on the edge: an echinoid fauna with a mixed environmental signal from the Eocene of Jamaica Conrad van den Ende1 • Stephen K. Donovan2
Received: 18 February 2015 / Accepted: 5 March 2015 Akademie der Naturwissenschaften Schweiz (SCNAT) 2015
Abstract An echinoid fauna from the Early–Middle Eocene of Jamaica has yielded six species of echinoid: the phymosomatoid Acanthechinus peloria (Arnold and Clark); the oligopygoid Oligopygus sp.; the clypeasteroids Fibularia jacksoni Hawkins and Neolaganum sp.; and the spatangoids Eupatagus alatus Arnold and Clark and Eupatagus sp. cf. E. clevei (Cotteau). Eupatagus alatus has a relatively low test, is broadest posterior of centre, and lacks an anterior sulcus; Eupatagus sp. cf. clevei is relatively higher and more inflated, more parallel-sided, and blunter anteriorly with an anterior sulcus. The discovery of F. jacksoni and Neolaganum sp. together with Oligopygus sp. is unexpected, as these species commonly have different ecological niches in the Eocene of Jamaica. In previous examples described from the Eocene succession of the island, oligopygoids favoured high-energy shelf edge settings, whereas Fibularia and neolaganids prefered lowenergy lagoonal settings. The assemblage as a whole likely represents an Early–Mid Eocene echinoid fauna inhabiting a shallow island shelf sea, in a transition between shelf edge and lagoonal setting. Keywords Yellow Limestone Group Guys Hill Formation Systematics Palaeoecology
& Stephen K. Donovan [email protected] Conrad van den Ende [email protected] 1
Leiden University, Postbus 9500, 2300 RA Leiden, The Netherlands
2
Department of Geology, Naturalis Biodiversity Center, Postbus 9517, 2300 RA Leiden, The Netherlands
Introduction Jamaica boasts a wide variety of fossil echinoids, first described in detail by Hawkins (1923, 1924, 1927, 1930) and Arnold and Clark (1927, 1934). Precise data concerning localities and horizons for most of Arnold and Clark’s species are unknown because of the manner of collection, mostly from road or railway construction workers who were asked about what were locally known as ‘stone sea eggs’ (Arnold and Clark 1927, p. 6). If these labourers were cooperative, Arnold was sold or given some specimens, or collected at the location from where the rocks came. From the associated locality data in Arnold and Clark (1927, 1934), we know that many of the echinoids that they figured and described originated from the Eocene Yellow Limestone Group (Donovan 1988a, 1993). More recently, the Jamaican Cenozoic echinoid fauna has been found to be particularly diverse, but stratigraphically unevenly known, with an inordinate number of taxa coming from the Eocene (Donovan 1993). During the mid-Early and mid-Middle Eocene, echinoid diversity in the Caribbean was at its height, declining towards the Late Eocene (McKinney et al. 1992; Dixon and Donovan 1994). Subsequent studies of Jamaican fossil echinoids have filled some of these gaps by concentrating on the post-Eocene record (for example, Oligocene—
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