Journal of Paleontology, 92(4), 2018, p. 596–610 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2018.7
Four new species of the Jurassic to Cretaceous seep-restricted bivalve Caspiconcha and implications for the history of chemosynthetic communities
Robert G. Jenkins,1 Andrzej Kaim,2 Yoshinori Hikida,3 and Steffen Kiel4
1School of Natural System, College of Science and Engineering, Kanazawa University, Kanazawa City, Ishikawa Prefecture 920-1192, Japan ⟨
robertgj@staff.kanazawa-u.ac.jp⟩ 2Institute of Paleobiology, Polish Academy of Sciences, ul. Twarda 51/55, PL−00−818 Warszawa, Poland ⟨
kaim@twarda.pan.pl⟩ 3Nakagawa Museum of Natural History, 28-9 Yasukawa, Nakagawa Town, Hokkaido 098-2626, Japan ⟨
nmhikida@coral.ocn.ne.jp⟩ 4Swedish Museum of Natural History, Department of Palaeobiology, Box 500 07 104 05 Stockholm, Sweden ⟨
steffen.kiel@
nrm.se⟩
Abstract.—Four new species of the methane seep-inhabiting kalenterid bivalve genus Caspiconcha Kelly in Kelly et al., 2000 are described: Caspiconcha basquensis from the late Albian of northern Spain, C. yubariensis from the late Albian of northern Japan, C. raukumaraensis from the late Albian to mid-Cenomanian of New Zealand, and C. lastsamurai from the Campanian of northern Japan. The earliest confirmed record of the genus is known from the latest Jurassic. It reached its maximum diversity in the Albian and declined in diversity and abundance through the Late Cretaceous. The youngest species, C. lastsamurai, is currently known from a single specimen only.
UUID:
http://zoobank.org/2f84cfd3-216c-4f1b-8c9f-c808a47f7aaa Introduction
Chemosynthesis-based ecosystems are most commonly found around hydrothermal vents and methane seeps in the deep sea. Most of themegafauna at these sites consist of highly specialized animals living in symbiosis with sulfur- and/or methane- oxidizing bacteria, which provide them with nutrients. At mod- ern vents and seeps, these aremainly vestimentiferan tubeworms, bathymodiolin mussels, and vesicomyid bivalves—all restricted to these environments. Mesozoic vents and seeps were also inhabited by animals endemic to such environments, although their taxonomic affinities were different. Common were rhynch- onellide brachiopods of the Dimerelloidea, a group that dis- appeared from vents and seeps by the end of the Early Cretaceous (Campbell and Bottjer, 1995a, b; Sandy, 2010; Peckmann et al., 2011; Kiel et al., 2014). Among mollusks, gastropods of the Abyssochrysoidea were common, including large-sized taxa (Goedert and Kaler, 1996; Kaim et al., 2008, 2009, 2014; Kiel et al., 2010), and bivalves restricted to the seep environment included several genera of Lucinidae (Kiel, 2013) and the large kalenterid genus Caspiconcha Kelly in Kelly et al., 2000. Initially described from Greenland, Caspiconcha is now
known from seep deposits from the Atlantic, Pacific, and Tethys Oceans and from both hemispheres (Kelly et al., 2000; Kiel and Peckmann, 2008; Kiel et al., 2010, 2013; Agirrezabala et al., 2013; Jenkins et al., 2013). Its shell morphology indicates the presence of a byssus, and when found in situ, it is usually oriented with the anterior part about 30° downward relative to the bedding plane, suggesting a semi-infaunal/epifaunal mode of life (Kelly et al., 2000; Kiel and Peckmann, 2008). Its large size (exceeding 300mm in length) and its abundance at
many Early Cretaceous seep deposits suggest that Caspiconcha harbored chemotrophic bacteria in its gills, like the dominant bivalves at vents and seeps today (Kelly et al., 2000; Jenkins et al., 2013). So far, there are three nominal species of Caspiconcha: the type species C. whithami Kelly in Kelly et al., 2000 from the Barremian of Greenland; Caspiconcha major (Gabb, 1869) from Tithonian to Albian seep deposits in California (Jenkins et al., 2013); and Caspiconcha rubani Kiel, Campbell, and Gaillard, 2010 from the Berriasian of the Crimea. Several other species have been left in open nomenclature pending more exhaustive taxonomic work and/or collecting effort. Here we formally describe four of these species and discuss the evolutionary history of Caspiconcha and other seep-related kalenterids/modiomorphids.
Geologic setting
The material is from localities in Spain, New Zealand, and Japan that have been described elsewhere (Fig. 1). They are briefly outlined here, with references to more detailed reports.
Ispaster, Spain.—More than 50 limestone bodies crop out on an intertidal platform composed mostly of turbidites along the coast of the Bay of Biscay in the Basque country, Spain, between the villages Ea and Ispaster. They were identified as ancient methane-seep deposits using stable carbon isotope, petrographic, and biomarker evidence, are of late Albian age, and belong to the Ogella unit of the Black Flysch Group (Agirrezabala et al., 2013). All investigated specimens descri- bed here as Caspiconcha basquensis n. sp. are from float boulders of seep limestone found along the beach at this section.
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