Journal of Paleontology, 92(2), 2018, p. 196–206 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.96


A new species of the asteroid genus Betelgeusia (Echinodermata) from methane seep settings, Late Cretaceous of South Dakota


Daniel B. Blake,1 William K. Halligan,2 and Neal L. Larson3


1Department of Geology, 3028 NHB, 1301 W. Green St., Urbana, Illinois 61801, USA ⟨dblake@illinois.edu⟩ 2Northwest Paleontological Association, 1627 NW Viewmont Ct., Silverdale, Washington 98383, USA ⟨bhalligan@wavecable.com⟩ 3Larson Paleontology Unlimited, 12799 Wolframite Rd., Keystone, South Dakota 57751, USA ⟨ammoniteguy@gmail.com⟩


Abstract.—Betelgeusia brezinai new species (Radiasteridae, Paxillosida, Asteroidea) is described from diversely fossiliferous Upper Cretaceous methane seep deposits of South Dakota. Asteroids are rare at modern chemosynthetic settings, although a hydrothermal vent occurrence is known, and two possible fossil methane seep occurrences have been reported. The Radiasteridae is important to the interpretation of crown-group asteroid phylogeny. Two extant genera are assigned to the family: Radiaster is known from relatively few but geographically widely dispersed largely deeper-water settings, and Gephyreaster is uncommon over a range of depths in the North Pacific Ocean. Jurassic and Cretaceous radiasterids have been described from geographically widely separated localities. In morphological-based phylogenetic analyses, the Radiasteridae has been assigned to the order Paxillosida, and Gephyreaster is similarly placed in a molecular evaluation; Radiaster has not yet been treated in a molecular study. In molecular treatment, an approximately traditional Paxillosida is a sister taxon to a significant part of the traditional Valvatida. Comparative morphology of Mesozoic and extant asteroids enables a hypothesis for a stemward, Mesozoic paxillosidan.


Introduction


Diverse invertebrate faunas have been described from the widely distributed methane seep deposits of the Upper Cretac- eous Pierre Shale of the Western Interior (Landman et al., 2012). Echinoderms, including crinoids, echinoids, ophiuroids, and asteroids, have been collected; the known asteroid specimens are treated here.Aguide and background to theWestern Interior seep ecosystems was furnished by Shapiro and Fricke (2002), and an overview of ancient chemosynthetic settings was pro- vided by Campbell (2006). Although echinoderms are important deep-water benthic invertebrates (Gage and Tyler, 1991), they are of limited and incompletely understood significance in chemosynthetic settings. In the Gulf of Mexico, an extant species of the upper-slope predatory forcipulate asteroid Sclerasterias Perrier, 1891, was reported to be a seep colonist (Carney, 1994), and a diversely fossiliferous Oligocene setting in Oregon provides another potential seep occurrence (Burns and Mooi, 2003, p. 95). Recently and for the first time, asteroids are reported from hydrothermal vents (Mah et al., 2015), these occurrences including a new family, a new genus, and two new species, the taxa emerging stemward in one major branch of forcipulatacean diversification. All new Pierre Shale seep asteroid specimens, excepting a


single fragment, are assigned to Betelgeusia brezinai new species, family Radiasteridae. The Radiasteridae today is known from relatively few but geographically widely separated largely deeper-water settings (448–2423 m, 245–1,325 fathoms; Clark, 1946), and because of its somewhat problematic mor- phology, the genus and family long have been taxonomically


difficult (Clark and Downey, 1992, p. 89). Positioning of the Radiasteridae within crown-group diversification (see the following) argues to its phylogenetic significance. A single small Pierre Shale fragment is assigned to the


Forcipulatida. Forcipulate subdivisions of Spencer and Wright (1966) are broadly typical of traditional morphology-based taxonomic arrangements whereas a recent molecular study (Mah and Foltz, 2011b) introduced significant changes placed in a historical biogeographic framework. Because of the limited data available for the single fossil, and because of taxonomic complexities, the fragment is assigned to the Pedicellasterinae in the traditional sense of Spencer and Wright (1966); placement in the updated framework (Mah and Foltz, 2011b) is not attempted.


Previous reports of Upper Cretaceous Western Interior asteroids


Two asteroids were reported from the Upper Cretaceous of the Western Interior, one from the Turonian–lower Campanian Cody Shale of Wyoming (Weller, 1905; Branson, 1947) and another from the Pierre Shale of Colorado (Griffitts, 1949, p. 2025). Gill and Cobban (1966, p. A23) reported arms of an asteroid associated with hundreds of small echinoids in a con- cretion collected from near the top of the upper Campanian Baculites reesidei Zone; although echinoids were illustrated, the asteroid was not. An asteroid arm was included among echinoderm remains in a middle Campanian cold seep setting (Kato et al., 2017).


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