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

Published online by Cambridge University Press:  05 February 2018

Daniel B. Blake
Affiliation:
Department of Geology, 3028 NHB, 1301 W. Green St., Urbana, Illinois 61801, USA 〈dblake@illinois.edu〉
William K. Halligan
Affiliation:
Northwest Paleontological Association, 1627 NW Viewmont Ct., Silverdale, Washington 98383, USA 〈bhalligan@wavecable.com〉
Neal L. Larson
Affiliation:
Larson 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.

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Copyright © 2018, The Paleontological Society 
Figure 0

Figure 1Map of South Dakota, USA, showing approximate asteroid collecting localities.

Figure 1

Figure 2Upper Campanian ammonite zonal table of the Western Interior. *Age dates from Cobban et al. (2006). Zone of occurrence of the asteroid Betelgeusia brezinai n. sp. in bold.

Figure 2

Figure 3AMNH loc. 3529. All asteroid specimens at this locality were found within the black outline, 2–3 m north of the micritic mass of the carbonate core (arrow).

Figure 3

Figure 4Betelgeusia brezinai n. gen. n. sp. (1–4) American Museum of Natural History, holotype AMNH-FI 111823; (1, 2) dorsal and ventral views, the primary ossicles partially obscured by accessories and foreign shelly material; (3) interbrachium toward top of (2); mouth frame to right, many accessories remaining, fasciolar channeling between actinal series is not closely aligned with marginal series (to left); (4) marginal form, fascioles, and accessories. (5, 6) Paratype AMNH-FI 111824; (5) ventral lateral view of arm, superomarginals granulate, inferomarginal with robust edging spinelets, accessories more nearly granular on ventral surface; edges of actinal rows, these aligned, separated by fasciolar grooving; (6) ventral view showing adambulacral form, alignment of actinals, marginal form; comparatively few accessories remain. (7) Paratype AMNH-FI 111852, the only specimen derived from locality AMNH-FI 3418; MAO, form and positioning of actinals and marginals; see Fig. 5.1. (1, 2, 6, 7) Scale bars=10.0 mm; (3–5) scale bars=5.0 mm.

Figure 4

Figure 5(1–13)Betelgeusia brezinai n. gen. n. sp. (1) Paratype AMNH-FI 111852, disk in ventral aspect, aligned series of imbricate actinals separating two mouth angle ossicle (MAO) pairs (upper left) from inferomarginal series (far right); compare (10, 11). (2, 3) Paratype AMNH-FI 111825, arm tip in dorsal and ventral aspect; (2) the terminal is large, as is common among paxillosidans (including the Radiasteridae) with attenuated arm tips; (3) arm tip upturned as is common in life, an orientation enabling extension of sensory distal tube feet into the environment; marginals with aligned, transverse accessory pustules; marginals abut spinose adambulacrals. (4–6) Paratype AMNH-FI 111826, marginal series and associated ossicles in dorsal, lateral, and ventral views; (4) ossicular debris including few abactinals and actinals that were displaced dorsally; (5) angular openings at abradial edge of superomarginals suggest pedicellariae openings, these otherwise unknown among radiasterids; (6) inferomarginal pustule configuration and a few remaining accessories; actinals largely disrupted. (7–9) Paratype AMNH-FI 111827; (7) superomarginals and displaced small paxilliform abactinals; (8) both marginal series, lateral surfaces showing fasciolar ridges; (9) inferomarginals above with spinelet pustules; displaced actinals below. (10, 11) Paratype AMNH-FI 111828, actinal and marginal series in ventral and inclined ventral views; the strongly imbricating and aligned actinals are characteristic of radiasterids, here potentially partially displaced taphonomically, but of overall orientation likely similar to those assumed during normal body flexure. (12) Paratype AMNH 111829, dorsal aspect near juncture of arm and disk, compare (1); superomarginal form, inferomarginals extending laterally beyond superomarginals; abactinal form. (13) Paratype AMNH-FI 111830, fragment in ventral aspect, shingled actinal rows (arrows) extend adradially from two inferomarginals. (14, 15) Pedicellasterinae? gen. indet. sp. indet., figured specimen AMNH-FI 111853, two views of the single available fragment; (14) dorsal ossicular views, cross-shaped body-wall ossicles are characteristic of forcipulates; a single ambulacral (arrow) is comparatively large, the figure ‘8’ or wasp-shape indicates a single row of podia rather than offset podial series of the Asteriidae; (15) dominantly ventral ossicular views, adambulacral (arrows) form is consistent with a pedicellasterid assignment. (1–13) Scale bars=1.0 mm; (14, 15) scale bars=2.0 mm.