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Journal of Paleontology 92(2):196–206
Pleistocene and Holocene. The seep supported a highly diverse fauna including ammonites, crinoids (Lakotacrinus brezinai Hunter et al., 2016 and an unknown feather star), two types of tubeworms, two types of bryozoans, various gastropods and bivalves (including teredinids and inoceramids), unidentified crabs, a ghost shrimp, and echinoids (Larson et al., 2014). Preservation of the asteroids is varied, including both articulated and fragmentary specimens, exposing both surfaces, the suite recovered both from an approximately 3×5m area in the carbonate shell hash and loose in theweathered tan shale (Fig. 3). Locality AMNH-FI 3418: Didymoceras cheyennense Zone,
Pierre Shale, upper Campanian, Late Cretaceous; Custer County, South Dakota. Exact locality information is available to qualified researchers from the American Museum of Natural History. A vertically exposed carbonate seep cross sectionmeasuring
13m high and 20m wide, surrounded by black and gray shales with orange and yellow partings near the carbonates (Landman et al., 2012). The base is buried beneath slumped black and dark-gray shale, but the roughly cylindrical carbonate ‘core’ and its conduit-like structures are readily
visible.Adetailedmap of the seep face (Landman et al., 2012, fig. 2) and site photographs (Larson et al., 2014, fig. 9a, b) have been published. The seep contains a diverse fauna of well-preserved fossils includingmany ammonites, a nautiloid, bivalves, gastropods, the articulate crinoid
Lakotacrinus brezinai Hunter et al., 2016, tube worms, sponges, fish, and crabs (Landman et al., 2012; Larson et al., 2014).
Diagnosis.—Betelgeusid in which ossicles of marginal series are similar, relatively robust, rectangular in outline. Marginal fascioles narrow, deep; intermarginal articular ridges subdued, closely fitted, overlapping flanges not strongly differentiated. First actinal row overlapping onto adambulacrals. First adam- bulacrals strongly overlapping MAO. Accessories include granules and short, robust spinelets; elongate, delicate spines lacking.
Description.—Disk large, interbrachia broadly rounded, arms triangular, tapering abruptly to rounded tips; overall body form low arched in life. Abactinals small but proportionately robust, granular to weakly paxilliform. Abactinal size diminishing distally and radially but otherwise uniform, abactinals aligned in longitudinal and transverse rows; no apparent differentiation of
carinal series or primary circlet. Abactinals covered by closely fitted, uniform, small, robust spinelets or granules; abactinals and granules forming closely fitted surface lacking distinct gaps suggestive of respiratory papulae. Madreporite not recognized, although potentially occurring in lost portions of available disks. Marginal ossicles in two series; series paired, ossicles of
both series robust, block-like, rectangular in vertical outline. Inferomarginals protrude slightly laterally beyond margins of superomarginals, more strongly so at interbrachia, protrusion
less distinct more distally. Marginal fascioles narrow, well defined, angular. Superomarginal dorsal surface weakly arched longitudinally; transverse profile broadly rounded adradially, more sharply curved toward arm margin. Superomarginal ossicular surfaces closely covered by uniform, closely spaced small granules; small, thickened spinelets can occur at abradial edge, preservational textures suggesting spinelets might not have been developed on all ossicles or all specimens. Both longitudinal and transverse inferomarginal ventral profiles nearly flat, transverse profile curving sharply near abradial margin, abradial inferomarginal edge upright, tightly rounded. Ventral inferomarginal surfaces bearing about five rows of small pustules; accessories entirely granulate, or with scattered spinelets; abradial margin granulate or bearing short, robust spinelets. Elongate spines lacking from both marginal series. Actinal fields large, two ossicular series aligned with each
inferomarginal, although arrangement locally somewhat irregular. Ten to 12 actinals in those inferomarginal series arising at interbrachial midline in specimens R~ 18–20mm. Actinal series diminishing uniformly in ossicular number, terminating at about seventh or eighth marginal, at which point inferomarginal series abut adambulacrals. Supplemental actinal series intercalated on disk away from inferomarginals. Actinals of each series aligned, successive series separated by a distinct but shallow groove; actinal grooves approximately, not sharply, aligned with inferomarginal fascioles and tissue gaps between successive adambulacrals. Actinals small, exposed surfaces subcircular, bearing one or more pustules; ossicles strongly overlapping, imbricated toward furrow. Actinal series aligned with interbrachial inferomarginals diverge toward adambulacrals leaving triangular area immediately distal to mouth-angle pair occupied by somewhat irregularly arranged actinals. Actinal ossicular surfaces bearing small spinelets or granules. Actinals adjacent to adambulacrals raised, bearing spinelets differentiated to form part of subadambulacral spinelet series.
Adambulacrals approximately aligned with actinal rows.
Adambulacrals broadly rectangular in outline, wider than long; proximal-adradial extremity angled toward mouth area. Tissue gaps between sequential adambulacrals well defined. Furrow accessory ridge V-shaped, directed toward furrow; furrow spine ridge clearly set off from subambulacral spine bases and rows, these two or three in number. Abradial margin of adambulacral overlapped by first actinal. Adambulacral spinelets short, robust. Ambulacrals not exposed in available specimens. Mouth-angle pair narrow, outline elliptical to weakly ovate,
broader end of oval directed toward mouth area. Mouth-angle pair surface broadly arched, bearing spinelets similar to those of adambulacrals. First adambulacrals enlarged, abutting adradial lateral faces of mouth-angle pair, together forming robust, bud- like configuration. Actinal series nearly reaching distal edge of mouth-angle pair.
Figure 4. Betelgeusia 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=10.0mm; (3–5) scale bars=5.0mm.
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