SOFT-TISSUE PRESERVATION of the HIND GUT in a NEW GENUS of CLADID CRINOID from the MISSISSIPPIAN (VISEAN, ASBIAN) at ST ANDREWS, SCOTLAND by THOMAS W
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[Palaeontology, Vol. 50, Part 4, 2007, pp. 951–959] SOFT-TISSUE PRESERVATION OF THE HIND GUT IN A NEW GENUS OF CLADID CRINOID FROM THE MISSISSIPPIAN (VISEAN, ASBIAN) AT ST ANDREWS, SCOTLAND by THOMAS W. KAMMER* and WILLIAM I. AUSICH *Department of Geology and Geography, West Virginia University, Morgantown, WV 26506-6300, USA; e-mail: [email protected] Department of Geological Sciences, 155 South Oval Mall, The Ohio State University, Columbus, OH 43210, USA; e-mail: [email protected] Typescript received 20 February 2006; accepted in revised form 11 August 2006 Abstract: Soft-tissue preservation of the hind gut, or anal by pointing down current between the arms to avoid fouling sac, in the tegmen of Tubulusocrinus (gen. nov.) doliolus of the ambulacra. Its smaller size may also have required less (Wright) from the Mississippian (Visean, Asbian) Pitten- energy to produce than a heavy-plated sac. The hind gut is weem Formation at St Andrews, Scotland, is the first of its apparently preserved by haematite replacement, which was kind known in crinoids; it sheds important new light on the probably altered from original authigenic pyrite that formed nature of the cladid tegmen. Many cladid crinoids had a cal- soon after catastrophic burial. cite-plated anal sac that may have functioned like a chimney to prevent fouling of the ambulacra. The tubular, uncalcified Key words: Anal sac, crinoids, Mississippian, Scotland, teg- anal sac of Tubulusocrinus may have functioned like a hose men, soft tissues. The crinoid theca contains the visceral mass of the thought to be the result of rapid disintegration of the animal and consists of the aboral cup and tegmen, tegmen plates shortly after death, presumably because which are composed of calcite plates. The free arms they were loosely embedded in a leathery integument typically extend from the theca at the junction between rather than being closely sutured together. Alternatively, the aboral cup and tegmen. In the Palaeozoic subclass the tegmen of many cladids may have lacked calcitic Cladida, the aboral cup consists of closely sutured plates and consisted simply of a leathery integument plates that are nearly always better preserved than the like the epidermis of other echinoderm classes or the tegmen, which was commonly more loosely sutured. naked tegmen of comatulids (Breimer 1978). However, The cladid tegmen includes the mouth, madreporite this latter possibility has been difficult to evaluate and anal sac (Wachsmuth and Springer 1897, pl. 3; because soft-tissue preservation in crinoids is essentially Kammer and Ausich 1996, figs 7.21, 7.22). The pre- unknown. The discovery of soft-tissue preservation of sumed functions of the cladid anal sac include housing the hind gut in the tegmen of Tubulusocrinus gen. nov. the hind gut and gonads (Lane 1984), and physically from the Mississippian, or Lower Carboniferous (Heckel separating the anus from the mouth to avoid faecal and Clayton 2005), of Scotland is remarkable and sheds contamination of ingested food (Ausich et al. 1999), important new light on the nature of the cladid thereby serving a function similar to the anal tube in tegmen. camerate crinoids (Baumiller 1990). In the cladids the anal structure is variously shaped and sized, and may range from a small opening in the aboral cup, such as SYSTEMATIC PALAEONTOLOGY in Gasterocoma (Moore et al. 1978, figs 376.6, 377.5), to a large variety of inflated and heavily plated sacs Terminology follows Ubaghs (1978) and higher-level (Ubaghs 1978, fig. 159). However, in the great majority taxonomy follows Moore and Teichert (1978), Simms and of taxa, the tegmen and anal sac are poorly known or Sevastopulo (1993), Ausich (1998) and McIntosh (2001). not known at all, even when the aboral cup and arms All specimens are in the Wright Collection at the are well preserved (Strimple 1973). This is generally National Museums of Scotland, Edinburgh (NMS). ª The Palaeontological Association 951 952 PALAEONTOLOGY, VOLUME 50 Class CRINOIDEA Miller, 1821 1952b Ureocrinus doliolus (Wright); Wright, p. 325, pl. Subclass CLADIDA Moore and Laudon, 1943 13, figs 4–5. Order DENDROCRINIDA Bather, 1899 Types. Holotype, NMS G. 1958.1.1279, a complete crown preser- Remarks. We follow McIntosh (2001) in placing pinnulate ving an uncalcified anal sac. Two paratypes, NMS G. cladid crinoids in the Order Dendrocrinida, which contains 1958.1.1280 and 1281, isolated cups. both pinnulate and non-pinnulate taxa. The Poteriocrinida as defined by Moore et al. (1978) is probably a polyphyletic Description. Crown well preserved, very tall, narrow, vase-shaped where proximal arms are constricted in a girdle shape. Aboral grouping composed of several pinnulate taxa derived from cup cone-shaped, becoming slightly constricted at the radials, the Dendrocrinida sensu Moore et al. (1978). height to width ratio c.1Æ1; plates smooth, lacking ornamenta- tion; infrabasals pentagonal, prominent, clearly visible in side view and one-third to one-half cup height, with height to width Family SCYTALOCRINIDAE Moore and Laudon, 1943 ratio c.1Æ6; basals hexagonal, elongate, height to width ratio 1Æ1– 1Æ6, increasing with ontogeny; radials pentagonal, height to Genus TUBULUSOCRINUS gen. nov. width ratio c.0Æ8, with plenary facets and distinct fulcral ridge extending the entire width of facets, fossae shallow. Three anal Derivation of name. Latin tubulus, little tube. plates in cup; radianal largest; anals arranged in typical advanced cladid arrangement with anal X above and to the left of radianal, Type species. Ulocrinus doliolus Wright, 1936. and right tube plate above radianal. Anal sac expressed as an adoral tube, non-calcified and Diagnosis. Crown tall, slender, constricted at top of non-plated, elongate, with a terminal circular opening now preserved as an ellipse. Fine annular ridges along the uncalci- aboral cup and proximal primibrachials in a girdle shape, fied anal sac indicate an original leathery integument. Preser- five atomous arms with long pinnules; aboral cup cone- vation apparently iron oxide replacement of soft tissues of shaped with thin plates, higher than wide; infrabasals and sac, as indicated by red-brown colour. Uncalcified anal sac is basals higher than wide; radials wider than high with slightly three-dimensional, indicating filling with either excre- extremely shallow plenary facets; uncalcified anal sac long ment or post-mortem mud; grey mud is visible at terminal and slender, presumably an originally leathery tegmen. opening. Anal sac exits tegmen area at CD interray between arms and above primibrachial 4 of the C ray. Lower part of the anal structure consists of plates above the anals of the Tubulusocrinus doliolus (Wright, 1936) cup and adjacent to primibrachials 1–3 of the C ray. At least Plate 1, figures 1–7; Table 1 11 small tegmen plates have been deformed post-mortem and squeezed between the arms of the C and E rays; pores are present along the sutures between tegmen plates. 1934 Hydriocrinus sp. Wright, p. 244, pl. 13, fig. 1; Arms five, atomous in all rays; brachials longer than wide, text-fig. 3. subcuneate with a distinct pinnule attachment scar along the 1936 Ulocrinus doliolus Wright, p. 404, pl. 9, fig. 5; ambulacrum at the distal end of each brachial on the longest text-figs 28–32. side of the brachial; pinnules extremely long, extending to as 1938 Ulocrinus doliolus Wright; Wright, p. 337, pl. 14, much as ten brachials on the well-preserved D ray arm. Column fig. 2. subpentagonal proximally, becoming circular by fourth colum- 1939 Ulocrinus doliolus Wright; Wright, p. 30, pl. 2, nal; four preserved columnals are homeomorphic with crenulate fig. 2; pl. 8, fig. 12; text-figs 31–35. sutures indicating symplexy. 1945 Ureocrinus doliolus (Wright); Wright and Strimple, p. 224, pl. 9, fig. 6. 1952a Ureocrinus doliolus (Wright); Wright, p. 116, Remarks. Wright (1952a) apparently did not recognize pl. 19, figs 10, 13; text-figs 61–65. the soft anal sac and interpreted it as an arm (his text- EXPLANATION OF PLATE 1 Figs 1–7. Tubulusocrinus doliolus (Wright, 1936). 1–3, NMS G. 1958.1.1279, holotype; Encrinite Bed, Pittenweem Formation, Strathclyde Group, St. Andrews, Fife, Scotland. 1, complete crown with long arms (from left to right) D, E and A rays preserved with just the proximal portions of B and C ray arms preserved, uncalcified anal sac compressed between D and E rays on slab; · 1Æ15. 2)3, close-up of uncalcified anal sac coated with ammonium chloride (2) and uncoated, in colour (3); note also oral surface of E ray arm with pinnule attachment scars, and a small cluster of tegmen plates near the base of the arm and above the primibrachials of the C ray; · 5Æ0. 4)5, NMS G. 1958.1.1281, paratype; Macgregor Marine Bands, Aberlady Formation, Strathclyde Group, Thornton Burn, East Lothian, Scotland; A–C ray and D–E ray views; · 2Æ0. 6–7, NMS G. 1958.1.1280, paratype; Encrinite Bed, Pittenweem Formation, Strathclyde Group, St. Andrews, Fife, Scotland; B–C ray and D–A ray views; · 3Æ0. PLATE 1 2 1 4 5 67 3 KAMMER and AUSICH, Tubulusocrinus 954 PALAEONTOLOGY, VOLUME 50 TABLE 1. Measurements (in mm) of Tubulusocrinus doliolus (Wright, 1936). Crown Cup Infrabasal Basal Radial Arm Pinnule Anal sac H H,W H,W H,W H,W L L L Ray CBCBD NMS G. 1958.1.1279 107 13Æ1, 11Æ94Æ6, 3Æ06Æ2, 4Æ03Æ9, 4Æ8911316 NMS G. 1958.1.1280 – 8Æ4, 7Æ94Æ4, 2Æ63Æ1, 2Æ72Æ7, 3Æ0– – – NMS G. 1958.1.1281 – 10Æ7, 9Æ74Æ2, 2Æ75Æ6, 4Æ03Æ1, 4Æ1– – – fig. 63) drawing in subcuneate brachials, although the heavily plated, plicate anal sac unlike the uncalcified anal sac is barely visible in his photograph (pl. 19, fig. 10). sac of Tubulusocrinus. The anal sac does appear to have sutures suggestive of brachials, but this is the result of the soft sac being Occurrence.