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(Chelicerata: Eurypterida), a Large Sweep-Feeder from the Carboniferous of South Africa C

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(Chelicerata: Eurypterida), a Large Sweep-Feeder from the Carboniferous of South Africa C Transactions of rhe Royal Society of Edinburgh, 76, 339-358, J985 CyrtoctefJUS wittebergensis sp. nov. (Chelicerata: Eurypterida), a large sweep-feeder from the Carboniferous of South Africa C. D. Waterston, B. W. Oelofsen, R. D. F. Oosthuizen ABSTRACT: Cyrtoctenus winebergensis sp. nov. is described from a unique holotype from the Witteberg Group of the Cape Supergroup. It is a giant hibbertopteroid eurypterid having combs and specialised movable spines of crytoctenid type (St0rmer & Waterston 1968) on the more distal podomeres of the second to fourth prosoroal appendages. The function of the combs and their associated movable spines is discussed and it is suggested that together they formed a unique adaptation of eurypterid structures to sweep filter~feeding, the combs forming the filters and the spines the cleaners. The digestive tract is remarkably preserved and shows a spiral valve, posterior to tbe stomach, which is interpreted as an adaptive feature in this large arthropod to increase tbe absorptive area of the gut. The new evidence provided by the South African specimen bas required the re~interpretation of the disarticulated Cyrloclenus specimens previously described from Europe. Disjecla membra recently obtained from the Tournaisian of Foulden, Berwickshire, whicb may belong to CynoClenus, are described and show characters previously unknown in Scottish material but similar to certain features in the South African specimen. The taxonomic relationships within the Hibbertopteroidea are discussed in the light of tbe new combination of characters found in C. wittebergensis. Two families are recognised in the superfamily, the Hibbertopteridae, including Hibber/opterus and Campylocephalus, and the new family Cyrtoctenidae which is here erected to include Cyrtoclenus, Dunsoprerus and possibly also Haslimima. KEY WORDS: Berwickshire, Gondwanaland, Hibbertopteroidea, intestine, sweep~feeding, taxonomy, Witte berg Group. Our knowledge of the Eurypterida is derived, for the roost 1.2. Holotype part, from specimens found in North America, Europe and The species is known from a singie specimen (University of Asia. Discoveries of eurypterids in tbe southern hemispbere Stellenbosch, Zoology Department USS.IT.01) found at have been rare and usually fragmentary, often occurring as longitude 22"36' latitude 33°10', 6 km NE of Zwartskraal isolated examples (Kjellesvig-Waering 1961, p. 108-11). The which is 18 km N of Klaarstroom in tbe District of Prince finding of a large and almost complete' specimen in the Cape Albert, Cape Province, South Africa. The locality lies in the Province of South Africa is therefore notable. That it should southern Karoo some 390 km ENE of Cape Town and 60 k..m also provide a key to our understanding of the puzzling NE of Oudtshoorn. The specimen came from the lower part. European genus Cyrloctenus (St0Tmer & Waterston 1968) of the Waaipoort Formation, tbe uppermost subdivision of adds greatly to the interest of the find. the Witteberg Group of the Cape Supergroup (see 3.2). It is preserved in a nodule which has been broken open and now exists as a number of pieces. The specimen is displayed as 1. Description internal and external moulds. Because much of tbe gut is Cynoc/enus St~rmer & Waterston 1968 preserved (see 2.3) it is known that the specimen is a Revised diagnosis. Cyrtocterud ewypterid (see 5.1) in which cadaver and, from its position in tbe beds when found, it is the anterior movable spines of the more distal podomeres of known to have beeD preserved lying on its back. Because of the secood, third and fourth prosomal appendages are decay or predation, some of the ventral structures have been modified to form 'fingers' each associated with a fixed comb lost or have been slightly displaced. Nothing of the specimen probably developed as a modification of the posterior spine. was preserved beyond the nodule. CynOClenus wittebergensis sp. nov. 1.3. Prosoma 1.1. Diagnosis The proportions of the prosoma are seen in the scale Cynoctenus having an oval oceUar node, and large-scale drawing Figure 1. The sbape is generally semi-circular with a crenulations 00 the distal margins of the podomeres. broad antero~median protrusion. The maximum wldth Ornament generally coarse V-shaped or rounded lunules. (485 mm) lies near the posterior margin. The postero-Iateral The axial portions of the tergites and post-abdominal angles are produced as rounded ears. The prosomallength is segments ornamented with coarse longitudinal ridges and 355 rom . In life the carapace must have been strongly furrows . elevated since in its present state the surface of the cardiac L 340 C. D . WATERSTON. B. W . OELOFSEN AND R . D. F. OOSTHUIZEN lobe lies 138 mm above the level of the postero-Iateral ears. The compound eyes are raised on palpebral lobes and lie just posterior to the mid-line with their axes converging anteriorly. The paired ocelli lie in the posterior half of (he oval ocellar node which occurs betlVeen the posterior portion of the lateral eyes. Anterior to each lateral eye (here is an arcuate furrow in the prosomal surface. The slope of the antero-median protrusion increases anteriorly until, at (he anterior margin, it is vertical. The surface of the protrusion bears irregularly spaced longitudin­ al grooves and ridges which radiate anteriorly. Three pairs of curved emarginations occur (Fig. 1) which increase in size posteriorly. The posterior pair occur where the prosomal margin swings anteriorly at the base of the antero-mc:dian protrusion. There is a marginal brim seen as an external mould some 10 mm wide at the anterior of the prosoma. The brim has a shallow embayment at the anterior mid-line. On either side of this, it turns outwards and extends laterally on the protrusion and is continued onto the semi-circular body of the prosoma. Here it becomes narrower posteriorly and fades out before reaching (he post-latera) angles. This brim is twisted into a more vertical position at the emarginations of (he antero-median protrusion. At the anterior margin the brim bears ~trongly developed circular bosses packed closely together each of which shows the base of a movable hair or spine (Fig. I1h). Posteriorly these give place to broad folliculated lunules. closing laterally, and then 10 rather narrow lunules some of which are folliculated. The cardiac region of the prosoma appears to be smoolh but fields of large V-shaped lunules closing post-laterally occur in the antero-lateral region extending post-laterally towards the post-lateral angles from a line joining the base of the antero-median protrusion and the lateral eyes. Mesially lunules in these fields become rounded and broader while laterally they become narrow and asymmetric. Numerous strong. narrow concentric tcrrace-lines are developed on the anterior slope of the eye-furrows. The posterior margin of the prosoma carries strong and large narrow lunules and ridges. The ventral structures of the prosoma have been shifted anteriorly and IOwards the left in relation to the carapace. The metaslOma i.. not present and was probably displaced beyond the nodule. The ventral marginal plates are largely obscured by the appendages and the sutures are not seen. 1.4. Prosomal appendages The proximal podomeres are shown in the ventral view of Ihe prosoma (Fig. 2a) and our interpretation is given in the scale drawing Figure 2b. The coxa of 11mb VI. lacking the gnathobase, is preserved on the right side but on the left side it is missing so that the 300mm ventral view of the whole of the coxa of left V is seen. The coxa of right VI can be removed with the matrix 10 reveal the ventral aspect of the coxa of right IV. This is again F"Igure 1 Cyrlocrenus willebergensis sp . nov. Diagrammatic recon­ complete except for the gnathobase and its shape is shown in struction (rorn scale drawings of the dorsal surface. Figure 2b, the covered margins being indicated by a broken Fil!:ure 2 CYrlocrenus willebergensis sp. nov. (a) Photograph of the ventral structures of the prosoma. (b) Interpretative drawing oC the above. Stipple = matrix. black = large cracks. dark shade = prosomal doublure or fragments 01 margioal platcs, ligllt shade = anhrodial membrancs, horizontal lines = matrix infilling appendages. broken lines = margins of coxa of right rv revealed when overlying coxa of righ( VI is removed. r =- right, I = left. II-VI = second to sixth prosomal appendages, 1--4 '" first to fourth podomeres of prosomal appendages, a = spiral coprolite. b = venlral surface of prosoma, c = displaced spine or mould of edge of left coxa of VI. A NEW CYRTOCTENID EURYPTERID FROM SOUTH AFRICA 341 b L---..J 30mm 342 C. D. WATERSTON. B. w. OELOFSEN AND R. D. F. OOSTHUIZEN line. The coxal series on the left side is complete, each coxa widens to the crenulated distal margin. The groove is flanked overlapping that anterior to it and the character of the by acute shoulders ornamented by strong tile-like lunules. gnathobases of all these limbs is evident. The shape of the Podomere 5 carries a strong aotero-ventral spine only the coxa of limb II of both left and right is seen but that of limb base of which has been preserved. The edge of the nodule is III is obscured. It is evident from the leh side that the teeth reached at the proximal end of podomere 6. It is evident, on the gnathobase of limb III are 'normal' in that they are however, that ;t closely resembled 5, the posterior groove similar to those found on the same limb in other eurypterids being present. of comparable size. Those On the gnathobase of IV, As in limb VI, the more distal podomeres of limb V which however, are thinner and on V they are spine-like. are present on the left side occur in a separate piece (Fig.
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