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An Ordovician Lobopodian from the Soom Shale Lagerstätte, South Africa

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An Ordovician Lobopodian from the Soom Shale Lagerstätte, South Africa [Palaeontology, Vol. 52, Part 3, 2009, pp. 561–567] AN ORDOVICIAN LOBOPODIAN FROM THE SOOM SHALE LAGERSTA¨ TTE, SOUTH AFRICA by ROWAN J. WHITTLE*,à, SARAH E. GABBOTT*, RICHARD J. ALDRIDGE* and JOHANNES THERON *Department of Geology, University of Leicester, Leicester LE1 7RH, UK; e-mails: [email protected]; [email protected] Department of Geology, University of Stellenbosch, Private Bag XI, Stellenbosch 7602, South Africa; e-mail: [email protected] àPresent address: British Antarctic Survey, Madingley Road, Cambridge, CB3 0ET, UK; e-mail: [email protected] Typescript received 18 July 2008; accepted in revised form 27 January 2009 Abstract: The first lobopodian known from the Ordovician and Carboniferous. The new fossil preserves an annulated is described from the Soom Shale Lagersta¨tte, South Africa. trunk, lobopods with clear annulations, and curved claws. It The organism shows features homologous to Palaeozoic mar- represents a rare record of a benthic organism from the ine lobopodians described from the Middle Cambrian Bur- Soom Shale, and demonstrates intermittent water oxygena- gess Shale, the Lower Cambrian Chengjiang biota, the Lower tion during the deposition of the unit. Cambrian Sirius Passet Lagersta¨tte and the Lower Cambrian of the Baltic. The discovery provides a link between marine Key words: Lagersta¨tte, lobopodian, Ordovician, Soom Cambrian lobopodians and younger forms from the Silurian Shale. Cambrian lobopodians are a diverse group showing a in an intracratonic basin with water depths of approxi- great variety of body shape, size and ornamentation. mately 100 m (Gabbott 1999). Dominantly quiet water However, they share a segmented onychophoran-like conditions are indicated by a lack of flow-induced sedi- body, paired soft-skinned annulated lobopods, and in mentary structures and the taphonomy of the fossils. The most cases body sclerites (Bergstro¨m and Hou 2001). Soom Shale sediment was largely anoxic; geochemical Only one undescribed specimen of lobopodian has previ- analyses indicate that euxinic bottom waters prevailed at ously been identified between the late Cambrian and the times (Gabbott 1998). Carboniferous (von Bitter et al. 2007) (Table 1). Here we The Soom Shale community consisted of invertebrates, describe a new occurrence of a Late Ordovician lobopo- early vertebrates and algae. In particular there is a num- dian and discuss the morphological interpretation of the ber of arthropod taxa (Moore and Marchant 1981; Fortey specimen. and Theron 1994; Braddy et al. 1995, 1999; Gabbott et al. 2003; Whittle et al. 2007), conodonts (Theron et al. 1990; Aldridge and Theron 1993; Gabbott et al. 1995), agna- GEOLOGICAL SETTING AND FAUNA thans (Aldridge et al. 2001), brachiopods (Aldridge et al. 1994), scolecodonts (Whittle et al. 2008), orthoconic The argillaceous Soom Shale Member is a 10–15 m thick cephalopods (Gabbott 1999) and enigmatica (Aldridge unit and is the lower member of the Cedarberg Forma- et al. 2001). Many of the fossils exhibit soft part preserva- tion, which occurs towards the top of the Table Moun- tion, which can include muscle tissue (Gabbott et al. tain Group in South Africa. The Soom Shale occurs 1995). It appears that soft tissues were replicated by au- immediately above glacial tillites and dropstones are pres- thigenic clay minerals and alunite group minerals, some- ent at the base of the member. Water temperatures are times with a high degree of fidelity (Gabbott 1998; thought to have been relatively cool (Gabbott 1998) and Gabbott et al. 2001). in this respect the Soom Shale represents an unusual restricted marine fauna (Aldridge et al. 1994). The Soom Shale Member has been correlated with MATERIALS AND METHODS the persculptus graptolite Biozone of Hirnantian (Late Ordovician) age (Sutcliffe et al. 2000; Young et al. 2004). The repository of the specimen (C1974) is the Council of Palaeogeographical reconstructions indicate that it was Geosciences of South Africa, Bellville. It was discovered at deposited at approximately 30–45°S (Young et al. 2004), Keurbos Quarry near Clanwilliam (32°16¢ S, 18°58¢ E) in ª The Palaeontological Association doi: 10.1111/j.1475-4983.2009.00860.x 561 562 PALAEONTOLOGY, VOLUME 52 TABLE 1. Fossil lobopodians from the Early Cambrian to the Tertiary. Helenodora and specimens found from the Cretaceous onwards have been interpreted as onychophorans. Taxa, authorship, year of publication Age Distribution Luolishania longicruris Hou and Chen, 1989 Early Cambrian Chengjiang Lagersta¨tte, China Paucipodia inermis Chen et al., 1995 Early Cambrian Chengjiang Lagersta¨tte, China Cardiodictyon catenulum Hou et al., 1991 Early Cambrian Chengjiang Lagersta¨tte, China Hallucigenia fortis Hou and Bergstro¨m, 1995 Early Cambrian Chengjiang Lagersta¨tte, China Microdictyon sinicum Chen et al., 1989 Early Cambrian Chengjiang Lagersta¨tte, China Onychodictyon ferox, Hou et al., 1991 Early Cambrian Chengjiang Lagersta¨tte, China Jianshanopodia decora Liu et al., 2006 Early Cambrian Chengjiang Lagersta¨tte, China Miraluolishania haikouensis Liu and Shu, 2004* Early Cambrian Chengjiang Lagersta¨tte, China Aysheaia pedunculata, Walcott, 1911 Middle Cambrian Burgess Shale, Canada A.? prolata Robison, 1985 Middle Cambrian Burgess Shale, Canada Hallucigenia sparsa (Walcott, 1911) Middle Cambrian Burgess Shale, Canada Hadranax augustus Budd and Peel, 1998 Early Cambrian Sirius Passet Lagersta¨tte, North Greenland Xenusion auerswaldae Pompeckj, 1927 Early Cambrian Baltic region Orstenotubulus evamuellerae Maas et al., 2007 Cambrian Sweden Not yet formally described von Bitter et al., 2007(fig. 2E, F) Silurian Eramosa Lagersta¨tte, Canada Helenodora inopinata Thompson and Jones, 1980 Carboniferous Mazon Creek of northern Illinois Cretoperipatus burmiticus Engel and Grimaldi, 2002** Cretaceous Amber of Myanmar (Burma) Tertiapatus dominicanus Poinar, 2000 Eocene Baltic amber Succinipatopsis balticus Poinar, 2000 Eocene Baltic amber *In Liu et al. (2004), was considered to be a junior synonym of Luolishania longicruris by Ma et al. (2006) contested by Liu et al. (2008b). **In Grimaldi et al. (2002). a light grey siltstone. In fifteen years of collecting this is fact, plesiomorphic while others were not demonstrable the only known specimen. It occurs in multiple pieces in the majority of fossil forms. He further noted that the that comprise part (C1974 a, d), and counterpart (C1974 presence of lobopodian features in Kerygmachela and b–c, e). The specimen is incomplete, with the anterior Pambdelurion indicated that lobopodians were not mono- and possibly the posterior portions missing. The fossil phyletic. Liu et al. (2007) supported the view that lobopo- was studied using an optical microscope, drawn with the dians are paraphyletic, and cladistic analyses by Ma aid of a camera lucida, and photographed with and with- Xiaoya (pers. comm. 2008) suggest that the group is para- out ammonium chloride coating, using a digital camera phyletic or polyphyletic. Given the continuing uncertain- (Canon EOS 5D). A Hitachi S-3600N Scanning Electron ties surrounding these phylogenetic relationships, we use Microscope Energy Dispersive X-ray facility (SEM EDX) the Phylum Lobopodia here with equivocation. was used in partial vacuum mode for chemical analyses The proposed affinity of the Cambrian lobopodians of the uncoated specimen. with extant onychophorans (e.g. Robison 1985; Ramsko¨ld and Chen 1998) has been the subject of some debate. Bergstro¨m and Hou (2001) noted similarities to tardi- SYSTEMATIC PALAEONTOLOGY grades and Liu et al. (2008a) argued that lobopodians have a much closer relationship to arthropods than to Phylum LOBOPODIA Snodgrass, 1938? either onychophorans or tardigrades. Remarks. In recent analyses of panarthropod relationships doubts have been raised regarding the monophyly of the Class XENUSIA Dzik and Krumbiegel, 1989 Lobopodia. Ramsko¨ld and Chen (1998) concluded that Cambrian lobopodians form two clades that join the Description. The specimen is incomplete, with a length of at extant onychophorans in an unresolved trichotomy; they least 70.7 mm and a width of at least 31 mm. The central body combined the three clades within the total group Ony- portion appears sub-cylindrical and shows clear transverse annu- chophora. Budd (1999), however, regarded the support lations in some places (Text-figs 1–2), visible at a density of for a monophyletic ‘Onychophora’ to be weak. He argued c. 7–8 ⁄ mm (Text-fig. 3F). The body is elongated and tapers towards the presumed posterior, appendages decrease in size and that some of the characters considered by Ramsko¨ld and the central trunk extends beyond what is probably the final pos- Chen (1998) to be synapomorphies of this group were, in WHITTLE ET AL.: ORDOVICIAN LOBOPODIAN FROM THE SOOM SHALE 563 TEXT-FIG. 1. Lobopodian specimen C1974 from the Soom Shale. Two sets of appendages are visible on the specimen, on either side of the main trunk (see Text-figure 2 for composite explanatory drawing). A, Part (C1974 a, d), the trunk of the organism is mostly preserved in positive relief. B, Counterpart (C1974 b–c, e), the main trunk is mostly preserved in negative relief. 5 mm A 5 mm B terior appendage. At the anterior end, appendages become more branch (Text-figs 1–2, 3A), which is further divided into three crowded and this end of the fossil is incomplete (Text-figs 1–2). or four tips distally. This degree of complexity is not clear on There are no cephalic or caudal structures that clearly indicate any of the other appendages, and thus a11 may be a modified the orientation of the fossil. However, there is variation in the anterior-most appendage. Posterior of a8–a11 there are seven position and size of the lobopods which has been noted in other appendages labelled a7–a1, which are simple lobes with clear taxa in relation to orientation. Paucipodia has a body that tapers margins (Text-figs 1–2); these appendages decrease in size at both ends, extending beyond the final lobopods; appendages towards the posterior of the organism. On some (for example a7 are longest in the middle and become shorter towards the ante- to a4) there are traces of transverse annulations (Text-figs 2, rior and posterior (Hou et al.
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