See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/228534815 Organophosphatic stem group brachiopods - implications for the phylogeny of the Subphylum Linguliformea Article in Fossils and Strata · February 2008 CITATIONS READS 28 612 3 authors: Lars E Holmer Leonid E. Popov Uppsala University National Museum Wales 290 PUBLICATIONS 5,487 CITATIONS 305 PUBLICATIONS 5,253 CITATIONS SEE PROFILE SEE PROFILE Michael Streng Uppsala University 58 PUBLICATIONS 830 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Unveiling the astonishing orgy of Cambrian explosion: integrating fossil records from the Cambrian Könservat-Lagerstätten View project Lower Palaeozoic brachiopod faunas from Baltoscandia, the south Urals and the United Kingdom View project All content following this page was uploaded by Lars E Holmer on 28 May 2014. The user has requested enhancement of the downloaded file. OrganophosphaticBlackwell Publishing Ltd stem group brachiopods: implications for the phylogeny of the subphylum Linguliformea LARS E. HOLMER, LEONID POPOV AND MICHAEL STRENG Holmer, L.E., Popov, L. & Streng, M. 2008: Organophosphatic stem group brachiopods: implications for the phylogeny of the subphylum Linguliformea. Fossils and Strata, No. 54, pp. 3–11. ISSN 0024-1164 The recognition of potential organophosphatic-shelled stem group brachiopods has important implications for the understanding of brachiopod phylogeny. These groups fall outside the two currently recognized classes of the subphylum Linguliformea – the Lingulata and Paterinata. However, their organophosphatic shell structure and evidence of penetrative setae demonstrate that they are linked phylogenetically with the linguliforms. The proposed Early Cambrian stem-group brachiopods include the problematic, possibly vermiform, organophosphatic sclerite-bearing tannuolinids and the more brachiopod-like Mickwitzia and Heliomedusa. A columnar shell fabric, which was considered previously as a derived feature of acrotretids, is now known also from the tannuolinid Micrina as well as from Mickwitzia, thus indicating that this type of shell structure may be a plesiomorphic character; it was retained in acrotretids and some lingulids, like the Lingulellotretidae, which is here shown to include a wide variety of columnar fabrics. A columnar shell structure (sensu lato) is also identified here from the enigmatic South American Ordovician linguliform brachiopod Bistramia. The shells of Mickwitzia and Heliomedusa also have various types of thicker cylindrical columns (‘tubes’), some of which were clearly open to the exterior surface and can be inferred to have contained setal structures penetrating the shell. Identical perforations are present in Micrina, and a similar function can be inferred for both the columnar fabric of some recently discovered paterinids described here and possibly also of some siphonotretids, indicating that these groups may also be closer to the stem of the brachiopods. ᮀ Brachiopoda, Lingulellotretidae, Linguliformea, Paterinida, phylogeny, shell structure, Siphonotretida. Lars E. Holmer [[email protected]] and Michael Streng [[email protected]], Department of Earth Sciences/Palaeobiology, Uppsala University, Norbyvägen 22, 75236 Uppsala, Sweden; Leonid Popov [[email protected]], Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, Wales, UK. The discovery by Williams & Holmer (2002) that the This paper provides new data on the distribution phosphatic stratiform laminae of the brachiopod- of the columnar shell fabric (sensu lato), including new shaped, two sclerites of Micrina Laurie exhibit a evidence for Micrina–Mickwitzia-type penetrative setae columnar shell fabric (sensu lato) including striated within new groups of organophosphatic brachiopods, apatitic columns (‘tubes’) that, at the surface, must and provisionally explores the implications for the have contained chitinous brachiopod-like setae, and phylogeny of the subphylum Linguliformea. the subsequent identification of identical structures in the stem group brachiopod Mickwitzia (Holmer et al. 2002) re-emphasized the importance of shell Materials and methods structure in phylogenetic studies. Following these findings, a surprisingly rich record of Early Cambrian The organophosphatic-shelled valves examined in organophosphatic-shelled stem group brachiopods is this paper were isolated either by dissolving various beginning to emerge (Holmer et al. 2003, 2004; Peel Cambrian and Ordovician carbonate rocks in 10% 2003; Skovsted & Holmer 2003; Balthasar 2004; Li & acetic acid or, if for material from a non-carbonate Xiao 2004). In particular, the new discoveries confirm unit, mechanically prepared specimens. that the distribution of Micrina–Mickwitzia-type All natural and fractured surfaces where either columnar penetrative setal structures and the acro- coated with gold and examined using high vacuum tretoid columnar shell fabric (see Holmer 1989; scanning electron microscopy (SEM), or in the case Williams & Holmer 1992) occurs both within stem of type museum material, left uncoated and examined and crown group brachiopods. either with a LEO 1530 environmental SEM with © 2008 The Authors, Monograph compilation © 2008 The Lethaia Foundation 4 Holmer et al. FOSSILS AND STRATA 54 (2008) field emission (EBC, Uppsala University) or a provisional, and as noted by Holmer et al. (2002, CamScan MaXim 2040S SEM with variable vacuum p. 880), ‘the phylogenetic range of columnar and (National Museum of Wales and Cardiff University). apatitic tubes has yet to be fully determined among The details of the specimens used to illustrate the the Brachiopoda and Problematica’. shell structures and other features are as follows: Acrotretoid columnar structure • Micrina etheridgei (Tate) – Lower Cambrian Wilkawillina Limestone, Wilkawillina Gorge, Flinders As defined originally (Holmer 1989, p. 31) and used Range, South Australia (Williams & Holmer 2002). later by Williams & Holmer (1992), this term referred • Mickwitzia cf. occidens Walcott – Lower Cambrian only to ‘acrotretoid shell fabric of discrete apatitic (Botomian) Ella Island Formation, northeast Greenland lamellae connected by microscopic perpendicular (Holmer et al. 2002; Skovsted & Holmer 2003). columns’ (Williams et al. 1997, p. 427), and was • Cryptotreta? undosa (Moberg) – Lower Cambrian generally considered to represent a synapomorphic Kalmarsund Sandstone, Kalmarsund, Sweden character for the order Acrotretida (Holmer 1989). (Åhman & Martinsson 1965). In general, the typical acrotretoid columns are solid • Lingulellotreta malongensis (Rong) – Lower structures, around 1.5–5 μm in diameter, with thin Cambrian (Botomian–Toyonian), Ushbaspis limbata axial canals that penetrate the successive sets of and Redlichia chinensis–Kootenia gimmelfarbi compact laminae. Cusack et al. (1999) and Williams biozones, Ushbas River, Malyi Karatau, Kazakhstan & Cusack (1999) identified an acrotretoid columnar (Holmer et al. 2001). structure in the Lower Cambrian lingulid Lingulel- • Aboriginella denudata Koneva – Upper Cambrian, lotreta, indicating for the first time that this fabric Eolotagnostus scrobicularis beds (sample 1413-1), was more widespread than previously suspected. The Shabakty River, Malyi Karatau, Kazakhstan (Holmer cylindrical structures described by Holmer et al. et al. 2001). (2002) and Skovsted & Holmer (2003) from Mickwitzia • Vaculina obscura Koneva – Middle Cambrian, are identical with the acrotretoid columns (Fig. 1E, F). Glyptagnostus stolidotus Biozone (sample 1352- III), Kyrshabakty River, Malyi Karatau, Kazakhstan Micrina–Mickwitzia columnar structure (Holmer et al. 2001). • Mirilingula postuma Holmer, Popov, Koneva and Williams & Holmer (2002) identified a different, but Bassett – Lower Ordovician (Tremadocian; basically columnar fabric (referred to as ‘canals’) in sample 382 m), Batyrbai, Malyi Karatau, Kazakhstan the Lower Cambrian stem group brachiopod Micrina (Holmer et al. 2001). (Fig. 1A). In Micrina, the columns (generally around • Bistramia elegans von Hoek – Ordovician (Caradoc), 10 μm in diameter, but increasing in width with Cochabamba, El Cristo de la Concordia, Bolivia growth) are generally orthogonal to the shell surface, (Holmer & Popov 2000). with a well-defined, wide central canal penetrating successive compact laminae; the columns sometimes The illustrated specimens are deposited in the Museum open to the outer shell surface through a pore. An of Evolution – Palaeontology, Uppsala (PMU); identical type of columnar shell structure is also National Museum of Wales, Cardiff (NMW); found in species of the Lower Cambrian stem group Geological Museum of Copenhagen (MGUH); South brachiopod Mickwitzia, and although its shell has Australian Museum, Adelaide (SAM). been described generally as ‘punctate’ (e.g. Laurie 2000), Holmer et al. (2002) and Skovsted & Holmer (2003) showed that the ‘punctae’ of Mickwitzia actually constitute thicker columns (‘tubes’) that are Terminology of the columnar generally disposed orthogonally to the laminar shell, (sensu lato) shell fabric and some of them were open to the exterior through pores (Fig. 1D, E), from which it was hypothesized The main types of shell fabrics within extinct that setal structures may have emerged. Balthasar linguliform brachiopods have been described and (2004) proved that some of the orthogonal columns summarized mainly by Holmer (1989),