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Stratigraphic Distribution and Suggested Evolution of Dendroid Graptolites from the Silurian of Eastern Australia

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Stratigraphic Distribution and Suggested Evolution of Dendroid Graptolites from the Silurian of Eastern Australia University of Wollongong Research Online Faculty of Science - Papers (Archive) Faculty of Science, Medicine and Health 1-1-2010 Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia Barrie Rickards University of Cambridge Anthony Wright University of Wollongong, [email protected] Follow this and additional works at: https://ro.uow.edu.au/scipapers Part of the Life Sciences Commons, Physical Sciences and Mathematics Commons, and the Social and Behavioral Sciences Commons Recommended Citation Rickards, Barrie and Wright, Anthony: Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia 2010, 177-190. https://ro.uow.edu.au/scipapers/634 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: [email protected] Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia Abstract Five evolutionary lineages are proposed for Silurian species of the benthic dendroid graptolite genus Dictyonema, based largely on the exceptional eastern Australian records of the genus, comprising at least 25 species. These are: A, the delicatulum lineage with bifurcating ventral autothecal apertural spines; B, the paululum lineage with single ventral apertural spines or processes; C, the elegans lineage with isolated thecal apertures ± processes; D, the sherrardae lineage with dorsal apertural processes; and E, the venustum lineage with simple autothecal apertures. Brief comments are also made on other dendroid genera occurring in Australian strata, namely: Acanthograptus, Koremagraptus, Callograptus, Dendrograptus, Stelechocladia, Thallograptus and Palaeodictyota. Other non-graptoloid benthic hemichordates also listed are the tuboids Galaeograptus, Reticulograptus and Cyclograptus and the rhabdopleuran ?Rhabdopleura. Age ranges of all the species attributable to all of the above genera are tabulated. Keywords Silurian, Australian dendroids, graptolites, Dictyonema, lineages, GeoQUEST Disciplines Life Sciences | Physical Sciences and Mathematics | Social and Behavioral Sciences Publication Details Rickards, B. & Wright, A. (2010). Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia. Memoirs of the Association of Australasian Palaeontologists, 39 177-190. This journal article is available at Research Online: https://ro.uow.edu.au/scipapers/634 Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia BARRIE RICKARDS† & ANTHONY WRIGHT RICKARDS, R.B.† & WRIGHT, A.J., 2010:10:29. Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia. Memoirs of the Association of Australasian Palaeontologists 39, 177-190. ISSN 0810-8889. Five evolutionary lineages are proposed for Silurian species of the benthic dendroid graptolite genus Dictyonema, based largely on the exceptional eastern Australian records of the genus, comprising at least 25 species. These are: A, the delicatulum lineage with bifurcating ventral autothecal apertural spines; B, the paululum lineage with single ventral apertural spines or processes; C, the elegans lineage with isolated thecal apertures ± processes; D, the sherrardae lineage with dorsal apertural processes; and E, the venustum lineage with simple autothecal apertures. Brief comments are also made on other dendroid genera occurring in Australian strata, namely: Acanthograptus, Koremagraptus, Callograptus, Dendrograptus, Stelechocladia, Thallograptus and Palaeodictyota. Other non-graptoloid benthic hemichordates also listed are the tuboids Galaeograptus, Reticulograptus and Cyclograptus and the rhabdopleuran ?Rhabdopleura. Age ranges of all the species attributable to all of the above genera are tabulated. R.B. Rickards (deceased November 5, 2009), Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ; and Emmanuel College, Cambridge CB2 3AP, UK; A.J. Wright ([email protected]), School of Earth and Environmental Sciences, University of Wollongong, NSW 2522, Australia. Received 9 June 2010. Keywords: Silurian, Australian dendroids, graptolites, Dictyonema, lineages. RESEARCH on Australian Silurian graptolites particularly difficult because the rhabdosomal has revealed that benthic dendroid graptolites are stipes are often narrow and the constituent much more common than previously supposed thecae small and thread-like. Furthermore, (e.g. Rickards et al. 2003), and that they exhibit many colonies are preserved with the thecae considerable diversity, particularly in the case facing normal to bedding (either upwards or of Dictyonema J. Hall, 1851. Llandovery (early downwards), and hence the stipe may be seen Silurian) strata in Australia have yielded probably in dorsoventral view obscuring the autothecal the most diverse dendroid fauna yet known, profile as well as the apertural processes. As a especially in the upper part of the series. result, dendroids are often described in general At least 25 Silurian species of Dictyonema terms based on the overall shape and colony have been identified (Rickardset al. 1995, 2003, dimensions: whether it is conical or flabellate; 2005, 2009; Rickards & Jell 2002; Rickards & small or large; or has a holdfast or ‘roots’. The Wright 1997, 1999, 2001), and their evolution is shape of the colony, whether conical, flabellate discussed below. All these records, apart from the or of some other form, is itself often difficult to Queensland graptolites documented by Rickards determine and there is no certain information as & Jell (2002), are from New South Wales; no to whether or not rhabdosomal form is a species- Victorian dendroids were mentioned by Rickards specific character. Many species of Dictyonema & Sandford (1998) but some were described by have quite similar combinations of these attributes Harris & Thomas (1948). No Australian Silurian and to distinguish them – to identify them – it dendroids are known outside Victoria, Queensland is necessary to measure more closely stipe and and New South Wales. dissepimental dimensions and, if possible, to For general information and important reviews identify the nature of the autothecae. of Australian Silurian biostratigraphy the reader In this paper we rely heavily on the nature of is directed to Pickett et al. (2001), Talent et al. the autothecae, coupled with other biocharacters (2003) and Strusz (2007). such as stipe spacing; lateral and dorsoventral stipe Preservation of graptolites often poses width; nature, size and frequency of dissepiments; problems, and dendroid graptolites can be nature of interstipe spaces; branching patterns; 178 AAP Memoir 39 (2010) A delicatulum lineage: species with bifurcating ventral, apertural processes or spines D. delicatulum delicatulum Lapworth, 1881: late Llandovery D. elongatum elongatum Bouček, 1957: Přídolí D. e. subelongatum Rickards et al., 1995: ?Llandovery to Ludlow D. delicatulum sp. cf. D.delicatulum Lapworth, 1881: late Llandovery D. regulare Bouček, 1957 (+ D. sp. of Rickards et al., 1995) nilssoni Zone (Ludlow) D. d. barnbyensis Rickards & Wright, 1997: late Ludlow (cf. is Přídolí) D. sp. A, Rickards & Wright, 1997: late Ludlow D. sp. 1, Rickards et al., 2003: early griestoniensis Zone (Llandovery) D. sp., Rickards et al., 1995: nilssoni Zone (Ludlow) B paululum lineage: species with single ventral, apertural spatula‐like spine or process D. paululum paululum Bulman, 1928: turriculatus Zone (Llandovery) D. p. hanoverense Rickards et al., 2003: parultimis Zone (Přídolí) D. p. australis Rickards & Jell, 2002: early crenulata Zone to griestoniensis Zone (Llandovery) D. zalasiewiczi Rickards et al., 2009: turriculatus Zone (Llandovery) C elegans lineage: species with both ventral and dorsal apertural margins isolated. D. elegans Bulman, 1928: late Wenlock to Ludlow. D. williamsae Rickards et al., 2003: early griestoniensis Zone (Llandovery) D. warrisi Rickards et al., 2003: early griestoniensis Zone (Llandovery) D sherrardae lineage: species with pronounced dorsal apertural processes D. sherrardae sherrardae Rickards et al., 1995: nilssoni Zone to late Ludlow D. s. mumbilensis Rickards & Wright, 1997; late Ludlow D. jenkinsi Rickards et al., 2003: early griestoniensis Zone (Llandovery) D. sp. nov.: riccartonensis Zone* E venustum lineage: species with simple autothecal apertures or short denticles. D. venustum Lapworth, 1881: turriculatus to griestoniensis Zones D. g. krafti Rickards & Wright, 1997: late Ludlow D. favosum Sherrard, 1956: nilssoni Zone (Ludlow) D. subtile Bouček, 1957: Ludlow D. cf. subtile Bouček, 1957: nilssoni Zone (Ludlow) D. falciferum Bulman, 1928: crispus to griestoniensis Zones (Llandovery) D. muirae Rickards et al., 2003: turriculatus to griestoniensis Zones (Llandovery) D. sp. cf. D. corrugatellum Lapworth, 1881: turriculatus to upper riccartonensis Zone* Table 1. List of Australian Dictyonema species in autothecal groupings and with age attributions, based on Australian and non-Australian material. and (occasionally) bithecal type. In Table 1 we list and, where necessary, draw particular attention to the species of Dictyonema relevant to the lineages these taxa in the figures and text. we describe below, together with a summary of the autothecal type; the known age of each species THECAL TYPES (usually dated with graptoloids);
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