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A Critique of Graptolite Classification, and a Revision of the Suborders Diplograptina and Monograptina

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A Critique of Graptolite Classification, and a Revision of the Suborders Diplograptina and Monograptina Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 A critique of graptolite classification, and a revision of the suborders Diplograptina and Monograptina John Rigby SUMMARY: Three broad styles of modern graptolite classifications are identified, each being based on a framework laid down in the nineteenth century. Each style is critically reviewed with regard to its potential for the expression of presently know phyletic relationships. Following the style of classification adopted by Bulman (1970), family and subfamily taxa within the suborders Diplograptina and Monograptina are revised. Over the last century there have been many virgula, a hollow rod running down the centre of attempts to produce a satisfactory classification certain biserial forms and along the dorsal edge of the graptolites. Despite the large number of the monograptid stipe. Forms without the produced, most can be assigned to one of three virgula possessed a nema, thought by Mu in 1950 styles, each based on work done before 1900 by to be a solid rod. In fact this structure is now just two authors, Lapworth in 1880 and Frech in considered to be same as the virgula, and hence 1897. Their two methods of classification differed this basic division of Frech (1897) and the widely, and it is their differences in approach 'Chinese' classification is unsound. The Axono- which today give us such extremes and lack of lipa (forms without the virgula) comprised the conformity as far as graptolite classification is equivalent forms of the 'Western' system's Didy- concerned. The three styles, developed since mograptina, whilst the Axonophora (forms with 1950, are as follows: the virgula) comprised those forms included in 1 A 'Chinese' system, as typified by the work of Bulman's (1970) suborders Glossograptina, Dip- Mu (1950, 1973), Mu & Zhan (1966), and Yu lograptina, and Monograptina. Such a division & Fang (1979). also places too much emphasis upon just one 2 A 'Soviet' system, typified by the work of stage of graptolite evolution, viz. the evolution of Obut (1957, 1964). the diplograptid form from the didymograptid. 3 A 'Western' system, based upon the work of Mu & Zhan (1966), however, established a new Bulman (1955, 1963b, 1970), and Jaanusson suborder Axonocrypta, equal in rank to the (1960). Axonophora and Axonolipa, and effectively Obviously the early works have been modified, altering the content of these two taxa, as it but broadly the 'Chinese' authors have followed contains forms originally assigned to the Axono- the work of Frech (see Table 1), the 'Soviet' style lipa (e.g. the genera Cardiograptus, Phyllo- is an amalgamation of both Frech and Lapworth, graptus) as well as taxa originally placed in the whilst 'Western' authors have followed Lap- Axonophora (the family Cryptograptidae). This worth (see Table 2). is where the first major problem lies. The new suborder was established for genera which had more than one septum dividing the various series The classifications of thecae found in biserial, triserial and quadri- serial genera. In effect, in these genera each thecal The 'Chinese' classification series has its own bounding (dorsal) septum. This subordinal taxon was then subdivided into fami- As will be seen from Table 1, the Chinese lies on the basis that the Cryptograptidae con- classification from 1950 until 1965 comprised the tained monopleural forms, the Cardiograptidae two suborders Axonolipa and Axonophora, contained dipleural forms, whilst the Phyllograp- these forming the major taxa of the order Grap- tidae contained triserial and quadriserial forms. toloidea. Each suborder was simply divided into However, Jones & Rickards (1967) established a number of families, each seemingly held to be of that the axonophorus graptolite Diplograptus equal standing. Several major problems arise (now Cystograptus)penna also had two septa, because of this simple division, and indeed one 'secreted' by each thecal series, and enclosing because of the lack of certain other taxonomic between them the virgula (presumably the situa- levels. At the highest (subordinal) level, divisions tion of two series of thecae producing their own were made upon the presence or absence of the septa must also occur in Dicranograptus and From HUGHES, C. P. & RICKARDS,R. B. (eds), 1986, PalaeoecologyandBiostratigraphy of Graptolites, Geological Society Special Publication No. 20, pp. 1-12. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 TABLE 1. Graptolite classifications discussed in the text Frech 1897 Mu 1950 Bulman 1955 Obut 1957 Jaanusson 1960 Bulman 1963b Order Axonolipa Sub-order Axonolipa Class Graptolithina Class Graptoloidea Order Graptoloidea Order GraptoIoidea Family Dendrograptidi Family Anisograptidae Order Graptoloidea Order Axonolipa Sub-order Didymograptina Sub-order Didymograptina Family Dichograptidi Family Dichograptidae Family Dichograptidae Sub-order Dichograptina Family Dichograptidae Superfamily Dichograptacea s.f. Didymograptini Family Tetragraptidae Section Goniograpti Family Bryograptidae Family Nemagraptidae Family Dichograptidae s,f. Tetragraptini s.f, Tetragraptinae Section Temnograpti s.f. Bryograplinae Family Dicranograptidae Family Abrograptidae s.f. Phyllograptini s.f. Holograptinae Section Schizograpti s.f. Pterograplinae Family Abrograptidae Family Corynoididae Family Didymograptidae Section Dichograpti Family Dichograptidae Sub-order Corynoidina Superfamily Leptograptacea Order Axonophora s.f. Didymograptinae Section Tetragrapti Family Tetragraptidae Family Corynoididae Family Leptograptidae Family Diplograptidi s.f. Pterograptinae Section Didymograpti s.f. Holograptinae Sub-order Glossograptina Family Dicranograptidae Family Retiolitidi Family Azygograptidae Family Corynoididae s.f. Tetragraptinae Family Glossograptidae Sub-order Glossograptina Family Monograptidi Family Corynoididae Family Cryptograptidae Family Didymograptidac Sub-order Diplograptina Family Cryptograptidae Family Climacograptidi Family Leptograptidae Family Leptograptidae Family Azygograptidae Family Diplograptidae Family Glossograptidae s.f. Leptograptinae Family Dicranograptidae Family Corynograptidae Sub-order Diplograptina s.f. Pleurograptinae Family Diplograptidae Sub-Ordcr Leptograptina Family Diplograptidae Family Dicranograptidae s.f. Climacograptinae Family Dicranograptidae Family Lasiograptidae s.f. Diplograptinae Family Leptograptidae Family Retiolitidae Sub-order Axonophora s.f. Petalograptinae s.f. Archiretiolitinae Family Cryptograptidae Family Lasiograptidae Order Axonophora s.f. Plectograptinae Family Diplograptidae Family Retiolitidae Sub-order Diplograptina s.f. Retiolitinae Family Glossograptidae s.f. Plectograptinae Family Diplograptina Family Peiragraptidae Family Hallograptidae s.f. Retiolitinae s.f. Climacograptinae Family Dimorphograptidae Family Retiolitidae s.f. Archiretiolitinae s.f. Diplograptinae Sub-order Monograptina Family Dimorphograptidae Family Dimorphograptidae s.f. Cryptograptinae Family Monograptidae Family Monograptidae Family Monograptidae Family Glossograptidae Family Cyrtograptidae s.f. Monograptinae s.f.Monograplinae Family Retiolitidae s.f. Cyrtograptinae s.f. Cyrtograptinae s.f. Retiolitinae s.f. Plectograptinae Family Dimorphograptidae Sub-order Monograptina Family Monograptidae Family Diversograptidae Family Cyrtograptidae Family Linograptidae Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 TABLE [ (contd.) Obut 1964 Jaanusson 1965 Bulman 1970 Mu 1973 Yu & Fang 1979 Class Graptoloidea Class Graptolithina Order Graptoloidea Order Graptoloidea Order Axonolipa Order Graptoloidea Sub-order Axonolipa Sub-order Axonolipa Sub-order Dichograptina Sub-order Didymograptina Sub-order Didymograptina Family Dichograptidae Superfamily Multistipinacea Family Bryograptidae Superfamily Dichograptacea Family Dichograptidae Family Holograptidae Family Loganograptidae s.f. Bryograptinae Family Dichograptidae Section Goniograpti Family Pterograptidae Family Dichograptidae s.f. Pterograptinae Family Abrograptidae Section Temnograpti Family Tetragraptidae Family Goniograptidae Family Dichograptidae Family Leptograptidae Section Schizograpti Family Didymograptidae Family Holograptidae Family Tetragraptidae Superfamily Dicranograptacea Section Dichograpti Family Azygograptidae Family Pterograptidae s.f. Holograptinae Family Sinograptidae Section Tetragrapti Family Corynoididae Family Prokinnegraptidae s.f. Tetragraptinae Family Dicranograptidae Section Didymograpti Family Sinograptidae Family Tetragraptidae Family Phyllograptidae Superfamily Corynoididacea Family Sinograptidae Family Kinnegraptidae Superfamily Paucistipinacea Family Didymograptidae Family Corynoididae Family Abrograptidae Family Atopograptidae Family Didymograptidae Family Sinograptidae Family Corynoididae Family Abrograptidae Family Kalpinograptidae Family Abrograptidae Family Nemagraptidae Family Leptograptidae Family Sinograptidae Family Azygograptidae Family Dicranograptidae s.f. Leptograptinae Family Kinnegraptidae Family Corynoididae Sub-order Glossograptina s.f. Pleurograptinae Family Atopograptidae c~ Sub-order Leptograptina Family Glossograptidae Family Dicranograptidae Family Abrograptidae Family Dicranograptidae Family Cryptograptidae s.f. Dicranograptinae Family Leptograptidae Family Leptograptidae Sub-order Diplograptina s.f. Tangyagraptinae s.f. Leptograptinae Family Diplograptidae s.f. Pleurograptinae Order Axonophora Family Lasiograptidae Sub-order Axonocrypta Family Dicranograptidae
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