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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 Sub-order Diplograptina Family Dicaulograptidae Family Phyllograptidae s.f. Dicranograptinae Family Diplograptidae Family Peiragraptidae Family Cardiograptidae s.f. Tangyagraptinae s.f. Climacograptinae Mu & Zhan 1966 Family Retiolitidae Family Cryptograptidae Family Azygograptidae s.f. Diplograptinae s.f. Retiolitinae Family Corynoididae s.f. Petalograptinae Sub-order Axonocrypta s.f. Archiretiolitinae Sub-order Axonophora Family Cryptograptidae Family Phyllograptidae s.f. Plectograptinae Family Diplograptidae Sub-order Axonocrypta Family Glossograptidae Family Cardiograptidae Family Dimorphograptidae Family Lasiograptidae Superfamily Dipleurinacea Family Hallograptidae Family Cryptograptidae Sub-order Monograptina Family Reteograptidae Family Phyllograptidae Family Retiolitidae Family Monograptidae Family Archiretiolitidae Family Cardiograptidae s.f. Archiretiolitinae Family Cyrtograptidae Family Retiolitidae Superfamily Monopleurinacea s.f. Retiolitinae s.f. Cyrtograptinae Family Plectograptidae Family Cryptograptidae s.f. Plectograptinae s.f. Linograptinae Family Peiragraptidae Family Dimorphograptidae Family Dimorphograptidae Sub-order Axonophora Sub-order Monograptina Family Monograptidae Superfamily Biseriacea Family Monograptidae s.f, Monograptinae Family Diplograptidae Family Diversograptidae s.f. Cyrtograptinae Family Lasiograptidae Family Cyrtograptidae Family Reteograptidae Family Linograptidae Family Archiretiolitidae Family Retiolitidae Family Plectograptidae Superfamily Semibiseriacea Family Peiragraptidae Family Dimorphograptidae Superfamily Uniseriacea Family Monograptidae s.f. Monograptinae s.f. Cyrtograptinae Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

TAaLE 2. A comparison of the classifications of Lapworth 1879-1880 and Bulman 1970

Lapworth 1879-1880 Bulman treatise 1970

! Section Monograpta 1 Sub-order Monograptina Family Monograptidae Family Monograptidae --* Sub-family Monograptinae Genus Monograptus Genus Monograptus Genus Rastrites Genus Rastrites -- Sub-family Cyrtograptinae Genus Cyrtograptus Genus Cyrtograptus

2 Section Diplograpta Sub-order Diplograptina Family Diplograptidae Family Diplograptidae Genus Climacograptus Genus Climacograptus Genus Cryptograptus Genus Diplograptus Genus Diplograptus s.gen. Cephalograptus Genus Cephalograptus Family Dimorphograptidae s.gen. Dimorphograptus Genus Dimorphograptus Family Lasiograptidae Family Lasiograptidae Genus Retiograptus (nom. null) Genus Glossograptus Genus Hallograptus Genus Hallograptus Genus Lasiograptus Genus Lasiograptus Genus Gymnograptus Family Retiolitidae Family Retiolitidae Sub-family Retiolitinae Genus Retiolites Genus Retiolites Sub-family Archiretiolitinae Genus Clathrograptus Genus Reteograptus Genus Trigonograptus (unrecog. genus) Genus Gymnograptus

3 Section Didymograpta Sub-order Didymograptina Family Dichograptidae Family Dichograptidae Genus Didymograptus Genus Didymograptus Genus Tetragraptus Genus Tetragraptus Genus Dichograptus Genus Dichograptus Genus Loganograptus Genus Loganograptus Genus Clonograptus? Genus Clematograptus Genus Amphigraptus Genus Temnograptus Genus Temnograptus Genus Trichograptus Genus Trichograptus Genus Schizograptus Genus Schizograptus Genus Goniograptus Genus Goniograptus Genus Bryograptus Genus Bryograptus Genus Azygograptus Family Phyllograptidae Genus Phyllograptus Genus Phyllograptus

4 Section Dicellograpta Family Dicellograptidae Family Dicranograptidae Genus Dicellograptus Genus Dicellograptus Genus Dicranograptus Genus Dicranograptus Family Leptograptidae Family Nemagraptidae Genus Amphigraptus Genus Amphigraptus Genus Pleurograptus Genus Pleurograptus Genus Leptograptus Genus Leptograptus Genus Coeno. =Amphi. = Climato. 4 Sub-order Glossograptina Family Glossograptidae Genus Glossograptus Family Cryptograptidae Genus Cryptograptus

* A dash so --, indicates the absence of a taxon in one classification, whilst present in the other. t Clonograptus is now placed in the Dendroidea, family Anisograpti- dae. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

Graptolite classification 5 Oncograptus, i.e. genera which are initially bi- as a taxon than, for example,the retiolitids, even serial but later become uniserial, otherwise one though the latter are considered to represent only series of thecae would be open dorsally). As the a certain stage of elaboration of the diplograptid 'Chinese' classification regards Cystograptus to grade, whilst the monograptids in the 'Western' be an axonophorous genus, and if all other system represent a grade unto themselves, thus axonophorous biserial graptolites are considered equalling the diplograptids as a whole. to be of a similar structure, then the Axonocrypta One recent Chinese classification by Yu & has been based on a single criterion not unique to Fang (1979) does, however, differ from those that taxon, and hence should not stand as previously published (see Table 1). These authors presently defined. again utilized the suborders Axonophora, Thus, all three sub-orders of the 'Chinese' Axonolipa and Axonocrypta, but these were classification are based upon the presence or divided into seven superfamilies. The taxon absence of a single character, as shown in the Axonolipa was divided into the Multistipinacea simple key chart shown below: and Paucistipinacea, much in the same way that (1)Does the graptolite have more than one Bulman (1970) divided the family Dichograpti- septum? dae into multiramous and pauciramous forms-- Yes = Axonocrypta, No = go on to (2) unfortunately Yu & Fang (1979) include within (2) Does the graptolite have a virgula? the Paucistipinacea several families (including the Yes = Axonophora, No = Axonolipa. Sinograptidae and Leptograptidae) which con- Hence Chinese workers must place minor taxa tain genera with just as many (if not more) stipes into one of these three suborders before any as those within the Multistipinacea. Thus the attempt is made to look at phyletic relationships. terms are not as self-explanatory as they would Such dependence on one character doubtless seem, and suggest that superfamily taxa based on leads to great artificial constraints upon the such criteria are not viable. The Axonocrypta was classification. For example, the Cryptograptidae, divided into the Dipleurinacea and Monopleur- having two septa, are placed in the Axonocrypta, inacea, and so the monopleural condition, repre- despite having a virgula that could indicate a sented by the suborder Glossograptina in the closer affinity to forms outside that suborder than 'Western' classification, seems to be growing in to those within it (note that no genera within the importance in the 'Chinese' system. families Cardiograptidae or Phyllograptidae pos- The remaining suborder, the Axonophora, sess a known virgula), or indeed could indicate comprises three superfamilies, the Biseriacea, the that by having both a virgula and two septa it Semibiseriacea, and the Uniseriacea. These do at should be separated from both the other first sight seem to be good divisions, allowing for suborders. the first time in a 'Chinese' classification for the Such a system could also lead to incorrect monograptids to be separated from and raised in assumptions being made--the possession of both rank equal to the whole of the diplograptid grade. 'essential' characters could lead one to deduce However, the production of a superfamily Semi- that the Cryptograptidae represent an interme- biseriacea for the families Dimorphograptidae diate between the Axonocrypta and the Axono- and Peiragraptidae indicates the key nature of phora. A study of the proximal development led these divisions--to consider two such families as Jaanusson (1960) to conclude that there is no equal to the rest of the diplograptids and the intermediate stage between the 'bifidus' develop- monograptids contradicts the known facts. Again ment of the former and the 'diplograptid' deve- it would seem that these taxa are based on just one lopment-thus it seems that the virgula deve- character, in this case the stipe seriality. It should loped on two separate occasions, and hence the be noted that Mu (1980) suggested a new termino- two groups should be given equal ranking in logy for the superfamily taxa in this classification, separate taxa. but otherwise the classification remained This poor choice of subordinal characters unchanged. effectively means that the familial taxa are the The family taxa of these classifications are first groupings that could be phyletically viable. based on several features--mainly following Mu As the suborders in the 'Western' and 'Soviet' (1950) and ultimately Frech (1897). Basically the classifications are postulated phyletic groupings Axonolipa is divided into families established in themselves this problem does not arise (even upon how many primary stipes the included though Axonolipa and Axonophora are utilized forms possess, these being divided into subfami- in the latter they are ranked at ordinal level, thus lies depending upon whether lateral branching is releasing the subordinal taxa for postulated phy- present. This obviously does not apply to families letic groups). In 'Chinese' classifications the result such as the Corynoididae, where the included is that the monograptids are no more 'important' forms are unusual. Again, dividing a family Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

J. Rigby

internally by using branching assumes that one though in flattened material we know that lateral style developed from the other by loss or acqui- features especially are 'lost', and all we see in sition of branches; this certainly need not be the silhouette is a very rough approximation of true case, and so once more leads to unnatural thecal shape. Thus when species assigned to such groupings. For example, the family Tetragrapti- form genera become available as isolated material dae is divided into the subfamilies Tetragraptinae they are often found to exhibit widely different (without branches) and Holograptinae (with morphology from the original diagnosis and from lateral branches). Such a division is no more than each other, e.g. see Sudbury (1958). In such a a simple identification system, and takes no situation, not only have such species to be account of phylogeny. removed from that genus, but the generic diag- Families within the Axonophora are estab- nosis must be amended. Genera based on rhabdo- lished upon different criteria. The Monograpti- somal form are equally unsatisfactory, as forms dae, Dimorphograptidae, Peiragraptidae, and the with similar rhabdosome form can have widely three retiolitid families are recognizable by their different thecal form--further problems arise own unique features, the first being totally uniser- when specimens are fragmented, and so overall ial, the second uni-biserial, the third initially form is lost. Such a method of establishing genera biserial and immediately uniserial, whilst the is totally different from that used in the 'Western' latter three are composed of a meshwork. Again, classification, where most forms remain in the however, straightforward appearance has played form genus Monograptus until they are suffi- a role in the erection of taxa. Dimorphograptid ciently well known morphologically and phyleti- genera certainly evolved from various diplograp- cally to assign them generic status. There seems tid ancestors, and at best can only be regarded as little point in establishing genera on poorly diplograptids affected by a time-restricted known material only to have to emend or remove trend--that they should be afforded familial rank it at a later date. equal to the Diplograptidae is unacceptable. The Peiragraptidae also developed from a diplograp- The 'Soviet' classification tid ancestor, see Strachan (1954), again restricted in time (and also in occurrence), and should not In a similar way to Chinese authors, Obut (1957, be given familial status. Yu & Fang (1979) placed 1964) initially divides the classification into the these two families together in the superfamily taxa Axonolipa and Axonophora (note that Semibiseriacea, despite the wide chronological Russian authors do not utilize the Axonocrypta). difference between their occurrence and their However, these taxa were ranked at an ordinal dubious taxonomic status. Unfortunately, most level, and as Obut utilized much the same familial authors to date have assigned these taxa familial taxa as Mu (1950) (with the addition of newly rank. erected taxa), this higher ranking allows interme- The other families of the Axonophora (viz. the diate taxa to be included, and this has been done Diplograptidae, Lasiograptidae, and Reteograp- by introducing two suborders into each order. tidae) are somewhat similar to each other. Reteo- With this new arrangement, 'groupings' of fami- graptidae are identified upon a reduced periderm lies can be made, placing together those with with clathria (included by Bulman (1970) within similar structure or known affinity in the same the Retiolitidae, subfamily Archiretiolitinae), suborder. This ensures that such known, common whilst the Lasiograptidae are distinguished from similarities between forms is not lost by an overall the Diplograptidae by their thecal shape, the grouping with other different taxa as occurs in the somewhat reduced periderm in some genera, early 'Chinese' and 'Western' classification-- strengthening lists, and the presence of a lacinia. i.e. Mu (1950) and Bulman (1955). For example, It should be noted that none of these characters Obut (1957) uses the suborders Diplograptina by itself seems worthy of affording this taxon and Monograptina, the diplograptid and mono- familial status. One major difference between graptid grades obviously separated, even though 'Chinese' and 'Western' workers is in the erection each consists of several families. In the 1950 and acceptance by the former of many mono- classification of Mu, however, the monograptids graptid genera compared to the relative conserva- are only assigned familial rank, and so are tism of the latter. Most of these genera are based immediately equalled by each diplograptid upon flattened material, and thus rely upon the family. Hence in Mu's and Bulman's earlier silhouettes of the theca and rhabdosomal form. systems the monograptids effectively lose status. Despite the fact that there is a tremendous range It is strange, however, that once these of thecal form within the monograptids, attempts suborders were introduced by Obut it was deemed are made to assign thecal form to one of just a few necessary to continue using the taxa Axonolipa styles (e.g. triangulate, lobed, hooked, spinose), and Axonophora. Although their constraints on Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

Graptolite classification postulated phyletic relationships are somewhat order of the class Graptolithina, so as to conform offset by the introduction of the suborders, their with the other taxa of the subphylum Stomochor- continued presence does imply that the suborders data, and allow a unified approach to the classifi- included in each should be regarded as more cation of not only the graptolites but other related closely allied to each other than to those in the groups. Although the same approach was other order. Although Obut (1957) considered adopted by Bulman in 1970, the graptolites had that the diplograptids were descended from the by then been assigned to the phylum Hemichor- Dichograptidae, and that the early monograptids data. In 1955 Bulman simply divided the Grapto- evolved from the diplograptids, he still main- loidea into a series of families and subfamilies. tained division into Axonolipa and Axonophora. Thus no taxon had priority over any other, and Without this initial division this classification although some phyletic relationships were doubt- would not have differed too greatly from that of less known they could not be expressed in such a Bulman (1970) (although 'Soviet' authors do not system. Indeed in this respect this early Treatise utilize Jaanusson's (1960) suborder Glossograp- Volume was no more capable of expressing tina, widely used in 'Western' classifications). affinity than was the classification of Mu (1950). The suborders of Obut were based upon several The various 'grades' were lost completely--e.g. features, such as proximal end development, the diplograptid grade was represented by four thecal type, branching, and presence of a nema or isolated families, and had no separate entity as virgula. Thus there is a much broader base upon such. which to establish taxa, rather than the single In 1960, Jaanusson became the first of the character so often used by other authors. recent Western workers to adopt the division of As to the utilization of familial taxa, in the the order Graptoloidea into four suborders, Axonolipa Obut mainly uses those of Mu (1950), without the constraints of Frech's taxa Axono- together with several newly established taxa. The lipa and Axonophora. His subsorder Didymo- families placed by Jaanusson (1960) in his graptina, which roughly corresponds in content suborder Glossograptina were retained by Obut to Obut's order Axonolipa (except for the in the suborder Diplograptina, and thus the former's separation of the Corynoidina), con- monopleural condition of the Glossograptidae tains the comprehensive family Dichograptidae, and Cryptograptidae, held to be so important by the families Nemagraptidae (replacing the family Jaanusson, was not confined to a single taxon. Leptograptidae of Mu (1950), Bulman (1955), Certain Soviet workers also follow the and Obut (1957), and over which it has taxonomic 'Chinese' practice of accepting (and themselves priority), Dicranograptidae, and Abrograptidae. establishing) new monograptid genera based Thus the suborder Leptograptina of Obut (1957) upon flattened, deformed, and imperfectly known is abandoned. Jaanusson established a separate material. Thus redefinition of three 'Russian' suborder Corynoidina on the basis that the monograptid genera (Pribylograptus, Lagaro- included genera were unique amongst the grapto- graptus, and Coronograptus) was necessary once loids, and possessed certain features indicative of more detailed information became available a dendroid ancestor. Later work by Bulman (Rickards 1976). (1963b) and Skevington (1965) suggested other- wise. Probably Jaanusson's most revolutionary act was to raise the glossograptids to subordinal The 'Western' classification rank. Although Hadding (19 i 5) had shown these Bulman's (1955) classification differed consider- forms to be monopleural, they had always been ably from those of Mu (1950) and Obut (1957), included in the classification at familial level, mainly in his rejection of the taxa Axonolipa and equal in rank to the diplograptid families. How- Axonophora. Presumably this was for the rea- ever, Jaanusson had raised the diplograptids to sons he gave in 1938, namely that no hard and fast subordinal level, and did likewise to the glosso- line can be drawn between them, based on the graptids on the basis that although both groups knowledge that the nema and virgula are struc- had a virgula, the proximal development of each turally the same, and hence the presence of an axis precluded the development of one group from the (which is what Frech's orders refer to) merely other. Thus the virgula had evolved in two reflects the degree of scandency achieved by the different groups, each of which had to be afforded rhabdosome, coupled with a progressive reduc- the same taxonomic rank. tion in the number of stipes. By taking this At the familial and subfamilial level, Jaanusson attitude Bulman was able to avoid the limitations erected the subfamily Peiragraptinae for that and false phyletic associations imposed by such genus which is seemingly a development from the poorly conceived taxa. diplograptids, and indeed this reflects its taxo- The taxon Graptoloidea was ranked as an nomic position better than the familial status Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

J. Rigby

afforded by Bulman (1970). Jaanusson also and dicellograptids all resumed equal familial reduced the lasiograptids to subfamily rank, on status within the Didymograptina, and thus their the basis that the known proximal development various relationships (shown by Bulman and morphological characteristics did not war- (1963a,b) and Jaanusson (1965)) are not rant full family rank--again this author would expressed here. Otherwise this 1970 work is much support such a view. The major difference at this the same as that of 1963b, except for the reintro- level, however, from the work of Obut, is the duction of the sections of the family Dichograpti- inclusion of the monograptids as only a family dae utilized in Bulman (1955). The term 'section' within the suborder Diplograptina, stating that is presumably used to aid the division of the the separation of the diplograptids and mono- family without implying any phyletic affinity graptids into such widely separated taxa is out of between the included genera. Thus the common proportion. ancestorship of these forms is recognized by their Bulman's 1963b classification did not follow inclusion within the family taxon, and yet avoids his 1955 format. He too employed suborders, but raising each section to a familial level in itself, as continued to ignore Frech's taxa. The Leptograp- happens in the 'Chinese' and 'Soviet' classifica- tina and Corynoidina of Obut and Jaanusson, tions. respectively, were incorporated within the taxon Didymograptina, although the former taxon was retained as a superfamily. Bulman did not agree Conclusions that the Corynoidina warranted such high rank- ing (because he thought its probable derivation From the reviews of each of the three styles of was from a true graptoloid), and thus afforded the classification identified it would seem to the taxon family rank. He did, however, recognize author that the 'Western' style represents the best Jaanusson's suborder Glossograptina (and again approach to the problem available at the in 1970). The use of such suborders meant that the moment. In the main it allows for good correla- classification was far more able to express rela- tion between and within groups as regards pos- tionships than was his 1955 classification. The sible phylogeny--i.e, it has the potential to be exclusion of Frech's (1897) taxa means that the highly expressive. The 'Chinese' and 'Soviet' suborders are quite independent of each other, systems (especially the former) tend to rely upon thus avoiding any two being forced together with single characters for the erection of taxa, which the resulting phyletic implications. are often ill conceived and more of an identifica- In utilizing the rank of superfamily in his 1963b tory rather than a phyletically oriented grouping. work Bulman started a trend ultimately followed by Jaanusson (1965) and Bou6ek (1968). It should A revised classification of the be noted that Jaanusson (1965) considered the sub-orders Diplograptina and term Dicranograptacea to have taxonomic prior- ity over Leptograptacea (one of Bulman's super- Monograptina families). Furthermore, on the grounds of (then) Each suborder is discussed in turn, with the newly postulated phyletic evidence he considered author's revised classification illustrated first, and that the dicranograptids had derived from sino- a following explanation of the differences graptid ancestors (the latter placed by Bulman between this and the classification of Bulman (1963b) in the Dichograptidae); thus, according (1970). to Jaanusson, the superfamilies used should have been the Dicranograptacea (comprising the sino- Suborder Diplograptina (Lapworth 1880; amend. graptids and dicranograptids), and the Dicho- Bulman 1970) graptacea (comprising the dichograptids and leptograptids). In a review of the taxonomic The author's classification implications of prothecal folds, Bulman (1969) thought a dicellograptid ancestor within the sinograptids was unlikely. Nonetheless, this does Family Diplograptidae (Lapworth 1873) not affect the fact that using the superfamily Diplograptid genera: taxon is essentially good policy in that the more Diplograptus, Amplexograptus, taxa there are, the better chance there is of Cephalograptus, Climaeograptus, illustrating detailed relationships. Cystograptus, Glyptograptus, G. This system of superfamilies was however ( Pseudoglyptograptus), Orthograptus, abandoned in Bulman's (1970) Treatise Volume. Petalograptus, P. ( Pseudoclimacograptus ) , The leptograptids were included with the Nema- P. (Metaclimacograptus), P. graptidae, and the dichograptids, sinograptids, ( Clinoelimacograptus ) Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

Graptolite classification

Dimorphograptid genera: tricted to several zones within the Llandovery Akidograptus, Dirnorphograptus, (the acuminatus to convolutus Zones). There is no Rhapidograptus reason that these forms should be afforded Peiragraptid genera: anything more than generic rank. When it was Peiragraptus believed that these dimorphograptid forms repre- sented an intermediate between the diplograptid Family Lasiograptidae (Lapworth 1879) and monograptid grades it was quite reasonable Genera: for them to be ranked more highly. Lasiograptus, Gymnograptus, Hallograptus, lb. Peiragraptidae." most of the points men- Neurograptus, Nymphograptus, tioned above apply equally well to this mono- Dicaulograptus generic taxon. The family was established for the genus Peiragraptus Strachan, being considered by Family Retiolitidae (Lapworth 1873) that author to have developed from a diplograp- Subfamily Retiolitinae (Lapworth 1873) tid ancestor. It is at present known from just one Genera: locality, and although no definite ancestor can be Retiolites, Arachniograptus, illustrated, it seems unnecessary to afford family Pseudoplegmatograptus, rank to a form which can at best be regarded as an Sinostomatograptus, Stomatograptus isolated variation of the diplograptid grade, and Subfamily Plectograptinae (Bou6ek & M/inch which is obviously a diplograptid in which the 1952) thecae of the second series have failed to develop Genera: due to the suppression of th22--such a condition Plectograptus, Gothograptus, Holoretiolites, would require only a relatively simple modifica- Paraplectograptus, Spinograptus tion. The possibility ofa lasiograptid ancestor has not been ruled out, but should this be held as an Family Archiretiolitidae (Bulman 1955) obstruction to placing this genus within the Genera: Diplograptidae, it would seem to the author Archiretiolites, Orthoretiolites, better to place the taxon incertae sedis rather than Phormograptus, Pipiograptus, raise it to a level which throws the classification Plegmatograptus, Reteograptus out of balance. 2. The Lasiograptidae. There is considerable doubt as to whether the lasiograptid genera Differences from Bulman's 1970 class~cation should be afforded separate familial ranking from the Diplograptidae, to which they are at present 1. The Diplograptidae. This family is now taxonomically equal. Those lasiograptids pre- enlarged to incorporate genera from the aban- served well enough to show proximal develop- doned families Dimorphograptidae and Peira- ment are not radically different from forms graptidae. The reasoning against the continuing included within the Diplograptidae (see Rickards use of these families is as follows: & Bulman 1965). They do possess well-developed ta. Dimorphograptidae: Figure 1 indicates the lists supporting a reduced periderm, but other wide range of origins postulated for the dimor- details, such as thecal shape, surely only warrant phograptid genera and species. distinction of at most generic level, and the As illustrated in Fig. 1 the three dimorphograp- presence of a lacinia (again in only certain tid genera represent a trend of proximal end lasiograptid genera) cannot be accepted as indica- protraction and loss of early thecae in otherwise tive of family rank. normal diplograptid genera and species, res- The lasiograptids could conceivably be consi-

FIo. 1. Range of origins of dimorphograptid genera and species

Orthograptus? Dimorphograptus Rhapidograptus Akidograptus Dirnorphograptus acuminatus spp. toernqu&ti ascensus elongatos I Distally indistinguishable from I Orthograptus sp. Glyptograptus climacograptid. Glyptograptus sp. persculptus s.sp. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

IO J. Rigby

dered worthy of familial rank if they could be together with the subfamilies Retiolitinae and shown to have developed from the diplograptids Plectograptinae, constituted the family Retioliti- as a single coherent group. Further problems dae. A study of the stratigraphic occurrence of arise because of the poorly known nature of these taxa, however, shows that the genera of the certain genera assigned to the Lasiograptidae, Archiretiolitinae died out in the upper Ordovi- such as Nymphograptus, Neurograptus, and to a clan, with no retiolitids being found from the certain extent Hallograptus, and it would appear extraordinarius to the Silurian magnus Zone that normal practice is to identify the genus and inclusive, after which we have the occurrence of then by convention alone place it within the members of the Retiolitinae. Although the two Lasiograptidae. However, as far as thecal mor- subfamilies have obvious morphological similari- phology and the presence of a lacinia are con- ties, it is impossible to accept that the family as it cerned, the group does seem fairly coherent, and stands is anything but polyphyletic. Because of so for the present the author retains this family the large stratigraphic interval between the disap- taxon until more is known of the detailed rela- pearance of the archiretiolitids and the appear- tionships between this group and the Diplograp- ance of the retiolitids, the former are considered tidae. by the author to be worthy of a rank equal to the 3. The Dicaulograptidae. This family has been major taxon of the later retiolitids, at present a abandoned by the author, and the single genus familial level. This attempts to provide a more included within the Lasiograptidae. The taxon phyletic rather than form-orientated classifica- was established by Bulman (1970) for the genus tion. Family rank may in fact be too high for Dicaulograptus (type species Lasiograptus hys- either group of retiolitids when comparing them trix, see Rickards & Bulman 1965). This species with the Diplograptidae. was given generic rank by these two authors 5. The Retiolitidae. As stated above, the two because of the uniqueness of its thecae, both in Silurian retiolitid subfamilies were derived com- degree and nature of the introversion of the pletely separately from the Ordovician forms, and apertural margin, and the nature of the thecal indeed must have developed from members of the spines; indeed the thecae were likened more to Diplograptidae (as opposed to a postulated lasio- forms within the Dicranograptidae than within graptid ancester for certain archiretiolitid genera the Lasiograptidae. Furthermore, a study of the --see Strachan, 1976). Although the Silurian proximal development of representatives of the retiolitids do seem to form compact separate genera Dicaulograptus and Lasiograptus shows groups (i.e. the earlier Retiolitinae and later that each has a very different mode of initial Plectograptinae), a link has to be envisaged construction, D. hystrix showing a streptoblastic between them as there were no biserial forms, and L. harknessi a prosoblastic condition. How- other than the earlier group, surviving stratigra- ever, as the question of lasiograptid taxonomy, phically late enough to give rise to the latter. As it phylogeny, and the validity of the taxon itself all is there is a stratigraphic gap (equal to most of the require further scrutiny, there seems little point in riccartonensis Zone) where no retiolitids have further differentiating the included forms at any been found, and so for the present it is convenient taxonomic level higher than genus until more to retain the separation of the Silurian retiolitids detailed phylogenetic relationships are known, into two subfamilies. both within the Lasiograptidae and between the It could be argued that as the retiolitids evolved lasiograptids and diplograptids. Indeed the wide from the Diplograptidae then they should be range of characters and variables shown by the regarded as no more than subfamilies of that representatives of some lasiograptid genera (e.g. family. However, as each of these groups (the Gymnograptus) would indicate that even to differ- Archiretiolitidae and Retiolitidae) diverged entiate at a generic level is attempting too much widely once established, not from other diplo- until the above-mentioned criteria have been graptids but from other retiolitid genera, it seems established. best to retain them as separate families. Presumably Dicaulograptus developed from either a lasiograptid or diplograptid ancestor, Suborder Monograptina (Lapworth, 1880) and as such (being of isolated occurrence and without evident descendants) does not warrant a The author's classification rank equal to the whole of either of these families, and hence the genus is retained within the Lasio- graptidae on account of the more similar thecal Family Monograptidae (Lapworth 1873) form. Subfamily Monograptinae 4. The Archiretiolitidae. In Bulman (1970) this Genera: taxon (then the subfamily Archiretiolitinae), Monograptus, Rastrites, C. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

Graptolite classification II

(Cucullograptus), C. (Lobograptus), creases the stratigraphic range of the Cyrtograp- Monoclirnacis, Pristiograptus, Saetograptus, tinae, and indeed there may be a case to reintro- A tavograptus, Bohemograptus, duce the former taxon at a later date, simply Coronograptus, Lagarograptus, including the genera Linograptus, Abiesgraptus Pribylograptus and Neodiversograptus, which do form a coherent Subfamily Cyrtograptinae (Bou6ek 1933) group of Ludlow and Devonian genera. Genera: Cyrtograptus, Averianowograptus, Barrandeograptus, Linograptus, Future considerations Abiesgraptus, Diversograptus, Neodiversograptus, Sinodiversograptus There are at present two alternatives available to those wishing to classify the diplograptid and monograptid graptolites. The first alternative is that utilized by the author in this work, whereby the two groups are ranked at an equal subordinal Differences from Bulman's 1970 classification level. The second, as favoured by Jaanusson The author abandons the family Cyrtograptinae, (1960), retains the diplograptids as the major and incorporates the genera formerly included taxon whilst the monograptids are included ther- within its two subfamilies (the Cyrtograptinae ein at a lower taxonomic level. The decision to and Linograptinae) as a subfamily (the Cyrto- accept either is obviously a personal one based on graptinae) of the family Monograptidae--the the degree of importance assigned to the mono- genera formerly included within this taxon graptids as a group once they had developed from (together with several additions: see list) of the diplograptids. However, it seems to the Bulman 1970 now constitute the subfamily author that should the latter alternative become Monograptinae. acceptable, then the suborder Diplograptina The cyrtograptid and linograptid form was should be divided into two major superfamilial undoubtedly achieved through several separate taxa, the Diplograptacea and the Monograpta- monograptid lineages (see Rickards et al. 1977), cea, thus retaining the monograptids at a level and hence the Cyrtograptinae and Linograptinae higher than that of a single family, equalled by used by Bulman were no more than form taxa. In each rather than all diplograptid families. an effort to remove such discrepancies, all forms possessing cladia are placed within the subfamily ACKNOWLEDGEMENTS: The author would like to thank Cyrtograptinae, although this is still no more Dr R.B. Rickards and Dr D.E. White for much useful discussion and also colleagues at Cambridge, especially than a 'form taxon'. The subfamily Linograp- A.T. Kearsley and S.D.G. Campbell, for all their help. tinae is dropped completely, as the genera in- Financial support for a C.A.S.E. Studentship from the cluded there can easily be accommodated within Natural Enviromnent Research Council, and the Insti- an emended diagnosis of the Cyrtograptinae. tute of Geological Sciences, London is also acknow- Abandoning the Linograptinae effectively in- ledged.

References

BOU~EK, B. 1933. Monographie der Obersilurischen 1963b. The evolution and classification of the Graptoliten aus der Familie Cyrtograptidae. Praca Graptoloidea. Q. Jl geol. Soc. London, 119, 401-18. geol. pal. ust. Karlovv Univ. 1, 1-84. -- 1969. 'Prothecal folds' and the origin of Dicello-

-- 1968. On the phylogeny and taxonomy ofgrapto- graptus. In." CAMPBELL, K.S. (ed.), Stratigraphy and lites. Proc. IPU 23rd Int. geol. Congr. %14. Palaeontology." Essays in Honour of Dorothy Hill, & MONCtI, A. 1952. The Central European pp. 1-16. Australian Natl Univ. Press. Retiolites of the Upper Wenlock and Ludlow. Sb. -- 1970. Graptolithina, In." TEICHERT, C. (ed.) Trea- Ustred. Ustava geol. 19, 1-15. tise on Invertebrate Palaeontology, V (2nd ed.). BULMAN, O.M.B. 1938. Graptolithina. In: SCH~NDEW- Geol. Soc. America and Univ. Kansas Press. OLF, O.H. (ed.) Handbuch der Paliiozoologie, 2D, FRECH, F. 1897. Lethaea geognostica. I. Lethaea 1-92. Borntraeger, Berlin. palaeozoica, l. Bd., Graptolithiden. pp. 544-684. -- 1938. The proximal end of Cyrtograptus. Geol. Schweizerbart, Stuttgart. Mag. 75, 539-43. HADDING, A. 1915. Om Glossograptus, Cryptograptus -- 1955. Graptolithina. In," MOORE, R.C. (ed.) Trea- och tvenne dem n/irst~ende graptolitsl/igen. Forh. tise on Invertebrate Palaeontology, V. Geol. Soc. Geol. Foren. Stockholm, 37, 303 36. America and Univ. Kansas Press. JAANUSSON. V. 1960. Graptoloids from the Ontikan and -- 1963a. On Glyptograptus dentatus (Brongniart) Viruan (Ordov.) limestonesofEstonia and Sweden. and some allied species. Palaeontology, 6, 665-89. Bull. geol. Instn. Univ. Uppsala, 38, 289-366. Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021

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1965. Two multiramous graptoloids from the RICKARDS, R.B. 1976. Classification of Monograptus: a Lower Didymograptus shale of Scandinavia. Forh. redefinition of some Llandovery graptolite genera. Geol. Foren. Stockhohn, 86, 413-32. In: KALJO, D. (ed.) Stratigraphy. Proc. 2nd Soviet JONES, W.D.V. & RICKARDS, R.B. 1967. Diplograptus Graptolite Colloquium ( Tallin 1973), pp, 155-63.

penna Hopkinson 1869, and its bearing on vesicular -- & BULMAN, O.M.B. 1965. The development of structures. Palaeontol. Z. Berlin, 41, 173-85. Lasiograptus harknessi (Nicholson, 1867). Palaeon- LAPWORTH, C. 1873. On an improved classification of tology, 8, 272-80. the Rhabdophora. Geol. Mag. 10, 500-4, 555-60. , HUTT, J.E. & BERRY, W.B.N. 1977. Evolution of 1879-80. On the geological distribution of the the Silurian and Devonian Graptoloids. Bull. Br. Rhabdophora. Ann. Meg. nat. Hist., London, 3, Mus. nat. Hist. (Geol.) 28, 1-120. 245-57, 449-55; 4, 333-41, 423-31; 5, 45-62, SKEVINGTON, D. 1965. Graptolites from the Ontikan 278-85, 359-69; 6, 16-29, 185-207. Limestones (Ordovician) of Oland, Sweden. II. Mu, A.T. 1950. On the evolution and classification of Graptoloidea and Graptovermida. Bull. geol. Instn. graptolites. Geol Rev. Peking, 15, 171-83. Univ. Uppsala, 68, 1-74.

-- 1973. Evolution, classification and distribution of STRACHAN, I. 1954. The structure and developmment of graptoloidea and graptodendroids. S¢i. Sin. Peking, Peiragraptusfallax, gen. et. sp. nov., A new grapto- 17, 227-38. lite from the Ordovician of Canada. Geol. Mag. 154, --- 1980. Researches on the Graptolithina of China. 509-13.

Acta. palaeontol. Sin, 19, 143-51. -- 1976. Relationships within the Archiretiolitinae.

-- & ZHAN, S.G. 1966. On the probable development In." KALJO, D. (ed.) Graptolites and Stratigraphy. and systematic position of Glossograptus. Sci. Sin. Proc. 2nd Soviet Graptolite Colloquium (Tallin, Peking, 15, 92-8. 1973), pp. 210-3. OBtn', A.M. 1957. Klassifikatsiya i ukazatel rodov StJDmJgv, M. 1958. Triangulate monograptids from the graptolitov. Ezhegodnik Vsesoyuznogo Paleontolo- Monograptus gregarius Zone of the Rheidol Gorge. gicheckogo Obsehchectva, 16, 11-47. Phil. Trans. R. Soc. London, B241, 485-555.

-- 1964. Podtip Stomochordata. Stomokhordovye. Yu, J. & FANG, Y. 1979. On the classification of In: Yu, A. ORLOV (ed.) Osnovypaleontogii: Echino- Graptoloids. Acta palaeontol. Sin, 18, 435-42. dermata, Hemichordata, Pogonophora i Chaetog- natha, pp. 279-337. Nedra Press, Moskva.

J. RIGBY, C/O Texaco Ltd., Producing Dept., 1 Knightsbridge Green, London SWIX 7QJ, U.K.