On the origin of dimorphograptids LIJI-JIN Li Ji-Jin: On the origin of dimorphograptids. Bull. geol. Soc. Denmark, vol. 35, pp. 171-177, Copen­ hagen, July 1st, 1987. Previous authors usually considered the Diplograptus stage-*Akidograptus stage-*Rhaphidograptus stage —* Dimorphograptus stage to be an evolutionary series. After research on material of dimorphograp­ tids from the Lower Silurian Kaochiapien Formation, southern Anhui in China, and taking into account the results from analyses on dimorphogvaptids in general, the writer considers that Dimorphograptus of the elongatus group and Bulmanograptus of the confertus group probably evolved from Parakidograptus, while Dimorphograptus of the hubeiensis group and Bulmanograptus of the deminutus group probably evolved from Glyptograptus and Rectograptus respectively. Rhaphidograptus probably evolved from Cli- macograptus. Li Ji-Jin, Nanjing Institute of Geology and Palaeontology, Academia Sinica, Chi-Ming-Ssu, Nanjing, China. August, 29th, 1985. The dimorphograptids mentioned here include the vesiculosus Zone, such as Dimorphograptus three genera, namely, Dimorphograptus (with erectus Elles et Wood, Dimorphograptus maxi­ glyptograptid thecae), Bulmanograptus (with rec- mus Li, Dimorphograptus minor (Li), Dimor­ tograptid thecae) and Rhaphidograptus (with cli- phograptus elongatus Lapworth, Bulmanograptus macograptid thecae). Akidograptus and Paraki­ confertus acuminatus Li, Bulmanograptus similis dograptus are not dimorphograptids because in Li, Bulmanograptus ningguoensis Li, the unise­ these two genera the first theca (thf) in the sec­ rial part of the rhabdosome is composed of 3-19 ond series of the rhabdosome is normal and is thecae; whereas in the dimorphograptids occur­ neither reduced nor lost (Li & Ge 1981). ring in the cyphus and gregarius zones, such as Previous authors (Bulman, 1938; Mu & Li, Dimorphograptus brevis Li, Bulmanograptus al- 1960; Chen & Lin, 1978; etc.) considered the Di­ ternis Li, Bulmanograptus anhuiensis sp. nov., plograptus stages Akidograptus stage (belong­ there is only one theca in the uniserial part of the ing to the diplograptid type) —* Rhaphidograptus rhabdosome. Similar results can also be obtained stage—* Dimorphograptus stage (belonging to the from analyses of dimorphograptids material monograptid type) to be an evolutionary series. (Elles & Wood, 1901-1918; Manck, 1923; Moreover, Chen & Lin (1978) further considered Miinch, 1952; Obut, Sobolevskaya & Bondarev, that the dimorphograptids with only one theca in 1965; Obut & Sobolevskaya 1966; Obut, Sobo­ the uniserial part represented the primitive group levskaya & Nikolaev, 1967; Obut, Sobolevskaya in different genera of the Dimorphograptidae; & Merkureva, 1968; Churkin & Carter, 1970; they directly evolved from the Akidograptus after Rickards, 1970; Schauer, 1971; Hutt, 1974; Bjer­ the loss of the first theca in the second series. La­ reskov, 1975; Lenz, 1982). It is helpful to list the ter, due to the loss of the thecae one by one in the stratigraphic range and the number of thecae in second series of the rhabdosome, and the unise­ the uniserial part of the rhabdosome in the spe­ rial part gradually becoming longer, they became cies assigned to the three genera (see tables 1-3). the monograptids. Based on the present mate­ From these 3 tables, it can be seen that rial, the paper presents a preliminary discussion amongst the dimorphograptids, the species with on the origin of Dimorphograptids. more thecae in the uniserial part of the rhab­ While making a study on the Lower Silurian dosome made their appearence earlier strat- Kaochiapien Formation graptolites from south­ igraphically, such as D. elongatus Lapworth, Bul­ ern Anhui in China (Li, 1983), the writer discov­ manograptus confertus (Lapworth), and Rhaphi­ ered that in the dimorphograptids occurring in dograptus extenuatus (Elles & Wood); whereas 172 Li Ji-Jin: On the origin of dimorphograptids Table 1. Stratigraphic range of species in Dimorphograptus. Table 2. Stratigraphic range of species in Bulmanograptus. e Zones e Zones l l theca theca f f o o r r uniseria uniseria e e t t th th n n acumniatus convolutus i vesiculosus Numbe par acumniatus vesiculosus cyphus gregarius gregarius convolutus par i Species Numbe Species 1 D. elongatus Lapworth + + 10-19 B. confertus (Nicholson) + + + 3-4 D. e. flexuosus Schauer + 10-12 B. c. swanstoni (Lapworth) + + + 4-6 D. erectus Elles et Wood + 3-4 B. c. acuminatus Li + 5 D. hunanensis Wang + 6 B. nankingensis (Sun) + 2-3 D. minor (Li) + 5 B. similis Li + 2 D. maximus Li + 3 B. ningguoensis Li + 4 D. guanyinqiaoensis Ye + 2 B. decussatus + 2 (Elles et Wood) D. urvantzevi Obut et Sob. + + 6 B. d. partiliter + 3 D. procerus Manck + + 5 (Elles et Wood) D. ciliatus Manck + + 3-4 B. longissimus (Kurck) + + 2-3 D. incisus Manck + + 3 B. epilongissimus + + 3^1 (Rickards) D. erectus nicholsoni + + 2-3 Rickards B. physophora (Nicholson) + + + 1 D. guichiensis Li + B. macilentus aculeus + 1 Chen et Lin D. sichuanensis Ye + B. deminutus Ni + 1 D. altemis Li + B. alaskensis + + 1 (Churkin et Carter) D. longicaudatus + + Chen et Lin B. macilentus Mu et al. + + 1 D. brevis Li + + B. primus + 1 (Obut et Sobolevskaya) D. zintchenkoae + (Obut et Sob.) B. anhuiensis sp. nov. + 1 D. tenuilongissimus + (Obut et Sob.) B. spiniferus + 1 (Obot et Sobolevskaya) D. longicaudM s fusiformis + Chen et Li i B. secundus + + 1 (Obut et Sobolevskaya) D. hubeiensis Ni + evidence demonstrates that the species with more those species with only one theca in the uniserial thecae in the uniserial part did not evolved from part of the rhabdosome appeared later, such as those species fewer thecae in the uniseral part. Dimorphograptus hubeiensis Ni, B. anhuiensis sp. Judging from the type of development at the nov. and Rhaphidograptus sinicus Mu et al. This proximal end, the thecal features and the shape Bulletin of the Geological Society of Denmark, . 35, 1987 173 Table 3. Stratigraphic range of species in Rhaphidograptus. Zones e l theca f o r uniseria e t th n sedgwickii cyphus convolutus Numbe i vesiculosus Species I par Rhaphidograptus extenuatus + 2-5 (Elles et Wood) Rhaphidograptus sichuanensis + 1 Ye Rhaphidograptus minutus + + 1 Chen et Lin Rhaphidograptus toernquisti + + + + + 1 (Elles et Wood) Rhaphidograptus maslov + 1 Obut et Sobolevskaya Rhaphidograptus sinicus + 1 Mu et al. Fig. 1. Evolution of Dimorphograptus and Bulmanograptus in the Lower Silurian of Guichi, Anhui. of the rhabdosome, the species D. brevis occur­ At the same time, the species D. elongatus ring in the cyphus Zone of the Lower Silurian Lapworth appearing in the vesiculosus Zone of Kaochiapien Formation in southern Anhui, is the Lower Silurian in eastern Thuringen, D. D. quite similar to Glyptograptus elegans Packham from the lower part of the same zone, or the same horizon; likewise, the species B. anhuiensis occurring in the upper part of the gregarius Zone is also quite similar to Rectograptus parakido- graptoides Li from the lower part of the same zone. The writer believes that the above-men­ tioned D. brevis and B. anhuiensis probably have evolved from G. elegans and R. parakidpgrap- toides respectively due to loss of the first theca in the second series of the rhabdosome. (see Fig. 1). The species D. hubeiensis occurring in the con­ volutus Zone of the Lower Silurian Lungmachi Formation in Yichang, Hubei (Ni, 1978) resem­ bles Glyptograptus tamariscus (Nicholson) from the lower part of the same zone; likewise, the species Bulmanograptus deminutus Ni appearing in the cyphus Zone, resembles Rectograptus bel- lulus (Tornquist) from the same horizon. There­ fore, it seems that the above-mentioned D. hu­ beiensis and B. deminutus very probably have evolved from G. tamariscus and R. bellulus re­ spectively as a result of loss of the first thecae in Fig. 2. Evolution of Bulmanograptus and Dimorphograptus in the second series of the rhabdosome (see Fig. 2). the Lower Silurian of Yichang, Hubei. 174 Li Ji-Jin: On the origin of dimorphograptids 1 , , sedgwickii .<3 O- convo/utus o« <o* Sv lin 1 3 W H 1 s i1 J \ gregarius 1 ft If vesicu cyphus morphograpt \ ^ 8- ' \ / vesiculosus § Vj 1 " \ h acuminatus ? O &2 o m,i\ M O % 5 3tnm persculptus j I $ s i S / ! o Fig. 4. Evolution of Rhaphidograptus. ! T3 JC s. Sf o ^ j)inm into being. Therefore, G. persculptus seem by no Fig. 3. Evolution of Dimorphograptus in the Lower Silurian of means to be evolved into R. toemquisti. Eastern Thuringen, D.D.R. In species of dimorphograptids with more than two thecae in the uniserial part (exclusive of the Rhaphidograptus), the first theca (th}) in the first R. (Schauer, 1971), is very similar to Paraki- series of the rhabdosome are generally sent forth dograptus acuminatus (Nicholson) appearing in from the sicula at a higher position, and the in­ the acuminatus Zone. The former probably has itial bud begins growing directly upwards, repre­ evolved from the latter with loss of most of the senting a relatively advanced stage in the devel­ thecae in the second series of the rhabdosome. In opment of the dimorphograptids (i.e. the mono- D. elongatus the rhabdosome became further graptid type of development); Parakidograptus is curved dorsally, and might have given rise to quite near to this type of development because in Dimorphograptus elongatus flexuosus Schauer this genus the first theca (thj) was sent forth from (see Fig. 3). the sicula at a higher position, the initial bud at The species Rhaphidograptus toemquisti (Elles first grew downwards, but very soon turning up­ & Wood) ranging from the vesiculosus Zone to wards. Thus it further evolved to Dimorphograp- the sedgwickii Zone of the Lower Silurian in Brit­ ain (Elles & Wood, 1901-1918; Rickards, 1970) is very similar to, and can be hardly distinguished from Climacograptus rectangularis M'Coy occur­ ring from the acuminatus Zone to the gregarius Zone (Elles & Wood, 1901-1918). The former very probably has evolved from the latter due to the loss of the first theca (th?) in the second series (See Fig. 4). In Rickards, Hutt & Berry (1977)'s consider­ ation, R.