Brief Report Acta Palaeontologica Polonica 59 (4): 921–926, 2014
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Brief report Acta Palaeontologica Polonica 59 (4): 921–926, 2014 Morphology and palaeoecology of a new edrioblastoid from the Furongian of China XUE-JIAN ZHU, SAMUEL ZAMORA, and BERTRAND LEFEBVRE A new edrioblastoid Cambroblastus guolensis is described Here, a new species of Cambroblastus is described from the from the Furongian (late Cambrian) Sandu Formation Furongian of China. This record extends the palaeogeographic (South China). This represents the second occurrence of a distribution of the first edrioblastoids. The aims of this brief Cambrian edrioblastoid, and the first ever reported from report are to analyze and describe the morphology of Cambro- Asia, extending the palaeogeographic range of this very rare blastus sp. nov., and for the first time, to provide evidences for echinoderm grade. Surprisingly it preserves a complete stem attachment strategies in late Cambrian edrioblastoids. and a distal holdfast suggesting edrioblastoids were hard substrate attachers living in soft bottom quiet environments. Institutional abbreviations.—NIGPAS, Nanjing Institute of Ge- ology and Palaeontology, Chinese Academy of Sciences, China. Introduction Geological setting and palaeoenvironment Edrioblastoids are an extremely rare grade of Lower Palaeo- zoic echinoderms known only from a limited number of spe- The specimen was collected from mudstone and marl beds of cies ranging from the late Cambrian to the Late Ordovician. the Sandu Formation, Guole Town, Jingxi County, Guangxi They displayed a globular theca with five recumbent ambula- Province, southwest China (Fig. 1). Guole Town lies in Yangtze cra constructed with large, biserial and exposed flooring plates Area of South China Region. The Yangtze Area represented a and large, simple or complex cover plates. All known species shallow shelf during Cambrian time (Zhou and Zhen 2008). have a polyplated stem to elevate the theca above the substrate, In addition to Cambroblastus sp. nov., the Sandu Formation but their attachment mechanism is still unknown (Mintz 1970; has yielded a diverse associated fauna comprising aglaspidi- Smith and Jell 1990; Guensburg and Sprinkle 1994; Guensburg dids, brachiopods (e.g., Billingsella, Guoleella, Palaeostrophia, et al. 2010). Plectotrophia), other echinoderms (e.g., “Phyllocystis” jingx- The first edrioblastoid described in the literature was Astro- iensis), graptolites (e.g., Callograptus, Dyctionema), hyolithids, cystites ottawaensis Whiteaves, 1897 from the Late Ordovician trilobites (e.g., Akoldinioidia, Dictyella, Guangxiaspis, Sher- of North America. However, because of its unusual morphol- goldia, Sinosaukia, Tamdaspis), and undescribed palaeoscole- ogy, Astrocystites was successively interpreted as a primitive cids (Han and Chen 2008; Zhan et al. 2010; Lerosey-Aubril et cystoid (Whiteaves 1897), an edrioasteroid (Bather 1900, 1914; al. 2013). Co-occurring trilobites indicate an age equivalent to Piveteau 1953), a blastoid (Hudson 1925), an intermediate form the Probinacunaspis nasalis–Peichiashania hunanensis Zone between eocrinoids and blastoids (Hudson 1927), or as a mem- of northwestern Hunan, and thus part of the Furongian, Stage 9 ber of a separate class (Edrioblastoidea) closely related either to (Zhu et al. 2007, 2010). Abundant articulated trilobites strongly blastoids (Fay 1962, 1967), eocrinoids (Mintz 1970), or echino- suggest rapid burial, likely as the result of an obrution event zoans (Sprinkle 1973). All recent cladistic analyses indicate that (Zhu et al. 2010). These taphonomic conditions probably also edrioblastoids are a derived group of edrioasterid edrioasteroids explain the exquisite preservation of echinoderms. closely related to cyathocystids (Smith and Jell 1990; Guen- sburg and Sprinkle 1994; Sumrall et al. 2013). Systematic palaeontology Since the original description of A. ottawaensis, only few other occurrences of edrioblastoids have been reported. They Phylum Echinodermata Bruguière, 1791 include Cambroblastus enubilatus Smith and Jell, 1990 from the (ex Klein, 1734) late Cambrian of Australia, and Lampteroblastus hintzei Guen- Class Edrioasteroidea Billings, 1858 sburg and Sprinkle, 1994 from the early Floian (Early Ordovi- cian) of Utah. Late Ordovician occurrences include Astrocystites Order Edrioblastoida Fay, 1962 distans from Australia, based on poorly preserved specimens Genus Cambroblastus Smith and Jell, 1990 (Webby 1968; Webby et al. 2000), as well as possible isolated Type species: Cambroblastus enubilatus Smith and Jell, 1990; Chats- remains from Virginia (Sprinkle 1973) and Sweden (Paul 1976). worth Limestone, Furongian; Queensland, Australia. Acta Palaeontol. Pol. 59 (4): 921–926, 2014 http://dx.doi.org/10.4202/app.2012.0116 922 ACTA PALAEONTOLOGICA POLONICA 59 (4), 2014 106°E prise numerous, tightly sutured flooring plates and one single China biseries of elongate primary cover plates. In Cambroblastus, Yunnan Baise Vietnam stem meres are almost as high as wide, whereas they are more Tianyang elongate and much wider than high in Astrocystites. Main differ- Guangxi ences between Cambroblastus and Lampteroblastus concern the shape and ornamentation of the theca, the extent and structure Napo of ambulacra, and the stem morphology. In Cambroblastus, the Guole Debao theca is globular, and composed of numerous plates ornamented with multiple delicate ridges. In Lampteroblastus, the theca is more cylindrical, and composed of a reduced number of plates, VIETNAM Jingxi each ornamented with strong primary ridges. The ambulacra are A 0 10 20 km 23°N significantly more extensive in Cambroblastus than in Lampt- South China Region eroblastus, and they comprise four series of cover plates (in- stead of two in Lampteroblastus). Finally, the stem is short and Yangtze Area (Platform) tapering in Lampteroblastus, whereas it is long and cylindrical, Jiangnan Area Cathaysia with a distal expanded holdfast in Cambroblastus. (southern shelf or Pearl River Area of the The presence of multiple cover plates series in Cambroblas- (deep basin) Yangtze tus is probably a plesiomorphic feature shared with other primi- Northern Platform) tive edrioasteroids (e.g., Cambraster, Edriodiscus, Kailidiscus, Qiangtang- country boundary Stromatocystites). Simao Region province boundary VIETNAM national/provincial highway B fossil locality/type locality Cambroblastus guolensis sp. nov. Figs. 2, 3. Fig. 1. Location (A) and geological setting (B) of the studied site (modified from Zhou et al. 2008). Etymology: Referring to the town of Guole (China), where the holotype was collected. Emended diagnosis.—An edrioblastoid with irregular, polyplat- Holotype: NIGPAS156159, a single specimen with both part and coun- ed stem, distal polyplated and expanded holdfast, 3–4 irregular terpart preserved as natural mould in a yellow brownish mudstone. All circlets of strongly ornamented thecal plates, ambulacra com- parts are well preserved with the exception of the summit and anal posed of large, exposed flooring plates and complex cover plates. pyramid. : Daba Village, Guole Town, Jingxi County, Guangxi Pro- Discussion.—Cambroblastus enubilatus was originally descri- Type locality vince, southwest China. bed based on poorly preserved material from the Furongian of Type horizon: Sandu Formation, Furongian, late Cambrian. Australia, which prevented the detailed observation of several aspects of its morphology (Smith and Jell 1990). The specimen Material.— Holotype only. described herein from the Furongian of South China shows Diagnosis.—A species of Cambroblastus with widely exposed many similarities with C. enubilatus, and is thus assigned to flooring plates, and a distal holdfast composed of numerous the same genus: same plating patterns for the stem and the- elements, smaller than those of the stem. ca, comparable morphology and extent of ambulacra, similar Description.—Theca of holotype slightly flattened, about 11 arrangement and size of ambulacral elements (flooring plates mm high and 10 mm large (at widest diameter). Theca bulb- and primary cover plates). Moreover, the exquisite preservation shaped, with large oral area and very wide ambulacra. About 80 of the Chinese material of Cambroblastus makes it possible to polygonal thecal plates exposed on both part and counterpart. modify the original diagnosis of the genus, so as to accommo- Thecal plates large (1 to 1.5 mm in diameter), with central date additional information both on the structure of ambulacra elevated area, ornamented with a series of prominent ridges and the morphology of the holdfast. For example, Smith and Jell connecting adjacent plates. Ridges about 4 to 5 per plate side, (1990) suggested that ambulacra were roofed by only two series relatively straight across plate sutures, more irregular towards (left and right) of large, alternating cover plates. The better pre- central elevated areas of thecal plates. Hexagonal “deltoid” served Chinese material allows the identification, perradially, of plates in interambulacral position, in contact and along adjoin- two additional series of smaller (secondary) cover plates. The improved knowledge of the morphology of Cambro- Fig. 2. Holotype of edrioblastoid edrioasteroid Cambroblastus guolensis → blastus makes it possible to compare it with unprecedented sp. nov. (NIGPAS156159) from the Furongian (late Cambrian) of China. details with the two other known genera of edrioblastoids: As- A, C. General view of the specimen attached to a trilobite pygidium, show- trocystites and Lampteroblastus. Cambroblastus differs from ing the division