Mongolitubulus spinosus ( Hinz, 1987 )

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 486

Mongolitubulus spinosus ( Hinz, 1987)

Fig. 58 .

Material.—Ten specimens from samples 6/59.3, 6/66.2, 7/54, and 7/55, including SMNH Ar 63450 from sample 7/55; correlated with the Judomia Zone , upper Atdabanian Stage; ten specimens, including SMNH Ar 63451, from sample 7/70; Calodiscus -Erbiella Zone, lower Botoman Stage; Emyaksin Formation, Bol’shaya Kuonamka River. Seven specimens, including SMNH Ar 63452 and 63453, from sample 1/9; carbonate concretions in the basal Kuonamka Formation, Malaya Kuonamka River; Bergeroniellus expansus Zone , upper Botoman Stage.

Description.—Gently curved hollow calcium phosphatic spines nearly circular in cross-section. The wall consists of two layers. The outer layer has a cancellate ornamentation consisting of irregular transversal rows of polygons with serrated edges. The polygons are extended longitudinally, with their apical part somewhat raised and pointed towards the apex of the spine. Inner layer without sculpture, smooth and folded at the base of spine ( Fig. 58D 2 ). The basal part is flaring ( Fig. 58A ). The specimens reach 3 mm long and are up to 0.2 mm in diameter.

Remarks.—In addition to the type species, M. squamifer Missarzhevsky, 1977 , such other specias as M. aspermachaera Topper, Skovsted, Harper, and Ahlberg, 2013 , M. henrikseni Skovsted and Peel, 2001 , M. reticulatus Kouchinsky, Bengtson, Clausen, Gubanov, Malinky, and Peel, 2011 , M. spinosus ( Hinz, 1987) , M. unialata (Zhang, 2007) , and M. unispinosa Topper, Skovsted, Brock, and Paterson, 2007 are included within Mongolitubulus Missarzhevsky, 1977 , shown to represent the spines of a bradoriid ( Skovsted and Peel 2001; Topper et al. 2007, 2013).

Ornamentation of M. spinosus herein is very similar to that of M. spinosus from Britain, described as Rushtonites spinosus by Hinz (1987: 11) and Brasier (1989a: pl. 7.2), as well as to the spines attributed to Tubuterium ivantsovi Melnikova, 2000 from Siberia (lower Kutorgina Formation, middle Lena River, Botoman Stage; Melnikova 2000: pl. 8; Ponomarenko 2005: pls. 29, 30). The apically raised edges of polygons in Rushtonites spinosus ( Hinz 1987: pl. 11: 2, 4, 7, 9) appear to be more rounded, however, than in M. spinosus herein and in Tubuterium ivantsovi , but this can be a preservational effect. Tommotitubulus grausmanae ( Vasil’eva 1994: pl. 1: 1 therein and Vasil’eva 1998: pl. 46: 2, 5, 6) from the lower Botoman Stage of Siberia is considered herein to be a junior synonym of M. spinosus .

M. spinosus differs from the other, younger, species from the Kuonamka Formation, M. reticulatus , in ornamentation and in having a straight, not bent apical part. The outer layer in M. reticulatus has a reticulate ornamentation consisting of longitudinally extended polygons forming a regular pattern of straight or gently spiralling rows directed towards the apex ( Kouchinsky et al. 2011: figs. 33–35). The wrinkled outer surface of M. aspermachaera from the Furongian of Baltica bears tubercles ( Topper et al. 2013). The ornamentation of M. henrikseni Skovsted and Peel, 2001 from the beds equivalent to the Botoman Stage in Greenland and Australia ( Skovsted and Peel 2001; Skovsted et al. 2006) and M. squamifer Missarzhevsky, 1977 from beds in Mongolia, Kazakhstan, and Greenland correlated with the upper Atdabanian–Botoman Stages ( Missarzhevsky 1977; Missarzhevsky and Mambetov 1981; Skovsted and Peel 2001) represents well-defined scale-like protuberances. The outer surface of M. unispinosa spines bears short second-order spines and rhombic scales inclined adapically, but subdued in the apical area ( Topper et al. 2007). A flaring basal part is known from all species attributed herein to Mongolitubulus , except for M. squamifer ( Skovsted and Peel 2001) .

Stratigraphic and geographic range.— Mongolitubulus spinosus ( Hinz, 1987) occurs in the Lower Comley Limestones (Beds Ac2–Ac3, after Brasier 1989b), Callavia Zone, Britain , correlated with the upper Atdabanian–lower Botoman Stages. On the Siberian Platform, it is known from the Judomia Zone of the upper Atdabanian Stage and from the Botoman Stage.

Figures

Fig. 58. Bradoriids Mongolitubulus spinosus (Hinz, 1987) from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River and basal Kuonamka Formation, Malaya Kuonamka River, Anabar Uplift, Siberia, fragments of spines. A. SMNH Ar 63450, sample 7/55; A1, lateral view; A2, close-up of A1 showing ornamentation; A3, oblique basal view; A4, oblique transversal view on the apical end of the fragment. B. SMNH Ar 63452, sample 1/9; lateral view. C. SMNH Ar 63453, sample 1/9; lateral view. D. SMNH Ar 63451, sample 7/70; D1, lateral view; D2, oblique transversal view on the basal end of the fragment. Scale bar: 300 μm, except A1, 120 μm; A2, 60 μm.

Fig. 2. Derivation of fossiliferous samples (arrows with numbers) and chemostratigraphic correlation of sections 1 and 3 (Malaya Kuonamka River) with sections 6 and 7 (Bol’shaya Kuonamka River). Correlation with carbon isotope features II–VII from stratotypes of south-eastern Siberian Platform (Brasier et al. 1994) according to Kouchinsky et al. (2001). Note that the zero level in all sections corresponds to the water level above which the sections were exposed in 1996. Description of fauna from the lower part of the Emyaksin Formation in complementary outcrops at the Bol’shaya Kuonamka River (below that zero level) will be published elsewhere. Fauna from the overlying Kuonamka Formation is published by Gubanov et al. (2004) and Kouchinsky et al. (2011).