Mongolitubulus squamifer Missarzhevsky, 1977

Betts, Marissa J., Claybourn, Thomas M., Brock, Glenn A., Jago, James B., Skovsted, Christian B. & Paterson, John R., 2019, Shelly fossils from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia, Acta Palaeontologica Polonica 64 (3), pp. 489-522 : 496

Mongolitubulus squamifer Missarzhevsky, 1977

Fig. 5 .

1977 Mongolitubulus squamifer ; Missarzhevsky 1977: 13, pl. 1: 1–2.

1981 Mongolitubulus squamifer ; Missarzhevsky and Mambetov 1981: 79, pl. 14: 1–2.

1985 Mongolitubulus squamifer ; Meshkova 1985: 127–128, pl. 46: 1–3.

1986 Mongolitubulus squamifer ; Rozanov 1986: 89, fig. 4.

1986 Rhombocorniculum aff. insolutum ; Brasier 1986: 253, fig. 5j–k.

1988 Mongolitubulus squamifer ; Peel and Blaker 1988: 56, fig. 2.

1988 Rhombocorniculum n. sp.; Landing 1988: 687, fig. 11.6.

1989 Mongolitubulus squamifer ; Missarzhevsky 1989: 31, figs. 1, 3.

1989 Mongolitubulus squamifer ; Wrona 1989: 543.

1996 Mongolitubulus squamifer ; Esakova and Zhegallo 1996: 103, pl. 4: 9–13.

2001 Mongolitubulus squamifer ; Skovsted and Peel 2001: 137, fig. 2.

2001 Mongolitubulus ex gr. M. squamifer ; Demidenko in Gravestock et al. 2001: 87, pl. 11: 5a, b.

2002 Mongolitubulus squamifer ?; Landing et al. 2002: 301, fig. 4.19.

2003 Mongolitubulus squamifer ; Dzik 2003: figs. 2, 3.

2004 Mongolitubulus squamifer ; Wrona 2004: 43 , figs. 23A–H, 24.

2006 Mongolitubulus squamifer ; Brock and Percival 2006: 86, fig. 5E–J.

2007 Mongolitubulus squamifer ; Topper et al. 2007: 76, fig. 5A–H.

2009 Mongolitubulus squamifer ; Wrona 2009: 367, fig. 13A, B.

2011 Mongolitubulus squamifer ; Topper et al. 2011: fig. 7I–K.

Material. —Five broken spines from Clast 1, and 10 broken spines from Clast 5, eight figured ( SAM P57227–57234). All from the Dailyatia odyssei Zone, WPC, Kangaroo Island, South Australia.

Description. —Isolated, broken or fragmentary hollow spines. Spines are straight or slightly curved, and bear distinctive, regularly arranged, rhomboid scales along their length ( Fig. 5 ). Individual scales can be up to ~25 μm wide, and inclined at an angle to the spine, oriented toward the tip or narrower end of the spine. Where spines retain a flared base, scales are reduced to low pustules ( Fig. 5F ).

Remarks. —All material in the WPC is represented by isolated, broken spines. A single, fragmentary specimen retains the flared base ( Fig. 5F ). While several Mongolitubulus species have been recovered with the spine and shield intact, the type species Mongolitubulus squamifer is known only from isolated spines, and none have been found attached to a bradoriid shield ( Topper et al. 2013). The taxonomic difficulties associated with isolated bradoriid spines are well documented (Skovsted et al. 2006; Topper et al. 2007, 2013; Li et al. 2012; Caron et al. 2013). Li et al. (2012) showed that the ornament on Mongolitubulus spines is similar on spines of the trilobite Hupeidiscus orientalis ( Li et al. 2012) . However, as Topper et al. (2013) pointed out, there is a significant size difference between the trilobite spines and those attributed to Mongolitubulus , which are generally larger. Caron et al. (2013) also showed a strong similarity between Mongolitubulus spines and the dorsal spines of the lobopod Hallucigenia . Distinguishing between disarticulated spines of bradoriids and lobopods may be difficult, but Caron et al. (2013) suggested that the spines of Hallucigenia lack flaring spine bases, and the presence of such structures in the WPC material support the bradoriid affinity of M. squamifer .

Mongolitubulus squamifer spines from the WPC are consistently broken, so their maximum length cannot be ascertained, however the largest specimen is ~300 μm in width, which conforms to the maximum width of M. squamifer spines ( Topper et al. 2013). The WPC specimens also exhibit the distinctive rhombic scales characteristic of the species ( Fig. 5 ). On the specimen that retains the flared base, the scales are reduced to rounded pustules, and are more widely spaced ( Fig. 5F ). This is similar to the ornament on spines of other Mongolitubulus species which becomes gradually less pronounced on the proximal parts closer to the shield (Betts et al. 2014, 2017b).

Stratigraphic and geographic range.— Mongolitubulus squamifer had a global distribution during the early Cambrian, and is known from Mongolia, Maly Karatau ( Kazakhstan), east and west Avalonia, Laurentia, and glacial erratics from King George Island, Antarctica ( Topper et al. 2007). South Australia, Arrowie Basin: M. squamifer ranges from the Pararaia tatei Zone ( AJX-M section, Mount Scott Range, northern Flinders Ranges) to the Pararaia janeae Zone ( DBS section, Donkey Bore Syncline, central Flinders Ranges) ( Betts et al. 2017b: fig. 13). Stansbury Basin: WPC clasts, Kangaroo Island.

Figures

Fig. 5. Spines of the bradoriid arthropod Mongolitubulus squamifer Missarzhevsky, 1977 from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. A. SAM P57227. B. SAM P57228. C. SAM P57229. D. SAM P57230. E. SAM P57231. F. SAM P57232, fragment with flared base. G. SAM P57233. H. SAM P57234, close-up of rhomboid scales.