Polonodus clivosus (Viira, 1974)

Zhen, Yong Yi, 2011, Middle to Late Ordovician (Darriwilian-Sandbian) Conodonts from the Dawangou Section, Kalpin Area of the Tarim Basin, Northwestern China, Records of the Australian Museum 63 (3), pp. 203-266 : 233

publication ID	https://doi.org/ 10.3853/j.0067-1975.63.2011.1586
persistent identifier	https://treatment.plazi.org/id/03CCEB77-FFCE-636C-FE58-FA9F91A2FA80
treatment provided by	Felipe
scientific name	Polonodus clivosus (Viira, 1974)
status

Treatment

Fig. 17L–M View Figure 17

Ambalodus n.sp. Viira, 1967: 323, fig. 3.24a–b.

Polyplacognathus n.sp. A Fåhraeus, 1970: fig. 3F–G.

Ambalodus n.sp. A Fåhraeus, 1970: fig. 3J–K.

Ambalodus clivosus Viira, 1974: 51–52 , 134, pl. 8, fig. 1, text-figs 37–38.

Ambalodus ? n.sp.Viira, 1974: 52, pl. 8, figs 2–3, text-fig. 39.

Polonodus clivosus (Viira) .– Löfgren, 1978: 76, partim only pl. 16, figs 12–13; Stouge, 1984: 73, pl. 13, figs 6–13; Ding et al. in Wang, 1993: 191, pl. 32, figs 16,?17.

Polonodus sp. H Ding et al. in Wang, 1993: partim only pl. 37 fig. 5.

Material. Two specimens from one sample at top of the Dawangou Formation (see Table 2).

Remarks. Polonodus clivosus was erected as a form species recovered from subsurface core material of Darriwilian age in the east Baltic (Viira, 1974, pl. 8, fig. 1, text-figs 37–38), and is interpreted herein as representing paired sinistral and dextral Pa (polyplacognathiform) elements. These have a node-like cusp with a row of node-like denticles extending the whole length of the longer anterior process and the short posterior process, and are also present on the inner lateral and secondary inner lateral processes. The anterior and posterior platforms of the holotype (Viira, 1974, pl. 8, fig. 1) form a gently curved outline in upper view without the outer lateral process. Specimens with four processes from the same core sample as the holotype of P. clivosus were referred to as Ambalodus ? sp. n. by Viira (1974, pl. 8, figs 2–3, text-fig. 39), and are considered herein as representing the paired sinistral and dextral Pb (ambalodiform) elements of P. clivosus . Although Löfgren (1978) recognized that the Polish specimens from the erratic boulders accommodated in P. clivosus by Dzik (1976) belonged to separate species (see discussion above), her definition of P. clivosus also doubtfully included Newfoundland material (Table Head Formation) ascribed to Polyplacognathus n.sp. A and Ambalodus n.sp. A by Fåhraeus (1970). However, the Swedish specimens she illustrated ( Löfgren, 1978, pl. 16, figs 12–13) bear a long outer lateral process, implying that the holotype of P. clivosus might have the outer lateral process broken off. This view was then accepted by Stouge (1984), who was the first to revise this species as consisting of a bimembrate species apparatus, but his definition of this species was largely based on the material from Newfoundland. P. clivosus differs from the corresponding elements of P. newfoundlandensis in lacking a prominent notch between the anterior process and the secondary inner lateral process of the Pa element ( Stouge, 1984, pl. 13, fig. 13), and in having larger denticles on the anterior process of the Pb element ( Stouge, 1984, pl. 13, fig. 11). The definition of P. clivosus given by both Löfgren (1978) and Stouge (1984) was also endorsed by Viira (per. comm., 2010), who confirmed that the original holotype of P. clivosus (Viira, 1974, specimen Cn 245, text-fig. 37, pl. 8, fig. 1) “has a broken outer lateral process which is seen clearly on the basal view”.

One specimen ( Fig. 17L–M View Figure 17 ) recovered from the same sample AFT-X-K13/ 13 in association with P. newfoundlandensis also had the outer lateral process broken off, and is identical with the holotype of P. clivosus (Viira, 1974, text-fig. 37, pl. 8, fig. 1). It differs from P. newfoundlandensis in lacking a prominent notch between the anterior process and the secondary inner lateral process, and in having a more prominent and laterally more compressed cusp and denticles on the anterior and posterior processes.

Kingdom	Animalia
Phylum	Chordata
Class	Conodonta
Order	Conodontophorida
Family	Polyplacognathidae
Genus	Polonodus