Ovalocephalus undetermined
Creators: name: Fortey, Richard A.
name: Wernette, Shelly J.
name: Hughes, Nigel C.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Trilobita
Phacopida
Pliomeridae
Ovalocephalus
Ovalocephalus undetermined

description: Ovalocephalus sp.
Figs 10.10, 13
pars 1915 Calymene (Pharostoma) liluensis Reed; Reed, pl. 8, fig. 9.
? 1915 Pliomera (Encrinurella) insangensis Reed; Reed, p. 8, fig. 21.
Material. Pygidium from the Li-Lu Formation (Upper Naungkangyi Beds; Katian) at Nam Tu above Lilu, northern Shan State, Myanmar, Fig. 10.10 (Reed, 1915, pl. 8, fig. 9), GSI 11556; Cranidium from unknown northern Shan State horizon and locality, Fig. 10.13, unregistered and not previously figured by Reed.
Description. A single example of a pygidium is twice as wide as long, and with low transverse convexity.Anterior transverse width of the axis is approximately equal (tr.) to the anterior part of the pleural lobe. Axis tapers, but is effaced posteriorly, and rings low and band-like, three clearly defined by gently forwardly arched ring furrows that continue on to pleural fields. Fourth ring furrow faint, and narrow; no defined terminal piece. Pleural ribs: two welldefined gently downsloping to margin, the first probably slightly exceeding it, with deep pleural furrows between; third rib incompletely defined by shallow furrow that does not extend to margin. Narrow and convex articulating ridge visible on left hand side.
The external mould of a small cranidium was also discovered and cast while investigating the Reed collections, but we can find no indication that Reed examined it. The preservation is similar to that of other specimens from the “Upper Naungkangyi Beds” from northern Shan State and it is figured herein for the record Fig. 10.13).
Discussion. This pygidium described above is typical of those belonging to the genus Ovalocephalus Koroleva, and Reed (1915) was mistaken in associating it with the calymenoid cranidium on his pl. 8, figs 6,7. Zhou et al. (2010) reviewed the synonymy, taxonomy and included species of Ovalocephalus Koroleva. The single pygidium figured here is important as the first record from the Reed collections of a genus that is widely recorded in the Ordovician of eastern Asia and certain Kazakh terranes, and can be regarded as an indicator of subtropical Gondwana and peri-Gondwanan terranes until the late Katian, when it migrated to western Gondwana in response to what has been claimed as a short-lived episode of global warming (Fortey & Cocks, 2005). The pygidium is not determinable to species, but is unlike the stratigraphically earlier species reviewed in Zhou et al. (2010), which have noticeably posteriorly-turned pleural ribs. As an internal mould, the pleural furrows appear wider than in many species figured from better material. O. kanlingensis Zhang, 1981 (Darriwilian-Sandbian, material figured in Zhou et al., 2010) has similarly arranged pleural ribs, although the Reed material is inadequate for confident determination.
As noted above, two specimens attributed to Encrinurella insangensis by Reed (1915) are excluded from that species. The cranidium (Fig. 10.5) shows inflated posterolateral glabellar lobes, which appear to be part of the occipital ring. They resemble the circular basal glabellar lobes of Ovalocephalus, but these are pre-occipital (Zhou et al., 2010). It is conceivable that the lobes on the Burmese specimen have migrated backwards to a (pseudo) occipital position. There are indications on the internal mould of the glabella of large tubercles, which were presumably expressed on the dorsal surface. A partial thorax (Reed, 1915, pl. 8 fig. 21; Fig. 10.8) displays lateral inflated areas on the axial rings, which suggests it could belong with the cranidium. While excluded from Encrinurella, these specimens are possibly closer to Ovalocephalus, although if coarse tubercles are present it is unlike other species of that genus.
The unlocalised cranidium (Fig. 10.13) is more consistent with similarly preserved specimens of Ovalocephalus, including the type species O. tetrasulcatus Kielan, 1960. However, Zhou et al. (2010) illustrated a number of other late Ordovician Ovalocephalus species with elongate (sag.) glabellas with short glabellar furrows and our internal mould here is inadequate for precise identification. It is conceivable that it is the cranidium appropriate to Reed Ovalocephalus sp. pygidium but we cannot prove this without further collections.
description: Published as part of Fortey, Richard A., Wernette, Shelly J. & Hughes, Nigel C., 2022, Revision of F. R. C. Reed's Ordovician trilobite types from Myanmar (Burma) and western Yunnan Province, China, pp. 301-356 in Zootaxa 5162 (4) on pages 335-336, DOI: 10.11646/zootaxa.5162.4.1, http://zenodo.org/record/6810290