Ovalocephalus sp.

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, Zootaxa 5162 (4), pp. 301-356 : 335-336

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.

Figures

FIGURE 10. (1, 2) Lonchodamas? sp. (Reed) from the Li-Lu Formation (Katian), Lilu, northern Shan State, Myanmar. 1a, b. Pygidium (original of Reed 1915, pl. 5, fig. 6), GSI 11508, original and retrodeformation. 2. Cranidium (refigured from Reed 1915, pl. 5, fig. 5), GSI 11507. (3, 6) Lonchodamas shanensis (Reed) from the Hwe Mawng Beds (uppermost Katian), northern Shan State, Myanmar. 3. Pygidium (original of Reed 1915, pl. 5, fig. 3), GSI 11505, Hwe-hok. 6. Cranidium (original of Reed 1915, pl. 5, fig. 2), GSI 11504, Mong Ha. (4) Dionide hybrida (Reed), Cephalon (original of Reed 1915, pl. 5, fig. 7), GSI 11509, Hwe Mawng Beds (uppermost Katian), Hwe-hok, northern Shan State, Myanmar. (5, 8) Ovalocephalus? sp. indet. (Reed) from the Li-Lu Formation (Katian), Mân-ngai, northern part of Shan State, Myanmar. 5. Cranidium (original of Reed 1915, pl. 8, fig. 17), GSI 11563. 8. Thorax (original of Reed 1915, pl. 8, fig. 21), GSI 11567. (7) Pliomerina martellii (Reed), Cranidium (original of Reed 1917, pl. 8, fig. 15), GSI 11915, Shihtien Formation (Darriwilian), Pupiao, Baoshan Prefecture, western Yunnan, China. (9) Prionocheilus liluensis (Reed), Cranidium (original of Reed 1915, pl. 8 figs 6 and 7), GSI 11554, Li-Lu Formation (Katian), Lilu, northern Shan State, Myanmar. (10, 13) Ovalocephalus sp. (Reed) from the Li-Lu Formation (Katian), Lilu, northern Shan State, Myanmar. 10. Pygidium (original of Reed 1915, pl. 8, fig. 9), GSI 11556. 13. Cephalon; not previously figured; no GSI catalogue number. (11, 12) “Calymene” oldhami (Reed) from Lower Naungkangyi Beds (probable Darriwilian), Mâ Shio, northern Shan State, Myanmar. 11. Cephalon and thorax (original of Reed 1915, pl. 8, fig. 11), GSI 11558. 12. Cephalon and partial thorax (original of Reed 1915, pl. 8, fig. 10), GSI 11557. Scale bars = 2 mm for 1–3, 6, 8–13; = 5 mm for 4, 5; = 1 mm for 7.

FIGURE 13. (1) Hadromeros? submitis (Reed), Cranidium (original of Reed 1915, pl. 8, fig. 13), GSI 11560, Li-Lu Formation (Katian); Lilu, northern Shan State, Myanmar. (2) Placoparina? dravidicus (Reed), Pygidium (original of Reed 1915, pl. 8, fig. 12), GSI 11559, Lower Naungkangyi Beds; Mâ Shio, northern Shan State, Myanmar. (3) Sphaerocoryphe sp. (Reed), Cranidium (original of Reed 1906, pl. 5, fig. 26), GSI 8340, Naungkangyi Beds, Insang, northern part of Shan State, Myanmar. (4–9) Yanhaoia wynnei (Reed) from the Li-Lu Formation (Katian) and Hwe Mawng Beds (uppermost Katian), northern Shan State, Myanmar. 4. Cranidium (original of Reed 1915, pl. 9, fig. 3), GSI 11569, Mân-ngai. 5. Partial cranidium (original of Reed 1915, pl. 9 fig. 7), GSI 11573, Hwe Mawng. 6. Partial cranidium (original of Reed 1915, pl. 9, fig. 11), GSI 11577, Mong Ha. 7. Pygidium (original of Reed 1915, pl. 9, fig. 12), GSI 11578, Hpakhi. 8. Cranidium and thorax (cast from lectotype, original of Reed 1915, pl. 9, fig. 10), GSI 11576, Hwe Mawng. 9. Pygidium (original of Reed 1915, pl. 9, fig. 5), GSI 11571, Nawng Yu. (10–11) Dalmanitina? dagon (Reed) from the Li-Lu Formation (Katian) and Hwe Mawng Beds (uppermost Katian), northern Shan State, Myanmar. 10. Cranidium (refigured from Reed 1915, pl. 9, fig. 2), GSI 11568-11572, Mân-ngai. 11. Cephalon (original of Reed 1915, pl. 9, fig. 1), GSI 11568, Mân-ngai. (12) Illaenus sp. (Reed), Partial cranidium (refigured from Reed 1917, pl. 8, fig. 3), GSI 11906, Shihtien Formation (Darriwilian), Pupiao, Baoshan Prefecture, western Yunnan, China. Scale bar = 2 mm for 1, 3, 4, 6–9; = 5 mm for 2, 5, 10–12.