Bothriolepis sp.

Racheboeuf, Patrick, Phuong, Ta Hoa, Hung, Nguyen Huu, Feist, Monique & Janvier, Philippe, 2006, Brachiopods, crustaceans, vertebrates, and charophytes from the Devonian Ly Hoa, Nam Can and Dong Tho formations of Central Vietnam, Geodiversitas 28 (1), pp. 5-36 : 30

Bothriolepis sp. ( Fig. 19 )

Fish remains are derived from the basalmost member of the Dong Tho Formation at Cau Rong (CR1, Fig. 17B ). They consist of poorly preserved antiarch plates, the vermiculate ornamentation of which is strongly suggestive of the genus Bothriolepis ( Fig. 19 ). One of these plates can be readily identified as an incomplete posterior ventrolateral plate (PVL), as it shows overlap areas for the anterior ventrolateral and median ventral plates, respectively (oaAVL, oaMV, Fig. 19A 2, B2 ). Its lateral lamina gently increases in height posteriorly and its overall shape agrees with that of most generalized Bothriolepis species , such as B. canadensis (Whiteaves, 1880) , from the lower Frasnian Escuminac Formation of Canada ( Stensiö 1948). Although poorly informative, this material is nevertheless interesting as it suggests that the antiarchs of the Dong Tho Formation are quite different from those of the Ly Hoa Formation, described above. Despite a somewhat similar, siliciclastic lithology, no evidence for either Bothriolepis , or euantiarchs in general, occurs in the Ly Hoa Formation. Although bothriolepidids seem to occur somewhat earlier in eastern Asia and Australia than in Euramerica, their earliest occurence being in the late Emsian in China ( Zhu 2000), they become fairly abundant only in the early Eifelian (Wang S. T. 1993). This, again, suggests that the Ly Hoa Formation is significantly older, most probably Early Devonian in age, than the Dong Tho Formation, and is not a lateral facies of the latter.

Figures

FIG. 19. — Bothriolepis sp., lower part of the Dong Tho Formation, Givetian, Cau Rong, Minh Hoa District, Quang Binh Province, Vietnam, left posterior ventrolateral plate (BT 208a) in ventral (A) and lateral (B) views; A1, B1, photograph; B1, B2, camera lucida drawings. Abbreviations: oaMV, overlap area for the median ventral plate; oaAVL, overlap area for the anterior ventrolateral plate. Scale bars: 10 mm.

FIG. 17. — Locality map: A, Muong Xen area, Nghe An Province (MX 1, brachiopod locality of Noong De Pass); B, Quy Dat and Cau Rong areas, Quang Binh Province (CR1, antiarch and charophyte-bearing locality of Cau Rong; CR2, brachiopod-bearing locality of Cau Rong; BN1, brachiopod locality of Ba Nuong).

FIG. 2. —?Galeaspida gen. et sp. indet., Ly Hoa Formation,?Lower Devonian, Ly Hoa, Quang Binh Province, Vietnam, fragmentary head shield (BT 207a). Scale bar: 10 mm.