Oxydoras sp.

Carrillo-Briceño, Jorge D., Mora-Rojas, Laura, Hendricks, Kimberly, Vanegas, Andrés & Aguilera, Orangel, 2023, New clues on the palaeodiversity of the middle Miocene freshwater ichthyofauna from the Tatacoa Desert, Colombia, Geodiversitas 45 (10), pp. 327-351 : 335-336

Oxydoras sp.

( Fig. 3 C1-C3).

MATERIAL EXAMINED. — Incomplete neurocranium ( ULA-1316 ) .

LOCALITY. — Villavieja Fm. LA-3 (fish bed) (seeFig.1B; Appendix 1).

DESCRIPTION

ULA-1316 is an incomplete neurocranium of 51 mm in length, preserving only the anterior section of the skull ( Fig. 3 C1-C3), and is assigned here to Oxydoras . It preserves a complete mesethmoid bone clearly observable in both dorsal and ventral views. It has an elongate arrow-shape with a bifid anterior tip, and a convex profile in lateral view ( Fig. 3 C1). In dorsal view, the anterior section of both right and left frontals and both right and left lateral ethmoids are articulated to the mesethmoid; the most proximal section of the anterior cranial fontanelle is also preserved ( Fig. 3 C1). The ornamentation of the skull is not well defined, possibly as a result of erosion. In ventral view, the mesethmoid, vomer, remnants of what appear to be lateral ethmoids, and the parasphenoid are preserved ( Fig. 3 C2). The vomer has an arrow-shaped anterior section and seems to have reduced anterolateral processes; its posterior section is elongated and narrow, being enclosed in the anterior bifid tip of the parasphenoid.

REMARKS

ULA-1316 possess a mesethmoid bone similar to those present in living and fossil representatives of Oxydoras , which can be differentiated from the mesethmoid bones of any other living ( Birindelli 2014) or fossil (see Lundberg et al. 2010) species of doradid. The thorny catfish Oxydoras is represented by three extant species, Oxydoras niger (Valenciennes in Humboldt & Valenciennes, 1821), Oxydoras kneri Bleeker, 1862a , and Oxydoras sifontesi Fernández-Yépez, 1968 , from the Amazon, Essequibo, Orinoco and Paraná basins. These species occur over mud in streams and lakes, but are also present in large rivers ( Froese & Pauly 2022). The only fossil of Oxydoras known to date corresponds to an isolated mesethmoid bone from the Miocene of Peru illustrated by Lundberg et al. (2010). Although ULA-1316 resembles the skull of the extant O. niger (see Birindelli 2014; Prestes-Carneiro et al. 2019), and/ or the other two living species O. kneri and O. sifontesi , its incomplete and poor state of preservation make it difficult to associate this fossil specimen with any of these extant species. The skulls of the extant species of Oxydoras usually present well-defined ornamentation (see Birindelli 2014: fig. 25); in the case of ULA-1316, the ornamentation pattern is not well-defined or is absent, possibly as a consequence associated with taphonomic processes or erosion of the fossil during its exposure in the outcrop. Due to that, ULA-1316 is tentatively assigned to Oxydoras sp. This fossil specimen from the middle Miocene of the Honda Group, and the isolated mesethmoid bone from the Miocene ( Lundberg et al. 2010), are to date the only known fossils of Oxydoras .

Figures

FIG. 3. — Siluriforms from the Honda Group: A1-A3, complete lapillus otolith (Holotype) of †Sciades maldonadonis n. sp. (VPPLT-832) from the Honda Group. B1-B3, dorsal spine fragment of Ariidae indet.(VPPLT-1108);C1-C3, incomplete neurocranium of Oxydoras sp.(ULA-1316);D-M, Phractocephalus sp.;D, parietosupraoccipital frontal fragment (VPPLT-1272); E, F, parieto-supraoccipital bone fragments; E, VPPLT-1128; F, VPPLT-223; G, pterotic fragment (VPPLT-442); H, sphenotic fragment,VPPLT-421;I, indeterminate fragments,VPPLT-742;J, right pectoral girdle (IGM-s/n°);K-M, pectoral spines fragments;K, M, VPPLT-043; L, ULA-44; N-P, Hoplosternum sp.; N, O, parieto-supraoccipital; N, VPPLT-1453; O, ULA-829; P, left pectoral-fin spine, VPPLT-1250; Q-T, Doradidae indet.; Q, R, parieto-supraoccipital; Q, VPPLT-921; R, ULA-2997; S, T, fragmented pectoral-fin spines; S, VPPLT-43; T, VPPLT-1442; U1, U2, cf. Acanthicus sp., pectoral-fin spine, VPPLT-469; V1, V2, cf. Hypostomus sp., left pectoral-fin spine, VPPLT-504; W, X, Loricariidae indet.; W, skull fragment, VPPLT-1375;X, portion of a caudal fin, ULA-2413. Views: B1, U1, V2, anterior; C1, D-I, N-R, V1, dorsal; A1, dorsal face; C3, left lateral; A3, X, lateral; B2, U2, posterior; B3, J, right lateral; C2, ventral; A2, ventral face; K-M, S-T, W, indet. Abbreviations: acf, anterior cranial fontanel; ad, anterior dentations; adp-cl, anterior dorsal process of cleithrum; cl, cleithrum; fr, frontal; lf, left frontal; lle, left lateral ethmoid; mes, mesethmoid;pas, parasphenoid;pd, posterior dentations;pdp-cl, posterior dorsal process of cleithrum; pp-cl, posterior process of cleithrum; rf, right frontal; rle, right lateral ethmoid; sop, parieto-supraoccipital; vtp, vomeral tooth plate. Scale bars: A, N, V, 6 mm; B, E, F, L, O, Q-S, W, X, 5 mm; C, D, H, I, K, 10 mm; G, 7 mm; J, 20 mm; M, 8 mm; P, 3 mm; T, 4 mm; U, 9 mm.