Phractocephalus undetermined
Creators: name: Carrillo-Briceño, Jorge D.
name: Mora-Rojas, Laura
name: Hendricks, Kimberly
name: Vanegas, Andrés
name: Aguilera, Orangel
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Siluriformes
Pimelodidae
Phractocephalus
Phractocephalus undetermined

description: Phractocephalus sp.
(Fig. 3 D-M).
MATERIAL EXAMINED. — Fourteen skull fragments (IGM-87- 314, -2221-f-a, -2382-b (no. 2), and VPPLT-223, 421(no. 2), 422 (no. 2), 742, 1128, 1272, 1282, 1432); a pectoral girdle (IGM-s/n), and 12 pectoral/dorsal fragmented spines (IGM-2285-c, ULA-44, and VPPLT-043 (no. 4), 417, 473, 474, 1092, 1478, 1482).
LOCALITIES. — La Victoria Fm. Diomatal-Museo La Tormenta (VPPLT-1478, 1-482); Km-121 (VPPLT-043, 223, 742, 1128, 1432); Tatacoita (VPPLT-417, 421, 422, 470, 473, 474, 1092); San Nicolás (VPPLT-1272, 1282). — Villavieja Fm. Duke 46 (IGM-87-314); LA 2 (ULA-44). — Indeterminate Fm. Alrededor del Campamento de la Venta, Villa vieja (IGM-2382-h); Norte del Punto 16 (IGM-2221-h-a); NW del Campamento de la Venta, Villavieja (IGM-2285-c) (see Fig. 1B; Appendix 1).
DESCRIPTION
The dorsal surface of the skull, including the sphenotic, pterotic, and parieto-supraoccipital bones, has well-developed dorsal ornamentation characterized by dense, deep, and rounded pits surrounded by a thick and tall crest arranged in a mosaic (Fig. 3 D-I). The ornamentation in the frontal and the parieto-supraoccipital bones are characterized by elongated and parallel pits delimited by a stronger crest. These ornamentation patterns of elongated and parallel pits, gutter-like, are slightly interrupted at the middle part by changes in the ornamentation pattern that consist of disperse oval pits (Fig. 3 D). The postero-lateral laminar projections of the parieto-supraoccipital bone form a thick and strong arch on both sides. The external surface is densely ornamented with small pits irregularly arranged. However, the entire bone expansion is not complete, and the distal smooth edge is not preserved (Fig. 3 E-F). The ornamentation on the pterotic bone shows a pattern of parallel alignment of the pits. The largest pits are arranged in the medial region, and the minor ones are aligned in the outermost region of the bone (Fig. 3 G). The sphenotic has a stronger anastomosing ridge on the dorsal surface (Fig. 3 H). The pectoral girdle is robust with the posterior process of the cleithrum expanded in a thick laminar bone in a triangular-shape. The outer surface is densely ornamented with a series of pits arranged in oblique rows in most of the upper area, and pits in a random distribution on the lower area. Both, the anterior dorsal process and posterior dorsal process of the cleithrum are robust (Fig. 3J). The ornamentation in the pectoral spines form elongated, crossed and irregular crest without rounded or ovoid pits. The anterior edge has small acute spines oriented posteriorly and on the posterior edge the small spines are robust, and obtuse without a well-defined orientation (Fig. 3 K-M).
REMARKS
Phractocephalus is represented by the single extant species P. hemioliopterus. The fossil record of the genus includes † Phractocephalus nassi Lundberg & Aguilera, 2003, from the late Miocene Urumaco Fm in Venezuela, † Phractocephalus acreornatus Aguilera et al., 2008, from the late Miocene Solimões Fm in Brazil, and † Phractocephalus yaguaron Bogan & Agnolin, 2019, from late Miocene Ituzaingó Formation, Argentina. † Phractocephalus ivy Azpelicueta & Cione, 2016, from late the Miocene of Argentina was recently referred to the extant genus Steindachneridion Eigenmann & Eigenmann, 1919 (see Bogan & Agnolín 2019). The skull bones of Phractocephalus from the Honda Group can be distinguished from those of extinct species by the stronger ornamentation pattern, density, and depth of the circular pits surrounded by thick crest arranged in a mosaic-like pattern vs. less skull ornamentation in † P. acreornatus and † P. nassi. Skull bones in † P. yaguaron are strongly ornamented with reticulating ridges and subcircular pits (see Azpelicueta & Cione 2016; Bogan & Agnolín 2019), a pattern that is relatively different from the specimens from the Honda Group, where ornamentation, especially in frontal and the parieto-supraoccipital bones, show continuous elongated and parallel pits (see Fig. 3 D-F). Lundberg (1997) described a partial mesethmoid bone and a fragmented pectoral-spine (Lundberg 1997: fig. 5.9A) from the Fish Bed locality as extant P. hemioliopterus; nevertheless, these materials were later referred to as too incomplete to assess their species status (Lundberg & Aguilera 2003). The ornamental pattern on specimens from the Honda Group shows clear differences from the skull ornamentation in the extant P. hemioliopterus (e.g., see skulls illustrated in Lundberg & Aguilera 2003; Aguilera et al. 2008; Bogan & Agnolín 2019). Based on the skull and pectoral/dorsal spine ornamentation, the Phractocephalus specimens from the Honda group is most closely related to † P. nassi. Nevertheless, by the fragmentary conditions of bones and the absence of well-preserved diagnostic elements to support an accurate diagnosis and description, we tentatively use an open nomenclature for the Phractocephalus specimens from the Honda Group.
Phractocephalus hemioliopterus occurs in a broad range of habitats, from large rivers to flooded forests and lakes, with a wide distribution in the Orinoco and the Amazon (van der Sleen & Albert 2018). Recently, a reticulate nuchal plate attributed to Phractocephalus sp. was recorded from the middle Miocene Castilletes Formation in the Guajira Peninsula, northern Colombia (Ballen et al. 2021a), and this report, together with the other fossil Phractocephalus from northwestern Venezuela (Lundberg & Aguilera 2003) suggests a broader distribution of the genus during the Miocene and support ancient connections between trans-Andean and cis-Andean drainages.
Other siluriforms taxa reported herein (Table 1) and in previous works (e.g., Lundberg 1997, 2005) for the Honda Group include Hoplosternum Gill, 1858 (Fig. 3 N-P), the loricariids cf. Acanthicus Agassiz, 1829 (Fig. 3U 1-U 2), and cf. Hypostomus Lacépède, 1803 (Fig. 3V 1-V 2), and the pimelodids Brachyplatystoma (Fig. 4A 1-B 2), and Pimelodus Lacépède, 1803 (Fig. 4C). The goliath catfish † Brachyplatystoma promagdalena Lundberg, 2005, was described from the Fish Bed layer.Tentatively we designate the siluriforms as the most diverse fish group of the Honda Group (Fig. 5). Other bony fishes reported from the Honda Group (see Table 1) includes cynodontids or “dogtooth characins” (Fig. 4E 1-F 2), “piranha-like” and “pacu” serrasalmids (Fig. 4G 1-M), dipnoids (Fig. 4D 1-D 2), and osteoglossiforms (Fig. 4N 1-N 2).
description: Published as part of 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, pp. 327-351 in Geodiversitas 45 (10) on pages 336-338, DOI: 10.5252/geodiversitas2023v45a10, http://zenodo.org/record/8056044