Bunocephalulus serranoi Bogan and Agnolin, 2024

Bogan, Sergio & Agnolín, Federico L., 2024, First Fossil Record Of Aspredinidae: A New Species From The Late Miocene Of Northeastern Argentina, Zootaxa 5493 (4), pp. 392-400 : 394-396

Bunocephalulus serranoi Bogan and Agnolin , sp. nov.

Fig. 2A–B , 3A

Holotype. MAS-PV-795, nearly complete skull, pectoral girdle including the proximal end of pectoral spines, and incomplete Weberian apparatus ( Fig. 2 ).

Diagnosis. Bunocephalus species having skull with thick bones having prominent crests and bony margins having the following combination of characters ( Figs 2–3 ): 1—Presence of two prominent mounds at the level of the supratemporal fossae (vs. poorly developed in several species, such as B. doriae and B. erondinae ; whereas in other species, such as B. verrucosus these tubercles are prominent and form a knobby ornamentation; Cardoso, 2010; Friel & Carvalho, 2016); 2—Lateral ethmoid with dorsal surface having tall, rounded and well-defined margins that delimit a deep subtriangular excavation that shows a longitudinal groove at its bottom (in other species such as B. doriae the depression lacks a longitudinal groove, whereas in B. coracoideus the lateral ethmoid margins are narrower and delimit a subtriangular and deep excavation); 3—Lateral ethmoid and frontal lacking protuberances anterior and posterior to the orbits (vs. prominent in B. verrucosus and B. chamaizelus ); 4—Interorbital width representing 28.4% of total head length (more than 29% in B. kneri , B. aleuropsis , B. amaurus , and B. colombianus ; Carvalho et al. 2015); 5—Thick, but relatively narrow epiphyseal bar (vs. epiphyseal bar absent in B. minerim , B. hertzi and B. larai ; Carvalho et al. 2015; Esguícero et al. 2020); 6—Absence of a bump at the anterior half of the frontals, at level of the articulation with the hyomandibular bone (vs. present in B. aloikae , B. coracoideus , B. verruscosus and B. chamaizelus ); 7—Frontals, sphenotic, and pterotic bones show a well-developed ornamentation composed by pits and ridges, and lacking a honeycomb pattern (vs. reduced ornamentation in B. erondinae and B. doriae and strong ornamentation in B. verrucosus ; Cardoso, 2010); 8—Dorsal skull roof showing thickened and rounded crests that extend form the posterior margin of the parieto-supraoccipital and gently diverge towards the anterior margin of the skull, reaching the lateral ethmoid (vs. crests very shallow in some of the bones in B. doriae and B. coracoideus these); 9—Supratemporal fossae smaller than in B. doriae and B. coracoideus ; and 10—Pectoral spine having serration on the anterior surface (vs. absent in B. hartti ; Carvalho et al. 2015).

Description. Head depressed with slightly concave dorsal profile from snout to area of Weberian apparatus. Skull with total head length of 153 mm and interorbital width of 46 mm ( Fig. 2 ). External surface of skull bones with pitted and ridged ornamentation, lacking honeycomb pattern present in some species. Frontals, sphenotics, and pterotics surfaces with ornamentation composed of pits and ridges. Mesethmoid subrectangular in dorsal view and lacks well-developed cornua; with longitudinal dorsal concavity that extends along lateral ethmoid and frontals. Lateral ethmoid with short lateral process and longitudinal depression that extends posteriorly. Frontal together with lateral ethmoid forms strongly concave orbital margin. Frontals in contact with each other by means of well-developed epiphyseal bar that separates anterior and posterior cranial fontanels. Epiphyseal bar thick, rounded, and tall, and extends beyond frontals up to lateral process at posterior margin of orbit. Posterior cranial fontanel anteriorly delimited by transversely positioned epiphyseal bar and laterally by longitudinal thick crest of frontal. Sphenotic elongate with very thick lateral margin on anterior part, which together with longitudinal crests of frontal delimit a subtriangular concavity in dorsal view.

Posterior cranial fontanel wide and ovoidal in contour, and contacts posteriorly with deep and wide median groove; floor of median groove strongly ornamented by rugosities; lateral margins of groove tall and thick, forming longitudinal crests that converge posteriorly at supraoccipital bone and form shallow bump. Longitudinal crests with two prominent bumps at same level of supratemporal fossae. Supratemporal fossae shallow and not delimited by crests or ridges. Pterotic with laminar lateral expansion forming angle of about 90° with anteroposterior axis of skull; lateral expansion anteroposteriorly elongate.

Posttemporal-supracleithrum wide transversely with anterolateral process subtriangular and elongated, overlying dorsal process of cleithrum. Anteromedial and posterior processes of posttemporal-supracleithrum form nearly straight line, resulting in L -shaped element. Anteromedial and posterior processes of posttemporal-supracleithrum delimit subquadrangular fossa with anterior margin of parapophysis of fourth vertebra of Weberian apparatus.

Supracleithrum with central posterior process with rounded bump on anterior margin. Posteriorly, supracleithrum connected with thick dorsal lamina of Weberian apparatus visible as bump at level of parapophysis of fourth vertebra. Cleithrum with strongly ornamented outer surface composed of narrow ridges separated by concavities. Cleithrum with two posterior processes; posteriodorsal process subtriangular in contour and fits with supracleithrum; posterior process narrow and subtriangular in laterally, and strongly medially projected with wide posterior contact with the scapulocoracoid ventrally. Suture between scapulocoracoids with long, narrow denticulations, forming interdigitating articulation; suture area fan-shaped and transversely expanded. Posterior process of coracoid long and roughly rod-shaped; surface for articulation with cleithrum nearly straight. In ventral view, scapulocoracoid and cleithrum with ornamentation composed of well-defined, small pits. Body width at cleithrum 95 mm. Height of head between supraoccipital and intercoracoid suture 84 mm.

Pectoral spine incompletely preserved, relatively thick with serrations on anterior margin beginning on proximal portion. Posterior margin of pectoral spine serrated.

Etymology. The specific name honors the anthropologist Professor Antonio Serrano (1899-1982), born in Paraná, Entre Ríos province. He was a very active promotor of the “Asociación Estudiantil Pro-Museo Popular” that resulted in the creation of the Museo de Ciencias Naturales y Antropológicas de Paraná “Antonio Serrano” (MAS).

Figures

FIGURE 2. Holotype of Bunocephalus serranoi nov. sp. (MAS-PV-795) compared with extant Bunocephalus doriae (CFA- IC-6516) in A, C, dorsal; and B, D, ventral views. Abbreviations. Cl, cleithrum; Cl S, cleithrum suture; Cor, coracoid; Cor S, coracoid suture; Dor lam Web, dorsal lamina of the Weberian apparatus; Dor P, dorsal process of cleithrum; Hum P, humeral process of cleithrum; Hyo, hyomandibular; Op, opercle Po, preopercle; Scl, supracleithrum; Sp, pectoral spine. Scale bar: 5 mm.

FIGURE 3. A, holotype skull of Bunocephalus serranoi nov. sp. (MAS-PV-795), B, extant Bunocephalus doriae (CFA-IC- 8560) in dorsal view.Abbreviations.ACF anterior cranial fontanel; BU, bump; ELD, lateral ethmoid depression; EP, epiphyseal bar; F, frontal; LAT, lateral ethmoid; MGR, median groove; PCF, posterior cranial fontanel; PTE, pterotic; STF supratemporal fossa; SPH, sphenotic; SOC, supraoccipital or parieto-supraoccipital. Scale bar: 5 mm.