Makaira panamense Fierstine, 1978

Gracia, Carlos De, Correa-Metrio, Alex, Carvalho, Monica, Velez-Juarbe, Jorge, P ̆ rik, Tom ́ a ̆ s, , Carlos Jarami & Kri, nd Jurgen, 2022, Towards a unifying systematic scheme of fossil and living billfishes (Teleostei, Istiophoridae), Journal of Systematic Palaeontology (2091959) 20 (1), pp. 1-36 : 18

† Makaira panamense Fierstine, 1978

( Figs 7E, 9G, 11D–G, Supplemental material Fig. S5 A)

1978 † Makaira panamensis Fierstine : 2, figs 1, 2, 4c.

Emended diagnosis. An extinct species of Makaira characterized by the following combination of traits (autapomorphic characters indicated by an asterisk): triangular basioccipital process$; massive prenasals that in dorsal view are strongly fused at the 0.5 L region forming a solid structure$; narial cavities divided in two voids and distinctively enclosed only by prenasals$.

Holotype. USNM 18710, a large neurocranium with a poorly preserved rostrum with an estimated length of 953 mm ( Fig. 11D–G).

Occurrence. Only known from the late Miocene (6.4–5.8 Ma). Chagres Sandstone Member, Chagres Formation, Colon, Panama. The precise site of collection is unknown.

Remarks. The holotype is a large partial neurocranium with a poorly preserved rostrum, with an estimated length of 953 mm ( Fig. 11D–G). Only the left anterior half of the skull roof and one fourth of the distal rostrum are missing ( Fig. 11D, E). The specimen is slightly dorsoventrally compressed and twisted ( Fig. 11D, E). The neurocranium is wide, squared and depressed ( Fig. 11D–F). The orbit is elongated ( Fig. 11F) and the dorsal wall of the myodome is wider than high in the sidewalls. The vomer and the parasphenoid also are wide. The vomer has a small anterior projection and the angle of the parasphenoid is acute ( Fig. 11E, F). The basioccipital process is triangular, rather than elongated ( Fig. 11G), displays low paired ridges on the dorsal surface of the supraoccipital and the dorsal surfaces of the exoccipital form together a board posterior projection. For additional, more detailed descriptions of the skull see also Fierstine (1978).

The rostrum of † Makaira panamense ( USNM 18710) is broken at c. 0.5 L distance ( Fig. 11F). The distal-most part of the rostrum (0.25 L) is weathered, very poorly preserved and the distal tip is missing so that it is not possible to observe sutures ( Fig. 11D, E). The estimated length is 953 mm based on the preserved portion ( Fig. 7E) ( Fierstine 1978). In dorsal view, the premaxillae overlap the prenasals at their proximal end and the narial cavity is enclosed only by the prenasals ( Figs 7E, 11D, E, Supplemental material Fig. S5 A). The rostrum is massive and stout, and has an oval outline in cross-section at 0.5 L ( Fig. 9G). The internal canals are relatively large ( Table 3 ), located medially, centrally aligned and have an oval outline ( Fig. 9G). At the proximal end of the rostrum, the prenasals are massive, contact each other along the midline (Supplemental material Fig. S5 A), and are strongly fused forming a solid structure ( Fig. 11D, Supplemental material Fig. S5 A). Makaira panamense was not analysed in the PCA because all features at 0.25 L are lacking because of the incomplete distal section of the rostrum.