Palimphemus seymourensis, Schwarzhans & Mors & Engelbrecht & Reguero & Kriwet, 2017

Schwarzhans, Werner, Mors, Thomas, Engelbrecht, Andrea, Reguero, Marcelo & Kriwet, Jurgen, 2017, Before the freeze: otoliths from the Eocene of Seymour Island, Antarctica, reveal dominance of gadiform fishes (Teleostei), Journal of Systematic Palaeontology 15 (2), pp. 147-170 : 156-157

Palimphemus seymourensis sp. nov.

( Figs 4G—M , 6G—I )

Material. Holotype: NRM-PZ P.15973 ( Figs 4G—I , 6G—I ) . Paratypes: six specimens, NRM-PZ P.15974—15975 ( Fig. 4J—M ).

Occurrence. Telm 5 unit; ‘ Natica horizon’, Cucullea I member, La Meseta Formation, late Ypresian, early Eocene. Site IAA 2/95, Seymour Island, Antarctica.

Etymology. Named after the type locality Seymour Island in Antarctica.

Diagnosis. Outline droplet-shaped with broadly rounded anterior rim and slightly elevated predorsal region. OL: OH = 1.8—1.9. Inner face moderately convex. Sulcus narrow, with moderately widened collum and distinct, but short pseudocolliculum. CaL:OsL (measured from centre of collum) = 1.2—1.35. Colliculi often reduced towards outer margin, particularly ostial colliculum. Ventral furrow well developed, close to ventral rim of otolith.

Description. Moderately elongate and moderately thick droplet-shaped otoliths of up to 4.5 mm in length (holotype 4.5 mm long). OH:OT = 2.1—2.5. Dorsal rim highest anteriorly above ostial collum in a broadly rounded predorsal angle, somewhat undulating, posteriorly regularly declining without prominent angle. Ventral rim smooth, regularly curved, deepest below rear part of ostium. Anterior rim broadly rounded, with its tip mostly below ostium; posterior rim tapering with rounded tip at level of cauda.

Inner face moderately convex with slightly supramedian, narrow and rather shallow sulcus. Ostium slightly shorter than cauda and slightly narrower. Ostial and caudal colliculi well marked, with relatively wide collum in between and often reduced towards anterior and posterior tips of otolith. Collum somewhat narrowed from ventral with short but distinct pseudocolliculum. Dorsal depression narrow, with indistinct dorsal margin; ventral furrow well developed and close to ventral rim of otolith. Outer face slightly convex to nearly flat, with some radial furrows coalescing in a shallow umbo opposing the collum of the inner face.

Remarks. Otoliths of P. seymourensis vary slightly in the expression of the ornamentation of the dorsal rim and the outer face, irrespective of the size of the otoliths. Small specimens often show somewhat reduced colliculi terminating more distantly from the anterior and posterior otolith rims ( Fig. 4K, M ) than is the case in some larger ones ( Fig. 4J ).

Palimphemus seymourensis represents the first record of a gadid from Antarctica and the Southern Hemisphere, except for the occurrence of Gadiculus antipodus Schwarzhans, 1980 in the early Miocene of New Zealand and the Recent Micromesistius australis off the southern tip of South America and off New Zealand. In the Northern Hemisphere, Palimphemus is well recorded since the early Oligocene. From these species, such as P. brevicollum (Gaemers, 1994) (in Schwarzhans 1994), the new species differs in the relatively thin appearance, the wider collum with a longer pseudocolliculum, and the low index CaL: OsL (1.2—1.35 vs. 1.7—2.0). Early species of the related genus Trisopterus from the Oligocene of Europe show a narrow collum and no pseudocolliculum ( Schwarzhans 1994). The Paleocene and early Eocene of Denmark, England and Greenland have yielded species of the related fossil otolith-based genus Protocolliolus Gaemers, 1976 , which differ from Palimphemus otoliths in the slightly narrower collum without a pseudocolliculum, while the index CaL:OsL is similarly low as in P. seymourensis .

The discovery of P. seymourensis in the early Eocene of Antarctica now represents the earliest record of the genus. It further documents that the Gadidae have had a bipolar temperate distribution in the Palaeogene as opposed to the clearly temperate Northern Hemisphere dominance of today.

Figures

Figure 4. Drawings of Eocene otoliths from Seymour Island. A, B, Tripterophycis immutatus Schwarzhans, 1980, NRM-PZ P.15969, mirror imaged; A, inner face; B, dorsal view. C—F, Macruronus eastmani sp. nov.; C—E, holotype, NRM-PZ P.15970, mirror imaged; C, inner face; D, outer face; E, ventral view; F, paratype, NRM-PZ P.15971, inner face. G—M, Palimphemus seymourensis sp. nov.; G—I, holotype, NRM-PZ P.15973, mirror imaged; G, inner face; H, ventral view; I, outer face; J, paratype, NRM-PZ P.15975, mirror imaged, inner face; K—M, paratypes, NRM-PZ P.15974; K, inner face, mirror imaged; L, ventral view; M, inner face. N—R, Coelorinchus nordenskjoeldi sp. nov.; N—P, holotype, NRM-PZ P.15978; N, inner face; O, ventral view; P, outer face; Q, R, paratype, NRM-PZ P.15979, mirror imaged; Q, inner face; R, ventral view. S—U, Coelorinchus balushkini sp. nov., holotype, NRM-PZ P.15976; S, inner face; T, ventral view; U, outer face. V, W, Coelorinchus sp., NRM-PZ P.15911; V, inner face (strongly eroded); W, ventral view.

Figure 6. Eocene otoliths from Seymour Island. A, Argentina antarctica sp. nov., holotype, NRM-PZ P.15964, mirror imaged, inner face. B, C, Diaphus? marambionis sp. nov., holotype, NRM-PZ P.15966; B, inner face; C, ventral view. D—F, Macruronus eastmani sp. nov., holotype, NRM-PZ P.15970, mirror imaged; D, inner face; E, ventral view; F, outer face. G—I, Palimphemus seymourensis sp. nov., holotype, NRM-PZ P.15973, mirror imaged; G, inner face; H, ventral view; I, outer face. J—L, Coelorinchus nordenskjoeldi sp. nov., holotype, NRM-PZ P.15978; J, inner face; K, ventral view; L, outer face. M, N, Coelorinchus balushkini sp. nov., holotype, NRM-PZ P.15976; M, inner face; N, ventral view. O, P, Hoplobrotula? antipoda sp. nov., holotype, NRM-PZ P.15984, mirror imaged; O, inner face; P, ventral view. Q, Notoberyx cionei gen. nov., sp. nov.; holotype, NRM-PZ P.15987, inner face. R, Cepola anderssoni sp. nov., holotype, NRM-PZ P.15996, mirror imaged, inner face.