Macruronus eastmani, 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 : 154-156

Macruronus eastmani sp. nov.

( Figs 4C—F , 6D—F )

1985 Macruronus sp. Schwarzhans: 25, figs 40—42.

Material. Holotype: NRM-PZ P.15970 ( Figs 4C—E , 6D—F ). Paratypes: two specimens, NRM-PZ P.15971 ( Fig. 4F ). Other material: six fragmentary specimens, NRM-PZ P.15972.

Occurrence. Telm 5 unit; ‘ Natica horizon’, Cucullea I member, La Meseta Formation, late Ypresian, early Eocene. Site IAA 1/90, Seymour Island, Antarctica.

Etymology. Named in honour of Joseph T. Eastman (Athens, Ohio, USA) in recognition of his contribution to the knowledge of fossil Antarctic fishes. Together with Lance Grande, he was also the first to recognize the presence of fossil gadiforms in the Eocene of the La Meseta Formation.

Diagnosis. OL:OH = 1.85—1.95. Ventral rim regularly and moderately deeply curved. All rims and outer face intensely crenulated. CCL: OCL = 1.3. Collum rather wide, with distinct pseudocolliculum.

Description. Moderately large and thin otoliths up to at least 8 mm in length (holotype 6 mm long) and rather compressed for a species of the genus Macruronus . OH: OT = 3.7—4.0. Dorsal rim divided into three equally long stretches with broad, obtuse predorsal and rounded postdorsal angles at joints, pre- and postdorsal rims regularly inclined, mediodorsal rim flat to slightly concave, slightly backward inclined; predorsal angle consequently highest point on dorsal rim. Ventral rim regularly curved and moderately deep, deepest just anterior of collum. Anterior tip rounded, at level of ostium; posterior tip slightly projecting, rounded. All rims intensely crenulated, medioventral rim the least.

Inner face convex, bent along horizontal axis, with slightly supramedian positioned, moderately wide and shallow sulcus terminating close to anterior and posterior tips of otolith and almost joining them. Sulcus curved, deepest at collum, with ostium only slightly shorter than cauda. Ostial and caudal colliculi well marked, shallow; ostial colliculum anteriorly not reduced; caudal colliculum with slightly bent dorsal margin. Collum moderately wide, with distinct pseudocolliculum. Dorsal field with many long radial furrows, partly reaching into sulcus, and small dorsal depression; ventral field with distinct, thin ventral furrow moderately close to ventral rim of otolith, several faint radial furrows, mostly not extending across ventral furrow. Outer face concave with many long radial furrows coalescing in a shallow central ridge.

Remarks. The first otoliths of this species were recovered from the late Eocene of South Australia ( Schwarzhans 1985), but they were too poorly preserved to allow a specific identification at the time. The specimens from Seymour Island clearly represent the same species characterized by the relatively compressed shape when compared to other species of the genus, which always have an OL:OH well above 2.0, the deeper ventral rim, the rather long ostium ( CCL: OCL = 1.3) and the presence of a pseudocolliculum in the collum. Macruronus eastmani is the earliest known species of the genus, and the diagnostic characters are all considered plesiomorphic, except possibly for the pseudocolliculum.

Now, Macruronus is a typical endemic gadiform of the temperate Southern Ocean living above the lower shelf and the upper slope. It is identified as an old merlucciid lineage and it appears to have always been geographically bound to the same general area through its evolution during the Palaeogene and Neogene ( Schwarzhans 1980, 1985). In New Zealand, Macruronus is first recorded in the late Oligocene, after the establishment of the circum-Antarctic deep water current ( Schwarzhans 1980). During the Eocene, the Merlucciidae was represented by the extinct otolith-based genus Macrurulus Schwarzhans, 1980 in New Zealand.

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.