Definitive specimens of Merlucciidae (Gadiformes) from the Eocene James Ross Basin of Isla Marambio (Seymour Island), Antarctic Peninsula

Abstract

An isolated partial right dentary (BAS D.515.2) collected by the British Antarctic Survey prompted a re-evaluation of gadiform remains from the La Meseta Formation (conventionally middle Eocene) of Isla Marambio (Seymour Island), Antarctic Peninsula. Modern gadiforms (hakes and cods) range from the Arctic to Antarctic, inhabiting deep sea benthic, shore, estuarine, and freshwater environments. Based on a fossil record primarily composed of otoliths, they are known to extend back to the Eocene and Oligocene. The new specimen was recovered from the fossil penguin locality D.515. It is characterized by a single row of sharp, ankylosed teeth set upon robust bony pedestals. The surface anterior to the mental foramen exhibits ascending and descending ridges with slightly rugose texture. The ascending ridge is fractured, but partially covers the lateral aspect of the tooth row. BAS D.515.2 is unlike the dentary of macrourid gadiforms, also recovered from the Eocene of Antarctica. BAS D.515.2 preserves several features similar to previously published accounts of the gadiform ''yMesetaichthys'' from Isla Marambio. These specimens are probably the same taxon and their combined character suite indicates it is a member of Merluccidae. Thus, these are the only non-otolithic skeletal specimens of an Eocene hake known outside of the London Clay's yRhinocephalus.

Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica

“…4A, D; 5A and 6F), as also stressed by Claeson et al (2012). Most gadiforms have such open grooves (Fig.…”

“…It was the first de ter mined fos sil notothenioid, which Balushkin (1994) named Proeleginops grandeastmanorum. East man (2000) had been re luc tant to ac cept the mis iden ti fi ca tion, but later he ap par ently ac cepted it (see Claeson et al, 2012). Arratia et al (2004: p. 48) did not rec ognize Balushkin's re vi sion.…”

“…5) fig ured two premaxillary frag ments and two den tary frag ments from the Field Mu seum of Nat u ral His tory, Chicago col lec tion (FMNH), and de ter mined the for mer as "...a gadiform type...", while the den ta ries were de scribed as "...in deter mi nate tele osts...". The lat ter, how ever, are now called ...defin i tively Merlucciidae... by Claeson et al (2012).…”

“…were notothenioids, and they de cided that the premaxillaries were prob a bly from gadiforms, and the den ta ries were in de ter mi nate like the ver te brae. This opin ion was changed con cern ing den ta ries (Claeson et al, 2012) when de scrib ing a poorly pre served bone with frag men tary dentition, and the de termi na tion be came much more pre cise as merlucciids , fol low ing Jerzmañska and OEwidnicki (1992). Clearly these jaw frag ments are of the same sort as the more well-pre served ones de scribed here, just from much smaller fishes.…”

“…The con clu sion was gadiform re la tion ship for the fos sils, although the match with the ma jor ity of the ma te rial was poor, and they in di cated (Jerzmañska and OEwidnicki, 1992: p. 248) that the dentitions are quite dif fer ent. Claeson et al (2012) took the de ter mi na tion a step fur ther as merlucciid (al though very lit tle sim i lar ity with Melanonus), and they tried to in voke also the dentition as an ar gu ment. We find es pe cially the lat ter en tirely un con vinc ing, be cause Merluccius has very dif fer ent dentition.…”