Tripterophycis immutatus Schwarzhans 1980

Tripterophycis immutatus Schwarzhans, 1980

(Fig. 4A, B)

1980 Tripterophycis immutatus Schwarzhans: fig. 214.

1985 Tripterophycis immutatus Schwarzhans 1980; Schwarzhans: 22, figs 33—35.

Material. One large, posteriorly eroded specimen, NRM-PZ P.15969, Site IAA 2/95, La Meseta Formation, Seymour Island, Antarctica.

Description. A single, rather large otolith of about 6.7 mm in length. The specimen displays features characteristic for morid otoliths such as the thick appearance where otolith height and thickness is very similar, the flat inner face with the very peculiar sulcus with its flat, oval ostial colliculum and the ridge-like, sharp caudal colliculum sitting in a very depressed, deep cauda. The rear part of the thin, ridge-like caudal colliculum and the posterior tip of the otolith have been broken off in this particular specimen, as is often the case with morid otoliths.

Remarks. The single otolith is about twice the size of the otoliths hitherto recorded from South Australia and New Zealand and differs somewhat in being less elongate (OL: OH = 2.7 vs. 3.1—3.3), although this may be exaggerated by the lack of the rear tip of the otolith. We consider this difference as well as few minor variations in the thickness of the dorsal and ventral rims as an expression of ontogenetic changes.

The genus Tripterophycis now lives on the continental slope, like most morids, of the Southern Ocean. Its otoliths resemble the much more species-rich tropical to temperate genus Physiculus distributed through all oceans, differing primarily by the lack of a predorsal lobe and a bulge of the posterodorsal rim situated well behind the posterior tip of the crista superior. The Eocene T. immutatus likewise appears to have been a species with a circum-Southern Ocean distribution. A second, more elongate species is known from the Eocene of South Australia — T. elongatissimus Schwarzhans, 1985.