Stargazer (Teleostei, Uranoscopidae) cranial remains from the Miocene Calvert Cliffs, Maryland, U.S.A. (St. Marys Formation, Chesapeake Group)

Abstract

ABSTRACT Fishes of the genus Astroscopus are anatomically distinctive within the family Uranoscopidae, mostly because they are characterized by internal nares and are the only marine teleosts known to possess electric organs derived from extraocular muscles. The new world genus Astroscopus contains three extant species from tropical to temperate coastal waters of both sides of the American continent, plus fragmented isolated bones and otoliths of an indeterminate fossil species from the Pliocene and Pleistocene of the Coastal Plain of the eastern United States. Astroscopus countermani, sp. nov., a new stargazer from the Miocene (Tortonian) of Calvert Cliffs (Maryland), is described herein based on well-preserved three-dimensional cranial remains. These cranial remains represent the earliest known skeletal record for the family Uranoscopidae, as well as the earliest occurrence of the genus Astroscopus in the fossil record. Astroscopus countermani is typified by a unique neurocranial appearence, an obliterated orbital foramen, and a prominent ornamented tuberosity arising from the dorsolateral surface of the hyomandibula. Among the anatomical distinctive features of Astroscopus countermani is the relative enlargement of the interorbital portion of the neurocranium (with respect to its extant congeners), which appears to be related to a reduced development of the electrogenic organs. Paleoecological considerations suggest that Astroscopus countermani was a predatory fish that inhabited the subtropical and warm temperate Atlantic marine and paralic waters of North America during the Miocene.