A new large species of weakfish (Acanthuriformes: Sciaenidae: Cynoscion ) from the Upper Miocene of Argentina

Abstract

Cynoscion cionei sp. nov., a new species of weakfish (Acanthuriformes, Sciaenidae) recovered from Upper Miocene geologic deposits that crop out in Northeastern Argentina, is described. The type material comprises numerous anguloarticulars, but other cranial bones are also referred to the new species. Comparisons with living cynoscionine enera (Macrodon and Isopisthus) and with the phylogenetically close Atractoscion and Plagioscion confirm the assignment of the fossil specimens to the genus Cynoscion. The erection of the new species is based on a combination ofcharacters of the anguloarticular: broad and saddle-shaped glenoid cavity, with a large and hooked posterior process; upper ramus long and inclined cranially at an angle of 25°; lower ramus short; posterodorsal pad very strongly thickened, forming an angle of 45° with the horizontal pad; deep trough for the mandibular laterosensory canal; very robust horizontal pad; and large, flat, and finely sculptured ventral plate. Body length estimates on different bones suggest that Cynoscion cionei was similar in size to the largest extant species of the genus, with an average length of more than 900 millimeters. Paleoenvironmental reconstructions based on the analysis of facies in the upper levels of the Paraná Formation allow inference that Cynoscion cionei inhabited brackish and shallow waters in estuarine environments near the coastline of the “Paranense Sea,” as well as freshwater environments of the anastomosed “pre-Paraná” River which developed after the retreat of the epicontinental sea and are represented by the fluvial sediments of the lower member ofthe Ituzaingó Formation.