Tetraodontiformes (Osteichthyes, Actinopterygii) from the Miocene of Argentina: with the southernmost record of fossil Tetraodontidae

Soledad Gouiric-Cavalli,Alberto L Cione,Maria De Las Mercedes Azpelicueta

doi:10.5852/cr-palevol2021v20a27

Abstract

Teleostean evolution produced enormous variation in tooth morphology. This variation is related to the exploration and exploitation of very diverse dietary niches. Among extant fishes, several taxa of the order Tetraodontiformes (e.g. pufferfishes, porcupinefishes and ocean sunfishes) have evolved highly specialized beak-like tooth structures. Here we provide the first description of tetraodontiform crushing beaks from Argentina. A single complete premaxillary beak recovered from the early Miocene Gaiman Formation in Chubut Province is assigned to Molidae based on its premaxillaries being completely fused to one another along the midline, general morphology, and size. Moreover, due to the putative presence of rows of teeth fused to the thick and massive bone structure, the specimen might belong to the genus Ranzania Nardo, 1840. Several premaxillary beaks recovered in the late Miocene Paraná Formation of Entre Ríos Province are assigned to Tetraodontidae Bonaparte, 1832 based on the presence of long, slender, rod-like, and parallel dental units; premaxillae not fused in the midline but articulated by interlocking emarginations, and a few small and one large trituration dental units. Argentinian tetraodontiform fishes inhabited the warm-temperate Paranense and Patagoniense Seas (marine transgressions developed in southeastern South America) during the early-late Miocene; these specimens are the southernmost fossil record of the group worldwide. Tetraodontiforms are extremely rare in recent Argentinian marine waters. The new fossil records agree with the higher sea water surface temperatures suggested both locally and worldwide for the Miocene.

Highlights

Bony-fish dentition shows a remarkable variability in morphology (e.g. Berkovitz & Shellis 2017)
Backscattered electrons (BE) detectors of two sectors BSED were employed in order to observe variations in the atomic number (Z) of the elements detected on surface
Within the Tetraodontiformes, we assign the Paraná Formation specimens to the tetraodontoids or gymnodontids because they have crushing beaks composed of upper and lower jaw bones fused with teeth which characterizes this beak-toothed group

Summary

INTRODUCTION

Bony-fish dentition shows a remarkable variability in morphology (e.g. Berkovitz & Shellis 2017). The beak-like dentition of several tetraodontids (i.e., porcupinefishes, pufferfishes, ocean, and sunfishes) is a complex of bony and dental tissues with teeth that form intraosseusly (Trapani 2001). Tetraodontoidei or Gymnodontes (i.e., Triodontidae Bleeker, 1859, Tetraodontidae, Molidae, Diodontidae, and Avitoplectidae Bemis, Tyler, Bemis, Kumar, Rana & Smith, 2017) have beak-dentitions originating by the fusion of teeth and their jaw bones (Tyler 1980; Andreucci & Britski 1982). We provide a qualitative study of beaked-dentitions found in the early Miocene Gaiman Formation (Chubut Province, Patagonia Argentina) and the late Miocene of Paraná Formation (Entre Ríos Province, North Eastern Argentina). We compare these records with those of other parts of the globe

MATERIAL AND METHODS

DISCUSSION