Tetraodontidae gen. et sp. indet.

Fig. 31

Material examined

UNITED STATES OF AMERICA – Mississippi • 6 isolated jaws; Catahoula Formation; SC 2013.28.604, SC 2013.28.605 (Fig. 31A–C), SC 2013.28.606, SC 2013.28.607 (2 specimens), SC 2013.28.608 (Fig. 31D–F) .

Description

Specimen SC 2013.28.608 is a right premaxilla measuring 4 mm in antero-posterior length, 1.5 mm in dorso-ventral height, and 1 mm in greatest medio-lateral width. In aboral view, the jaw is thickest mesially but tapers distally, it has an arcuate appearance (convex labially), and the internal bony structure has a spongy appearance (Fig. 31F). In labial view, the jaw surface is convex and appears to consist of a uniform layer of shiny tissue (Fig. 31E). In oral view, much of the triturating surface is rather thin and the labial margin is sharp. In symphyseal view, the articular surface (for the left premaxilla) bears a series of fossae that are separated by thin dentine lamellae. Additionally, what appears to be a circular triturating pad occurs on the oral surface, just distal to the symphysis (Fig. 31D).

Also included in our sample are jaw fragments that are comprised of stacked rows of teeth. In labial view, the teeth are very low (apico-basally) and elongated (mesio-distally). Tooth length varies among the teeth in a row, and they have roughly rectangular outlines. The teeth in each row may butt directly against each other, or the tapered ends may overlap the end of the preceding/succeeding teeth (Fig. 31B). The teeth in successive rows may not perfectly overlie those in previous rows, and younger teeth may be longer or shorter than the tooth immediately below. In lingual view, the teeth are embedded in osteodentine (Fig. 31A).

Remarks

The specimens are very small, but SC 2013.28.608 is similar to the premaxillae of fossil tetraodontoid taxa that have been described. The premaxilla of the Pliocene Spheroides hyperostosis Tyler et al., 1992 bears a single triturating tooth on the oral surface, whereas that of the Oligocene Archaeotetraodon winterbottomi Tyler & Bannikov, 1994 has three. The premaxilla of Eotetraodon Tyler, 1980 is incompletely known, but the dentary or E. tavernei Tyler & Bannikov, 2012 bears two triturating teeth. Lagocephalus striatus Aguilera et al., 2018 was recently described from the Middle Miocene strata of Panama, but the morphology of the triturating surface of the premaxilla is presently unknown. Similarly, the premaxilla morphology of Leithaodon sandroi Carnevale & Tyler, 2015 from the Middle Miocene of Austria is unknown. Unfortunately, the knob-like triturating pad of SC 2013.28.608 is ablated and it is difficult to determine whether the triturating surface consists of one or two teeth. Additional specimens, particularly cranial material, are necessary to accurately determine the generic affinity of the Catahoula Formation pufferfish.

The jaws of two other groups of tetraodontiform fishes, Diodontidae and Triodontidae, have anterior beak-like structures, but these differ from the Catahoula Formation specimens by being composed of alternating stacked rows of sub-triangular teeth with pointed apices (Thiery et al. 2017). The Catahoula Formation pufferfish specimens are significant because, to our knowledge, they represent the first Oligocene record of Tetraodontidae in the Western Hemisphere.