Lutjanidae Gill 1861

Lutjanidae gen. et sp. indet. Fig. 26C–I Material examined UNITED STATES OF AMERICA – Mississippi • 112 isolated teeth; Catahoula Formation; MMNS VP-7685 (4 teeth), MMNS VP-7685.1 (Fig. 26C–D), MMNS VP-7685.2 (Fig. 26E–F), SC 2013.28.677 to 28.682, SC 2013.28.683 (100 teeth) • 1 jaw; Catahoula Formation; MMNS VP-8341 (Fig. 26G–I). Description Specimen MMNS VP-8341 is an incomplete left dentary measuring roughly 4 cm in length and 1.5 cm in maximum height. In labial view, the oral and aboral margins are moderately convex. Much of the labial face is convex and smooth, and there are several large fenestrae penetrating the surface (Fig. 26G). Aborally, the jaw is thin and developed into a ridge-like structure bearing conspicuous oblique ridges. The anterior jaw margin is vertical and straight. Slightly posterior to this margin is a conspicuous constriction where the jaw measures only 7.5 mm in height. The lingual surface is smooth (Fig. 26I). In oral view, the jaw is convex antero-posteriorly, it is thickest at its blunt anterior end, and there is a single row of large tooth alveoli flanked by a medial tooth patch (Fig. 26H). All of the large alveoli occur along the labial margin and have a circular outline. The sizes of the alveoli demonstrate that the largest teeth were located anteriorly, but teeth decreased slightly in size towards the posterior end of the tooth row. The lingual tooth patch is widest anteriorly but narrows posteriorly, and it consists of numerous tiny and circular alveoli (Fig. 26H–I). The isolated teeth attain up to 5 mm in total height. They are conical and straight to postero-medially curved to varying degrees (Fig. 26E and 26C, respectively). Well-preserved specimens show that the entire crown was covered by enameloid, but this is often only preserved on the upper one-half of the tooth. Interestingly, the apparently thinner enameloid covering along the lower one-half of the tooth is often a lighter color shade compared to the darker color of the upper one-half. Fine vertical fluting may occur on the posterior crown surface. Specimens that are ablated at the base show that the internal dentine is layered. Teeth have a circular basal outline, and the deep pulp cavity is framed by a thick wall of dentine (Fig. 24D, F). Remarks We compared the jaw and teeth described above to those of numerous extant fishes occurring in the Gulf of Mexico and found that they are very similar to representatives of Lutjanidae, particularly Lutjanus. The Catahoula Formation teeth are nearly identical to the large anterior teeth occurring on the premaxilla of L. jocu (Bloch & Schneider, 1801) (MSC 49315, SC uncurated specimen), but they are also similar to equivalent teeth of L. synagris (Linnaeus, 1758) (MSC 49478) and L. campechanus (Poey, 1860) (MSC 45233, MSC 49309). The fossil jaws differ by having a lingual tooth patch consisting of numerous tiny alveoli, as opposed to there being one or two rows of moderately-sized teeth in this region (as observed on the extant taxa noted above). Several interpretations could account for the variation in tooth size that we observed in the Catahoula Formation sample, including intra- and/or interspecific variation. It is possible that differences in tooth size are related to ontogeny within a single species, as the teeth of a 10 cm TL L. campechanus (MSC 45233) are simply smaller versions of teeth occurring in a 57.5 cm TL individual (MSC 49309). Additionally, the teeth along the jaws of one individual become smaller antero-posteriorly within the jaws. Although it is possible that the teeth and dentary available to us represent different species, there is currently no definitive evidence that more than one lutjanid taxon occurs within the Catahoula Formation. Ebersole et al. (2019) reported teeth like those described above as Osteoglossidae indet. (i.e., bony tongues), derived from middle Eocene deposits in Alabama. However, a reexamination of these teeth as part of the current study leads us to believe that the Eocene teeth instead belong to Lutjanidae, a taxon that is common in the Gulf of Mexico today (see Hoese & Moore 1998). In contrast, extant osteoglossids are freshwater fish occurring in South America, Africa, and Southeast Asia to northern Australia (Nelson et al. 2016). Nevertheless, the lutjanid teeth in our Catahoula Formation sample represent the first Oligocene occurrence of this taxon in the Gulf Coastal Plain of the USA.