Siluriformes Cuvier 1816

Siluriformes fam., gen. et sp. indet. Fig. 24G–K Material examined UNITED STATES OF AMERICA – Mississippi • 8 isolated fin spines; Catahoula Formation; MMNS VP-6651 (Fig. 24I), MMNS VP-7560 (Fig. 24J–K), SC 2013.28.750 (Fig. 24G–H), SC 2013.28.751 to 28.755. Description The sample includes incomplete pectoral fin spines potentially representing two morphologies. Three specimens are the proximal end of right spines (i.e., Fig. 24G–H). These have a flared, shelf-like dorsal process at the base, and this structure is roughly perpendicular to the spine length. The spine itself was elongated, curving towards the posterior, distally tapering, and dorso-ventrally flattened. The anterior margin is convex, whereas the posterior margin is lined with small circular depressions. The dorsal and ventral surfaces of the spine are convex and bear fine longitudinal striations. There is a triangular, antero-ventrally located fossa at the spine base. The remaining specimens are incomplete spines and ablated spine fragments. Specimens MMNS VP-6651 (Fig. 24I) and MMNS VP-7560 (Fig. 24J–K) are large incomplete spines where MMNS VP-6651 lacks its base and MMNS VP-7560 lacks its base and distal tip. Both specimens are elongated, narrow and thin, and curving along their length. Additionally, MMNS VP-6651 preserves a bluntly pointed distal tip. Both specimens exhibit numerous dorsal and ventral parallel ridges along their entire preserved length. Furthermore, the anterior margin is rounded, whereas the posterior margin bears a single row of basally directed, triangular denticles (Fig. 22J–K). Both specimens also show that these denticles increase in size distally (Fig. 24I). The other ablated spine fragments exhibit a comparable morphology. Remarks There are several extant catfish species within Ictaluridae and Ariidae that have ornamented fin spines, and we cannot confidently identify our fragmentary specimens beyond the ordinal level. However, two taxa may be represented based on the morphological variation we observed in the Catahoula Formation sample, with one having a dimpled posterior margin and the other barbed. It is possible that the morphologies represent the same spine, where the barbed section was located distal to the preserved portions of the spines in our sample. Ariidae fin spines have been reported from Eocene strata (Ebersole et al. 2019) and Ictaluridae spines from the Late Miocene (Ebersole & Jacquemin 2018) and Pleistocene (Jacquemin et al. 2016) of Alabama, but to our knowledge, the Catahoula Formation specimens represent the first North American Oligocene record of catfishes. These fishes were not identified in the Oligocene marine paleofaunas of North and South Carolina (Case 1980; Müller 1999; Cicimurri & Knight 2009; Cicimurri et al. 2022). Barbed fin spines could be confused with myliobatiform caudal spines, as both exhibit barbed margins. However, myliobatiform caudal spines are barbed on their right and left lateral margins (as opposed to only the posterior margin on our specimens), the dorsal surface is covered with enameloid (which is lacking on catfish spines), and they are symmetrical in dorsal view.