Albulidae, Bleeker, 1859

Albulidae View in CoL View at ENA gen. et sp. indet.

Fig. 23I–S View Fig

Material examined

UNITED STATES OF AMERICA – Mississippi • 6 isolated pharyngeal bones; Catahoula Formation ; MMNS VP-6578 ( Fig. 23I–K View Fig ), MMNS VP-6967 (3 specimens), SC 2013.28.692 , SC 2013.28.693 • 48 isolated teeth; Catahoula Formation ; SC 2013.28.594 ( Fig. 23L–N View Fig ), SC 2013.28.595 (46 teeth), SC 2013.28.840 ( Fig. 23O–Q View Fig ) • 9 sagittae; Catahoula Formation ; MMNS VP-7454 , SC 2013.28.802 , SC 2013.28.803 , SC 2013.28.804 (2 specimens), SC 2013.28.911 ( Fig. 23R–S View Fig ), GLS otolith comparative collection (3 specimens) .

Description

Our sample includes ablated pharyngeal bones, isolated teeth, and otoliths (sagittae). The pharyngeal bones are ablated, but each specimen exhibits a very flattened and slightly polished oral surface and more convex, roughened aboral surface. A probable basibranchial (MMNS VP-6578) is antero-posteriorly elongated but narrow. The oral surface of each specimen includes several scattered teeth ( Fig. 23I View Fig ), which are only visible in outline because of their in vivo wear down to the level of the bone surface. Numerous openings within the oral surface are interpreted to represent alveoli for missing teeth. Enameloid crowns of replacement teeth are visible in profile ( Fig. 23J View Fig ) and aboral views ( Fig. 23K View Fig ).

Nearly all the isolated teeth are highly worn through in vivo use, and the remaining portion of these specimens consists of the crown and a short basal area. In profile view, the crowns are high and basally tapering ( Fig. 23M, P View Fig ), but their original unworn height is unknown. The crown is covered with a thin layer of smooth enameloid that does not reach the tooth base. In occlusal view, the crown has a circular outline, and the triturating surface largely consists of exposed dentine framed by thin enameloid ( Fig. 23L, O View Fig ). In basal view, the circular pulp cavity is framed by a thick wall of dentine ( Fig. 23N, Q View Fig ).

The sagittae ( Fig. 23R–S View Fig ) are very small, with only a few exceeding 4 mm. They have a somewhat oblong to elliptic outline (sensu Smale et al. 1995), and the margins are generally smooth. The inner face is conspicuously convex and twisted, and a prominent long sulcus occurs primarily in the dorsal and posterior regions. The sulcus has a wide, anterodorsally opening ostium that is filled with colliculum. The caudal area has an anterior sub-horizontal portion and a posterior downturned portion that is usually deeply excavated. A caudal keel is present on well-preserved specimens. The outer face is concave, twisted (especially in adults), thickest postero-dorsally but thinning toward the anterior, and annual growth rings are often visible to the naked eye.

Remarks

Albulid pharyngeal bones, isolated teeth, and otoliths are represented in our sample. These fossils cannot be confidently assigned to any particular genus, and we cannot ascertain whether the remains represent more than one taxon. A single tooth recovered from the Glendon Limestone Member of the Byram Formation of southwestern Alabama was identified as Albula sp. by Ebersole et al. (2021), and several isolated teeth were reported from the late Rupelian Ashley Formation of South Carolina ( Cicimurri et al. 2022). Cicimurri & Knight (2009) also mentioned the occurrence of albulid teeth in the Chattian Chandler Bridge Formation of South Carolina. Albulid otoliths have been reported from the Rupelian Rosefield Formation in Louisiana ( Stringer et al. 2001).

The small overall size of the Catahoula Formation otoliths is in stark contrast to those of Eocene albulids, which approach 20 mm in length ( Ebersole et al. 2019). Otoliths can attain even larger sizes, as a specimen from the Eocene Clinchfield Formation of Georgia measures 21.48 mm ( Stringer et al. 2022a). Although albulid otoliths occur within numerous Paleogene lithostratigraphic units within the Gulf Coastal Plain, they are typically not abundant ( Breard & Stringer 1995, 1999; Stringer & Breard 1997; Stringer & Miller 2001; Schweitzer et al. 2014). Nolf & Stringer (2003) reported only five specimens of Albula sp. among the 5559 otoliths (0.09% of total sample) from the upper Eocene (primarily Priabonian) Yazoo Clay in Louisiana, and albulid otoliths represented a slightly higher 1.33% of the total sample (n = 20) from the Clinchfield Formation ( Stringer et al. 2022a). Far fewer otolith specimens were obtained from the Catahoula Formation, but those of albulids constitute 2.47% of the sample.