PARALBULA IN NORTH AMERICA: REVISITING AN ENIGMATIC CAMPANIAN – LATE PALEOCENE TELEOST WITH HOPE FOR NEW INSIGHTS

Paralbula is a common genus of teleost fish in Campanian to Thanetian units nearly throughout North America, though it is also found in Europe and Africa where it survived into the Eocene. The genus, and the entire family Phyllodontidae, is known almost solely from uncommon basibranchial and parasphenoid tooth plates and common, isolated teeth. As a result, important paleoecological interpretations and phylogentic relationships are inferred entirely from tooth characteristics, tooth plate form, and stratigraphic distribution. Most gross generic anatomical characteristics are completely unknown.

Paralbula is most common in North America, where its isolated teeth are often very abundant within marine vertebrate fossil assemblages. The genus is found almost exclusively in deposits representing near-shore and/or marginal marine environments, where the rounded, phyllodont dentition characteristic of the family is thought to represent an adaptation for crushing invertebrate shells or exoskeletons. Paralbula appears to occur rarely in fluvial sediments, suggesting either that these fish were diadromous, or that those remains are allochthonous.

Within North America, only two species of Paralbula are recognized. P. casei is far more common, with remains collected from middle Campanian through Paleocene (Thanetian) sediments across the continent. Until recently, P. marylandica was known only from two basibranchial tooth plates from the Thanetian Aquia Formation of Maryland. However, a recent discovery of autochthonous P. marylandica remains from the Maastrichtian – Danian basal Hornerstown Formation in New Jersey (NJSM 21877) requires a revision of this species’ geographic and stratigraphic range. More importantly, these remains consist of multiple skull elements, including several toothed elements, and scales; thus constituting by far the most complete set of remains known from any specimen within the genus, and highly unusual for the Phyllodontidae as a whole.