Characterization of coelacanth scales from the Early Cretaceous freshwater locality of Las Hoyas, upper Barremian (Cuenca, Spain)

Abstract

Coelacanths are rare, mostly marine fishes, but the species from the Lower Cretaceous Spanish locality of Las Hoyas (Barremian) is a freshwater form and we know almost nothing about it. The Las Hoyas specimens are very rare and relatively incomplete, but there are still many things we can learn from the isolated skeletons and scales. First, the coelacanth scales were distinguished from other superficially similar scales (i.e., other “amioid” scales). Coelacanth scales are distinguished by the presence of a smooth central surface, a particular pattern of arrangement of concentric growth cessation marks, and mainly a relatively short posterior field with thick elongated ridges. Only a few articulated coelacanth specimens have been recovered from Las Hoyas to date, and only 7.3% (n = 11) of the total isolated scales are coelacanth. The Las Hoyas coelacanth scales represent relatively large individuals. This suggests that a natural population of the coelacanth may have not inhabited permanently the freshwater pool represented by the excavated area of Las Hoyas because small juveniles should be the most common sizes.