EVOLUTION OF LATE CRETACEOUS BONY FISHES IN THE GULF COAST AS INDICATED BY OTOLITHS

Osteological remains of Late Cretaceous actinopterygians in the Gulf Coast have provided limited information on the evolution and diversity of bony fishes during this geologic interval. However, otoliths or earstones of bony fishes have afforded additional and supplementary information on the composition and evolutionary development of Late Cretaceous teleosts. Otoliths collected from Late Cretaceous localities in Texas and Mississippi indicate a diverse assemblage of bony fishes and clearly reflect that these teleosts are more advanced than once presumed. Although Late Cretaceous associations based on otoliths in the Gulf Coast point to the presence of primitive families such as albulids, pterothrissids, congrids, and ophidiids, ample evidence of modern families represented by perciform taxa such as apogonids, caristiids, pempherids, and bathyclupeids exists. The Perciformes represent the most advanced, highly diversified group of Recent fishes and the largest vertebrate order in number of species. Cretaceous fish faunas had long been considered as more primitive in nature with little relationship to modern families. Skeletal remains of Late Cretaceous fishes from the Gulf Coast and worldwide are yet to indicate the unquestionable presence of perciforms. However, Late Cretaceous otoliths from Texas and Mississippi clearly provide evidence of perciforms not known from the osteological record.

The perplexing differences between the Late Cretaceous bony fishes indicated by osteological material and the otolith record appear to be related to several important factors. Osteological fish material tends to be recovered from a very different environment than otoliths. Osteological remains, especially entire or partial fish skeletons, tend to be found in deeper, mostly carbonate facies. However, otolith associations usually reflect faunas from relatively flat, muddy bottoms in shallow-water, clastic sedimentation environments with the addition of mesopelagic elements. Furthermore, the otoliths tend to represent small fishes, which apparently constituted the prey of larger predators such as sharks, marine turtles, and larger teleosts. The Late Cretaceous otolith assemblage provides important data on the evolution and diversity of actinopterygians not revealed by osteological material.