First isotopic and multidisciplinary evidence for nonmarine coelacanths and pycnodontiform fishes: palaeoenvironmental implications

The Recent coelacanth Latimeria chalumnae, one of the best known 'living fo ssils', dwells in deep marine water. Fossil coelacanths have been globally related to marine environments, specially after the Triassic, an associatio n that has led to a general belief that they have always been marine. Previ ous reports of fossil coelacanths in continental deposits have been largely neglected. Prior to this report, uncontested Cretaceous freshwater coelaca nths were unknown. In turn, the pycnodontiform fishes have always been cons idered exclusively marine, apart from a few controversial exceptions. Here we present the first multidisciplinary evidence for nonmarine coelacanths a nd pycnodonts. Our conclusions are based upon palaeogeographic, sedimentolo gic, taphonomic, and palaeoecologic criteria, strongly supported by stronti um (Sr-87-Sr-86) and stable carbon and oxygen isotopic studies. The coelaca nth, provisionally attributed to the genus 'Holophngus', and the pycnodonti forms Eomesodon sp. and Macromesodon aff. bernissartensis were unearthed at the Early Cretaceous locality of Las Hoyas (Cuenca, Spain), where they gre w in and inhabited a freshwater environment without marine influence. Fossi l coelacanths and pycnodonts cannot, therefore, be used as unambiguous indi cators of a marine environment. Caution is needed when using a single or a few taxa as palaeoenvironmental indicators, especially fish; in this sense, communities are much more reliable. Arguments based on actualism or taxono mic uniformitarianism, morphologic convergence and functional morphology ar e truly significant only within the framework of a sound multidisciplinary approach to the study of the palaeoenvironment. (C) 1998 Elsevier Science B .V. All rights reserved.