History of two lineages: Comparative analysis of the fossil record in Amiiformes and Pycnodontiformes (Osteischtyes, Actinopterygii)

Amiiformes and pycnodontiformes are two orders of neopterygian fishes that were broadly distributed, and frequently appeared together, during the Mesozoic. Comparison of their fossil record reveals both common traits and signifi cant differences. They both appeared in the Western Tethys and reached maximum diversity during the Cretaceous. The differences in their evolutionary history involve dissimilar patterns of diversity and disparity; pycnodonts are more diversifi ed taxonomically and present larger ecomorphological disparity. This implies that they used different strategies to compete with teleosts, which were unable to displace them from their specialized niches for more than 100 ka. The reasons why this did not happen sooner are diffi cult to approach, and may include radical environmental changes (i.e., marine transgressions, opening of the Atlantic, closing of the Tethys and opening of the Mediterranean). It is nonetheless clear that the evolutionary novelties of the Teleostei per se were not enough to grant them advantage in the competition for the ichthyofagous and durophagous niches at least during the Late Triassic, the whole Jurassic and the Early Cretaceous.