Abstract
The extinct group of the Pycnodontiformes is one of the most characteristic components of the Mesozoic and early Cenozoic fish faunas. These ray-finned fishes, which underwent an explosive morphological diversification during the Late Cretaceous, are generally regarded as typical shell-crushers. Here we report unusual cutting-type dentitions from the Paleogene of Morocco which are assigned to a new genus of highly specialized pycnodont fish. This peculiar taxon represents the last member of a new, previously undetected 40-million-year lineage (Serrasalmimidae fam. nov., including two other new genera and Polygyrodus White, 1927) ranging back to the early Late Cretaceous and leading to exclusively carnivorous predatory forms, unique and unexpected among pycnodonts. Our discovery indicates that latest Cretaceous–earliest Paleogene pycnodonts occupied more diverse trophic niches than previously thought, taking advantage of the apparition of new prey types in the changing marine ecosystems of this time interval. The evolutionary sequence of trophic specialization characterizing this new group of pycnodontiforms is strikingly similar to that observed within serrasalmid characiforms, from seed- and fruit-eating pacus to flesh-eating piranhas.
Highlights
Pycnodonts have been known and studied for more than two centuries[1] since they are one of the most remarkable fishes present in Konservat-Lagerstätten of Mesozoic and early Cenozoic age (e.g., Solnhofen and Monte Bolca)[2,3]
We report the discovery of peculiar isolated jaw elements from the Paleogene and latest Cretaceous phosphate deposits of the Ouled Abdoun Basin, Morocco
During the evolutionary history of this group of pycnodontiforms, the most remarkable adaptation is the strong reduction of the number of tooth rows in both vomerine and prearticular dentitions combined with the development of sharp labiolingually compressed teeth, documenting a gradual transformation from typical crushing tooth plates towards slicing blades
Summary
Pycnodonts have been known and studied for more than two centuries[1] since they are one of the most remarkable fishes present in Konservat-Lagerstätten of Mesozoic and early Cenozoic age (e.g., Solnhofen and Monte Bolca)[2,3] This group of deep-bodied actinopterygians appeared in the Late Triassic and became extinct during the Eocene epoch, with a peak of diversity occurring during the early Late Cretaceous[2,3,4]. We report the discovery of peculiar isolated jaw elements (i.e., vomers and prearticulars) from the Paleogene and latest Cretaceous phosphate deposits of the Ouled Abdoun Basin, Morocco These specimens, characterized by a derived cutting-type dentition, are shown to belong to an unexpected new lineage of macropredatory, flesh-eating pycnodonts. This new group of pycnodonts shows convergent evolution with serrasalmid fishes, a modern group including the durophagous pacus and the famous piranhas[12,13]
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