Exceptionally preserved fossils illuminate the paleobiology and interrelationships of ray-finned fishes, Thodoris Argyriou

Ray-finned fishes (Actinopterygii) correspond to over half of living vertebrate species, and share an evolutionary history of >425 Ma, which is documented by a rich fossil record. Yet, due to the distorted (crushed) nature of most ray-fin fossils, our understanding of the evolution of the group lags behind that of land vertebrates. In this frame, the study of exceptionally preserved specimens from Lagerstätte-deposits can lead to major advancements in knowledge, as they often preserve hard and soft tissue anatomical information that is typically lost in other fossils.

In this talk, I will compile examples from my recent work on exceptionally preserved Paleozoic–Mesozoic actinopterygians. The presence of in-situ fossilized feces of actinopterygians from the Triassic of Monte San Giorgio, Switzerland, has permitted the detailed reconstruction of their once containing gastrointestinal tracts. Surprisingly, gut anatomy resembled that of large chondrichthyans, revealing previously unknown morphological disparity in actinopterygian guts. Additional fossils from the same site permitted the recognition of live-bearing †saurichthyid fishes, and the differentiation between contained embryos and cannibalized prey, while hinting at aspects of reproductive biology. Exquisitely-preserved crania of †Saurichthys (Triassic) and †Brachydegma (Permian) were studied with µCT, to provide novel skeletal and neurosensory information for phylogenetic analyses. New results contradicted longstanding hypotheses of interrelationships, while providing compelling homological frameworks for understanding the evolution of key anatomical structures, such as the opercular, or the hyoid apparatus.

Finally, I will briefly introduce my current project on aulopiform fishes. I specifically aim at tracing the interrelationships of Cretaceous–recent aulopiforms, and the deep-time origins of modern families. Ultimately, I seek to investigate, from an evolutionary point of view, the reasons of their partial demise and shift in habitat occupation, following the Cretaceous/Paleogene Extinction.