The enigmatic Omphalosaurus: the key to the early evolution of ichthyosaurs in the Triassic?

• Applicant: Professorin Dr. Nadia Belinda Fröbisch, since 8/2023
• Subject Area: Palaeontology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440685415

The Early and Middle Triassic witnessed one of the great events in vertebrate history, the evolution of the first marine reptiles, i.e., secondarily aquatic amniotes. Several different phylogenetic lineages of terrestrial diapsid reptiles adapted to the marine environment and radiated quickly and globally. Among these, the Icht-hyosauria and the Sauropterygia are the major lineages that gave rise to the dominant marine reptile groups of the Jurassic and Cretaceous, the Neoichthyosauria and the Plesiosauria. Marine reptiles suddenly appear in the fossil record from three to six million years after the great end-Permian mass extinction event. While many of these early marine reptiles were adapted to hunting fish, another frequent mode of feeding is duro-phagy, feeding on benthic hard-shelled prey such mollusks and crustaceans. Marine reptiles are thus part of the reorganization of marine trophic webs towards their current state. The enigmatic Omphalosauridae are eroneously considered durophagous but fit neither of these feeding molds, seemingly having been adapted to consuming ammonites in the open sea. The most common genus, Omphalosaurus, is also the most wi-dely distributed marine reptile genus of the Early and Middle Triassic, with fossils from all over the northern hemisphere. However, Omphalosauridae are notably lacking in the very well sampled Chinese faunas. Instead, a peculiar and putatively toothless clade of early ichthyosaur relatives, the Nasorostra, have been described from the Early Triassic of eastern China based on two skeletons named Cartorhynchus brevirost-ris and Sclerocormus parviceps, respectively. Unpublished work and own observations now strongly suggest that these animals had an omphalosaurid dentition and that Nasorostra is the same as Omphalosauridae. If true, this would have profound implications for our understanding of ichthyosaur evolution because it would question several hypotheses, i.e., that ichthyosaurs originated in eastern Asia, that the Chinese toothless hupesuchians are their closest relatives, and that suction feeding was the ancestral feeding mode of ichthyo-saurs. Understanding Omphalosauridae will lead to a new understanding of the early evolution of ichthyo-saurs. I want to test the hypothesis that Nasorostra is the same as Omphalosauridae by analyzing in detail a recently collected large Omphalosaurus skeleton and other materials from the Augusta Mountains (Nevada, USA) and new specimens of Nasorostra from China, in particular a three-dimensionally preserved skull and anterior skeleton of Sclerocormus. I want to use current technologies such as micro-CT, photogrammetry, bone histology, and scanning electron microscope to provide a detailed description of the anatomy of this animal, particularly of its dentition, and to reconstruct jaw function. The work will result in a new scenario of ichthyosaur origins and its role in the early stages of rebuilding of marine ecosystems after the end of the Permian.

• DFG Programme: Research Grants
• Ehemalige Antragstellerinnen / Ehemalige Antragsteller: Professor Dr. Martin Sander, from 1/2022 until 8/2023; Dr. Tanja Wintrich, until 1/2022