Giant ichthyosaurs of the Late Triassic: current challenges at excavating a new specimen from France

International audienceAmong marine reptiles of the Mesozoic, ichthyosaurs exemplify a typical case of morphologicaladaptation toward a pelagic lifestyle. Beside their extensive stratigraphic range, spanning the earlyTriassic to mid-Cretaceous interval, they are noteworthy for having achieved gigantic (up to 21 m totallength) body sizes during the first third of their evolutionary history. Such sizes were never paralleledin subsequent ichthyosaur lineages. The presence of such giants, belonging to Shastasauridae andCymbospondylidae, is now well attested from the North American fossil record, especially prior to theNorian (e.g. Nicholls and Manabe, 2004; Scheyer et al., 2014; Sander et al., 2021). Although alreadyrecorded from Asia by limited material such as Himalayasaurus (Motani et al., 1999), the Europeanrecord also begins to unveil giant forms of younger stratigraphic age (Fischer et al., 2014; Martin et al.2015; Lomax et al., 2018; Sander et al., 2022). Yet, despite their giant size, the European record islimited to a handful of partial skeletal elements. Here, we report new postcranial material belonging toa giant shastasaurid from the Rhaetian of Var, southern France. We recount the logistical attempts atretrieving skeletal elements of a single individual cropping out from the middle of a cliff since 2015.The elements recovered so far are referred to Shonisaurus sp. on the basis of vertebral morphology.Although challenging in its extraction, such specimen holds promises for questioning the ecologicalrole of giant ichthyosaurs and the reason of their extinction at the end of the Triassic.Fischer, V., Cappetta, H., Vincent, P., Garcia, G., Goolaerts, S., Martin, J. E., Roggero, D. & Valentin, X. (2014).Ichthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic–Jurassic boundary.Naturwissenschaften, 101(12), 1027-1040.Lomax, D. R., De la Salle, P., Massare, J. A., & Gallois, R. (2018). A giant Late Triassic ichthyosaur from the UK and areinterpretation of the Aust Cliff ‘dinosaurian’bones. Plos one, 13(4), e0194742.Nicholls, E. L., & Manabe, M. (2004). Giant ichthyosaurs of the Triassic—a new species of Shonisaurus from the PardonetFormation (Norian: Late Triassic) of British Columbia. Journal of Vertebrate Paleontology, 24(4), 838-849.Martin, J. E., Vincent, P., Suan, G., Sharpe, T., Hodges, P., Williams, M., Howells, C. & Fischer, V. (2015). A mysteriousgiant ichthyosaur from the lowermost Jurassic of Wales. Acta Palaeontologica Polonica, 60(4), 837-842.Motani, R., Manabe, M., & Dong, Z. M. (1999). The status of Himalayasaurus tibetensis (Ichthyopterygia). Paludicola, 2(2),174-181.Sander, P. M., Griebeler, E. M., Klein, N., Juarbe, J. V., Wintrich, T., Revell, L. J., & Schmitz, L. (2021). Early giant revealsfaster evolution of large body size in ichthyosaurs than in cetaceans. Science, 374(6575), eabf5787.Sander, M. P., Pérez de Villar, P. R., Furrer, H., & Wintrich, T. (2022). Giant Late Triassic ichthyosaurs from the KössenFormation of the Swiss Alps and their paleobiological implications. Journal of Vertebrate Paleontology, e2046017.Scheyer, T. M., Romano, C., Jenks, J., & Bucher, H. (2014). Early Triassic marine biotic recovery: the predators' perspective.PLoS One, 9(3), e88987