http://orcid.org/0000-0003-3638-1194
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Abstract
A new taxon, Cymbospondylus duelferi sp. nov., is described from the late Anisian of the Fossil Hill Member of the Favret Formation of the Augusta Mountains, Pershing County, Nevada, USA. The holotype and only specimen consists of a fairly complete skull associated with articulated and disarticulated postcranial material. Body length reconstruction revealed a medium-sized individual with an estimated body length of 4.3 m. Dorsal vertebrae as well as the left humerus of this specimen are associated with three strings of articulated tail and posterior dorsal vertebrae, which are on average 68% smaller than the vertebrae of the medium-sized individual. Due to the small size of these vertebrae and their position within the trunk region, they most likely represent fetuses. Cymbospondylus duelferi sp. nov. provides the second-oldest evidence for viviparity in ichthyosaurs. In the course of this study, the skull morphology of C. petrinus and C. nichollsi was reviewed, resulting in revised character scorings for both. Phylogenetic analyses demonstrate a sister-taxon relationship of the new taxon with C. petrinus, which was found in the same stratigraphic unit, the Fossil Hill Member, that also crops out at the classical Fossil Hill locality in the Humboldt Range, where the member is part of the Prida Formation. Cymbospondylus duelferi sp. nov. shares a very similar skull morphology with C. petrinus and C. nichollsi, whereas the shoulder girdle morphology differs. Because there is no evidence for ontogenetic differences or sexual dimorphism in the new specimen, a third species of Cymbospondylus – neglecting the type species C. piscosus that is only known from five vertebrae – is recognized from the Fossil Hill Member. Further occurrences of the genus in the Lower and Middle Triassic of Svalbard (Boreal Ocean) and Europe (Tethys) point to a very fast radiation and dispersal of cymbospondylids during the Middle Triassic.
https://zoobank.org:pub:906F5F32-9090-496D-8FC7-680D25EED5EF
Acknowledgements
We are grateful to Jose Soler and Valeria Jamarillo for preparation of the specimen, and to Maureen Walsh for curation (all LACM). Erin Maxwell (SMNS) kindly made the data matrix from Maxwell et al. (Citation2019) available before final publication and provided helpful technical advice, as did José Luis Carballido (Museo Egidio Feruglio, Trelew, Argentina). The specimen was collected under BLM Paleontological Resources Use Permit N-92625. The help of BLM staff at the Winnemucca field office is gratefully acknowledged. We thank the reviewers, A. Roberts (Bath) and L. L. Delsett (Oslo), as well as the handling editor, Susannah Maidment, for their constructive comments and thorough review. Their comments greatly improved our manuscript. Tom Young and his Great Basin Brewery (Reno) generously supported our fieldwork. The study was funded by grants from the Deutsche Forschungsgemeinschaft (project numbers 388659338 and 264173172) to P. Martin Sander and the National Geographic Society (grant number 9599-14) to Lars Schmitz.
Supplemental material
Supplemental material for this article is available here: http://dx.doi.org/10.1080/14772019.2020.1748132.
Associate Editor: Susannah Maidment