Abstract
A new, largely complete eusauropod dinosaur with cranial and postcranial elements from two skeletons, Mierasaurus bobyoungi gen. nov., sp. nov. from the lower Yellow Cat Member (Early Cretaceous) of Utah (USA), is the first recognized member of Turiasauria from North America. Moreover, according to our phylogenetic results, Moabosaurus utahensis from the lower Yellow Cat Member of Utah (USA) is also a member of this clade. This group of non-neosauropod eusauropods, which now includes five genera (Losillasaurus, Turiasaurus, Mierasaurus, Moabosaurus and Zby), was previously known only from the Jurassic of Europe. These recent discoveries in Utah suggest that turiasaurs as a lineage survived the Jurassic-Cretaceous extinction boundary and expanded their known range, at least, into western North America. The revised spatiotemporal distribution of turiasaurs is consistent with the presence of a land connection between North America and Europe sometime during the late Tithonian to Valanginian (c.147-133 Ma). Mierasaurus and Moabosaurus are the only non-neosauropod eusauropods known from North America, despite being younger than the classic neosauropods of the Morrison Formation (c.150 Ma).
Highlights
Sauropod dinosaurs were the largest vertebrates ever to walk the Earth[1,2] and were a diverse and successful group[3]
During the Late Jurassic, neosauropods were very abundant in North America: the Morrison Formation has yielded more than 430 specimens[53]
Even Late Jurassic North American taxa with uncertain affinities, such as Haplocanthosaurus, have been placed within Neosauropoda in most previous analyses[3,27,28] and by the current study, so no confirmed non-neosauropod sauropods have ever been described in the Morrison Formation[3,27,53]
Summary
Sauropod dinosaurs were the largest vertebrates ever to walk the Earth[1,2] and were a diverse and successful group[3] They had achieved a global distribution by the Middle Jurassic and maintained their dominance until the end of the Cretaceous[3,4], their evolutionary history was not without its crises. Ma) a time interval in which sauropod remains are rare globally[5,12] This discovery supports a more complex pattern of turnover among sauropods during the Jurassic-Cretaceous transition and is consistent with previously proposed palaeobiogeographic and palaeogeographic connections between Europe and North America after the Tithonian[13,14,15,16]. This relatively rare group of sauropods are represented in North America by a new taxon described here as Mierasaurus bobyoungi gen. nov, sp. nov. (Figs 1–5), which is closely related to the Kimmeridgian-Tithonian turiasaurs (Losillasaurus, Turiasaurus and Zby) of Europe[1,9,10] and the recently published Early Cretaceous taxon (from the lower Yellow Cat Member) Moabosaurus utahensis[17], after the revised phylogenetic placement of the latter proposed in this work (Fig. 6 and Supplementary Figs S4 and S5)
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