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| Bagualia alba Pol, Ramezani, Gomez, Carballido, Carabajal, Rauhut, Escapa & Cúneo, 2020 Illustration: Jorge Gonzales |
Abstract
Sauropods, the giant long-necked dinosaurs, became the dominant group of large herbivores in terrestrial ecosystems after multiple related lineages became extinct towards the end of the Early Jurassic (190–174 Ma). The causes and precise timing of this key faunal change, as well as the origin of eusauropods (true sauropods), have remained ambiguous mainly due to the scarce dinosaurian fossil record of this time. The terrestrial sedimentary successions of the Cañadón Asfalto Basin in central Patagonia (Argentina) document this critical interval of dinosaur evolution. Here, we report a new dinosaur with a nearly complete skull that is the oldest eusauropod known to date and provide high-precision U–Pb geochronology that constrains in time the rise of eusauropods in Patagonia. We show that eusauropod dominance was established after a massive magmatic event impacting southern Gondwana (180–184 Ma) and coincided with severe perturbations to the climate and a drastic decrease in the floral diversity characterized by the rise of conifers with small scaly leaves. Floral and faunal records from other regions suggest these were global changes that impacted the terrestrial ecosystems during the Toarcian warming event and formed part of a second-order mass extinction event.
Keywords: Eusauropoda, Toarcian, Pliensbachian, Sauropoda
Systematic palaeontology
Dinosauria Owen, 1842;
Sauropoda Marsh, 1878;
Eusauropoda Upchurch, 1995
Bagualia alba gen. et sp. nov.
Etymology: bagual, wild horse (Spanish), for the type locality; alba, dawn (Spanish) in allusion to its early age.
Holotype: MPEF-PV 3301, posterior half of skull articulated with seven cervical vertebrae (Museo Paleontológico Egidio Feruglio, Trelew, Argentina).
Locality and Horizon: Bagual Canyon, 5 km south of Cerro Cóndor, Chubut, Argentina. Lower levels of the Cañadón Asfalto Formation dated at 179.17 ± 0.12 Ma (see below and electronic supplementary material), Early Jurassic, Toarcian.
Referred specimens: MPEF-PV 3305–3348 representing remains of at least three individuals (based on repeated elements) found at the same site. The specimens are similar sized (repeated humeri varying up to 15% in length) and include craniomandibular remains (premaxilla, maxilla, nasal, dentary, surangular), multiple isolated teeth, cervical, dorsal, and caudal vertebrae, and limb elements (see electronic supplementary material).
Diagnosis: basal eusauropod diagnosed by the following characters (autapomorphies indicated with *): pointed process on the anteroventral end of the premaxilla and anterodorsal end of the dentary*; anterior margin of the premaxilla without a marked step*; orbital margin of the frontal with a close V-shape pointed medially*, resulting in a short contribution to the orbit; supratemporal fenestra about as anteroposteriorly long as lateromedially wide*; strongly marked proatlantal facets on the laterodorsal margin of the foramen magnum; concave ventral margin of the distal portion of the cultriform process*; axis with the anterior process in the dorsal part of neural spine (convergent in Jobaria and Europasaurus); accessory lamina below the PCDL in middle cervical vertebrae*; EPRL present in middle cervical vertebrae. See electronic supplementary material for further details on diagnostic features.
D. Pol, J. Ramezani, K. Gomez, J. L. Carballido, A. Paulina Carabajal, O. W. M. Rauhut, I. H. Escapa and N. R. Cúneo. 2020. Extinction of Herbivorous Dinosaurs linked to Early Jurassic Global Warming Event. Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2020.2310
Global warming triggered the evolution of giant dinosaurs