 |
| Macrocollum itaquii
Müller, Langer & Dias-da-Silva, 2018 |
Abstract
The rise of sauropodomorphs is still poorly understood due to the scarcity of well-preserved fossils in early Norian rocks. Here, we present an association of complete and exceptionally well-preserved dinosaur skeletons that helps fill that gap. They represent a new species, which is recovered as a member of a clade solely composed of Gondwanan Triassic taxa. The new species allows the definition of a set of anatomical changes that shaped sauropodomorph evolution along a period from 233 to 225 Ma, as recorded in the well dated Late Triassic beds of Brazil. In that time span, apart from achieving a more herbivorous diet, sauropodomorph dinosaurs increased their size in a ratio of 230% and their typical long neck was also established, becoming proportionally twice longer than those of basal taxa. Indeed, the new dinosaur is the oldest-known sauropodomorph with such an elongated neck, suggesting that the ability to feed on high vegetation was a key trait achieved along the early Norian. Finally, the clustered preservation mode of the skeletons represents the oldest evidence of gregarious behaviour among sauropodomorphs.
Systematic palaeontology
Dinosauria Owen, 1842
Saurischia Seeley, 1887
Sauropodomorpha Huene, 1932
Unaysauridae clade nov.
Type genus: Unaysaurus tolentinoi Leal et al., 2004.
Definition: Most inclusive clade including Unaysaurus tolentinoi Leal et al., 2004, but not Plateosaurus engelhardti von Meyer, 1837 nor Saltasaurus loricatus Bonaparte & Powel, 1980.
Diagnosis: Unaysauridae differs from all other sauropodomorphs by a substantial cranial expansion of the medial condyle of the astragalus. In addition, a promaxillary fenestra is also unique for the group of sauropodomorphs, although cranial elements are still unknown for Jaklapallisaurus asymmetrica.
Macrocollum itaquii gen. et sp. nov.
Etymology: The generic name combines the Greek word μακρο (= long) and the Latin word ‘collum’ (= neck), referring to the elongated neck of the new taxon. The specific epithet honours Mr José Jerundino Machado Itaqui, one of the main actors behind the creation of CAPPA/UFSM.
Locality and horizon: The specimens were collected at the Wachholz site (29°36′46.42″ S; 53°15′54.06″ W), Agudo, Rio Grande do Sul, Brazil; upper portion of the Candelária Sequence, Paraná Basin. Stratigraphically correlated beds from a nearby site were dated as early Norian (ca 225.42 ± 0.37), Late Triassic.
Diagnosis: Macrocollum itaquii differs from all other known sauropodomorphs based on a unique combination of characters: antorbital fossa perforated by a promaxillary fenestra; medial margin of the supratemporal fossa with a simple smooth curve at the frontal/parietal suture; proximal articular surface of metacarpal I transversely narrow; acetabulum not fully open; ischiadic longitudinal groove not reaching the caudal half of the ischium; absence of trochanteric shelf on the femur; medial condyle of distal femoral articulation subrectangular in distal view; proximal end of metatarsal II with a straight medial margin (see electronic supplementary material, figure S2 for further details).
Rodrigo Temp Müller, Max Cardoso Langer and Sérgio Dias-da-Silva. 2018. An Exceptionally Preserved Association of Complete Dinosaur Skeletons Reveals the Oldest Long-necked Sauropodomorphs. Biology Letters. 14(11); 20180633. DOI: 10.1098/rsbl.2018.0633
Mom's Phone Call Helps Uncover Oldest Long-Necked Dinosaur on Record shar.es/aa2quM via @LiveScience
Three ancient skeletons, ancestors of giant dinosaurs, unearthed in Brazil phys.org/news/2018-11-ancient-skeletons-ancestors-giant-dinosaurs.html via @physorg_com
Pesquisadores do Cappa, da UFSM e da USP descobrem mais antigo dinossauro de pescoço longo ufsm.br/2018/11/20/descoberto-no-brasil-o-mais-antigo-dinossauro-de-pescoco-longo/
Three ancient skeletons, ancestors of giant dinosaurs, unearthed in Brazil phys.org/news/2018-11-ancient-skeletons-ancestors-giant-dinosaurs.html via @physorg_com
