Tuesday, July 10, 2018

[Paleontology • 2018] Ingentia prima • An Early Trend Towards Gigantism in Triassic Sauropodomorph Dinosaurs

Ingentia prima
 Apaldetti, Martínez, Cerda, Pol & Alcober, 2018

Illustration: Jorge A. Gonzalez   twitter.com/PolDiego

Dinosaurs dominated the terrestrial ecosystems for more than 140 Myr during the Mesozoic era, and among them were sauropodomorphs, the largest land animals recorded in the history of life. Early sauropodomorphs were small bipeds, and it was long believed that acquisition of giant body size in this clade (over 10 tonnes) occurred during the Jurassic and was linked to numerous skeletal modifications present in Eusauropoda. Although the origin of gigantism in sauropodomorphs was a pivotal stage in the history of dinosaurs, an incomplete fossil record obscures details of this crucial evolutionary change. Here, we describe a new sauropodomorph from the Late Triassic of Argentina nested within a clade of other non-eusauropods from southwest Pangaea. Members of this clade attained large body size while maintaining a plesiomorphic cyclical growth pattern, displaying many features of the body plan of basal sauropodomorphs and lacking most anatomical traits previously regarded as adaptations to gigantism. This novel strategy highlights a highly accelerated growth rate, an improved avian-style respiratory system, and modifications of the vertebral epaxial musculature and hindlimbs as critical to the evolution of gigantism. This reveals that the first pulse towards gigantism in dinosaurs occurred over 30 Myr before the appearance of the first eusauropods.

Fig. 1: Skeletal anatomy of Ingentia prima gen. et sp. nov. from the Quebrada del Barro Formation, northwestern Argentina.
a–k, Holotype (PVSJ 1086). l–s, Referred material (PVSJ 1087). a–d, Mid-posterior cervical vertebrae, C5–C10 articulated series (a), close up of the pneumatic fossa with internal subfossae on the centrodiapophyseal fossa (cdf)26 of C8 (b) and C9 (c), and a complex of subfossae on the prcdf26 of C10 (d). e, Right partial scapula. f–i, Right forelimb: humerus (f), and the radius and ulna in proximal (g) and anterior (h) view, and distal articulation (i). j, Right manus in plantar view. k,l, Metacarpal I in proximal (k) and dorsal (l) view. m,n, Radius and ulnae with respective proximal ulna: right radius-ulna (m) and left radius-ulna (n) in posterior view. o, Left proximal end of fibula. p–r, Right partial pes: distal tarsal III–IV in proximal view (p), metatarsal I and II in dorsal view (q) and isolated phalanges (r). s, Four anterior caudal vertebrae and a distal one (bottom left).

 cen, centrum; dp, diapophysis; dt, distal tubercles of radius-ulna; f-sf, fossa-subfossae complex; ft, fibular tubercle; nc, neural canal; ol, olecranum; pm, posteromedial margin of the ulna; prz, prezygapophysis; rf, radial fossa; rib, rib. Scale bars: 10 cm in a and i–s; 2 cm in b–d; 20 cm in e–h; 120 cm for the skeleton. Red, holotype; yellow, referred specimen; orange, holotype and referred specimen.

Systematic palaeontology
Dinosauria Owen, 1842 
Saurischia Seeley, 1888 
Sauropodomorpha von Huene, 1932 

Lessemsauridae clade nov. 

Etymology. Related to Lessemsaurus sauropoides Bonaparte, 1999. 

Definition. The clade Lessemsauridae is defined here as L. sauropoides Bonaparte, 1999 and Antetonitrus ingenipes Yates and Kitching, 2003, and all the descendants from their most common ancestor. 

Ingentia prima gen. et sp. nov. 

Etymology. Ingentia’, huge (fem., Latin); ‘prima’, first (fem. Latin), referring to the large body size acquired during the early evolution of Dinosauria.


Cecilia Apaldetti, Ricardo N. Martínez, Ignacio A. Cerda, Diego Pol and Oscar Alcober. 2018. An Early Trend Towards Gigantism in Triassic Sauropodomorph Dinosaurs. Nature Ecology & Evolution.  DOI: 10.1038/s41559-018-0599-y  

Huge new gentle giant dinosaur the size of a double decker bus discovered  metro.co.uk/2018/07/09/huge-gentle-giant-dinosaur-size-double-decker-bus-discovered-argentina-7695748 via @MetroUK

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