[D] Nyasasaurus parringtoni [sG] [T]
Describer
Charig, 1967 vide Nesbitt, Barrett, Werning, Sidor & Charig 2012
Time
Triassic Middle Anisian
Classification
Dinosauria
Fossilsite
(Parrington’s locality B36) from the Lifua Member of the Manda beds, Ruhuhu Basin,Tanzania
Info
Nesbitt, S. J., Barrett, P. M., Werning, S., Sidor, C. A., and A. J. Charig. (2012). The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters. 2013 9, doi: 10.1098/rsbl.2012.0949
Abstract
The rise of dinosaurs was a major event in vertebrate history, but the timing of the origin and early diversification of the group remain poorly constrained. Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identifiedas either the earliest known member of, or the sister–taxon to, Dinosauria. Nyasasaurus possesses a unique combination of dinosaur character states and an elevated growth rate similar to that of definitive early dinosaurs. It demonstrates that the initial dinosaur radiation occurred over a longer timescale than previously thought (possibly 15 Myr earlier), and that dinosaurs and their immediate relatives are better understood as part of a larger Middle Triassic archosauriform radiation. The African provenance of Nyasasaurus supports a southern Pangaean origin for Dinosauria.
Etymology
Nyasa, from Lake Nyasa near the type locality, and sauros, Greek for lizard; parringtoni, in honour of Francis Rex Parrington, collector of the holotype.
Holotype
NHMUK R6856 (The Natural History Museum, London, UK); right humerus, three partial presacral vertebrae and three sacral vertebrae.
Referred specimen
SAM-PKK10654 (Iziko South African Museum, Cape Town, South Africa) (¼Thecodontosaurus alophos); three cervical vertebrae and two posterior presacral vertebrae.
Locality and age
The holotype was collected from a single locality (Parrington’s locality B36) from the Lifua Member of the Manda beds, Ruhuhu Basin, southern Tanzania. The Lifua Member is late Anisian (Middle Triassic) in age, on the basis of biostratigraphic comparisons with the tetrapod fauna of the Cynognathus Assemblage Zone (subzone C) of South Africa. Cynodonts (Aleodon brachyrhamphus and Scalenodon angustifrons), dicynodonts (Sangusaurus edentatus and Angonisauruscruickshanki) and the rhynchosaur Stenaulorhynchus stockleyico-occur at the same horizon in the immediate vicinity.
Diagnosis
Nyasasaurus parringtoni was a 2–3 metre long (estimated from vertebral dimensions) dinosauriform with the followingunique combination of humeral character states: ventrally elongated deltopectoral crest; laterally deflected apex of the deltopectoral crest; distinct notch central to the apex of the deltopectoral crest; pointed expansion on the proximal surface near the dorsal extent of the deltopectoral crest; proximal surface of the humerus continuous with the lateral surface of the deltopectoral crest; and distinct fossa present on the posterodorsal surface, just ventral to the proximal surface. Humeral histology indicates rapid growth characterized by complex vascularization, highly woven bone tissue and the absence of any lines of arrested growth. The vertebrae also have a distinct combination of character states, including: at least three sacral vertebrae; dorsoventrally tall sacral ribs; and hyposphene–hypantrum intervertebral articulations in the presacral vertebrae.