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14 August 2015 Functional Morphology and Biomechanics of the Cynodont Trucidocynodon riograndensis from the Triassic of Southern Brazil: Pectoral Girdle and Forelimb
Téo Veiga De Oliveira, Cesar Leandro Schultz
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Abstract

Non-mammalian cynodonts provide insights on several points about mammalian evolution, such as the postural change and locomotory advances within the group. Unfortunately, complete skeletons of Triassic cynodonts are rather uncommon and where more complete specimens are found they can offer a global vision on some traits not available from partial specimens. This is the case of the cynodont Trucidocynodon riograndensis, from the Triassic of Brazil, that has preserved its forelimbs providing some insights into locomotory properties. The movements between interclavicle and clavicle must have been limited, as such as those occurring between the latter and the scapulocoracoid although the long acromion process of this should have permitted a greater degree of freedom. Some of the more significant movements were those on the shoulder joint, in which the maximum adduction should have been ca. 35° relative to the parasagittal plane and the greater abduction ca. 55°. The maximum adduction occurred when the humerus was in the more retracted position during stride and the variation in the adduction/abduction should have been significant to the limb posture during its recovery stroke. The long olecranon and the distal overlapping between radius and ulna suggest the predominance of simple flexion/extension on the forearm without significant pronation/supination. The poorly preserved hand suggests that Trucidocynodon could have evolved a slight semidigitigrad condition in its forelimbs. All these features give to this cynodont an important role in the evolution of the mammalian locomotory properties indicating that some features, such as the possibility of greater humeral adduction, evolved early in cynodont lineage.

© 2016 T.V. de Oliveira and C.L. Schultz. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Téo Veiga De Oliveira and Cesar Leandro Schultz "Functional Morphology and Biomechanics of the Cynodont Trucidocynodon riograndensis from the Triassic of Southern Brazil: Pectoral Girdle and Forelimb," Acta Palaeontologica Polonica 61(2), 377-386, (14 August 2015). https://doi.org/10.4202/app.00171.2015
Received: 2 May 2015; Accepted: 1 July 2015; Published: 14 August 2015
KEYWORDS
Biomechanics
Brazil
Carnian
Cynodontia
limb posture
Triassic
Trucidocynodon
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