The life standing position of kannemeyeriid dicynodonts (Amniota, Therapsida): incorporating the track evidence

DOMNANOVICH, NADIA; MARSICANO, CLAUDIA

La Plata

Congreso; XX Jornadas Argentinas Paleontología de Vertebrados; 2004

The dicynodonts, a very specialized group of herbivores, were among the most abundant tetrapods during the Permian. At the beginning of the Triassic they were relatively scarce and underwent a modest, second radiation during the Middle Triassic represented by the kannemeyeriids. This group includes the massively built South American Stahleckeria and Ischigualastia, and the North American Placerias. Traditionally, the kannemeyeriid limb posture has been restored with the forelimbs in a sprawling fashion and a nearly upright posture for the hindlimbs. This different posture between the two sets of limbs was suggested to be indicative of a dichotomy in function: the forelimbs were involved mainly in the support of the body and the hindlimbs in generating locomotor forces. Trackways can provide a good evidence for limb posture if the trackmaker can be identified with a reasonable degree of certainty. The manual and pedal location, their orientation, and stride length, among other parameters, may be used to restore the normal walking posture in extinct animals. Matching the skeletal restorations of Stahleckeria, Ischigualastia and Placerias with Middle-Late Triassic trackways of large footprints, interpreted as dicynodont trackways, from Argentina and South Africa shows that the manus were almost directly beneath the glenoids, as were the pedes with respect to the acetabula. Moreover, the trackways show that in some cases the manus imprints almost touch the midline. This evidence strongly argues against a sprawling forelimb posture in this large herbivores and suggests a more upright stance and parasagittal gait for both the fore and hindlimbs. Stahleckeria and Ischigualastia, and the North American Placerias. Traditionally, the kannemeyeriid limb posture has been restored with the forelimbs in a sprawling fashion and a nearly upright posture for the hindlimbs. This different posture between the two sets of limbs was suggested to be indicative of a dichotomy in function: the forelimbs were involved mainly in the support of the body and the hindlimbs in generating locomotor forces. Trackways can provide a good evidence for limb posture if the trackmaker can be identified with a reasonable degree of certainty. The manual and pedal location, their orientation, and stride length, among other parameters, may be used to restore the normal walking posture in extinct animals. Matching the skeletal restorations of Stahleckeria, Ischigualastia and Placerias with Middle-Late Triassic trackways of large footprints, interpreted as dicynodont trackways, from Argentina and South Africa shows that the manus were almost directly beneath the glenoids, as were the pedes with respect to the acetabula. Moreover, the trackways show that in some cases the manus imprints almost touch the midline. This evidence strongly argues against a sprawling forelimb posture in this large herbivores and suggests a more upright stance and parasagittal gait for both the fore and hindlimbs.