Bipedal locomotion in Tropidurus torquatus (Wied, 1820) and Liolaemus lutzae Mertens, 1938.

Bipedalism has evolved on numerous occasions in phylogenetically diverse lizard families. In this paper we describe, for the first time, bipedal locomotion on South American lizards, the sand-dweller Liolaemus lutzae and the generalist Tropidurus torquatus. The lizards were videotaped running on a racetrack and the sequences were analyzed frame by frame. The body posture, as a whole, diverged a lot during bipedal locomotion between the two species, even though there was no difference regarding their sprint performance. The locomotor behavior of L. lutzae is, in general, more similar to the one observed on other sand-dweller lizards. Certain particularities are common, such as the digitigrade posture at footfall and throughout stance, trunk angles; and tail posture. In contrast, T. torquatus exhibited high trunk angles and dragged its tail, in a posture compared to basilisks. This body posture could be related to certain characteristics and obstacles of a microhabitat such as the one around lakes and streams (basilisks) and the one with compact shrubby vegetation (T. torquatus).