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

Abstract

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).Keywords: bipedality, kinematics, locomotion, Tropidurus, Liolaemus. Bipedalismo em Tropidurus torquatus (Wied, 1820) e Liolaemus lutzae Mertens, 1938Resumo O bipedalismo apareceu em inúmeras ocasiões em famílias de lagartos filogeneticamente diversas. Neste trabalho, descrevemos, pela primeira vez, locomoção bipedal em lagartos sul-americanos, o lagarto de hábito terrestre Liolaemus lutzae e o generalista Tropidurus torquatus. Os lagartos foram filmados correndo em uma pista de corrida e as seqü-ências foram analisadas quadro a quadro. A postura corporal, como um todo, divergiu bastante durante a locomoção bipedal das duas espécies, mesmo quando não houve diferença significativa em relação ao desempenho locomotor. O comportamento locomotor de L. lutzae é, em geral, similar ao observado em outros lagartos especialistas em solos arenosos. Certas particularidades são comuns, como a postura digitígrada no momento de apoio e durante a fase de apoio; ângulos do corpo e postura da cauda. Em contraste, T. torquatus exibiu altos ângulos corporais e arrastava sua cauda, numa postura comparada à dos lagartos basiliscos. Este tipo de postura corporal pode estar relacionado com certas características e obstáculos de um microhabitat como ao redor de rios e riachos (basiliscos) e uma vegetação de arbustos compacta (T. torquatus).

Performance and three-dimensional kinematics of bipedal lizards during obstacle negotiation

“…The bipedal gait of A. sexlineata does not match the described gait for any one species but it most closely resembles that observed in Aspidoscelis tigris, despite A. sexlineata's smaller size (Urban, 1965;Irschick and Jayne, 1999a). Overall hindlimb movements were characterized by a vertical orientation of the femur and digitigrade posture throughout stance, which is consistent with previous descriptions of bipedal locomotion in Callisaurus draconoides (Irschick and Jayne, 1999a) and Liolaemus lutzae (Rocha-Barbosa et al, 2008). Trunk angle was highly variable during bipedal running, as was position of the forelimb.…”

“…Many groups, including cockroaches, lizards, small rodents and primates, can run using differing numbers of limb pairs, but only cockroaches and lizards must start running using all limb pairs before transitioning to a bipedal gait in the same locomotor bout (Snyder, 1952;Djawdan and Garland, 1988;Full and Tu, 1991;Thorpe et al, 2007). Despite its widespread occurrence in lizards, the mechanisms and advantages of bipedal locomotion are poorly understood (Snyder, 1949;Snyder, 1952;Snyder, 1962;Urban, 1965;Irschick and Jayne, 1999a;Irschick and Jayne, 1999b;Aerts et al, 2003;Clemente et al, 2008;Rocha-Barbosa et al, 2008). Early studies have suggested that bipedal running in lizards is inherently faster than quadrupedal locomotion, similar to bipedal locomotion in cockroaches (Snyder, 1962;Full and Tu, 1991).…”

The effects of multiple obstacles on the locomotor behavior and performance of a terrestrial lizard

“…Many lizard and rodent species have lower escape speeds in dense vegetation compared with open areas (Vasquez et al, 2002;Schooley et al, 1996;Goodman, 2009;Vanhooydonck and Van Damme, 2003). Species utilizing bipedal running may be able to exploit habitat types with uneven substrata because of the increases in visual perception and/or by reaching their maximum speed more quickly (Rieder et al, 2010;Djawdan and Garland, 1988;Rocha-Barbosa et al, 2008;Kohlsdorf and Biewener, 2006). Because two obstacles create the same negative performance effect on stride characteristics and velocity, bipedalism is likely only beneficial when negotiating a single obstacle (Fig.…”

In search of the pitching momentum that enables some lizards to sustain bipedal running at constant speeds

“…Some agamid species, such as the crested dragon Ctenophorus cristatus, are known for their long bipedal excursions over uneven terrain [6]. The south American iguanid lizards Liolaemus lutzae and Tropidurus torquatus perform sustained bipedal running on beach or dune sand [7]. Basilisk lizards (Basiliscus sp.)…”