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E.N. ARNOLD 
SYNOPSIS. Lacertid lizards occur in a wide range of structural habitats and 1) may be found on open ground-ranging from 
rocky surfaces, gravel and soil to firm and loose sand, or 2) be associated with quite dense low ground vegetation, or 3) climb 
through and over vegetation matrixes such as tall grass and herbs, bushes and tree canopy, or 4) climb on more or less continuous 
steep or even overhanging surfaces such as rock faces and tree boles. Some forms are largely confined to one of these broad 
structural niches while others occur more widely, but the locomotory requirements of the habitat occupied are usually reflected 
in morphology. The body may show some elongation in taxa that regularly travel through complex interstices of vegetation and 
similar habitats while it is quite short in forms that live on open ground; the tail is often extremely long in matrix climbers and 
may help spread weight in these. 
When forelimb span/hindlimb span is plotted against hindlimb span/ head + body length, lacertids group substantially 
according to their structural niche. In general, disparity in span of the limb pairs increases with hindlimb length: long hind and 
short fore limbs occur in open ground forms, shorter more equal limb pairs in climbers in matrixes and on continuous surfaces, 
and very short subequal limbs in forms associated with dense low ground vegetation. Sexual dimorphism in limb proportions is 
found in some taxa, females having shorter and usually more equal limbs, but it is not known if this reflects differences in 
structural habitat. Proportions of limbs may vary considerably among close relatives as do their growth patterns, indicating that 
they may be easily modified by natural selection. Variation also occurs in the relative lengths of the femur and crus. 
On open ground, long hind limbs can be effectively deployed and provide a high-gear system that contributes most locomotor 
thrust and produces high speeds. In dense ground vegetation etc. the forelimbs are probably used more and the short legs can be 
deployed effectively in confined spaces. Among matrix climbers, the same advantages can apply and in climbers as a whole the 
relatively short hind limbs provide low-gear thrust against gravity while the forelimbs also contribute and, in addition, prevent the 
foreparts falling away from steep surfaces. 
The caudifemoralis muscle, which is the main retractor of the thigh, has its origin in the proximal tail with multiple heads 
attached mainly to the non-autotomic pygal vertebrae. the number of these vertebrae increases in advanced ground-dwellers and 
this may enhance effective size of the muscle and hence limb power. In many lacertids, the most posterior part of the muscle, which 
is slender, extends a short distance on to the autotomic vertebrae and may consequently be lost during tail shedding. 
The complex movements of the hind limbs in ground-running lacertids are described including their effects in ameliorating the 
supposed problem of crural rotation. In the hind feet of open ground dwellers, the metatarsals and toes 14 increase in length, 
allowing the long claws which act like athlete’s spikes to gain purchase over a broad area. At the end of a stride, ground lizards 
may rise on to the tips of toes 2-4 of a single foot, something permitted by robust phalanges and restrictions on mesial flexion at 
the toe joints; toe 5 is scarcely used and often miniaturised. The gait of lacertids varies according to the degree the crus and foot 
are extended forwards, providing a variable gear system that alters as the lizard gains speed; however on very steep surfaces 
climbing species rarely extend the leg fully. 
In climbers on open surfaces, metatarsal 3 is longest allowing toe 3 to be deployed anteriorly or posteriorly . Toes are often 
spread broadly and a positive grip obtained by a system of digital kinking that allows them to shorten after claw insertion. While 
kinking is beneficial to climbing lizards, its exact pattern may be partly arbitrary and varies considerably across taxa. Slender 
phalanges and robust tendons reflect the fact that toes of climbing lizards are often under tension. Upward thrust is maximised 
by maintaining the grip of the feet as long as possible. This is facilitated by a system that allows differential flexion of the digits 
and by substantial flexibility of their joints. 
The morphologies that facilitate each of these two contrasting kinds of locomotion place constraints on the other. Most ground 
dwellers have great difficulty ascending steep surfaces, while climbers do not rise on the tips of the hind toes when running on 
the ground. Feet of forms using dense ground vegetation and of matrix climbers have their own characteristics but respectively 
tend to resemble the two kinds described above. Many lacertids show some intermediacy in limb morphology that reflects the 
conflicts and compromises of moving in more than one type of habitat. 
The mode of locomotion of the immediate ancestor of modern lacertids is unknown but some degree of climbing is widespread 
in the primitive Palaearctic assemblage, even though a number of ground forms also exist. In the Armatured clade some climbing 
appears to be primitive and there are clear shifts: to specialised climbing on open surfaces, to matrixes, to using dense ground 
vegetation and finally to open ground. 
INTRODUCTION 
Locomotion of lizards has recently become a fashionable area of 
enquiry, particularly locomotor performance and its relationship to 
the ecology and morphology of the forms concerned (see for 
instance summary by Garland & Losos, 1994). While performance 
has often been studied in detail and comparative ecology is fre- 
quently well understood, morphology has often been limited to 
simple measurements, especially hind limb length. Little has been 
written in this context about foot morphology and how this affects 
locomotion, the main exceptions being for specialised feet such as 
the adhesive pads of anoles and geckoes (see for example Russell, 
1976) 
The 230 or so species of lacertid lizards occupy a wide range of 
structural niches and, although they are morphologically quite uni- 
form in many respects, exhibit substantial variation in limb 
proportions and structure of the feet, features that are often used in 
systematics (see for instance Boulenger, 1920, 1921). Informal 
observations suggest that limb and foot differences confer perform- 
ance advantages in locomotion in particular habitats. This probable 
correlation between structure and function is explored here, and 
phylogenetic information used to get some idea of historical shifts in 
habitat and morphological features important in locomotion. As will 
become apparent the topic as a whole has many aspects and ramifi- 
cations, all of which are susceptible to detailed and rigorous 
exploration. The intention of this article is to provide a preliminary 
overview that will allow such investigations to be placed in a broad 
context. 
