Peterson - p. 2 
glenohumeral mobility may be a common factor but some lizards depend upon a 
long, highly flexible body axis to increase the reach of the limb, e.g. 
Gerrhonotus multicarinatus, while others modify the shoulder region to 
permit movement of the shoulder girdle on the body wall, e.g. Chamaeleo, 
Polychrus, Phenacosaurus and Anolis. In the majority of lizards the 
shoulder girdle is fixed to the body wall, (There is actual data for only 
a few, but literature reports on the existence of a critical ligamentous 
arrangement is reasonable evidence for the generality of a fixed girdle), 
Adaptation for rotation of the girdle in the sagittal plane as seen in these 
four lizard genera requires reorganization of three or four articulations 
between the girdle and dermal-axial elements, The girdle-axial muscles not 
only have different architecture and attachments, but must have different 
periods of activity in the locomotor cycle (EMG data). Parallel adaptations 
occur in the reptile-mammal transition and are the basis of the more widely 
discussed postural and weight transfer shifts in mammals, Not surprisingly, 
these arboreal lizards can approach mammalian postures and converge on 
mammalian locomotor mechanics in many respects. In Chamaeleo, Polychrus and 
Phenacosaurus slow movement permits the animal to avoid the large forces 
associated with impact and acceleration, thus decreasing (perhaps by half) 
the applied force. Adaptation for mobility is extreme; stress bearing 
arrangements are dramatically reduced (ligaments absent; clavicle absent or 
weakly articulated); muscles are arranged to provide maximum excursion of 
elements at the expense of more favorable leverage. Adaptation in the 
recovery musculature is more marked than that in the propulsive muscles. 
This correlates with the long reach and slow acrobatic maneuvers these 
animals use to change perches. The recovery stroke involves not only 
swinging the limb forward, but reaching, obtaining purchase and reorientation 
to a spatially different substrate, The range of movement in quadrants 
anterior to the shoulder is much greater in these arboreal forms than in 
their terrestrial relatives. Among other adaptations they have a more 
laterally facing shoulder articulation, 
Anoles parallel many of these adaptations, including most of those 
associated with modification of the recovery muscles (although different 
muscle groups are involved), more lateral orientation of the shoulder joint 
and girdle mobility. But they are less specialized for mobility than the 
related Polychrus or Phenacosaurus. This is not an indication of less 
arboreal specialization, but rather a different behavioral strategy relying 
on acceleration (leaping) to change perches and higher speeds for movement 
on a given substrate, An anole presents a mosaic of adaptations for 
compromising increased mobility with the stability required by higher speeds 
and leaping behavior, The compromise has been achieved by structural 
innovation, For example, many anoles have a clavicular mechanism which 
allows rotation of the girdle during protraction and the early stage of 
retraction (phases when the limb is in quadrants anterior to the shoulder 
joint), but fixes the girdle relative to the body wall when the forearm is 
being extended (forearm extension occurs at the onset of a leap and in 
landing and is the most important component of the propulsive stroke). If 
the girdle were free to displace during these periods, there is presumably 
