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42 LI Z A R D S O F T H E AM E R I C AN S O UT HW E ST
vessels. Then, these species have the ability to regenerate the tail—so that it can be lost again if need be! However, the regenerated part of the tail is just cartilage (covered with scales) and lacks bone and new fracture planes, so if tail autotomy occurs again (and this is not uncommon), the break occurs only in the original base of the tail, not in the new part. Tail autotomy may save the life of the lizard, but it obviously comes with costs. After autotomy, lizards have to deal with a major wound, are left with less caudal fat reserves, don’t run and maneuver as well, don’t have a tail to lose if a predator strikes before regeneration is complete, and (at least in subadult Common Sideblotched Lizards) fall in social status among conspecifics. This loss of social status can adversely affect a lizard’s chance of survival and decrease a male’s ability to defend a territory and mate. Thus, tail autotomy as a defense against predation is a last-ditch effort.
E X TE R N AL ANATO M Y AN D I DE N TI F IC ATIO N Authors: Lawrence L. C. Jones and Randall D. Babb Most lizards have an overall shape that is relatively elongate and prostrate, with a distinct head, neck, torso, front limbs, and hind limbs. This is similar to most salamanders (with which they are sometimes confused), but there is one very important difference—salamanders are amphibians and have smooth, usually slimy skins, while lizards are reptiles and have dry, scaly skin. From this generalized shape, there are many variations and exceptions. The variations in the shapes of lizards are often diagnostic at the family and genus level. For example, some lack legs, some are dorsoventrally flattened, some have very long tails, and so on. Most species of the American Southwest can be differentiated in the field with the aid of close-focusing binoculars, based on their overall shape and color pattern. However, there may be considerable variation in color patterns, even within a species. This variation is often diagnostic for difAdult male Cophosaurus texanus, Maricopa Co., AZ. ferentiating age classes, sexes, subspecies, pattern classes, and reproductive mode, but there is also normal variation to be expected within a single taxon. For example, there may be colormatching, where a lizard generally matches the background, as with horned lizards. The Greater Short-