Body Form and Trackway Pattern in Australian Desert Monitors (Squamata: Varanidae): Comparing Zoological and Ichnological Diversity

To what extent does ichnological diversity (the number of distinctive trace fossil morphologies) serve as a proxy for zoological diversity (species richness of trackmakers in the living fauna) in footprint assemblages made by terrestrial lower vertebrates? This question was investigated in a study of body form and trackway features of monitor lizards (varanids) from the Western Australian desert. Body-shape parameters deemed likely to affect trackway pattern of seven varanid species were measured. These lizards differ in average adult size, but there is considerable size overlap between adults of small-bodied species and juveniles of largebodied species. Although subtle species differences in body form were detected, these were largely swamped by intraspecific variability. Furthermore, the most distinctive features in which trails of monitor species differ reflect interspecific differences in foraging behavior rather than anatomical differences, and are features that would be difficult or impossible to recognize without actually capturing the trackmaker. These observations provide empirical support for the widely held belief that trace fossil diversity commonly under-represents zoological diversity. The degree to which this is so is likely to be influenced by trackmaker body size and metabolic physiology.