New methods and old pictures illuminate the status of Acanthodactylus boskianus asper (Audouin, 1827) (Reptilia, Lacertidae)

The publication entitled Description de l'Égypte, which carries scientific results from Napoleon Bonaparte's conquest of Egypt, includes illustrated descriptions of two lizards, Acanthodactylus boskianus (Daudin 1802), and the new A. asper (Audouin 1827). We note that their original drawings differ conspicuously in the degree of abruptness with which the dorsal scales are enlarged towards the rear of the back. However, this character has been overlooked by later researchers, who often found it difficult to distinguish the two nominal species by conventional transverse scale counts. We developed a method to quantify the degree of abruptness with which scale size changes along the back. For studying this new descriptor we reduced the expected within-sample variation by limiting the sample in two ways, (1) viewing the sexes separately, and (2) heeding the Seligmann effect and considering only whole-tailed individuals. However, the systematic problem persisted. According to our graphic analysis, in A. b. asper both the degree of abruptness of change in scale size, and when abrupt, the location of this change along the back, varied strongly but unimodally. The ranges overlap between provisional geographical areas. Similar abruptness in the change of dorsal scale size does not occur in the populations called A. b. boskianus and A. b. euphraticus. We conclude that the two classical illustrations must be considered as representing two extremes of a complex gradient. The taxonomic implication is to maintain the current trinomials in the complex until a major revision may direct otherwise.