To catch a chameleon, or actualism vs. natural history in the taphonomy of the microvertebrate fraction at Qesem Cave, Israel

Abstract

Qesem Cave is a unique Middle Pleistocene, hominin-bearing site in Israel that contains a rich microvertebrate accumulation. The microvertebrates are highly unusual in that half of them are from small reptiles, and most of the reptiles are chameleons, which are otherwise rare in the fossil record. Analysis of the lower vertebrate component shows uniform taphonomic characteristics: on average 17.6% of specimens show evidence of corrosion (the vast majority light), and specimen breakage is between 4.9 and 12.0%, depending on metric. Charring is negligible. Most species are small (body mass <60 g). These taphonomic attributes do not vary in the studied portion of the stratigraphic profile, nor do they systematically vary between taxa. Thorough study of all skeletal parts suggests that most individuals probably entered the cave as whole animals; the only exception is the large glass lizard, Pseudopus, which is represented mostly by the tail. These taphonomic data suggest a Barn Owl as the predominant accumulator. However, natural history observations on Barn Owls and chameleons are strongly at odds with this actualistic inference: Barn Owls are nowhere recorded as a major predator on chameleons. We argue that a focus on extant, especially European, populations could distort our understanding of their feeding biology and is vulnerable to counterexample. We propose a scenario that harmonizes actualism and natural history. We further identify a possible owl roost in Qesem Cave, the first time such a roost has been identified in a collapsed cave setting. These conclusions may have conservation implications for chameleons. They also suggest that the hearth adjacent to the microvertebrate concentration was situated in the twilight zone.