Holger Petermanna, Nicolas Mongiardino Kocha, Jacques A. Gauthier
The environment has an influence on an organism’s growth and differentiation during ontogeny. For extinct species in particular, the record of this interaction can be accessed through osteohistology. Such studies have, however, historically focused largely on dinosaurs and mammals, leaving the rest of Amniota understudied. Although accounting for nearly 40% of extant amniote diversity, Squamata (hereafter, “lizards” including snakes and amphisbaenians) is conspicuous for lack of osteohistological study. Here, an osteohistological study of the growth record of 29 individuals of the cnemidophorine teiid lizard Aspidoscelis tigris – Tiger whiptail – sheds light on the species’ growth patterns. We observed that size and age are not tightly coupled in A. tigris. Rather, growth in this lizard may be influenced by genetically determined growth strategies suited to the highly variable arid environments they inhabit, in conjunction with the environment in which individuals hatch. Hatchlings, which exhibit the highest growth rates, have the smallest home ranges and thus habitat variables such as the density of food and competitors could strongly influence final size. However, smaller size seems to favor longevity in A. tigris as the oldest individuals are below the median snout-vent length for the species. Surprisingly, ‘adult’ ontogenetic fusions in the skeleton did not correlate closely with age. Instead, they strongly correlate with size. Although a terminal asymptotic size appears fixed within a narrow size range, the rate at which they achieve it is highly variable. Our study reveals a complex organism-environment interaction governing growth and differentiation in Aspidoscelis tigris, that has implications for the interpretation of osteohistological data in fossil taxa.
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