Lateralized Feeding Behavior in a Paleozoic Reptile

Lateralized behaviors have been reported in a variety of extant vertebrates, including birds and reptiles [1-3] and non-human mammals [4-6]. However, evidence of lateralized behaviors in extinct vertebrates is rare, primarily because of the difficulty of identifying such behaviors with confidence in fossils. In rare instances, paleontologists can infer asymmetry in predatory or foraging behavior, including predation scars on trilobites [7], directionality of invertebrate traces [8], and even behavioral asymmetry in fossil non-human primates [9, 10]. Because lateralized behaviors have been linked to hemispheric (brain) lateralization in some vertebrates [11-15], evidence of lateralized behaviors in ancient vertebrates might yield clues about the evolutionary origins of vertebrate brain lateralization. Here, we show the earliest evidence of lateralized behavior in a fossil reptile based on repeatable observations of tooth wear in a large sample of intact jaws. The patterns of dental wear along the tooth rows of nearly one hundred jaws of the small, early Permian (289 million years ago) reptile Captorhinus aguti indicate that it exhibited lateralized behavior, preferring to feed using the right side of the jaw. Discovery of such a feeding behavior in this ancient, terrestrial, and omnivorous animal provides direct evidence of the deep history of directional behavior among amniotes and may indicate an early origin of brain lateralization.