Evolution of woodcutting behaviour in Early Pliocene beaver driven by consumption of woody plants.

Modern beavers (Castor) are prolific ecosystem engineers and dramatically alter the landscape through tree harvesting and dam building. Little is known, however, about the evolutionary drivers of their woodcutting behaviour. Here we investigate if early woodcutting behaviour in Castoridae was driven by nutritional needs. We measured stable carbon and nitrogen isotopes (δ13C and δ15N) of coeval subfossil plants and beaver collagen (Dipoides sp.) from the Early Pliocene, High Arctic Beaver Pond fossil locality (Ellesmere Island), in order to reconstruct Dipoides sp. diet. Isotopic evidence indicates a diet of woody plants and freshwater macrophytes, supporting the hypothesis that this extinct semiaquatic beaver engaged in woodcutting behaviour for feeding purposes. In a phylogenetic context, the isotopic evidence implies that woodcutting and consumption of woody plants can be traced back to a small-bodied, semiaquatic Miocene castorid, suggesting that beavers have been consuming woody plants for over 20 million years. We propose that the behavioural complex (swimming, woodcutting, and consuming woody plants) preceded and facilitated the evolution of dam building. Dam building and food caching behaviours appear to be specializations for cold winter survival and may have evolved in response to late Neogene northern cooling.

Author Correction: Giant beaver palaeoecology inferred from stable isotopes.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Giant beaver palaeoecology inferred from stable isotopes.

This is a multi-individual (n = 11), stable carbon and nitrogen isotope study of bone collagen (δ13Ccol and δ15Ncol) from the giant beaver (genus Castoroides). The now-extinct giant beaver was once one of the most widespread Pleistocene megafauna in North America. We confirm that Castoroides consumed a diet of predominantly submerged aquatic macrophytes. These dietary preferences rendered the giant beaver highly dependent on wetland habitat for survival. Castoroides' δ13Ccol and δ15Ncol do not support the hypothesis that the giant beaver consumed trees or woody plants, which suggests that it did not share the same behaviours as Castor (i.e., tree-cutting and harvesting). The onset of warmer, more arid conditions likely contributed to the extinction of Castoroides. Six new radiocarbon dates help establish the chronology of the northward dispersal of the giant beaver in Beringia, indicating a correlation with ice sheet retreat.