[Reprinted from original]

Original Title: Evolution of woodcutting
behaviour in Early Pliocene beaver
driven by consumption of woody
plants

Abstract:

Modern beavers (Castor) are prolifc 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 (d13C and d15N) 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.