NEOICHNOLOGY OF BEAVERS: A DIVERSE SUITE OF TRACES BY AN AQUATIC LANDSCAPE ENGINEER

Extant beavers, whose populations are rapidly rebounding (>15 million globally) following historic near-extirpation bottlenecks, produce a diverse suite of erosional and depositional features in Eurasia (Castor fiber), North America (Castor canadensis), and in several newly introduced regions (e.g., Patagonia). These include locomotion traces and trails, supply canals reinforced with manuports, several types of domichnia (bank burrows, lodges, huts), dams of various sizes (up to 800 m long; some mud-reinforced), gnawed tree stumps and branches (cone-shaped and asymmetric cuts), bark peeling, gnawing/rasping marks on bones and antlers (cf. Machichnus isp.), and the resulting byproducts (shavings and droppings). Lower openings of bank burrows, in combination with other traces, can be utilized as local water-level indicators. The majority of tree damage occurs within 10-20 m of stream banks, making relict gnawed stumps important proxies for paleo-drainage extent, as well as snowpack and water basin highstand level. For example, along the shores of Perry Lake (Jefferson County, Kansas) bark peeling and cone-shaped cuts 2-3 m above the ground level reflect the extraordinarily high lake levels due to floods of 2019. Biogeomorphic cascades accelerate bank erosion through vegetation removal (direct positive feedback) and secondary undercutting by native and introduced fish species attracted by felled trees. Small incisor marks (single width: <4 mm) by juveniles on near-ground adventitious roots within 1-2 m of stream channel (Montgomery County, Pennsylvania) may further exacerbate bank stability. Georadar is emerging as an effective subsurface imaging technique to map subsurface sections of burrows, as well as the geological context of dams and pond-meadow complexes. Given a substantial zoogeomorphic impact of a single family, it is likely that a compound effect of beaver activity throughout the Holocene is greatly underestimated due to riparian taphonomic processes (channel switching vs. rapid burial) and difficulty in interpreting relict structures. Whereas helical Daemonelix burrows of Tertiary dryland castorids have been studied in detail, the ichnological record of the Pleistocene beaver (Castoroides sp.) is scant, with potential implications to their role as landscape engineers.