TAPHONOMIC HISTORY OF BISON BONES FROM THE DES MOINES RIVER

Bison were locally extirpated in Minnesota before the 1850s. The recent discovery of a large number of bison bones in the Des Moines River near Jackson, MN raises questions about how and when these mammals became extinct in the area. The bones have radiocarbon ages from 1000 BP to 200 BP, predating European settlement in this location. This project examines the transport history of bones in the river and seeks to determine the extent to which humans butchered or hunted these bison.

To answer those questions, we collected a total of 865 bones, the majority of which were bison, from sandbars, banks, and within the shallow portions of the Des Moines River channel. Each bone was identified, catalogued and evaluated for taphonomic alteration, including burial, transport, predator/scavenger markings, and human modification such as cut marks. We assigned a taphonomic grade (1 to 5) to assess the degree of post-mortem alteration, where 1 is unaltered and 5 represents total loss of bone integrity. Most bones showed evidence of lengthy transport in the river, with an average taphonomic grade of 2-3. A large proportion of the bones showed teeth marks from scavenging. Many bones also show evidence of butchering by humans, mainly cut marks on ribs and long bones.

The degree of rounding and frequency of scavenger alteration suggests that these bones were exposed after death and traveled from sandbar to sandbar, continuously since the time of death. This taphonomic pattern argues against an extended period of burial followed by short transport time in the Des Moines River, such as might occur following burial in a catastrophic flood. Because a substantial number of bones have tool markings indicating human modification, combined with the extraordinary concentration of bison compared to other bone types, we hypothesize that the Des Moines River in this area was a long-lived kill site that predates European bison hunters