Experimental Study of Black Bear (Ursus americanus) and Grizzly Bear (U. arctos) Tooth Marks and Other Gnawing Damage on Bone

Abstract

Tooth mark and other gnawing damage modifications on bone from African carnivores have been extensively examined, but there are less data on North American carnivores, especially on Ursidae (bears). The present study examined gnawing damage by captive black bear (Ursus americanus) and grizzly bear (U. arctos) fed 55 proximal or distal femora from cattle (Bos taurus) in order to distinguish ursid gnaw damage characteristics. Tooth mark modifications examined include pits, punctures, scores, and furrows, while other gnaw damage modifications include crenellated margins, edge polish, scalloping, scooping, and crushed margins. Each tooth mark was processed through the open-source software ImageJ in order to obtain the area, perimeter, length, and width. Tooth pits had an average length of 3.5 mm and average width of 2.2 mm; scores had an average width of 1.5 mm. There was a statistically significant difference between ursid tooth pits and those created by various other scavenging species. Other common taphonomic effects included scalloping on the distal end of the femur, especially on the patellar articular surface; scooping on the proximal end of the femur, especially on the greater trochanter; and furrows, primarily on the distal end of the femur along the patellar articular surface and condyles. Cancellous scooping occurred in 35.2% of the entire sample, while scalloping occurred in 29.6% of the entire sample. These high percentages may be distinctive characteristics of ursid gnaw damage and therefore may help distinguish ursid scavenging from that of other carnivores.