Bison femur and metatarsus-species ID tips?

[ethos23]

Hello, I have a femur and metatarsal and thanks to this forum, I've been able to use plenty of reference to ID Bison as opposed to Bos with decent confidence. However, I'm wondering if there are any references or tips on identifying species. I hear B. antiquus is tricky to tell from B. bison, but are there consistent size differences?

 

Both were found in Ames, IA in Squaw Creek in sandbars after spring flooding.

 

This femur is 45 cm (~17.5 in) long and the distal is 11 cm (4.5 in) wide. The metatarsal is 20 cm (~8 in) long and 8 cm (3 in) wide.