Another in the AMNH animal series. 3 hours, ballpoint pen.
Their heads' shape kind of looks like eggs.
That's a terrific drawing. Great technique. You've done a good job separating the heavy fur that sits across the front of their body from the relatively bare fur at the rear of back half of their body. I would recommend one adjustment for any future drawing of a bison. The head should be significantly larger. If you see one live, you'll see how you have this immense head backed by large powerful shoulders followed by a relatively smaller rear. They are very much a front heavy animal.
Thanks for the tip! I drew this off a taxidermied specimen at a museum, I'll recheck my proportions when I get back there.