Answer to Freak of the Week #3

This unusual looking bone is actually from a very common animal, the domestic cow. It is the metacarpal, or long bone of the forefoot. That’s right, its a foot bone and not a long bone of the leg! And there’s more to the story that that. Its actually two fused metacarpals, from digits 3 and 4. So if you picture the long bones in your hand that connect with your middle finger and the ring finger, then fuse those two together youve got a strong, fused metacarpal. The cows other digits are lost through evolution, however a remnant of the 5th digit still remains as a small bone that articulates near the upper end of this metacarpal bone. Its interesting too that in dissection of a fetal or newborn calf, these 3rd and 4th metacarpals are not yet fused can still be separated into their individual bones!

Bison skeleton – metacarpals shown in red.
Why does the cow, and other large ungulates like deer, elk, sheep, goats, etc., find it advantageous to fuse their foot bones!? Basically it’s for strength and for speed. The two fused metacarpals are thick-walled and provide a very strong structure to support the weight of the animal. Also lengthening of the lower leg, by virtue of lengthening the foot, provides for greater speed. This is an advantage for prey species. These animals don’t need to manipulate the feet in different directions, they just need to move them in one direction forward. Thus they’ve fused and reduced the foot bones for a fast, strong, and stream-lined structure. The hoofed mammals are called unguligrade meaning that they walk on their toes. You can see this in the picture of the bison skeleton, and you’ll also see that the toes articulate with the rounded distal end of the metacarpal.

Metacarpal and metatarsal of domestic cattle.

These bones, the metacarpal from the forefoot and the metatarsal from the hindfoot, are brought to museums for identification because of their unusual appearance and heavy weight. These bones are so dense that many people think they’ve found a mineralized, fossil bone. Another interesting note, cattle and bison are so similar in the postcranial skeleton that individual bones can often be very hard to identify to species. Bison do tend to be a bit larger and more robust, however there are many breeds of cattle and there can be overlap in size between cattle and bison. Bison have been in Ohio since probably the Late Pleistocene and until about 1800, so if you find one of these bones its probably a cow but just might be an early bison!

Posted November 1, 2013

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