Bone marrow is rich in fat but is primarily locked inside the medullary cavities of long bones. In large animals, people frequently broke open the bones after removing the adhering meat using hammer and anvils in order to access the marrow. For smaller mammals, like jackrabbits, bones would have to be snapped open. We can identify marrow processing by looking at the fragmentation rates of different kinds of bones--skeletal parts with high marrow content should be broken more frequently.

I looked at the completeness of each long bone specimen, classifying specimens according to whether they are complete (>95% present), large (50-95% present), or small

(<50% present). Statistics show that fragmentation rates are not equal among long bones. The thigh bone and upper forelimb are more fragmented than the lower limbs in general, although the lower hindlimb was frequently snapped at least in one location. The lower forelimb, which has negligible amounts of marrow, was frequently found complete. Since there is no evidence that scavengers were consuming waste bone, humans most certainly were cracking open the bones to get the marrow.

But...the marrow is still found desiccated inside the bone! This is seen in the photos of the femur (left), humerus (center), and tibia (right).

I suspect that the Antelope Cave residents were cracking open stripped jackrabbit long bones for the marrow (most likely after eating the meat), but were not directly eating the marrow. Instead, they were stewing these bits of bone to acquire the nutrients as a broth.

To test whether marrow would be still present in such a case, I roasted a rabbit from the grocery store, made a delicious dinner, and then cracked open the left over bones. After simmering the bones for two hours, the marrow was still present inside! On top of this, the connective tissue (such as tendons) still adhering to the Antelope Cave specimens suggests that if they were simmering the bones, they were doing it for relatively short durations of time, as the connective tissue generally breaks down in less than 45 minutes.

Incidentally, Karl Reinhard at University of Nebraska and his colleagues analyzed the coprolites (again, fossilized poop) from Antelope Cave for Keith Johnson, and found that they likely were consuming stews that included sunflower, maize, and bits of rabbit (including mashed up bones).