On Friday I gave you these objects to identify from Cyler Conrad, who came across them from an archaeological dig in San Francisco Bay:

I hasten to add that there is no certain answer to what these objects are, but I think there were some useful observations made by contributors and I will share my thoughts. Please feel free to continue the discussion in the comments below.

Barbara Powell and henstridgesj made some great suggestions, mainly focusing on marine mammals, particularly among the Otarids (Sea-lions and Fur-seals). Some of these large mammals certainly occur in the San Francisco Bay area (well, the Northern Fur Seal Callorhinus ursinus, Guadalupe Fur Seal Arctocephalus townsendi, Steller Sea-lion Eumetopias jubatus, California Sea-lion Zalophus californianus are all there) and they have femurs that are broadly the right size and shape as the bone in the top image – the humerus in these species is quite different, possessing a distinctive crest on the shaft.

However, I’m a bit thrown by the articular surface visible in the top image. In the Sea-lions and Fur-seals the femur has two distinct and narrow articulations with the tibia and fibula, since these animals bear weight on their hind flippers. The fact that the top specimen only shows one broad and fairly poorly defined articulation makes me think it may belong to a Phocid seal (which drag their hind flippers), which for this area would either mean a Northern Elephant Seal Mirounga angustirostris or Harbour Seal Phoca vitulina.

Given the size, I would think it would either be the femur from a large male Harbour Seal (although males are only slightly bigger than females) or a smaller female Elephant Seal, but unfortunately I can’t find comparative material to help draw a conclusion. What I have noticed is that the Harbour Seal does tend to have a relatively broader femur than we see here, but without an Elephant Seal femur for comparison I’m stumped.

The other bone looks like the first metacarpal of one of these animals and doesn’t really add much more information.

Alas, sometimes identifications are hard to make with confidence.