[Text & photos by Chuck Almdale]

I don’t know much about bones and certainly not about sea mammal bones. If anyone out there can I.D. this bone and point me towards an on-line source that can illustrate it, I’d be very grateful and will certainly give you credit.

We found the bone in question on Malibu Surfrider beach yesterday. By “we” I mean one of our group of birders came up and handed it to me, asking if I knew what it was. I should mention that the beach was almost completely covered from end-to-end and from high tide line to lagoon with driftwood, seaweed and shells, flotsam and jetsam from the recent storms. I quickly and confidently analyzed the bone as “probably marine mammal…I suppose” thereby exhausting my limited knowledge/guesswork. We wondered if it might be a fossil as it felt so rock solid. But I doubt that. I don’t think a real fossilized-into-rock bone would look like this.

It’s a fragment missing one end. What’s left is 8″ long and weighs just under 9 oz. or 250 grams. It feels very heavy and solid. The surfaces and edges are very worn and smooth.

View 1 (above) and 2 (below) show what looks to me like a socket at the near end of the bone, at bottom, about 1.25 inch across, the same diameter as the hole down the center of the bone.

View 3 below shows the other side of the bone with what looks like a wide groove about 0.5″ across and 2″ long, eroded along the left edge and smoothed on the right edge.

Below: another view (#4) of the end & side with socket showing as in views 1 & 2.

Another view (#5 below) of the flip side like view #3 except that the wide groove is now at the right end.

Below, the “groove” side again. The widest part is 2.5″ from bottom of groove directly vertical (i.e. not along the groove but straight up).

I googled around on-line and found an animated view of a harbor seal skeleton assembling itself. The whole film is interesting and very nicely produced, although the bones could be a little more accurately shaped, and not generic puffy bones. At time 3:35 you get to the left scapula (shoulder blade) and the left foreleg showing the humerus, radius and ulna. After watching the entire film, I returned to the left ulna as the most likely bone, although I wouldn’t call it a perfect match. Perhaps it’s a different species of seal or sea lion, although harbor seal is (I believe) the most common pinniped in the Malibu area.

The film then moves on to the right foreleg, then at time 4:50 moves on to the hips and rear legs including the femur, tibia and fibula. It’s possibly a tibia.

Below: Close up of the interior showing structural ridges.

I tried to find another site showing pinniped or whale bones in detail, but believe it or not, found nothing useful. Nothing! Even those sites claiming “I.D. your bone here!!!!” Nil, nada, zippo.

Below, the groove end showing small pits from heavy wear/erosion?

So…at least one of you osteologists out there, tell us what it is. Please.