A neighbour found a large piece of bone on the bank of the Fraser River in Richmond, BC. He facetiously called it "a dinosaur bone."
My first thought was sea lion, but I wasn't sure: California or Steller? The thing is pretty darn big. Steller?
It's mostly the cranium with remnants of zygomatic arch (cheek bones). Something didn't fit. A sea lion skull this big would have to be male, and should have well-developed sagittal crest (ridge down the middle of the cranium). No such feature here.
Hmmmm. It sure is big.
Northern Elephant Seal? They are not common in British Columbian inner waters, although increasingly they have been showing up, even breeding at the south end of Vancouver Island. I can't find a Richmond Record. The locality of the find was a few miles upstream from the mouth of the Fraser River, approximately 49 06 38 N 123 08 36W.
It seems to fit. The sheet of paper here shows an image of the skull of a male. The skull remnant perched next to it seems to match the portion posterior to the black line I drew. The image came from a commercial bone site.
I've sent images to a marine mammal expert to get a proper identification.
In any case, neat.
Update: Marine mammal paleontologist Robert Boessenecker, consulted on my behalf by paleontologist and blogger Neil Kelley, identified the skull as "definitely 100% Mirounga."
Mirounga is the genus for elephant seal.
Thank you to those who helped with this.