[blam]

"On the west coast, we know of one early individual who had a high N15 to C13 ratio, suggesting an amazing 92.5% marine diet; and not just marine, but sea mammals!"

"In late prehistoric times the marine portion of the diet in this same area had dropped to about 10%."

Any idea why?

[Coyoteman]

"On the west coast, we know of one early individual who had a high N15 to C13 ratio, suggesting an amazing 92.5% marine diet; and not just marine, but sea mammals!"

"In late prehistoric times the marine portion of the diet in this same area had dropped to about 10%."

Any idea why?

Quick answer: In that area, as populations increased and subsequently changed, partially through migration, the diet had to expand to include large amounts of terrestrial foods. The earliest adaptations to marine resources gave way to largely terrestrial diets. It took thousands of years.