Found this bone (possibly a vertebra?) on the beach on the Pacific coast of Costa Rica's Nicoya Peninsula. Guessing it may be a marine mammal because of its weight and size 3 inches long), but it doesn't match the skeletons of any species I looked up. Also tried looking at skeletons of sharks and sea turtles to no avail.

If this is not a mammal, please redirect me to the right category, if possible.

Your truly, (a dedicated naturalist, looking to learn more)
-Jenny

Post's pictures

bone1.jpeg 

bone2.jpeg 

looks like a tuna vertebra

And a great find, too!