What does this vertebra come from?

[SharkySarah]

From Stratford hall  Virginia a decade ago. How do I know if it’s mammal or fish or something else?

[hemipristis]

a young porpoise/dolpin.  I say young because the epiphysis hasn't fused onto the vertebra (noticeable as the roughly-circular, irregular surface visible just to the left of your index finger in the second photo).