I don't think its a hood ornament part. There's no evidence of any plating on it. I own antique cars and I can tell you that older chromed parts (with the exception of the Korean war years '52 & '53) will show some chrome - even after being buried in the ground for a couple of decades.
Could it be part of a garden statue or from a fountain? It looks kinda like a fish fin to me...
DCMatt