but is just a small detail on a washed-up fish — a pectoral fin of the Longhorn Cowfish Lactoria cornuta
Here's the whole fish:
Cowfish are both beautiful and intelligent. Unlike humans, they release ostracitoxin when stressed. Their method of locomotion, limited by the rigidity of body and their lack of pelvic fins, resembles that of a hummingbird crossed with a coracle--they can hover like a hummingbird, their fins moving too fast for the human eye to see, but they can't dart any more than a teacup's saucer. Read about them and see a picture of how they should look—colourful and alive—on the superb MarineBio site, which reveals another fascinating fact about their ability to utter complaints.