Barbara Lerner needed a hand.

On a recent walk at South Beach, she found an object that piqued her curiosity, and sent Felix Neck an email to help in its identification. It looked bony, but was clearly only a part of something larger — and there was not much else to go on. With a photo, but not the specimen in hand, I began to dig into the possibilities: maybe a sea turtle, land or marine mammal, or something else.

Before throwing up my hands in despair, I reached out to an expert. With first-hand knowledge of marine life anatomy, Karen Dourdeville, Mass Audubon’s Sea Turtle Research Coordinator, identified the photo as the flipper bones of a marine mammal, likely a dolphin.

Specifically, the picture showed the carpals and metacarpals of the animal’s flipper. The flippers of Cetaceans (the scientific order of marine mammals that includes whales, dolphins and porpoises) could be compared to the hands of humans. They both have the same forelimbs as other mammals; these include the humerus, radius, ulna, carpals, metacarpals and phalanges.

There are differences too. Flippers are homologous to human hands, meaning that they share similar anatomy and a shared ancestry, though may have different functions. Flippers and hands are one example, another would be a bat wing and human arm.

Flippers and hands are not analogous, which describes structures with different anatomy and ancestry, though they serve similar functions. Butterfly and bird wings would be in this category.

Humans use our hands to manipulate objects, while dolphins use their flippers for navigating, maneuvering and swimming, so both types of hands have adapted differently for their functions. And, of course, dolphins and other Cetaceans don’t have elbows like us, their radius and ulna are instead fused. They also have fewer bones (even if both have five digits) in their flippers than humans have in our hands.

The term carpal, or carpus, is derived from a Greek word meaning wrist, which might have come from a Germanic root suggesting to turn or revolve.  The root, carp, is suggested as “pluck,” describing it use.

The flipper bones were in good hands, since Barbara knew what to do. That was to leave them where she found them, since marine mammals are a protected species and one cannot possess the animal or any parts of it without a permit.

She took only pictures and left the bones to return to the sea, not wanted them to get into the wrong hands. Though I am not pointing fingers, please do remember this when tempted to take home an interesting, but protected, beach find: don’t let your desire for these rarities get out of hand. 

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.