Every once in a while, traits thought to be lost forever suddenly reappear, like a dolphin or a whale born with complete hind limbs! Known as atavisms, these occurrences can teach us all sorts of things, like how limbs actually grow.

Humpback whale (Megaptera novaeangliae) pectoral fin, Iceland, N Atlantic

Mediterranean common octopus going out his home and being scared by a fish.

A humpback whale (Megaptera Novaeangliae) emerges from the blue waters of the Pacific Ocean and slaps its pectoral fin on the surface of the water.

Pod of Beluga (Delphinapterus leucas) swimming together underwater, surfacing, green from plankton (2006). St Lawrence, Canada.

Sperm whale fetus detail

A humpback whale (Megaptera Novaeangliae) in the North Pacific Ocean engages in lobtailing, slapping its flukes on the surface of the water.

A humpback whale (Megaptera Novaeangliae) slaps the surface of the water with one of it's pectoral fins. Possible reasons for this behavior, known as pec slapping, include dislodging parasites, stunning prey, or simply play.

dolphin

Pod of orcas (Orcinus orca) surfacing in unison, Antarctica

MS High angle panning right, Minke whale swimming underwater, ice floating in water, Antarctica

Sperm whale (Physeter macrocephalus) fluking up for deep dive, St Lawrence, Canada.

WA River dolphin surfacing and diving underwater again, South America

MS POV Spinner dolphins bow riding / Caribbean, Dominica

MS TS Sperm whale group swimming and male with penis out / Caribbean, Dominica

Humpback whale (Megaptera novaeangliae) surfacing, Iceland, N Atlantic

MS Humpback Whale (Megaptera novaeangliae) surfacing, Tail fluke rises as dives back down, Tonga

Sperm Whale - pov boat, CU back disappearing into water, tail rises in air & disappears into water, sea horizon, blue sky with white cloud

A humpback whale (Megaptera Novaeangliae) surfaces to breathe in the blue waters of the North Pacific Ocean off the coast of Maui. Several areas in the Hawaiian Islands have been designated as a Humpback Whale National Marine Sanctuary.

Minke whale (Balaenoptera acutorostrata), surfacing near camera with whale watching boat behind, (2002). St Lawrence, Canada.

Orca (Orcinus orca) breaching and splashing camera, Bay of islands, New Zealand

Minke whale (Balaenoptera acutorostrata) dancing around research vessel, good sound (2002). St Lawrence, Canada.

Orca (Orcinus orca) swims past camera, Bay of islands, New Zealand

Minke whale (Balaenoptera acutorostrata) surfacing high out of the, St Lawrence, Canada.