Buzz
At times, evolution fails to completely remove certain traits, leaving animals with vestigial organs. These unnecessary remnants can occasionally increase the likelihood of injury or even accelerate the species' extinction. However, many animals with such evolutionary leftovers simply go on with life. For scientists studying an animal's evolutionary history, these peculiar features can offer valuable insight.
10. Dog's Dewclaw
A dewclaw is a toe positioned higher up on a dog’s leg, and it serves no practical purpose. While dewclaws are common on the front legs of dogs, the rare version on the hind legs also appears. It is often recommended to remove these, as they can be hazardous to the dog. Since dewclaws are typically connected by a small flap of skin, they are prone to getting caught and torn off. The growing nail on a vestigial dewclaw may also lead to painful complications. As this toe does not touch the ground, the nail cannot wear down and can instead curl into the toe pad or leg.
Unquestionably, this situation is excruciating for the animal, particularly in hairy breeds where owners might overlook the hidden toe beneath the fur. In certain show dogs, the removal of vestigial toes is prohibited, as they are considered part of the breed's working standard. The Great Pyrenees and Briard are examples of such breeds. The Great Pyrenees even possesses a double dewclaw.
9. Whales With Limbs
Some whale embryos develop early traces of limbs, but these generally disappear as the animal matures. However, in rare instances, these limbs persist. Whales have been found with leg-like stumps that contain tibia or femur bones. Several such findings were made by whale hunters. In July 1919, a female humpback whale, killed by whalers near Vancouver Island, was discovered with two surprising stumps on its lower body. These were determined to be rudimentary hind legs measuring approximately 1.2 meters (4 ft) long.
In 1956, an adult female cachalot, hunted off the coast of Japan, was found to have a pair of 'back legs' more than 5 centimeters (2 in) long. Dolphins too retain a deep connection to their evolutionary past. When a pod of 450 blue-white dolphins was killed in 1963 by Japanese fishermen, one dolphin was found to have vestigial hind leg stumps. Scientists assert that these protrusions are not anomalies but a reversion to the ancestral body form of whales when they were still land-dwelling creatures.
8. Cockroach Wings
While all male cockroaches possess well-developed wings that often enable them to fly, females of some roach species either lack wings entirely or have underdeveloped ones. It’s curious why nature didn’t equip the females with functional wings instead, especially considering they might need to escape danger while carrying the future generation in their egg cases.
However, cockroaches aren’t exactly a threatened species. These persistent creatures have terrified homeowners and businesses alike across the globe, which might explain why females don’t require the ability to fly. Their evolutionary success is such that cockroaches haven’t faced the same pressures to adapt as other species. Even today, they showcase their 320-million-year-old design, proving that early life forms weren’t as primitive as some might believe.
7. Shark Teeth
At last, a shark that doesn’t rely on its teeth! While the beaches may not be completely free of danger, humanity can take comfort in the fact that this particular shark species doesn’t use its rows of 3,000 teeth. The enormous whale shark is a filter feeder that excels at everything on a grand scale. As the largest fish alive, females of the species can carry up to 300 pups, and don’t even think about insulting this shark—its spotted skin can grow as thick as 25 centimeters (10 inches).
These colossal creatures primarily feed on microscopic organisms. Consequently, their teeth have been reduced to a mere 3 millimeters (0.1 inches) over generations. These tiny teeth would be ineffective for biting. Instead, whale sharks possess 10 filter pads that trap food as the shark inhales seawater through its massive mouth and expels it through its gills. These ocean giants remain a mystery—little is known about their mating habits, migration paths, growth rates, or even their evolutionary history.
6. Boa Limbs
Considered primitive snakes, boa constrictors possess vestigial pelvic bones and hind limbs. Located in the lower part of the reptile’s body, these ancient legs even have claws. Though not immediately visible, an X-ray is often required to fully observe this unusual trait.
The remnants of leg bones in boa constrictors support the idea that snakes evolved from lizards. Millions of years ago, a group of lizards may have begun to develop shorter legs, possibly by accident. While the exact cause is unclear, this new body form offered enough advantage to the early snakes to help them reproduce and thrive. Over time, the legs vanished from sight, eventually becoming vestigial remnants hidden within the snake’s body. Pythons, another primitive group of constrictor snakes, retained their vestigial legs in a similar way. Both species also have two lungs, unlike most other snakes, which have just one.
5. Flightless Cormorant
The Galapagos cormorant is an example of nature taking an odd turn. It seems that nature has made a mistake with this unique aquatic bird—the Galapagos cormorant is unafraid of humans and, unfortunately, has lost the ability to fly. Its undersized wings appear as though they’ve been chewed on by rats. Despite this, cormorants are exceptional hunters in the water, and this species is no different. With its webbed feet and powerful legs, the Galapagos cormorant catches fish, octopus, and eels with remarkable speed. However, unlike penguins, the Galapagos cormorant doesn’t use its wings to help it maneuver underwater. In fact, its wings are entirely useless.
Similar to other cormorant species, the Galapagos bird is often seen perched on a rock after a dive, its wings spread wide to soak up the Sun. This behavior is typical for flying cormorants, as it helps them dry their non-waterproof feathers, making them ready to fly again. However, for the Galapagos cormorant, this vestigial habit is pointless, as its wings no longer serve any functional purpose. With its fearless nature and limited range, the inability to fly made this turquoise-eyed seabird particularly vulnerable, and it could face easy extinction from a single catastrophic event. For instance, if rats were to invade the islands, the Galapagos cormorant population could be in serious peril.
4. Plover Toes
Plovers, known for their clever tactic of faking a broken wing to distract predators from their young, are a fascinating shorebird. Black-bellied plovers, the largest of the plover species, are the only ones in North America that retain small, vestigial hind toes. These tiny toes, although hard to spot in the wild, are an interesting reminder of evolutionary leftovers. When plovers run in their distinctive stop-and-go fashion, these small toes are not easily visible.
To impress a mate, the male plover creates a modest nest by scratching the ground, and the female lays a clutch of multicolored eggs—ranging from pink to green to brown. Both parents take turns incubating and feeding the chicks, though the female typically loses interest after two weeks. From then on, the male takes over the responsibility of caring for the young until they are fully developed. The chicks are remarkably independent, often starting to feed themselves the day after hatching. These highly alert shorebirds can live up to 20 years.
3. Cheetah Claw Sheaths
This spotted cat has an intriguing organ that serves a real function when it's young but becomes vestigial as it grows. Baby cheetahs have a unique ability that adult cheetahs lack: they can fully retract their claws into their paws. Unlike other cats, cheetahs cannot fully retract their claws, which causes them to leave a distinct “dog-like” footprint when they walk. In the sand, their claw marks are as visible as their toe pads, unlike other cats whose tracks only reveal the pads.
As they mature, however, cheetah cubs possess fully functional claw sheaths into which their claws can disappear, much like other feline species. This ability is temporary, though. By the time the cubs reach 15 weeks, the sheaths deteriorate, and the cheetah's claws can no longer retract completely. After this stage, the claws remain visible and only partially retract, giving the cheetah its characteristic appearance.
2. Owl Hands
Some great gray owl chicks are born with tiny claw-like structures on the wrists of their wings—resembling little 'owl hands.' While certain bird species, such as the hoatzin of South America, make use of similar body parts, these owls seem to have no functional use for theirs. The young owls do not employ them for climbing branches or any other apparent purpose.
These vestigial hands on the great gray owl might suggest a long-lost ancestor that had a need for tree-climbing abilities. In comparison to other owls in North America, the great gray owl is considered quite primitive. It is the largest owl species on the continent, with both males and females reaching up to 84 centimeters (33 inches) in height. Though most great gray owls are born with wing claws, this ancient feature tends to fade as they mature. The reason for this remains unclear, but in rare cases, adult owls can retain these large but ultimately useless claws.
1. Slug Shell
Slugs are part of the snail family but are distinguished by their lack of shells. While some slugs still carry a shell inherited from their ancestors, it is now hidden within their mantle. This vestigial shell no longer serves as a home, but instead functions as a storage space for the slimy critter’s calcium. Calcium plays a vital role in the life of slugs and snails, regulating their bodily fluids, egg production, shell formation, muscle movement, and cell wall maintenance.
Without the safeguard of a shell, slugs have evolved various defense mechanisms to protect their soft bodies. Sea slugs, like the vividly colored nudibranchs, secrete toxins and sting potential threats. On land, slugs are more vulnerable and face many predators, including other slugs. In the face of danger, land slugs release a substance that imparts a bad taste and makes them difficult to hold onto.
