BIPEDAL ANIMALS: CHARACTERISTICS AND EXAMPLES - BIOLOGY

The two - legged animals are those who move from one place to another using two hindlimbs. These movements include running, walking, or jumping. Some modern species, despite having four legs, occasionally use a bipedal gait. Taking this aspect into consideration, the specialists have organized two large groups.

The first classification corresponds to obligate bipedal animals, in which running or walking is their main mode of locomotion. In contrast, facultative bipedal species move on two legs in response to a need, such as fleeing from a predator or to transport food.

Ostrich. Source: HombreDHojalata, from Wikimedia Commons For an animal to be considered a facultative bipedal, it must carry out the movement in a sustained manner, implying several steps that allow it to advance a certain distance.

Examples of bipedal animals

Bonobo (

The bonobo, also known as the pygmy chimpanzee, is a primate that has a slim body, narrow shoulders, and long hind limbs.

Its movement can follow different patterns: knuckle walking (quadruped), bipedalism and modified brachiation.

Its greater disposition to bipedalism, compared to other primates, could be due to the long bones of the thigh and legs. In addition, its body weight is differentially distributed and the foramen magnum is centered.

This species can walk on two legs when it is in the branches, being able to move up to 10 steps on a horizontal branch. On the ground, the Pan paniscus generally moves carrying plant stems or food on its forelimbs.

Their bipedal locomotion is characterized by the fact that their feet have a plantar position and for a short time of contact with the ground, compared to the quadruped gait. The middle part of the leg and the heel usually touch the ground simultaneously, during the initial contact with the ground.

White-handed gibbon (

Ladislav Král, from Wikimedia CommonsThis primate is characterized by a slim body, with arms much longer than legs. The coat can be black, dark brown, reddish or blond. Its face is black and is surrounded by a border of white hairs. The hands and legs are white.

The Hylobates lar is an arboreal animal, which moves between the forest canopy swinging with its arms. This form of movement is known as brachiation. However, on the ground it has another variety of displacements, such as jumping, running and quadratic climbing.

The gibbon is versatile in its terrestrial gait, being able to alternate between quadruped, bideed or tripedal, as needed. In its bipedal movement, this species increases the length and frequency of the stride, in order to increase speed.

The researchers argue that the morphological and anatomical adaptations of the white-handed gibbon for brachiation have not limited its excellent land-moving ability.

Red kangaroo (

Bardrock, from Wikimedia Commons This species, like all of its genus, has highly developed hind legs that are larger than the previous ones. The hind legs are large and adapted for jumping. The head is small compared to the body and the tail is muscular and long.

Kangaroos are the only large animals that jump around. The speed that the red kangaroo reaches is between 20 and 25 km / h. However, they can travel in short distances up to 70 km / h. For 2 kilometers, this species is capable of maintaining a speed of 40 km / h.

The bipedal jump could represent a great energy saving for the animal. This could explain the fact that this species lives in deserts and plains. In this environment it is important to reduce energy consumption, since the resources are quite dispersed in the area.

When it needs to move slowly, the kangaroo leans on its tail. In this way, forming a tripod with the two front legs, while bringing the rear legs forward.

Emperor penguin (

Figure 6. Emperor penguin (Aptenodytes forsteri). Source: Hannes Grobe / AWI, from Wikimedia Commons In its adult stage, this flightless bird can reach 120 centimeters in height and weigh up to 45 kilograms. Because she spends most of her time in water, her body is hydrodynamic. In addition, its wings are flat and rigid, similar to a fin.

The two legs are located far back on its body, which makes it difficult for its bipedal locomotion on land. However, in the water they act as a rudder. The fingers are joined by interdigital membranes. It has short tarsi and small, strong legs, slightly inclined upwards.

On land, the emperor penguin alternates its movement between walking, with awkward, wobbly steps, and sliding on its belly on the ice, propelling itself with its wings and legs.

Walking speed is 1 to 2.5 km / h. Compared to other animals of its weight and size, the emperor penguin uses twice as much energy when walking.

Ostrich (

Ostrich. Source: HombreDHojalata, from Wikimedia Commons This animal is the largest bird in the world, weighing between 64 and 145 kilograms. In addition to this, it is the fastest biped in long-distance races, reaching a speed of 60 km / h for 30 minutes.

The reason why the ostrich can maintain such an incredible rhythm is the particular morphology of its muscles, bones and the toes on its feet. The limbs of this animal are long and distal and the muscle mass is concentrated proximally.

The combination of these two characteristics allows the Struthio camelus to have a high stride frequency, allowing it to take big strides. Because the muscles are located higher up the leg, it allows the animal to move its legs more quickly, with very little effort.

Another factor that contributes to the ostrich being able to make long runs are its toes. This animal has only two toes and when it walks it does so on its toes. This peculiarity, typical of its species, helps it stay balanced when it is on uneven terrain.

Helmeted basilisk (

Matt Mechtley from Heidelberg, Deutschland, via Wikimedia Commons This lizard is similar to an iguana, but smaller in size and with a slimmer body. It has olive green skin, with a reddish-brown belly and a yellow or red throat. It has two ridges, a small one on the back and a round one on the head.

The particular characteristic of this species is that it can run on water in a bipedal position, which is why it is also known as the Christ lizard. He also marches in the same way on land, when he starts a race to flee from a predator.

If the helmeted basilisk feels threatened, it jumps into the water and starts running. The hind legs have dermal lobes that increase the support surface, allowing them to run quickly on the lake or river. When on the ground, these structures remain coiled.

As the speed decreases, the basilisk sinks, having to swim to shore. The total force generated, after the foot hits the water, produces the propulsive thrust for the lift during bipedal locomotion.

Six-line runners (Aspidoscelis sexlineata)

This lizard, within its species, is one of the fastest in the world. On short trips it could reach speeds of up to 30 km / h. Their body is slim and they have a long tail.

Although it is usually a quadruped animal, it moves bipedally when it needs to move over uneven terrain.

During this gait, the optional bipedal behavior is influenced by the displacement of the center of mass towards the back of the body, the angle of the trunk and the initial acceleration of the race.

The Aspidoscelis sexlineata, regardless of the existence of obstacles, most of the time it starts the race on two legs.

This species is bipedal almost exclusively in fast runs, possibly due to the fact that its center of gravity is in the front of its hind legs. Consequently, as the speed slows the animal falls forward.

Florida lizard (

Source: Glenn Bartolotti, from Wikimedia Commons It is a small-sized lizard, gray-brown or gray in color, with a body covered in spiny scales. It is endemic to the state of Florida, in the United States.

This species presents morphological and behavioral adaptations that help it maintain facultative bipedalism. This mode of locomotion is used during the speed race, which he does when he needs to travel a path with obstacles, such as branches or stones.

The Sceloporus woodi often moves quickly through uneven terrain, with vegetation, wood, sand and debris, with the intention of fleeing from an attacker or to guard its territory.

This type of gait is generally done on two legs, being much more efficient than when it is done using all four legs. Various studies have shown that, when approaching the obstacle, these lizards increase the vertical movement of their legs and raise their heads.

The lifting of the tail during acceleration results from the upward rotation of the trunk, through the angular variation of the caudal end. This allows for a sustained race on two legs, which generally continues once obstacles encountered on the track have been overcome.

Frilled Dragon (Chlamydosaurus kingii)

This species is one of the animals that represents Australia. It is unique not only for its large, colorful, and intimidating frill around the neck, but for its facultative bipedal locomotion.

The flying dragon is one of the few representatives of the genus Chlamydosaurus that uses bipedal movements during its routine feeding task.

Unlike the rest of the lizards, which show bipedalism only in high-speed races, this species can move on two legs in fast and low-speed marches.

The reason for being able to march on two legs at different speeds is that this animal can balance its body voluntarily, pulling back the upper part of the body and placing the head on the hind limbs.

American cockroach (

This insect is reddish-brown in color, with brown or yellow tones in the dorsal area of the pronotum. Its body is flattened, with a hard, waxy and smooth skin. They have 6 long legs, two pairs of wings, and a pair of antennae, almost the same length as the body.

This invertebrate is one of the fastest of its kind. At high speeds, this animal changes its locomotion from quadruped to bipedal. Quickness is achieved by increasing stride length, showing little increase in stride rate during brisk walking.

Other factors that contribute to the speed of movement are some morphological features typical of the American cockroach, such as the length of its body. In addition, this movement is favored by having narrow limbs, compared to the size of her body.

At high speeds, the Periplaneta americana raises its body from the substrate at a distance of 0.5 to 1 centimeter, increasing the angle of attack of the body from 0 to 30 °, with horizontal reference.

During the first half of the race, the animal uses four legs, the middle and back. The other half of the journey, the cockroach runs bipedally, propelling itself with its hind limbs.

References

Alexander RM (2004). Bipedal animals, and their differences from humans. NCBI. Recovered from ncbi.nlm.nih.gov.
(2019). Bipedalism. Recovered from en.wikipedia.com.
Encyclopedia.com (2016). Bipedalism. Recovered from encyclopedia.com.
Kinsey, Chase & Mcbrayer, Lance. (2018). Forelimb position affects facultative bipedal locomotion in lizards. The Journal of Experimental Biology. Research gate. Recovered from researchgate.com.
Wikipedia (2018). Facultative dipedalism. Recovered from en.wikipedia.com.
Evie E. Vereecke,, Kristiaan D'Aouˆt, Peter Aerts (2006). Locomotor versatility in the white-handed gibbon (Hylobates lar): A spatiotemporal analysis of the bipedal, tripedal, and quadrupedal gaits. ELSEVIER. Recovered from pdfs.semanticscholar.org.
Randall l. Susman, Noel l. Badrian, Alison J. Badrlan (1980). Locomotor Behavior of Pan paniscus in Zaire. American journal of physical anthropology. Recovered from s3.amazonaws.com.
Evie Vereecke, Kristiaan D'Août, Dirk De Clerca, Linda Van Elsacker, Peter Aerts (2003). Dynamic plantar pressure distribution during terrestrial locomotion of bonobos (Pan paniscus). American journal of physical anthropology. Recovered from onlinelibrary.wiley.com.
Nina Ursula Schaller, Kristiaan D'Août, Rikk Villa, Bernd Herkner, Peter Aerts (2011). Toe function and dynamic pressure distribution in ostrich locomotion. Journal of Experimental Biology. Recovered from dejab.biologists.org.
Chase T. Kinsey, Lance D. McBrayer (2018). Forelimb position affects facultative bipedal locomotion in lizards. Journal of Experimental Biology. Recovered from jeb.biologists.org.
Robert J. Full, Michael s. You (1990). Mechanics of a rapid running insect: two-, fourand sex-legged locomotion. Recovered from biomimetic.pbworks.com.

BIPEDAL ANIMALS: CHARACTERISTICS AND EXAMPLES - BIOLOGY - 2025