Locomotion

Like most reptiles, the majority of mammals travel across land. Mammals, however, move much further and more often than reptiles. Partly, this is made possible by the possession of a homeothermic body (see Warm Blood), partly it is also made possible by the way mammals' limbs articulate with (join) the body. The result of this is that a mammal moves its legs backwards and forwards beneath its body, whereas a reptile has its legs stuck out to the side, see diagram. The mechanics of mammalian walking and running can get quite complicated and involve the use of tendons and the back as energy storing springs to enhance efficiency. This has been especially well studied in cheetahs which dislocate and relocate their backs during each stride and in horses which some scientists in 1998 claimed gallop with 109% efficiency. For the sake of this site, though, we will keep things simple. The modes of locomotion used by animals have been divided up into more than 30 different types, and it is not unusual for an animal to change from one type of movement to another, i.e. from walking to jumping in a given period of locomotion. A horse for instance has three natural gaits, a walk such as the giraffe walk, a trot and a gallop.

 

Dog walk - The most common four-legged locomotion which you will observe is the walk, sometimes called the diagonal walk. This is used by most hoofed animals as well as cats and dogs. In this walk, the animal uses diagonally opposing legs, i.e. front left and right back legs move forwards then the front right and left back legs move and so on.

Giraffe walk - Giraffes and a few other animals such as brown bears and camels (see T. E. Lawrence, Seven Pillars of Wisdom) move both legs on one side and then both legs on the other side. In some cases the hind leg starts first so there is a slight lag. This is also called 'Pacing' and it is the first gait observed in young 'colts'.

The trot is the same gait as the dog walk but faster so that there is a moment in each stride when all four legs are off the ground.

Gallop - a gallop is a succession of leaps. The legs can hit the ground both front then both back feet together as in the ermine. Or the front feet can be set down one then the other, then both back feet together as in the hair.

Most terrestrial mammals can jump or leap, but some use this form of locomotion far more regularly than others. Leaping occurs either from two legs only as in a monkey or from all four legs simultaneously as in the pronghorn. Leaps can be mixed and cats for instance leap mostly from their back legs but get some lift from the front legs also, which leave the ground before the back legs do.

Primarily aquatic mammals such as seals, etc, have much more ungainly gaits. Most seals effectively crawl; stretching forward then hunching their back to bring the hind part of the body as far forward as possible then raising and pushing the front forward again. This is slow, but gets them where they need to be.

Elephant seals drag themselves forward with their front limbs only and Falkland Sea Lions use a sort of slow gallop like a hare. They can, however, move as fast as a running man when they want to.

We, of course, walk on two legs as on occasions do Gibbons, Gorillas and Chimpanzees. More familiar perhaps are the Kangaroos of Australia which jump on two legs as do Jerboas, Jumping mice and a variety of other smaller Australian marsupials. The Jerboa is the most fully bipedal of all these as it walks on two legs even when unhurried, whereas the others tend to walk on four legs but go up on two when jumping in order to move more quickly.

Brachiation is the more common means of locomotion of Gibbons and a variety of other primates. Brachiation means moving by swing from branch to branch with your arms.

Climbing trees can be achieved using gaits similar to both the Dog walk and the Giraffe walk, while Squirrels actually gallop up trees. Squirrels are also unique in being able to walk down trees as well. The ankles on their hind legs are so flexible that they can turn through 180 degrees allowing them to be equally useful going up and coming down.

Swimming - Many land mammals can swim, even and including the big cats. Even some bats can survive falling in the water. Hamsters fill their cheek pouches with air before taking the plunge. Some species are semi-aquatic and are equally at home in the water as on land, i.e. Otters, Hippopotamuses. For most terrestrial mammals, swimming involves walking in the water. In other words they use the same gait as they do on land. The more fully aquatic species are, however, more adapted to the water. Beavers fold their front legs under their chests while swimming.

Moving towards more fully aquatic species, Sea Otters float quite happily on their back while seals are so adapted to the water that they are clumsy and foolish looking on land. Different species swim in different ways. Many seals and sea lions use both front and hind limbs when swimming, but Elephant seals only ever use their hind limbs. In the Cetaceans which are fully aquatic, the hind limbs have been so adapted to become the tail flukes - a single member. This 'tail' has the flukes horizontal rather than vertical like the tail of a fish. Others will toboggan on snow.

Finally, some mammals have taken to the air. In fact about 20% of all species of mammals can fly. These are the bats. Apart from bats there are a few mammals which can glide. There are flying squirrels equipped with a flap of skin stretched between their fore and hind limbs which when stretched out allows them to glide often for considerable distances. They are found in Asia, Africa and America. There are also gliding marsupials in Australia, and a flying (gliding) Lemur in the Malay Archipelago. Gliding flight only goes down however and the animals have to climb up a tree eventually to regain the lost height.

Bats, however, really fly, most of them very well. Anyone who has, like me, tried to catch bats in a butterfly net at dusk will be only too aware of how agile they are. Bats have wings of skin stretched between greatly lengthened finger and arm bones. Bats tend to fly erratically, however, some species have been recorded flying at speed of over 20 kmphh (13 mph) in level flight and the record is for 25 kmph (15.5 mph) by a Big Brown Bat, Eptesicus fuscus.

Common Name Scientific Name Speed in kmph Speed in Mph
Cheetah Acinonyx jubatus 96+ 60
Pronghorn Antelope Antilocarpa americana 88.5 55
Wildebeest Connochaetes taurinus 80 50
Thomson's Gazelle Gazella thomsoni 80 50
Grant's Gazelle Gazella granti 80 50
European Hare Lepus europeaus 72 45
Domestic Horse Equus ferus 69.6 43.3
Grizzly Bear Ursus arctos 64 40
Coyote Canis latrans 64 40
Mountain Zebra Equus zebra 64 40
Lion Panthera leo 58 36
Polar Bear Ursus maritimus 56 35
Giraffe Giraffa camelopardalis 56 35
Grey Kangaroo Macropus giganteus 56 35
Cape Buffaloe Synceros caffer caffer 56 35
Black Rhinoceros Diceros bicornis 45 28
Grey Wolf Canis lupus 45 28
Wild Rabbit Onyctolagus cuniculus 40 25
African Elephant Loxodonta africana 40 25
Camel Camel bactrianus 16 10

 




Book Reviews


Analysis of Vertebrate Structure, by Milton Hilderbrand and George Goslow

 

 

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