Similar Characteristics of Perissodactyls
Differences among the Families
Toes
While all perissodactyls are mesaxonic odd-toed, some have one toe, some of three toes and some may only have an odd number of toes on their hind legs. Due to living in different habitats, the three families evolved difference among their toes. The Equidae Family only has one toe (their hoof). As inhabitants of grasslands, steppes and deserts where they have many predators and cannot hide easily, the Equidae Family has increased running efficiency by evolving from the original five toes to one toe so they could outrun predators. This is because the Equidae Family has long limbs, so their strides while running are larger. The Equidae Family would require less weight on the bottom of their limbs to make it easier to leap such distances. While a predator, such as a cheetah would have five toes with claws to grip onto their prey, the Equidae Family has no use for extra toes as they do not need to grip with their legs. Thus, the Equidae Family evolved into a single-toed ungulate.
While the Equidae Family has one toe, the Rhinocerotidae Family has three toes that spread evenly across their feet. Like the Equidae Family, as herbivores with no use for gripping in its flat savannas and grasslands, the Rhinocerotidae Family evolved to three toes to gain an advantage in speed while running. Rhinoceroses are incredibly fast creatures, and they usually run to charge in fights over territory or mates.
However, rhinoceroses still have a larger number of toes compared to the Equidae Family. This may be because they need these toes for a better grip when walking in slippery mud, or for a grip on the ground to support its weight when standing.
On the other hand, the Tapiridae Family has four toes on its front legs and three legs on its hind legs. Since tapirs live in lowlands or moist forests with areas with water (as they love to swim), the toes of a tapir are spread to create traction when climbing through mud. Furthermore, since they live in areas with lots of vegetation, they often trample through this vegetation to make paths. They may need their number of toes to grip and maneuver through the forests.
Size
While all perissodactyls have similar internal organ structures, the most noticeable difference among the three families is size. Originally, the ancestor of the perissodactyls was very small. Upon the mass extinction of the dinosaurs 65 million years ago, the Perissodactyla Order, along with other mammals began to fill empty ecological niches left by the dinosaurs, giving them opportunities to evolve into larger animals. Therefore, all perissodactyls are now between the ranges of 0.75m to 2.1m in height and 0.75m to 4m in length.
The Tapidirae Family is the smallest family when it comes to size ranges. They range from 0.75 m to 1m in height and 1.8m to 2m in length. Since tapirs live in moist areas and among forests, their size would be ideal for barreling through the vegetation in the woods without being too big to be obstructed by tree branches and trunks.
The Tapidirae Family is the smallest family when it comes to size ranges. They range from 0.75 m to 1m in height and 1.8m to 2m in length. Since tapirs live in moist areas and among forests, their size would be ideal for barreling through the vegetation in the woods without being too big to be obstructed by tree branches and trunks.
The Equidae Family ranges in sizes from very small to a medium-large size. While various subspecies of horses and donkeys were artificially selected to be either bigger or smaller (especially seen in the Miniature Donkey, which was bred to be tiny), the range of the Equidae Family is in between the other two families'. Members of the Equidae Family are usually between 1m to 1.5m in height and 1.0m to 2.75m in length. Wild members of the Equidae Family are usually in the intermediate range of sizes. The ancient ancestor of the perissodactyls used to be very small. The wild Equidae Family evolved into larger size with longer limbs to gain strength and for a faster speed to outrun predators. This evolutionary process took place through punctuated equilibrium, as ancestors of the Equidae Family showed both increases and decreases in size before suddenly increasing to the size it is today. Most Equidae are rather thin compared to the Rhinocerotidae Family, which is because they need less body weight to run faster. Today, some of the Equidae Family is domesticated and are bred into sizes based on the breeder's desires. For example, the miniature donkey was bred to be small while farm horses are bred to be bigger to be stronger.
The physical-size-wise largest family of the perissodactyls is the Rhinocerotidae Family. Their height ranges from 1.3m to 2.1m and their length ranges from 2.8m to 4m. Because they are located in environments with an abundance of open, grazing land, the large rhinoceros is able to retain such a big size without much difficulty in their lifestyle. The open plains provide a lot of space for these large rhinos to graze.
Head Structure (including Horns)
The Perissodactyla Order have elongated heads with eyes on the sides of their face and nostrils near the other end of the head. They have muscular mouths with surfaced teeth to easily take in and chew vegetation. However, there are many differences among the three families in terms of head structure aside from these basic components.
The Tapiridae Family of tapirs have a similar skull structure to the Equidae Family, as they both have broad molars to grind teeth as well as teeth at the front to clip off vegetation. The tapir's eyes are more at the centre on both sides of its face like the rhinoceros. The most prominent difference between the head of a tapir and the heads of other perissodactyls is their nose and upper lip, making a trunk-like shape used for grasping leaves and branches. None of the other perissodactyls have this feature. Since tapirs live in forests, they get their food from leaves and fruits off the branches of trees. The tapir's prehensile trunk allows them to grasp and pluck their food off of the branches, compared to horses and rhinos who graze on grass and therefore do not need to reach and pluck off objects. Tapirs often swim in ponds or lakes for protection against bugs or the sun. Thus, a tapir's trunk can also be used as a snorkle when swimming.
The Rhinocerotidae Family of rhinoceroses have different head shapes than the other two families. Rhinos do not have incisor teeth at the front of their jaw. As well, due to their big size, their teeth (and heads) are larger than the other families'. The most noticeable difference of a rhino head is their horned feature. Rhinos either have one or two horns, while no other family in the Perissodactyla Order do. These horns are made out of keratin - the same material as human fingernails and hair. Since rhinos are terrestrial fighters, they use these horns to fight off enemies or rivals for potential mates. They can also use the horns to defend against predators, although they only have humans for predators now, hyenas and crocodiles used to be their natural predators.
The Equidae Family of horses, zebras and donkeys have a longer muzzle than the other families', as well as high crowned teeth with a large exposed area. Living in grasslands, streppes and desserts, this family primarily feeds on grass. These animals have long muzzles so they have space for more teeth so they can take in and chew more grass easily. Their high crowned teeth also allow them to have a large exposed area to chew grass with, again contributing to getting more nutrients in less time.
Skin
The roughness, texture and the way skin is formed on the animals of the three families within the Perissodactyla Order varies. The skin of a tapir is fairly rough, to be able to run through vegetation within the forests. The skin of a rhino is thick and folded with flexible skin between thicker plates of skin. Its skin is this thick to protect them against injuries either evolved from predators in ancient times or from battling with other rhinos over territory and mates. The Equidae Family do not have thick skin like rhinos do, but they often have thick hides (hair on their skin) to protect them against nature - the sun, wind and rain.