Mammals are one of the most diverse groups of creatures in the animal kingdom, and it all comes down to their warm-blooded nature. Mammals can maintain a higher body temperature than reptiles and amphibians, which gives them a higher metabolism and the ability to be more active in general.
The result has been a number of evolutionary developments, including a clever diaphragm for more efficient oxygenation, a four-chambered heart to facilitate mobility and activity, and two-piece jaws designed for both herbivores and carnivores.
Mammals first appeared roughly 200 million years ago, which means mammals have had a long time to evolve in many fascinating directions. But how many different kinds of animals are there today?
Total number of recognized species: about 6,557.
Keeping track of all known species can be difficult as new species are unlocking faster than you might imagine. In fact, over the 13-year period from 2005 to 2018, the number of recognized mammalian species increased by 1,079. One factor is the lack of rigorous tables in the pre-21st century period, but it is estimated that about two dozen new species are discovered on average per year.
The American Society of Mammologists has created a mammalian diversity database to track new species discoveries and classification examples in real time. Whereas previously systems for classifying mammalian species were based on infrequently published volumes, the Internet made it possible to update MDDs in real time. Through careful scrutiny of peer-reviewed studies as they are published, this database remains the most accurate database for classifying mammalian species.
But understanding the number of mammalian species as a raw number does not necessarily reflect the scale and diversity of mammals. Fortunately, taxonomy breaks down the genealogy of mammals, dividing them into different orders. Fortunately, the mammalian diversity database also tracks the number of species depending on which order they belong to. This is how numbers break down.
Order Rodentia: about 2606 species
A staggering 40% of the world’s mammalian population belongs to the order Rodentia, which includes everything from widespread mice to huge and ubiquitous capybaras. All rodents are distinguished by the presence of constantly growing incisors, which must be used frequently to prevent potentially fatal overgrowth.
Order of bats: about 1447 species.
All living bats are bats, and among mammals they are unique in that they have developed the means to fly on an engine. This sets them apart from animals such as flying squirrels, which can simply glide in wind currents. Examples include a bat, a small brown bat, and a gray-haired bat. About 20% of mammalian species belong to the order of bats.
Order Eulipotyphla: about 548 species.
Hedgehogs, moles and shrews belong to the order Eulipotyphla, but they have a common feature – belonging to the most primitive mammalian species. Most of the members of this order are insectivores, and most of them are blind or have extremely poor eyesight. To compensate for this, species such as the star-bearing mole have developed an exceptional sense of touch.
Primates of the order: about 515 species.
Humans are the most advanced primates, but we share this troop with species as diverse as baboon and mountain gorilla. The common ancestor of all primates was the species that lived in trees, which also led to the development of more complex and articulated fingers. Primates are also often characterized by relatively large brains.
Artiodactyl order: about 356 species.
Members of the order Artiodactyla are also known as hoofed animals – another way of referring to animals that have hooves. They make up the most diverse group of large herbivores on the planet, and examples include everything from the common deer to the mighty giraffe. And although whales no longer have hooves, they descend from the same ancestors as artiodactyls and are classified as members of the order.
Order Carnivora: about 304 species
All Carnivora species share common ancestors that have evolved long and pointed canines to shut off prey and tear flesh, but examples also include omnivores such as the black bear and raccoon. All species in this order also exhibit five-claw forelegs that have been developed for both mobility and immobilization of prey.
Order Diprotodontia: about 150 species.
Most of the marsupials on the planet belong to this order, but among them there are representatives with very different designs, from koalas to wombats and kangaroos. They are united by a set of incisors, which are designed to chew the leaves, as well as the connected fingers on the hind limbs.
Order Didelphimorphia: about 127 species.
The possum species that developed in America are members of the order Didelphimorphia. They are also marsupials that can be distinguished by their strong incisors and lack of canines, but all American possums have five upper incisors and four lower incisors. Unlike members of the order Diprotodontia, most possums are carnivores or omnivores.
Order of Lagomorphs: about 107 species.
Rabbits, hares and pika belong to the order Lagomorphs. Their small build and overgrown incisors make these animals look like rodents, but they have parallel but distinct evolutionary histories. Unlike rodents, lagomorphs have four incisors at the top of their mouth, not just two.
Order Dasyuromorphia: about 77 species.
The carnivorous marsupials that make up this order live exclusively in Australia and on nearby islands such as New Guinea and Tasmania. Examples include the Tasmanian devil and a family of animals known as quolls. The first representatives of this species appeared about 55 million years ago.
Order Afrosoricida: about 55 species.
South African golden moles, Madagascar tenrecs, and African otter shrews were once assigned to the order Eulipotyphla, but deeper study of their origins has shown different origins. Today they and other regional beings occupy their own Order, demonstrating that sometimes parallel evolutionary traits can develop in isolation.
Order Scandentia: about 23 species.
Wooden shrews, derived from the Greek word for “climber”, are found only in the Asian subcontinent and adjacent islands. Many species look and act very similar to squirrels, but they share a more common ancestry with primates.
Order Cingulata: about 22 species.
Found exclusively in America, the creatures belonging to the order Cingulata are better known as armadillos. Their most distinctive feature is by far their armored carapace, and the waist animals mainly feed on insects and invertebrates.
Order Peramelemorphia: about 22 species.
The members of this order are very similar to rodents, but they live exclusively in Australia and on the nearby islands. They make up the majority of the living omnivorous marsupials. The order is made up of bandicoots and bilbies, the latter of which doesn’t even need to drink water.
Order Macroscelidea: about 20 species.
Just as Afrosoricida was redefined as a distinct order from similar creatures on the other side of the country, the elephant shrews were moved from Afrosoricida to their own order. Resembling small mice, these species have elongated hind legs, allowing them to jump long distances.
Order Macroscelidea: about 18 species.
Some of the most famous large grazing animals on the planet belong to Perissodactyla. Species such as zebra, rhino and horse have in common that they have hooves with an odd number of toes. Depending on the type, they can be supported by three fingers or only one.
Pylosa detachment: about 16 species.
The Pilosa order has a live representation only in America, but the species of anteaters and sloths fall under its classification. While these creatures may look very different, they share longer tongues and receding teeth, which allows them to feed on insects more efficiently. They also have long front legs with sharp claws for digging up prey.
Although the order classifications above cover most mammals on the planet, there are many smaller orders that are home to unambiguous species. These include the proboscis, which are home to two still living species of elephants. The anteater is the only member of the order Tubiulidentata. Dermoptera is almost as lonely as it is home to just two species of lemurs. The Monotreme order consists only of a platypus with a platypus and four echidna species, but its members are completely unique among mammals due to the fact that they lay eggs rather than give birth to live young.
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