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Description
Xenarthra is a group of placental mammals which evolved in South America around 60 million years ago and is made up of the armadillos, anteaters, and sloths. Since before the extinction of the dinosaurs and for the majority of the Cenozoic era, South America was an island continent and its endemic fauna was isolated from the rest of the planet. Many strange groups of mammals evolved to fill up ecological niches filled by different kinds of mammals elsewhere, with the xenarthrans being the among them. Shared characteristics of this group include extra articulations in the vertebral joints unlike other mammals, fused hip bones, internal testicles(like aquatic whales and hippos) and low body temperatures and metabolic rates compared to other placental mammals. One of the orders in this group is Cingulata, the armadillos. Today armadillos are small to medium sized insect-eaters; the giant armadillo being the biggest living species, about the size of a pig. They use their long claws and snouts for digging burrows and searching for insects and grubs to eat. The word armadillo translates to "little armored one" in Spanish. Their armour is made up of plates of dermal bone covered in small overlapping bony scutes covered in a layer of horny keratin. The armour is usually rigid over the shoulders and hips but comes in flexible overlapping bands over the back and flanks, and also covers the top of the head, feet and tail. An armadillos belly is covered in fur instead of armour. This armour is the armadillos primary defense, but contrary to popular belief only two species; the three-banded armadillos, are capable of rolling into a ball that shields their whole bodies. These animals will also use their sharp claws to fight predators or flee into a burrow. Up until the end of the last ice age their were giant plant-eating armadillos called glyptodonts with armour in the form of domed shells made up of bony scutes and rings of bone or even spiky clubs at the end of their tails. The largest glyptodonts were as big as cars. At least one glyptodont species, along with the nine-banded armadillo, migrated to North America after a land bridge formed between it and South America around three million years ago. The other order of xenarthrans, Pilosa, includes sloths and anteaters. Anteaters have changed very little in 50 million years and all living species from the tiny silky anteater, the two tamanduas, to the giant anteater are all built for feeding from small insects, especially ants and termites. Powerful limbs with sharp claws dig into ant hills and a long toothless-snout equipped with a tongue that can stretch longer than the length of the head can collect thousands of ants or termites in a single meal. Thick fur and skin protect anteaters from the bites of their prey, and their claws are powerful weapons against predators including jaguars, pumas, and humans. The smaller species have prehensile tails that allow them to climb trees in search of food and shelter, while the giant anteater forages on the ground. Sloths, unlike anteaters or armadillos, eat leaves instead of insects, and are highly well known for their incredibly low metabolism and slow pace. All six living sloths are arboreal, very rarely ever coming to the ground. To compensate for the low nutritional value of the leaves they eat, sloths have large, slow-acting stomachs and can take up to a month to digest a meal of leaves. They conserve energy with their famously low metabolic rate and body temperature, resulting in their lethargic lifestyle. Sloth fur often hosts a myriad of smaller organisms from symbiotic algae with give the sloths fur a green color to moths and other insects that nest in the tangled mop. Sloths have very little muscle tissue for their weight, and rely mostly on their curved claws to keep them up in the trees. The curvature of their claws and of their hands and feet allow sloths to hang without much effort from their impoverished muscles. Sloths have been known the eat, sleep, and even give birth while hanging. Due to their weak musculature and slow movements, sloths never leave the trees except, puzzlingly, to defecate about once a week in usually the same spot at the base of a tree. The reason for this behavior is unknown, and a sloth on the ground has little power to defend itself. Surprisingly, sloths are better swimmers than they are walkers and are often seen crossing rivers and narrow channels. In the past many more species of ground sloths existed than tree sloths, some species growing to gigantic sizes. The giant ground sloth Megatherium of the Pleistocene grew larger than an African elephant and taller than a giraffe. Ground sloths as well as being larger were likely much more active than living tree sloths. Their massive arms and claws allowed them to tear down small trees, and underneath their fur were small bony scutes like the glyptodonts, giving the sloths a sort of natural built-in chainmail. Several species migrated North along with some glyptodonts and armadillos since the formation of the Isthmus of Panama. Some ground sloths made it as far North as Alaska. Unfortunately both the giant ground sloths and the glyptodonts died out around 10,000 years ago(except for the smaller ground sloths of the Caribbean who survived until around 4,000 years ago) most likely due to climate changed caused by the end of the last glacial period and hunting by the first Native Americans. Living sloths, anteaters and armadillos face little immediate threat from humans as a whole, although certain species like the pygmy three-toed sloth and giant armadillo are dwindling in number because of human hunting and destruction of habitat. Xenarthrans do have important roles in human life, some South American tribes keep tamandua anteaters as pets in their villages to keep insects under control, and armadillos; due to their low body temperature, are instrumental in the study of leprosy. The unique adaptations and behaviors of this group have made them popular in television, movies, and in zoological parks.
Species shown:
Hoffman's two-toed sloth/ Choloepus hoffmani
Brazilian three-banded armadillo/ Tolypeutes tricinctus
Nine-banded armadillo/ Dasypus novemcinctus
†Spike-tailed glyptodont/ †Doedicurus clavicaudatus
Southern tamandua/ Tamandua tetradacyla
Giant anteater/ Myrmecophaga tridactyla
Brown-throated three toed sloth/ Bradypus variegatus
Screaming hairy armadillo/ Chaetophractus vellerosus
†Jefferon's giant ground sloth/ †Megalonyx jeffersonii
Species shown:
Hoffman's two-toed sloth/ Choloepus hoffmani
Brazilian three-banded armadillo/ Tolypeutes tricinctus
Nine-banded armadillo/ Dasypus novemcinctus
†Spike-tailed glyptodont/ †Doedicurus clavicaudatus
Southern tamandua/ Tamandua tetradacyla
Giant anteater/ Myrmecophaga tridactyla
Brown-throated three toed sloth/ Bradypus variegatus
Screaming hairy armadillo/ Chaetophractus vellerosus
†Jefferon's giant ground sloth/ †Megalonyx jeffersonii
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Beautiful!