Xenarthra

Xenarthra (; from Ancient Greek ξένος (xénos), meaning "strange, foreign", and ἄρθρον (árthron), meaning "joint") is a superorder and major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths, with some glyptodonts and ground sloths reaching sizes of several tonnes, much larger than any living xenarthran. Xenarthrans originated in South America during the late Paleocene about 60 million years ago. They evolved and diversified extensively in South America during the continent's long period of isolation in the early to mid Cenozoic Era. They spread to the Antilles by the early Miocene and, starting about 3 million years ago, spread to Central and North America as part of the Great American Interchange. Nearly all of the formerly abundant megafaunal xenarthrans became extinct at the end of the Pleistocene as part of the end-Pleistocene extinction event.

==Characteristics== Xenarthrans share several characteristics that are not present in other placental mammals. The name Xenarthra derives from the two ancient Greek words (), meaning "strange, unusual", and (), meaning "joint", and refers to their vertebral joints, which have extra articulations that are unlike other mammals. The ischium of the pelvis is also fused to the sacrum of the spine. Xenarthran limb bones are typically robust, with large processes for muscle attachment. Relative to their body size, living xenarthrans are extremely strong. Their limb bone structures are unusual. They have single-color vision. The teeth of xenarthrans are unique. Xenarthrans are also often considered to be among the most primitive of placental mammals. Females show no clear distinction between the uterus and vagina, and males have testicles inside the body, which are located between the bladder and the rectum. Xenarthrans have the lowest metabolic rates among therians.