What are the Primary Groups of Placental Mammal?
Placental mammals, infraclass Eutheria (meaning “true/good beast” in Greek) are the dominant group within mammals in general (a classification which also includes marsupials and monotremes), and the dominant group of terrestrial vertebrates. This has been the case since the extinction of the non-avian dinosaurs 65.5 million years ago. Although placental mammals consist of fewer species (about 4,900 total) than reptiles (8,200 species), amphibians (6,100 species), or birds (10,000 species), placental mammals are dominant in that they are the most numerous, occupy the most niches, are the largest, and a placental mammal almost always occupies the highest positions in the terrestrial food chain, Australia being the primary counterexample. Placental mammals consist of 20 orders contained within four superorders: Xenarthra &mdash (an early placental mammal breakaway family includes armadillos, sloths, and anteaters), Laurasiatheria (including the bulk of mammal species), Afrotheria (smaller
Placental mammals, infraclass Eutheria (meaning “true/good beast” in Greek) are the dominant group within mammals in general (a classification which also includes marsupials and monotremes), and the dominant group of terrestrial vertebrates. This has been the case since the extinction of the non-avian dinosaurs 65.5 million years ago. Although placental mammals consist of fewer species (about 4,900 total) than reptiles (8,200 species), amphibians (6,100 species), or birds (10,000 species), placental mammals are dominant in that they are the most numerous, occupy the most niches, are the largest, and a placental mammal almost always occupies the highest positions in the terrestrial food chain, Australia being the primary counterexample. Placental mammals consist of 20 orders contained within four superorders: Xenarthra (an early placental mammal breakaway family includes armadillos, sloths, and anteaters); Laurasiatheria (including the bulk of mammal species), Afrotheria (smaller group
