related). Some studies have indeed found the mesaxonian ungulates and paraxonian ungulates to form a monophyletic lineage, closely related to either the Ferae (the carnivorans and the pangolins) in the clade Fereuungulata or to the bats. Other studies found the two orders not that closely related, as some place the perissodactyls as close relatives to bats and Ferae in Pegasoferae and others place the artiodactyls as close relatives to bats. Taxonomy Below is a simplified taxonomy (assuming that ungulates do indeed form a natural grouping) with the extant families, in order of the relationships. Keep in mind that there were still some grey areas of conflict, such as the case with relationship of the pecoran families and the baleen whale families. See each family for the relationships of the species as well as the controversies in their respective article. Ungulata (= Euungulata) Perissodactyla (Mesaxonian ungulates) Hippomorpha Equidae: Horses, asses and zebras Ceratomorpha Tapiridae: Tapirs Rhinocerotidae: Rhinoceroses Artiodactyla (= Cetartiodactyla) (Paraxonian ungulates) Tylopoda Camelidae: Camels and llamas Artiofabula Suina Tayassuidae: Peccaries Suidae: Pigs Cetruminantia Ruminantia Tragulidae: Chevrotains Cervoidea Antilocapridae: Pronghorn Giraffidae: Giraffes and okapi Cervidae: Deer Moschidae: Musk deer Bovidae: Cattle and antelopes Whippomorpha Hippopotamidae: Hippopotamuses Cetacea Mysticeti Balaenidae: Bowhead and right whales Cetotheriidae: Pygmy right whale Balaenopteridae: Rorquals Odontoceti Physeteroidea Physeteridae: Sperm whale Kogiidae: Lesser sperm whales Platanistoidea Platanistidae: Indian river dolphins Ziphioidea Ziphiidae: Beaked whales Lipotoidea Lipotidae: Baiji (functionally extinct) Inioidea Iniidae: Amazonian river dolphins Pontoporiidae: La Plata dolphin Delphinoidea Monodontidae: Beluga and narwhal Phocoenidae: Porpoises Delphinidae: Oceanic dolphins Phylogeny Below is the general consensus of the phylogeny of the ungulate families. Evolutionary history Perissodactyla and Artiodactyla include the majority of large land mammals. These two groups first appeared during the late Paleocene, rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time. Some scientists believed that modern ungulates were descended from an evolutionary grade of mammals known as the condylarths; the earliest known member of the group was the tiny Protungulatum, an ungulate that co-existed with the last of non-avian dinosaurs 66 million years ago; however, many authorities do not consider it a true placental, let alone an ungulate. The enigmatic dinoceratans were among the first large herbivorous mammals, although their exact relationship with other mammals is still debated with one of the theories being that they might just be distant relatives to living ungulates; the most recent study