Page:The New International Encyclopædia 1st ed. v. 12.djvu/853

* MAMMAIilA. 759 TVrATWIVrAT.TA. the above mentioned genera are grouped in an order called Multituberculata. The other order of prototherian mammals, the modern Monotre- mata, is separated from the first order by almost the entire space of Tertiary time. One of these creatures, the duckbill, though toothless in its adult state, betrays its origin from a multituber- culate ancestor by having in its younger stages of gron-th broad flat teeth remarkably like those of the Gomphodontia and Multituberculata. The second subclass of primitive mammals, the Metatheria, comprises a single order, the Jlar- supialia. and this is divided into two suborders. Ihe more primitive Polyprotodontia are char- acterized by the presence of four or five incisor teeth in each jaw, and include the majority of Mesozoic mammals of Europe and Xorth Amer- ica; also the opossums (DidelphidiP), which ap- peared first in the Laramie (Upper Cretaceous) : the carnivorous marsupials (Dasyurid;e) of Australia, which can be traced back only into the Pleistocene: the bandicoots (Peramelida;) of Australia: and the banded anteaters ( Mvrmeco- bidie). of which no fossil forms have been found. All these are animals of comparatively small size, and they present variotis adaptations of the marsupial type to particular conditions of exist- ence. The most important Mesozoic genera of Polyprotodontia are Phascalotherium, Amphithe- rium. Amblotherium, Triconodon, Dryolestes, and Spalacotherium. and several others chieHy from tiie Upper Jurassic rocks of England and Wyom- ing. The remaining suborder of iletatheria, the Diprotodontia, is characterized by the presence of two large incisor teeth in each jaw, and its fossil and recent forms are almost wholly con- fined to Australia. This suborder contains the gigantic Diprotodon, its smaller ally Notothe- rium, and the peculiar 'pouched lion' of Owen (Thylacoleo), all extinct and found in Pleisto- cene deposits ; also the modern wombats, kanga- roos, and phalangers, fossil forms of which have been found in the superficial deposits of Aus- tralia and South America. Among the Eutheria the Edentata, Cetacea, and Sirenia are of uncertain origin. They began with nearly normal eutherian types in the Eo- cene, and they present through the Tertiarj- de- generating series of peculiar animals. The Eden- tata began in the Eocene, and during the Tertiary they developed some odd gigantic beasts — Jlega- therium, Mylodon, ilegalonyx, and Glyptodon (q.v.), the latter with a massive coat of armor plate. From these giant ancestors descended the comparatively small modern sloths, anteaters. and armadillos. The Cetacea is a group of mammals which through degeneration from the normal mammalian type has become peculiarly special- ized and adapted to a fish-like habit of life. The earliest form in the Eocene, Zeuglodon. though distinctively fish-like, has, among other char- acters typical of terrestrial mammals, the car- nivorous t.vpe of dentition. The hoofed mammals appear in the lowest Tertiarv" deposits of Xortli America as forms (suborder Condylarthra) that can with difficulty be distinguished from the earliest carnivores. These early ungulates (typified by Phenacodus from the Lower Eocene of Wyoming) have five useful toes on their plantigrade feet and each toe has a small hoof. The brain is small and slightly convoluted, and the teeth are of a generalized type -with low crowns and many tubercles. From the primitive Condylarthra seem to have been evolved all the later and more specialized forms of ungulates. The Perissodactyla comprise the extinct Titanotheroidea, large horned animals of Eocene and Miocene time (see Titaxotherilm) ; Hippoidea, the horses and their Eocene allies the paleotheres (see Hoese, Fossil.) ; Tapiroidea, in- eluding the tapirs and their extinct Eocene and Miocene allies the Lophiodontidae; Rhinocero- toidea, the rhinoceroses, with a host of extinct ancestors reaching back into Eocene time; and the Chalicotheroidea, a peculiar group related to both the Perissodactyla and the Edentata. The Amblypoda include five-toed ungulates of large size that lived during Eocene time, of which well- known genera are Corjphodon and Dinocerus. Artiodactyla, or even-toed ungulates, include the modern pigs, hippopotamus, camels, deer, cattle, etc., with long series of forms ancestral to these ranging back through Tertiary time. (See SwLXE; C'amel; Hippopotamus; Deeb; etc.) Here also belong the extinct families : Anthra- cotheridte, large animals of the older Tertiary of Xortli America and Europe; OreodontidK of the Miocene and Lower Pliocene of the United States; Anoplotherida;, medium-sized animals from the Eocene and Lower Jliocene of Euro])e ; and the ProtoceratidiE of the White River" Miocene of America. The ancestors of the modern elephants appear suddenly in the Miocene rocks with all the characters of the suborder well marked. Such evolution as takes place during Tertiary time is manifested in complication of the denti- tion and in the development of tusks and pro- boscis. The Toxodontia, Typotheria, and Litop- terna are suborders containing peculiar types of ungulates of uncertain atfinities found in the Tertiaries of South America ; and the Hyracoidea embrace only a few obscure fossil forms. See Elephant : ilAMMOTH : Mastodon ; etc. The Carnivora begin in the Eocene with gen- eralized carnivorous types as Creodonta (q^v. ) that are easily confounded with the early ungu- lates; in fact, the Creodonta is considered to be the ancestral group of both the L'ngulata and the Carnivora and possibly also of the Ganodonta (primitive edentates) and the Rodentia. Eight families of creodonts are recognized, mostly from the Eocene of Europe and the United States, The more important genera are Aretocyon, Mes- onyx, Patriofelis, Hyienodon. Some creodonts found in the Santa Cruz formation (Lower Ter- tiary) of Patagonia present interesting marsu- pial features. The true carnivores have larger^ more deeply convoluted brains and strong sec- torial teeth, with an accentuation of all other carnivore characteristics. The dogs, bears, weasels, civet cats, hyenas, cats, all have an- cestral lines extending more or less into the early Tertiary, and some instructive phylogenetic series have been demonstrated. The marine carnivores (Pinnipedia) possibly had their ancestor in the Eocene creodont Patriofelis. The shrews and moles of Eocene time present less marked differences from their modern de- scendants than do any other types of mammals. Almost nothing is known of the ancestry of the bats. Among the Rodentia, the characteristic feature in the dentition, namely the chisel-shaped incisor teeth growing from persistent pulps, is seen in fossils from the early Eocene. Such forms are Esthonyx and Tillotherium of North