Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/443

Rh UNGULATA.] MAMMALIA 421 This family includes but a single species, Dinomys Iranickii, known only from a single specimen obtained in Peru, which resembles Ccelogcnys paca in the general form of its body and in size. It is regarded by its describer, Professor Peters, as a connect ing link between the families Octodontidee, Chinchillidse, Dasy- proctidse, and Caviidee. Family 6. CAVIID.E. Terrestrial or natatorial Rodents, with short incisors, strong mandibular masseteric ridges, long and curved paroccipitals, and palate contracted in front. Fore feet with four digits, hind feet with three ; clavicles imperfect ; molars divided by enamel folds into transverse lobes ; milk teeth shed before birth. Other characters as in Dasyproctidss. Neotropical. Caria, limbs and ears short, subequal, tail none, includes several species widely distributed throughout South America, extending even to the Straits of Magellan, from one of which (C. aperea, prob ably) the common Guinea-Pig is derived. Dolichotis has the limbs and ears long, tail very short, with D. patagonica, a large species, nearly 3 feet long, inhabiting the gravelly plains of Patagonia. The palate is so much contracted in front that the premolars of opposite sides touch by their antero-internal edges. Hydrochosms, with all the feet fully webbed, also includes a single species, which is the largest of living Rodents. The skull (fig. 97) is distinguished, not only by its great size, but also by the enormous development of the paroccipital processes. See CAVY and CAPYBARA. SUBORDER II. EODENTIA DUPLICIDENTATA. Rodents with four incisors in the upper jaw (two of them very small, and placed directly behind the large middle pair), the enamel of which extends round to their posterior surfaces. At birth there are six of these incisors, but the outer one on each side is soon lost. The incisive foramina are large and usually confluent ; the bony palate is very narrow from before backwards ; there is no true alisphenoid canal ; the fibula is ankylosed to the tibia, and articu lates with the os calcis ; and the testes are permanently external. Section IV. LAGOMORPHA. Characters those of the suborder. Family 1. LAGOMYID.E. Terrestrial Rodents, with complete clavicles, subequal limbs, no external tail, and short ears. Skull depressed, frontals contracted and without post-orbital processes ; pm^or^ ; molars rootless, with transverse enamel folds. Palfearctic and Nearctic. Lagomys, with about a dozen species of small Guinea-Pig-like animals, inhabiting chiefly the mountainous parts of northern Asia (from 11,000 to 14,000 feet), one species only being known from south-east Europe and one from the Rocky Mountains. Family 2. LEPORID.S;. Terrestrial Rodents, with imperfect clavicles, elongated hind limbs, short recurved tail, and long ears. Skull compressed, FIG. 99. Skull of Lepus timidus. frontals with large wing-shaped post-orbital processes (fig. 99) ; pm ; molars as in Lagomyidee. Cosmopolitan (except Australasia). Lcpus includes about twenty species, which all resemble one another in general external characters. In all the fore limbs have five and the hind only four digits, and the soles of the feet are densely clothed with hairs similar to those covering the legs ; the inner surface of the cheeks also is hairy. Although the family has such a wide distribution, the greater number of the species are restricted to the Palacarctic and Nearctic regions, and a single species only (L. Irasiliensis] extends into South America, See HARE and RABBIT. FOSSIL RODENTIA. Fossil representatives of all the above-defined families, with the xception only of the small groups included under Anomaluridae, Haplodontidas, Lophiomyidx, Spalacidse, and Dinomyidsz, have been described from various deposits. Of these the earliest have been ound in the Upper Eocene of Europe and America, and belong to the family Sciuridae,, of which the genera Colonomys, Taxymys, Tillomys, Paramys, Ilcliscomys, and Mysyops have been character ized from jj& Eocene of North America, and Plcsiardomys from that of both America and France, while examples of even the recent enus Sciurus have been found in beds of the same age in the latter country. Other recent families have representatives in later deposits, as Castoridee with Stcncofiber and Palseomys from the Miocene of Europe and North America, Trogonoihcrium from that of India, Chalicomys from that of Germany, and Eucastor from North America, Myoxidw with Myoxus and Muridaz with Elomys, Decticus, Oreomys, and Cricctodon from the European Miocene, Hystricidae with Ercthizon extending back to the Miocene of India, Geomyidse with Entoptychus and Pleurolicus and Dasyproctidae with Pctciculus from the Miocene of North America, Lagomyidse with Titanomys and Myolagus from the European Miocene, and Leporidse with Palseolagus from corresponding North American beds. Later Tertiary strata have yielded Rodent remains more abundantly ; many of them referable to recent genera, or even closely allied to or undistinguishable from existing species, have been described from Brazilian bone-caves. Besides those referable to existing families, several fossil remains have been discovered which cannot be so classed. These have been included in three families -.Ischromyidss with Pseudotomus from the Eocene, and Ischromys and Gymnoptyclius from the Miocene of North America ; ThenHomyidse with Theridomys extending from the Eocene to the Pliocene of France, and Arch&omys, Issidioromys, and Dipoidcs from the Miocene ; and Castoroididee with Castoroidcs from post-Pliocene deposits of North America, and Amblyrhiza and Loxomylus from the bone-breccias of the island of Anguilla. The first-named family appears to be intermediate between the Sciuridse and Castoridse ; the second is allied to Geomyidse, and Dipodidss ; and the last, connected with Chinchillidse, includes Castoroidcs ohioensis, a species vastly exceeding in size the largest of existing Rodents. A fourth family, Mesothcriidse, including a single fossil form, Mesotherium cristatum, also of large size, from the Pliocene of South America, has been referred to this order, but it is evident that an animal which, besides presenting many other structural differences, possesses four lower incisors completely surrounded by enamel, and in which the mandibular condyle is transversely extended and the maxillaries articulate freely with the nasals, cannot be considered as coming under the definition of a Rodent. Thus, like the Insectivoi-a and Chiroptcra, fossil remains of Rodentia are found as far back as the Eocene period, and of these some are even referable to one or more recent genera, and differ but slightly from existing species, while all others are either capable of being classed in recent families or are more or less closely related to them. It follows therefore (if the age of the beds in which these remains were found has been correctly determined) that, as in the case of these orders also, the first appearance of true Rodents must be sought for much farther back in time, and the question of their descent must be deferred till the discovery of sufficient material admits of reliable generalizations. pp. 162-174; Id., Natural History of the Mammalia, vol. ii., &quot;Rodentia,&quot; (1848) ; Gervais, Diet. Univ. d Uist. Nat., xi., p. 202 (1848); Brandt, &quot; Untersuchungen Uber die craniologischcn Entwickelungsstufen und Classificati n der Nager der Jetzwelt,&quot; Mem. de VAcad. Imper. de St Petersburg (ISoo); Lilljeborg, Systematise (Efcersight af de Gnagande Daggdjuren, Upsala, 1866: Alston, On the Classification of the Order Glires,&quot; Proc. Zool. Soc., 1876, pp. 61-98 ; Trouessart, &quot; Catal. de Rongeurs, Vivants et Fossiles,&quot; Jiullet. Soc. d Etudes Scient. d Angers, 1880-1 ; various papers by Peters in Monatsb. Akad. Wissensch. Berlin, and by Alston, Anderson, Blandford, A. Milne-Edwards, Thomas, and others, in Proc. Zoo!. Soc., Jour. Asiat. Soc. Beng., Ann. Mag. Nat. Hist., &amp;lt;tc. [For the above sections on the Inscctivora, Chiroptcra, and Rodentia we are indebted to L&amp;gt;r G. E. Dobson.] ORDER UNGULATA. Under this term may be included provisionally a large and rather heterogeneous group of mammals, the existing members of which form the Fecora and Belluxot Linnseus, the Euminantia and Pachydermata of Cuvier. A few years ago it was found convenient to restrict the order to a well-marked and distinctly circumscribed group, coi prising the two sections known as Perissodaclyla and Artiodactyla, and to leave out such isolated forms as the Elephant and Hyrax ; but the discovery of a vast number ol extinct species, which could not be brought under the defil tion of either Perissodactyle or Artiodactyle Ungulates,