226 NOTOUNGULATA order viii 



Order VIII. NOTOUNGULATA Santiago Roth.^ 



Extinct herbivores, restricted to South America. Feet varying between the 

 plantigrade and semidigitigrade forms, and having from three to five toes. Skull flat 

 and low, with broad frontals and occiput. Zygomatic arch strong, extended posteriorly 

 to the supraoccipital crest. Nasals broad, nostrils usually at anterior extremity. Orbits 

 large and only partially separated from the temporal vacuity. The mastoid region 

 usually much expanded. Mandible high and massive, as a rule with strong symphysis. 

 Dentition ordinarily complete, usually without diastema, frequently having the upper 

 incisors enlarged and the remaining incisors, as well as the canines, premolars and 

 molars passing from one form of tooth to the next by gradual transitions. Teeth 

 brachyodont to hypsodont, prismatic. Upper molar's with an external ridge (ectoloph), 

 or a long, oblique protoloph, and a short, straight metaloph. Lower molars comprising 

 two semilunar ridges of unequal size and two inner pillars. Carpals alternating, free, 

 centrale lacking. Astragahis with a narrow trochlea, which is often furrowed, and 

 has also a convex articulation for the navicular. Fibida always articulating with 

 the calcaneum. Terminal phalanges developed as small blunt claws, as hoofs, or as 

 strong fissured claws. 



The Notoungulata exhibit in their external appearance many characters of 

 the Hyracoidea and those of rodents. The resemblance is seen principally in 

 the breadth and flatness of the cranial roof, in the powerful development of 

 the jugal arch, in the breadth of the occiput, in the position and size of the 

 orbits, in the height of the mandible, and in the enlargement of the foremost 

 incisors. The individual bones, too, are not unlike those of the Hyracidae 

 and some rodents. Close observation, however, reveals several fundamental 

 differences. For instance, the incisors are not compressed laterally as in 

 rodents, but in an antero-posterior direction. The reduction in the number 

 of teeth, too, is only slight in this group. The Notoungidata are dis- 

 tinguished from the Hyracoidea by the alternating arrangement of carpals, 

 by the articulation of the fibula with the calcaneum, by the simple lateral 

 articulation of the malleolus of the tibia with the astragalus, and above 

 all by the dentition. The teeth of the Hyracoidea are first bunodont, and later 

 the two ridges of the upper molars and the two semilunar ridges of the lower 

 molars become equal in size, whereas in the Notoungulata the metaloph 

 of the upper and the anterior semilunar ridge of the lower molars are always 

 much smaller than the protoloph and the posterior semilunar ridge. 



The molars of the Notoungulata (Fig. 309) are formed on the tritubercular 

 or tuberculo-sectorial type. The two outer cusps of the upper molars are very 

 close to the outer edge — ectoloph, the anterior inner cusp — protocone — 



^ Ameghino, Florentino, Contribuciones al coiiociniiento de los maim'feros de la Republica 

 Argentina. Buenos Aires, 1889. — Manimiferes eretaces de I'Argeutine. Bolet. del lustit. Geografico 

 Argentine, vol. xviii., 1897. — Recherches de morpliologie phylogeuetitiue sur les molaires superieurs 

 des ongules. Anal. Miis. Nac. Buenos Aiies, vol. ix., 1904. — Notices sur des ongults nouveanx 

 des terrains cretacesde Patagonia. Bol. Acad. Nat. de Cienc. de Cordelia, 1901, 1902. — Burmeister, 

 H., Description physique de la Republica Argentina, 1879, vol. iii. — Gaudry, A., Dentition de 

 quelques mammiferes. Mem. See. Geol. de France, Paleont., 1906.— Fossiles de Patagonie. 

 Annal. de Paleontologie, 1906, 1908. — Gregory, W. K., The orders of mammals. Bull. Amer. 

 Mus. Nat. Hist., New York, 1910, vol. xxvii. —Lydekker, R., Palaeontologia Argentina II. Anal. 

 Mus. de la Plata, 1893. — Roth, Santiago., Los ungulados suramericanos. Anal. Mus. de la Plata. 

 Paleontologia, 1903. — Scott, W. £., Classification of the Notoungulata. Science, vol. xxi., 1905. 



