102 



RODENTIA 



ORDER TI 



two with well-developed horns. These genera are found also in the Colpodon 

 beds with a few forms in the Pyrotherium beds, which are very similar to 

 some from the Eocene Notostylops beds. The genera Prostegotherium, Utaetus, 

 Meteufatus (Fig. 127), Machlydotheriiim Amegh., etc., include some of the 

 oldest known remains of fossil armadillos. 



Order VI. RODENTIA. Glires (Rodents).^ 



Extremities with daws, seldom with hoof-like nails. Dentition with \ I, less 



frequently with \ I. I very long, with persistent pulp, usually covered with enamel 



on only the anterior and outer surfaces, and with sharp, chisel-like gnawing surfaces. 



2-6 

 Cheek teeth — - separated from the incisors by a long diastema, brachyodont, 

 2-6 



bunodont, lophodont or prismatic. Articular condyle of the mandible fitting into a 



groove and capable of antero-posterior motion. 



The rodents form a homogeneous, very sharply defined order of Placentals, 

 possibly derived from primitive Insectivores, certain forms of which have 



a highly specialised den- 

 tition. They are for the 

 most part small burrow- 

 ing herbivorous animals, 

 and are sometimes also 

 adapted for climbing 

 and swimming. The 

 dentition and skeleton 

 are greatly modified in 

 adaptation to subsist- 

 ence and life habits. 



The skull (Fig. 128) 

 is for the most part low, 

 the muzzle long, and 

 the jDOsterior portion of 

 the head very abruptly 

 truncated. The smooth 

 cerebral hemispheres 

 are of moderate size, the 

 cerebellum and olfactory 

 lobes relatively large. 

 The nasal region is 

 capacious and filled by the turbinate bones. The nostrils always anteriorly 

 placed. The paroccipital process is frequently very long. The orbits are open 



1 Brandt, J. F. Mem. Acad. Imp. Sci. St. Petersb., 1835, 6 ser., vol. iii., pp. 77-336.— 

 Cope, E. D., The extinct Rodentia of North America. Amer. Naturalist, 1883, p. 43 ; 165 ; 

 370. — Forsyth Major, C. J., Nagertiberreste aus Bohnerzeu Siid-Deutschlands luid der Schweiz. 

 Palaeontogr., 1873, vol. xxii. — Ou fossil and recent Lagomoriiha. Trans. Linn. Soc. London, 1899. — 

 Matthew, W. D. Bull. Amer. Mus. Nat. Hist., New York, 1902, art. xxii. ; 1910, art. vi.— 

 Nehring, A., Beitrag zur Kenntnis der Diluvialfauna (Nager). Zeitschr. fiir Ges. Naturw., 1876, 

 xlvii. and xlviii. — Peterson, 0. A., New Rodents and Discussion of Daeriionelix. Mem. Carnegie 

 Mus., Pittsburgh, 1905, vol. ii. No. 4. — Schlosser, M. , Nager des europaisclien Tertiars. Palaeontogr., 

 1884, vol. xxxi. — Scott, W. £., Report of the Princeton Uuivers. Exped. to Patagonia, 1905, vol. v. 

 part iii. — TuUberg, T., System der Nagetiere. Nova Acta Soc. Scienc. Upsala, 1899. — Winge, H., 

 Jordfundne og nu levende Guavere (Rodentia) fra brasilien. E Museo Lundii Kjjabenhaven, 1888. 



Fig. 128. . 



Hydroclioerus capyhara Erxl. South America. Skull and lower jaw. 

 i/o (after Flower). Pmx, Preniaxilla; M.c, maxilla ; Na, nasal ; L, lachrymal ; 

 Fr, frontal ; Pa, parietal ; S5, squamosal ; Jw.jugal; Per, periotic ; i, upper 

 incisor; i], lower incisor; io, infraorbital canal; p::, zygomatic process 

 of the upper jaw ; pp, paroccipital process ; co, condyle ; a, angle ; cr, 

 masseter crest of the mandible. 



