MYLODON.
Mylodon.[752]—By this name is designated a gigantic edentate animal, allied to the Sloth, and formerly described as a species of Megalonyx, an almost perfect skeleton of which has been obtained from a fluviatile deposit, a few leagues to the north of the city of Buenos Ayres, and is now articulated and exhibited in the Museum of the Royal College of Surgeons of England.[753] The animal appears to have been imbedded entire, and soon after its death, for the parts of the skeleton were found but little displaced, and the very few bones that are wanting, are such as might easily have escaped the search of the collector. But this magnificent specimen of the extinct fauna of South America must be seen to be properly appreciated. The skeleton measures eleven feet from the fore part of the skull to the extremity of the tail, the latter being three feet in length; the circumference of the trunk around the tenth pair of ribs is nine feet nine inches; the Megatherium is eighteen feet in length, and its girth fourteen and a half feet. These particulars will serve to convey an idea of the relative size of these gigantic animals. From certain peculiarities in the construction of the skeleton of the Mylodon, Prof. Owen, perceiving from the teeth that it was a vegetable feeder, and probably lived on leaves and the tender buds of trees, and its enormous bulk and weight forbidding the assumption that it climbed up trees and suspended itself by the branches, like the diminutive existing Sloths,—assigns to this creature the task of uprooting and felling trees, and feeding upon the foliage of the forests it laid prostrate. A remarkable development of the substance of the bones of the skull is presumed to hare been a provision against the fatal effects of a fracture of the cranium, to which the Mylodon, from its supposed uprooting propensities, is conjectured to have been peculiarly exposed; and the skull of the specimen in the College bears proofs of having had two fractures, from both of which the animal recovered. But whoever looks at the skeleton will perceive that the fore-feet are admirably adapted for seizing and wrenching oft the branches, and the hinder feet for clasping the trunk of a large tree; and there is nothing to forbid the supposition, that the animal could obtain a constant and ready supply of food, by climbing up the stem to a sufficient height, and wrenching off the branches. Prof. Owen states, that the Mylodon unites the two great groups of the Unguiculata (animals with nails and claws), and the Ungulata (hoofed animals), for it has both hoofs and claws on the same feet.
[752] Signifying molar-tooth,—a name intended to express that the animal has only teeth adapted for grinding; but this term is equally applicable to all the other megatheroid animals.
[753] See "Description of the Skeleton of an extinct gigantic Sloth (Mylodon robustus)," &c., by Richard Owen, F.R.S. Hunterian Professor of the Royal College of Surgeons, 1 vol. 4to. with twenty-four plates, 1842. The lithographs in this work, by Mr. Scharf, are of the highest excellence: the figure of the entire skeleton of the animal, on a scale of two inches to a foot, is admirable.
The dental organs consist of four molars on each side the lower, and five on each side the upper jaw. The teeth are implanted in very deep sockets, and are of the same size and form throughout, with a conical pulp-cavity at the base, indicating that their growth continued during the life of the animal. In structure they resemble those of the Megatherium and Sloth (Bradypus); being composed of a pillar of coarse dentine, traversed by numerous vascular or medullary canals, which is invested with a layer of very fine, dense dentine, with minute calcigerous tubes, and the whole surrounded by a thick coating of cementum: no enamel enters into their composition. (Owen.)
V. Fossil Rodents.—Of the mammalia termed Rodentia or Gnawers (see Wond. p. 143), of which the Mouse, Rabbit, and Beaver are examples, the remains of several genera are found in a fossil state; particularly in the caverns containing the bones of Carnivora. Dr. Buckland collected from Kirkdale Cave-bones of a species of Hare or Rabbit, Mouse and Water-Rat (Reliq. Diluv. pl. xi.).
In the eocene gypseous strata of France, two species of Dormouse and two of Squirrel have been found. From the tertiary sand at Epplesheim, with the bones of the Dinotherium, those of a species of Hamster or German Dormouse (Cricetus) were obtained.
Fossil teeth of a species of Porcupine (Hystrix) occur in the pliocene deposits of Tuscany.
Of the Beaver (Castor), some undoubted remains have been collected in this country. Those of a species apparently identical with the recent Beaver of the Danube, have been discovered in the fresh-water deposits of Essex,[754] Norfolk, Cambridgeshire, and Berks, and in Scotland; and the remains of the very large extinct species first observed in Russia (and named, by M. Fischer, Trogontherium,) have been found in the subterranean forest at Bacton, in Suffolk.[755]
[754] See Mr. Brown’s Paper on Copford, Quart. Geol. Journ. vol. viii. p. 188.