MEOATHERIUM (properly Megalotherium)

This article appears in Volume V18, Page 78 of the Encyclopedia Britannica.

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MEOATHERIUM (properly Megalotherium) , a huge

extinct

EXTINCT

edentate mammal from the Pleistocene deposits of Buenos Aires, typifying the family Megatheriidae (or Megalotheriidae), and by far the largest representative of the Edentata. Except, indeed, for its relatively shorter limbs Megatherium americanum rivalled an elephant in bulk, the total length of the skeleton being 18 feet, five of which are taken up by the tail. The Megatheriidae, which include a number of genera, are collectively
In form, as shown in fig. 2, the teeth are quadrangular prisms, each of which is surmounted by a pair of transverse ridges. They grew apparently throughout life, and were implanted to a

great

GREAT

depth in the jaws, being 7 or 8 in: in length, with a

cross

CROSS

-section of at least an inch and a half. The ridges on the crown are due to the arrangement of the vertical layers of hard dentine (fig. 3, (I), softer vasodentine (v) and cement (c). The skull is relatively small, with the lower jaw very deep in its central portion, and produced in part into a long snout-like symphysis for the reception, doubtless, of a large and fleshy tongue (fig. 2). Unlike sloths, the megatherium has seven cervical vertebrae; and the spines of all the trunk-vertebrae incline backwards. The pelvis and hind-limbs are much more powerful than the fore-quarters; thereby enabling these animals, in all probability, to rear themselves on their hind-quarters, and thus pull down the branches of trees: if not, indeed, in some cases to bodily uproot the trees them-selves. Large chevron-bones are suspended to the vertebrae of the- tail,
which was massive, and probably afforded a support when the

monster

was sitting up. The humerus has no foramen, and the
This school was
I.Skeleton of the Megatherium, from the specimen in the Museum of the Royal College of Surgeons of England.
known as ground-sloths, and occupy a position intermediate between the sloths and the ant-eater: their skulls being of the type of the former, while their limbs and vertebrae conform in structure to those of the latter. As in the other typical

South

SOUTH
SOUTH, ROBERT (1634–1716)

American edentates, there are no teeth in the front of the jaws, while those of the cheek-

series

SERIES (a Latin word from serere, to join)

usually comprise five pairs,in the upper and four in the lower. In nearly all the other Pleistocene forms these teeth were subcylindrical in shape, with the summit of the crown (except sometimes in the first pair) forming a cup-like depression; enamel being in all cases absent. From all these Megatherium differs in the form and structure of the teeth.
(From Owen.)
whole fore-limb was very mobile. The first front toe was rudimentary, having no phalanges, but the fifth was rather less aborted, al-though clawless; the other three carried enormous claws, protected by reflected sheaths. The hind-foot is remarkable for the

great

GREAT

back-ward projection of the calcaneum, and likewise for the peculiar shape of the astragalus; the middle toe alone carries a claw, this being of huge size, and ensheathed like those of the fore foot. No trace
(From Owen.)
of a bony

armour

ARMOUR, PHILIP DANFORTH (1832-1901)

in the skin has been detected; but, from the evidence of other genera, it may be assumed that the

body

BODY

was clothed in a coat of long, coarse

hair

HAIR (a word common to Teutonic languages)

. Although similar teeth occur in the phosphorite beds of

South

SOUTH
SOUTH, ROBERT (1634–1716)

Carolina, which may have been transported from elsewhere, no undoubted remains of Megatherium are known from North America.
The typical species ranged from Argentina and Chili to Brazil. for certain small ground-sloths from Patagonia with Megatheriumlike teeth, see MYLODON. (R. L.*)

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