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TOXODONTIA

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Originally appearing in Volume V27, Page 114 of the 1911 Encyclopedia Britannica.

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TOXODONTIA , a sub-See also:

order of See also:

EXTINCT

extinct See also:

South See also:

AMERICAN

American See also:

TERTIARY

Tertiary ungulate mammals typified by the genus Toxodon, so named from the See also:

BOW (pronounced " bo ")

bow-like curvature of the molar See also:

TEETH (O.E. Eel); plural of tooth, O.E. top)

teeth. They all show signs of distant kinship to the See also:

PERISSODACTYLA (i.e. odd-toed)

Perissodactyla, as regards both See also:

LIMB

limb-structure and dentition; while some exhibit resemblance to the Rodents and Hyraxes—resemblances which, however, are probably to be attributed to See also:

PARALLELISM, PSYCHOPHYSICAL

parallelism in development. Under the sub-order Toxodontia may be inciuded not only the typical Toxodon, but the more aberrant Typotherium (fig. I) of the See also:

PLEISTOCENE

Pleistocene of Buenos Aires and the smaller Pachyrucus and Hegetotherium of the Patagonian See also:

SANTA

Santa Cruz beds. All the members of the sub-order have tall-crowned and curved cheek-teeth, some or all of which generally have persistent pulps, while at least one pair of incisors in each See also:

JAW (Mid. Eng. jawe, jowe and geowe, O. Eng. cheowan, connected with " chaw " and " chew," and in form with " jowl ")

jaw is rootless. The bodies of the cervical vertebrae have See also:

FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat articular surfaces, the bones of the two rows of the carpus alternate, and in the See also:

TARSUS (mod. Tersous)

tarsus the navicular articulates with the calcaneum, which, as in the See also:

Artiodactyla, is articulated to the fibula, while the astragalus, which is slightly grooved above, See also:

SKELETON

skeleton is not yet known, but it is ascertained that the femur differs from that of Toxodon in the retention of a third trochanter. Toxodon is typified by T. platensis from the Pampean formation of Buenos Aires. Toxodontotherium and Xotodon are allied but rather older types. Nesodon is from the Santa Cruz beds of See also:

PATAGONIA

Patagonia, the typical N. imbricatus having a See also:

SKULL

skull about a See also:

FOOT

foot in length, but N. ovinus was a smaller See also:

animal, about the See also:

SIZE

size of a See also:

sheep. is formed on the Perissodactyle See also:

plan. The number of toes varies between three and five, of which the See also:

MIDDLE

middle one is the largest, and the femur may or may not have a third trochanter. The Typotheriidae and Pachyrucidae are remarkable among the Ungulates for (After See also:

GERVAIS, PAUL (1816-1879)

Gervais.) the retention of clavicles, and for their curious approximation in dentition and certain characters of the skeleton to the See also:

RODENTIA

Rodentia.

The dental See also:

formula of Typotherium is i. c. $, p. i, m. ; that of the smaller Patagonian forms differs by the larger number (8) of pre-molars. The toes were unguiculate rather than ungulate in See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character, except the See also:

HIND

hind ones (four in number) of Typotherium. Certain allied Patagonian forms, such as Argyrohyrax, have been supposed to be related to the Hyraxes. The Toxodontidae differ from the preceding families by the loss of the clavicles and the reduction of the digits to three in each foot. The typical genus Toxodon is represented by animals the size of a (From See also:

BRITISH

British Museum [Nat. His.] See also:

GUIDE (in Mid. Eng. gyde, from the Fr. guide; the earlier French form was guie, English " guy," the d was due to the Italian form guida; the ultimate origin is probably Teutonic, the word being connected with the base seen in O. Eng. witan, to know)

Guide to the Fossil See also:

MAMMALIA (from Lat. mamma, a teat or breast)

Mammalia.) See also:

RHINOCEROS

rhinoceros, of which the entire skeleton is now known (fig. 2). The teeth, of which the formula is i. „ c. $ p. g_J, m. all grow from persistent pulps; those of the cheek-See also:

SERIES (a Latin word from serere, to join)

series are very tall, highly curved, and with a simplified See also:

CROWN

crown-structure.

In the older Nesodon, on the other See also:

hand, the cheek-teeth are shorter-crowned, and depart less widely from a generalized Perissodactyle type, the See also:

TOTAL

total number of teeth being See also:

FORTY

forty-four, and there being scarcely any See also:

gap in the series. Very remarkable changes occur in the dentition as See also:

AGE (Fr. age, through late Lat. aetaticum, from aetas)

age advances, most of the teeth eventually developing roots, although the second pair of incisors in each jaw was rootless. The See also:

COMPLETE

complete (R.

End of Article: TOXODONTIA

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