Page 476 - My FlipBook

486 DENTAL AyATOMY.

senting the cross-crests very much as in Phenaeodus. Oiceropotamits,
another genus from the Eocene of France, is akogether intermediate
between Falceochcerus and Anthnieotherium, the typical representative
of this family, in the pattern of the superior molars ; the external
cusps are somewhat crescentic, but the external rib is rudimentary or
absent. In the first molar the anterior of the two intermediate tuber-
cles only is present, while in the other two molai*s it is very small
and insignificant ; the two internal lobes are conic.
Following this genus in time come Anthracotherium, Hyopotamus,^
Ancodus, and others in which the anterior of the two intermediate
tubercles is the only one which is present in the upper molars. This
character, I am therefore disposed to believe, defines a natural group,
and should, in connection with the external rib and crescentic form of
the external cusps, be the test of limitation of this family.
Two derivatives of the Eocene Hi/ojxjtaiai, Xiphodon, and Anoph-
therium soon became specialized in their limb structure, but, strangely
enough, disappeared in the Early Miocene. Another line was com-
menced contemporaneously with that of the anthracotheroid in the
genus Dichohune, wherein the jjosterior intermediate tubercle only w^as
retained. It continues forward through the genus Cainofheritun into
the Upper Miocene deposits of Sansan, where it gradually faded from
existence, leaving no modified descendants. This, it appears to me,
constitutes another family, definable by the above character.
From the Anthracotheriddo have sprung all the modern artiodactyles,
with the possible exception of the cameloids and the existing suillines,
together with other stems which are extinct. Many extinct genera
complete the connections with the living forms in all the osteological
and dental details, which it is scarcely witliin the scope of the present
article to discuss.
In the production of a perfected double crescentic pattern of the
superior molars in this sub-order from the short-crowned semi-buno-
dont anthracotheroids, the anterior intermediate tubercle has gradually
usurped the function of the true antero-internal cusp, it having been
reduced to a small cusp situated internal to the mesial horns of the
inner crescents on the inner basal portion of the crown (see Fig, 265).^
Specialization of the dental organs of the Selenodontia is seen in the
following characters : (1) Formation of double crescents in the superior
and inferior molars ; (2) great elevation of the cusps and deposit of a
thick layer of cementum, filling up the valleys; (3) loss of the roots of
the molars and premolars, and their growth from persistent pulps ; (4)
reduction of the premolars to three in each jaw ; (5) subtraction of the
canines and incisors from the upper jaw (6) the reduction in size and
;
approximation of the lower canine to the incisors; and finally (7), the
' Gaudry places the appearance of this sonns in the sands of Beauchanip. wliioh
probably corres|)()nds with our Bridirer Beds or Upper Eocene. He also fixes the date
of appearance of Palrporhfrriia in Europe in the deposits of Saint-Geraud-le-Piiv, Middle
IMiocene. In this country Jhjfipril(im>iA does not apuear until the Lower Miocene,
whereas PnUp/tclKmix protiably extends into the Bridtrer epoch.
^For a further knowledtre of the fossil forms of these families the reader is referred
to the important worl< of Prof Albert (Jaudry, " Les Enchainements du Monde animal
dans les Temps geolo>i:i(pies," in which tiie more important genera are figured.