rupeds abounded. Some at least of the fossil remains formerly
referred to this class in the Wealden (a great freshwater deposit below
the chalk), have been recently shown by Mr. Owen to belong to
pterodactyls.[215] But in North America still more ancient indications
of the existence of the feathered tribe have been detected, the fossil
foot-marks of a great variety of species, of various sizes, some larger
than the ostrich, others smaller than the plover, having been observed.
These bipeds have left marks of their footsteps on strata of an age
decidedly intermediate between the Lias and the Coal.[216]

[Illustration: Fig. 8.

_Natural Size_.

Thylacotherium Prevostii (_Valenciennes_). Amphitherium (_Owen_). Lower
jaw, from the slate of Stonesfield, near Oxford.[218]]

[Illustration: Fig. 9.

Myrmecobius fasciatus (_Waterhouse_). Recent from Swan River. Lower jaw
of the natural size.[219]]

The examples of mammalia, above alluded to, are confined to the Trias
and the Oolite. In the former, the evidence is as yet limited to two
small molar teeth, described by Professor Plieninger in 1847, under the
generic name of Microlestes. They were found near Stuttgart, and
possess the double fangs so characteristic of mammalia.[217] The other
fossil remains of the same class were derived from one of the inferior
members of the oolitic series in Oxfordshire, and afford more full and
satisfactory evidence, consisting of the lower jaws of three species of
small quadrupeds about the size of a mole. Cuvier, when he saw one of
them (during a visit to Oxford in 1818), referred it to the marsupial
order, stating, however, that it differed from all known carnivora in
having ten molar teeth in a row. Professor Owen afterwards pointed out
that the jaw belonged to an extinct genus, having considerable affinity
to a newly discovered Australian mammifer, the _Myrmecobius_ of
Waterhouse, which has nine molar teeth in the lower jaw. (Fig. 9.) A
more perfect specimen enabled Mr. Owen in 1846 to prove that the
inflection of the angular process of the lower jaw was not sufficiently
marked to entitle the osteologist to infer that this quadruped was
marsupial, as the process is not bent inwards in a greater degree than
in the mole or hedgehog. Hence the genus amphitherium, of which there
are two species from Stonesfield, must be referred to the ordinary or
placental type of insectivorous mammals, although it approximates in
some points of structu