The law of geographical relationship above alluded to, between the living vertebrata of every great zoological province and the fossils of the period immediately antecedent, even where the fossil species are extinct, is by no means confined to the mammalia. New Zealand, when first examined by Europeans, was found to contain no indigenous land quadrupeds, no kangaroos, or opossums, like Australia; but a wingless bird abounded there, the smallest living representative of the ostrich family, called the Xivi, by the natives (_Apteryx_). In the fossils of the Post-Pliocene and Pleistocene period in this same island, there is the like absence of kangaroos, opossums, wombats, and the rest; but in their place a prodigious number of well preserved specimens of gigantic birds of the struthious order, called by Owen Dinornis and Palapteryx, which are entombed in superficial deposits. These genera comprehended many species, some of which were 4, some 7, others 9, and others 11 feet in height! It seems doubtful whether any contemporary mammalia shared the land with this population of gigantic feathered bipeds. To those who have never studied comparative anatomy it may seem scarcely credible, that a single bone taken from any part of the skeleton may enable a skilful osteologist to distinguish, in many cases, the genus, and sometimes the species, of quadruped to which it belonged. Although few geologists can aspire to such knowledge, which must be the result of long practice and study, they will nevertheless derive great advantage from learning what is comparatively an easy task, to distinguish the principal divisions of the mammalia by the forms and characters of their teeth. The annexed figures, all taken from original specimens, may be useful in assisting the student to recognize the teeth of many genera most frequently found fossil in Europe:-- [Illustration: Fig. 129. _Elephas primigenius_ (or Mammoth); molar of upper jaw, right side; one third of nat. size. _a._ grinding surface. _b._ side view.] [Illustration: Fig. 130. _Mastodon angustidens_ (Norwich Crag, Postwick, also found in Red Crag, see p. 149.); second true molar, left side, upper jaw; grinding surface, nat. size. (See p. 149.)] [Illustration: Fig. 131. Rhinoceros. _Rhinoceros leptorhinus_; fossil from freshwater beds of Grays, Essex (see p. 147.); penultimate molar, lower jaw, left side; two-thirds of nat. size.] [Illustration: Fig. 132. Hippopotamus. Hippopotamus; from cave near Palermo (see p. 154.); molar tooth; two-thirds of nat. size.] [Illustration: Fig. 133. Pig. _Sus scrofa_, Lin. (common pig); from shell-marl, Forfarshire; posterior molar, lower jaw, nat. size.] [Illustration: Fig. 134. Horse. _Equus caballus_, Lin. (common horse); from the shell marl, Forfarshire; second molar, lower jaw. _a._ grinding surface, two-thirds nat. size. _b._ side view of same, half nat. size.] [Illustration: Fig. 135. Tapir.