=Vegetation and climate.= The highest plants in structure, the _dicotyls_ (such as our deciduous forest trees) and the _monocotyls_ (represented by the palms), were introduced during the Cretaceous. The vegetable kingdom reached its culmination before the animal kingdom, and if the dividing line between the Mesozoic and the Cenozoic were drawn according to the progress of plant life, the Cretaceous instead of the Tertiary would be made the opening period of the modern era. The plants of the Tertiary belonged, for the most part, to genera now living; but their distribution was very different from that of the flora of to-day. In the earlier Tertiary, palms flourished over northern Europe, and in the northwestern United States grew the magnolia and laurel, along with the walnut, oak, and elm. Even in northern Greenland and in Spitzbergen there were lakes covered with water lilies and surrounded by forests of maples, poplars, limes, the cypress of our southern states, and noble sequoias similar to the "big trees" and redwoods of California. A warm climate like that of the Mesozoic, therefore, prevailed over North America and Europe, extending far toward the pole. In the later Tertiary the climate gradually became cooler. Palms disappeared from Europe, and everywhere the aspect of forests and open lands became more like that of to-day. Grasses became abundant, furnishing a new food for herbivorous animals. =Animal life of the Tertiary.= Little needs to be said of the Tertiary invertebrates, so nearly were they like the invertebrates of the present. Even in the Eocene, about five per cent of marine shells were of species still living, and in the Pliocene the proportion had risen to more than one half. Fishes were of modern types. Teleosts were now abundant. The ocean teemed with sharks, some of them being voracious monsters seventy-five feet and even more in length, with a gape of jaw of six feet, as estimated by the size of their enormous sharp-edged teeth. Snakes are found for the first time in the early Tertiary. These limbless reptiles, evolved by degeneration from lizardlike ancestors, appeared in nonpoisonous types scarcely to be distinguished from those of the present day. =Mammals of the early Tertiary.= The fossils of continental deposits of the earliest Eocene show that a marked advance had now been made in the evolution of the Mammalia. The higher mammals had appeared, and henceforth the lower mammals--the monotremes and the marsupials--are reduced to a subordinate place. [Illustration: Fig. 344. Phenacodus]