In the upper Cretaceous, cycads become rare.  The highest types of flowering plants gain a complete ascendency, and forests of modern aspect cover the continent from the Gulf of Mexico to the Arctic Ocean.  Among the kinds of forest trees whose remains are found in the continental deposits of the Cretaceous are the magnolia, the myrtle, the laurel, the fig, the tulip tree, the chestnut, the oak, beech, elm, poplar, willow, birch, and maple.  Forests of Eucalyptus grew along the coast of New England, and palms on the Pacific shores of British Columbia.  Sequoias of many varieties ranged far into northern Canada.  In northern Greenland there were luxuriant forests of magnolias, figs, and cycads; and a similar flora has been disinterred from the Cretaceous rocks of Alaska and Spitzbergen.  Evidently the lands within the Arctic Circle enjoyed a warm and genial climate, as they had done during the Paleozoic.  Greenland had the temperature of Cuba and southern Florida, and the time was yet far distant when it was to be wrapped in glacier ice.

Invertebrates.  During the long succession of the ages of the Mesozoic, with their vast geographical changes, there were many and great changes in organisms.  Species were replaced again and again by others better fitted to the changing environment.  During the Lower Cretaceous alone there were no less than six successive changes in the faunas which inhabited the limestone-making sea which then covered Texas.  We shall disregard these changes for the most part in describing the life of the era, and shall confine our view to some of the most important advances made in the leading types.

Stromatopora have disappeared.  Protozoans and sponges are exceedingly abundant, and all contribute to the making of Mesozoic strata.  Corals have assumed a more modern type.  Sea urchins have become plentiful; crinoids abound until the Cretaceous, where they begin their decline to their present humble station.

Trilobites and eurypterids are gone.  Ten-footed crustaceans abound of the primitive long-tailed type (represented by the lobster and the crayfish), and in the Jurassic there appears the modern short-tailed type represented by the crabs.  The latter type is higher in organization and now far more common.  In its embryological development it passes through the long-tailed stage; connecting links in the Mesozoic also indicate that the younger type is the offshoot of the older.

Insects evolve along diverse lines, giving rise to beetles, ants, bees, and flies.

Brachiopods have dwindled greatly in the number of their species, while mollusks have correspondingly increased.  The great oyster family dates from here.