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Updated: May 22, 2025
We saw that during the Mesozoic the Arctic continent was very largely submerged, and, while Europe and America rise again at the end of the Cretaceous, we find no rise of the land further north. A difference of elevation would, in such a world, make a great difference in temperature and moisture. Let us examine the animal record, however, before we come to any conclusion.
And should such an hypothesis eventually be proved to be true, in the only way in which it can be demonstrated, viz. by observation and experiment upon the existing forms of life, the conclusion will inevitably present itself, that the Paleozoic, Mesozoic, and Cainozoic faunae and florae, taken together, bear somewhat the same proportion to the whole series of living beings which have occupied this globe, as the existing fauna and flora do to them.
Apart from the few fragmentary remains from the English greensand, to which I have referred, the mesozoic rocks, older than those in which Hesperornis and Ichthyornis have been discovered have afforded no certain evidence of birds, with the remarkable exception of the Solenhofen slates.
The pretty nautilus is the only survivor to-day of the vast Mesozoic population of coiled-shell Cephalopods. A rival to the Ammonite appeared in the Triassic seas, a formidable forerunner of the cuttle-fish type of Cephalopod. The animal now boldly discards the protecting and confining shell, or spreads over the outside of it, and becomes a "shell-fish" with the shell inside.
They form a great contrast to the fish of the secondary strata, as, with the exception of the Placoids, they are all Teleosteans, only one genus, Pycnodus, belonging to the order of Ganoids, which form, as before stated, the vast majority of the ichthyolites entombed in the secondary are Mesozoic rocks.
"Professor Huxley speaks of a 'verbal fog by which the question at issue may be hidden; is there no verbal fog in the statement that the aetiology of crayfishes resolves itself into a gradual evolution in the course of the mesozoic and subsequent epochs of the world's history of these animals from a primitive astacomorphous form?
By this means the German, French, and English geologists have determined the succession of strata throughout a great part of Europe, and have adopted pretty generally the following groups, almost all of which have their representatives in the British Islands. GREAT or BATH OOLITE. JURASSIC. SECONDARY OR MESOZOIC. NEOZOIC. RECENT. Shells and mammalia, all of living species.
The Arctogaeal province is at present enormous, while the Australian is relatively small. Why should not these proportions have been different during the Mesozoic epoch?
As it is now known that many of the cycad-like Mesozoic plants bore flowers as the modern botanist scarcely hesitates to call them the gap between the Gymnosperms and Angiosperms is very much lessened. There are, however, structural differences which forbid us to regard any of these flowering cycads, which we have yet found, as the ancestors of the Angiosperms.
Professor Henslow adds a number of equally significant facts with the same tendency, so that we have strong reason to conceive the floral world as passing through successive phases of colour in the Tertiary Era. At first it would be a world of yellows and greens, like that of the Mesozoic vegetation, but brighter.
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