The New Dinosaurs
Reloaded
"The dinosaurs were some of the most magnificent creatures that ever lived. They evolved in the late Triassic period, about 220 million years ago, and from humble crocodile-like origins, became the most varied and abundant animals on Earth. [...] For over 180 million years they were the most successful life form on the planet.
And then they all disappeared.
The Great Extinction, as their disappearance has come to be known, befell the dinosaurs at the end of the Cretaceous period, about 65 million years ago. At this time not just the dinosaurs but about 75 per cent of all living creatures were wiped from the face of the Earth.
The rocks supply the evidence. The strata that date from before this time contain the fossils of the kinds of animals that had been present for 150 million years previously. Rocks that formed from continental deposits, such as shales and mudstones from river sediments, and sandstones from deserts, contain the remains of dinosaurs and flying pterosaurs. Rocks that formed in the sea, such as limestones and chalk, contain the fossils of sea reptiles like plesiosaurs and mosasaurs, the ubiquitous pterosaurs, and invertebrates like the tentacled shellfish, the ammonites.
Then there is a break in the strata and the rocks immediately above exhibit a different picture of life on Earth. No dinosaurs or pterosaurs are evident here. Nor are there fossils of marine reptiles or ammonites. Something had happened to change things completely. This break gives a useful boundary for geological dating. The time before the break is called the Cretaceous period of the Mesozoic era. Creta is the Greek word for chalk and the period is named for the deposits of chalk that were laid down in the sea at this time. The time immediately after the break is called the Palaeocene epoch of the Tertiary period. Palaeocene means the ancient epoch of modern life and the ‘modern life’ referred to here means, basically, the mammals.
Up to this point the mammals had been very small and insignificant, scuttling mouse-like among the feet of the dinosaurs and scrambling squirrel-like up trees beyond their reach. Throughout the 150 million-year Age of Reptiles they did not amount to much at all. Then, as the dinosaurs and the other great reptiles disappeared, they came into their own. It is the way of evolution that, once a particular animal dies out, something else will soon develop to take its place. Wherever there is a food source that is not exploited, an animal will evolve to exploit it. With the total disappearance of the great reptiles, there was a complete replacement by new creatures, and these new creatures were the mammals. Pigs and elephants evolved to take the place of the herbivorous dinosaurs. Strange wolf-like mammals called creodonts evolved to prey on them, taking the place of the carnivorous dinosaurs. In the absence of pterosaurs, the bats evolved. In the seas, whales and seals developed to take the place of the plesiosaurs and mosasaurs. The Age of Reptiles had clearly given way to the Age of Mammals.
For the purposes of this [project] none of that happened. The meteorite missed. The comet swarm passed by. The sea plants were able to adapt to the changing water temperatures. The land animals were able to resist the diseases and parasites of their neighbours.
In short, the animal life that had developed throughout the 150 million years of the Mesozoic era continued to evolve for at least another 65 million years without a break. And that is the basis for our [project]."
-- Dougal Dixon, The New Dinosaurs: An Alternative Evolution
