Out of Thin Air Dinosaurs, Birds, and Earth's Ancient Atmosphere (2006) / Chapter Skim
Currently Skimming:
10 The Cretaceous Extinction and the Rise of Large Mammals
10 The Cretaceous Extinction and the Rise of Large Mammals
Pages 223-228
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 223... ...
But the biggest similarity between those times, some 65 million years ago soon after the asteroid impact, and the world of today was that dinosaurs existed in neither. It was the disappearance of the dinosaurs that allowed mammals to fill the emptied world -- and fill it they did.
|
From page 224... ...
THE HISTORY OF CENOZOIC MAMMALS As we have seen, the ancestors of the mammals, the Paleozoic and early Mesozoic therapsids, were the dominant land animals until the Permian extinction, and even through the Triassic they maintained moderate diversity, if no longer being the most diverse and numerous of land animals as their Paleozoic forbearers had been. The first true mammals are found in rocks of late Triassic age -- at about the time of the first dinosaurs, in fact.
|
From page 225... ...
Through dint of hard work in the library and among numerous dusty museum drawers, he tabulated average size for over 2,000 kinds of mammals from the late Meso
|
From page 226... ...
A 2005 study by geochemist Paul Falkowsky suggested that the first appearance of "placental mammals" (the vast majority of mammals today, all of which have live births and nurse their young) could not take place until a critical level of rising oxygen was reached.
|
From page 227... ...
It thus looks as if the oxygen-level increase of the late Cretaceous -- an oxygenation event that at least in part helped spark the major diversity increase in dinosaurs -- also allowed the first evolution and successful implementation of a new kind of reproductive pattern, placental development (itself but one kind of live birth)
|
From page 228... ...
The 540-millionyear trip is over with this chapter. We have seen evidence of major changes in oxygen levels through time.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.