Geology Reference
In-Depth Information
This advantage, however, comes with costs. Endothermic animals must gather and store
energy that can be used to warm them up. This means they need to eat more calories
and more often than exothermic animals. They also have to be skilled at foraging or
hunting to meet the energy demands of their endothermic body system.
Filling every niche
In ecology, a
niche
is defined as an organism's position in the ecosystem relative to other
organisms. For example, some organisms (such as plants) are producers, while other or-
ganisms are consumers (anything that eats the plants). Mass extinctions (which I cover
in the next chapter) leave many open niches for the surviving organisms to fill. Success-
ful animals evolve and diversify to fill these niches, spreading into new environments
and adapting new lifestyles.
Warming themselves from within: Were dinosaurs
warm-blooded?
For a long time, scientists accepted that dinosaurs were reptiles and assumed that all dinosaurs were
exothermic (cold-blooded) the way modern reptiles are. But as scientists have continued to examine
the fossils of ancient reptiles and dinosaurs, they are no longer certain that the answer to this question
is so simple. Some of the arguments scientists make for dinosaur endothermy include these:
Birds are direct descendents of dinosaurs, and birds are endothermic.
The larger dinosaurs (like a Brachiosaurus) would have needed an endothermic circulatory sys-
tem to pump blood up their long necks.
Fossils of dinosaurs are found all over the globe, including the Arctic and Antarctic regions, sug-
gesting they had some way to keep warm in these cooler regions.
Evidence indicates that some dinosaurs had feathers or fur, features that are associated with
modern endothermic animals.
These arguments do not provide irrefutable proof for dinosaur endothermy. Opposing scientists point
out that a large dinosaur such as the Brachiosaurus would not need an advanced circulatory system if
it carried its neck straight (horizontal to the ground) rather than up (like a giraffe). Others claim that the
climate during the Mesozoic was warm enough, even at the North and South Pole, that endothermism
may not have been required for dinosaurs to live there. With only bones and partial skeletons to work
