synapsids. These were mammal-like that became extinct as this period ended. The animals that entered the Mesozoic era needed to adapt to changing temperatures. Reptiles were good at this, so they thrived. The first of these reptiles were called diapsids because they had two separate holes on either side of their skulls just behind their eyes. The dinosaurs came after and were also diapsids. The Jurassic Period and Cretaceous Period near the end of this era were mainly the dinosaurs. Plants were also very gigantic. There were a few small mammals but they did not dominate the land like the dinosaurs had. There was another mass extinction to end the Cretaceous period. The dinosaurs died off at this time, even though it wasn't as large an extinction event as the Permian-Triassic extinction. An asteroid impact likely caused this mass extinction.
THE CENOZOIC ERA The Cenozoic era marked the end of what we call the geologic eras. This was when mammals finally made their mark as being dominant. All of the major species evolved continuously as well during this time. Mammals survived the extinction that killed the dinosaurs, possibly because they didn't have as many needs for the scarce resources of the time. None were as big as the dinosaurs but a few were much larger than today's counterparts. The mammoths are well-known for being large but so were smaller mammals like beavers, which were more than 4 times larger than they are today. The continents had separated by this time to where they now are, except for Africa, South America, and India. These were too far south and moved northward to where they collided with the northern continents. The Alps and the Himalayas were created at this time; the Himalayas are still being built. The climate has become generally cooler since the beginning of the Cenozoic era. The overall landscape on earth has also become drier with more grasslands for grazing animals to better survive. There are not a lot of fossils from this time as it is too recent for this to have happened and is still part of the time we are in. It began 66 million years ago — a drop in the bucket when you consider the expanse of all geologic time. It has
49
