What seems to explain invader and endemic success with those migrations is what kind of continent the invaders came from, what kind of continent they invaded, and the invasion route. Asia contains large arctic and tropical biomes, unlike any other continent. North America barely reaches the tropics and only a finger of South America reaches high latitudes, and well short of what would be called arctic latitudes in North America. Africa’s biomes were all tropical and near-tropical. The route to was straight across at the same latitude, so the biomes were similar. About the same is true of the route to Africa from Asia. Asian immigrants were not migrating to climates much different from what they left. But the route to North America was via , which was an Arctic route. Primates and other tropical animals could not migrate from Asia to North America via Beringia, and even fauna from temperate climates were not going to make that journey, not in Icehouse Earth conditions. Oligocene North America was geographically protected in ways that Oligocene Europe and Africa were not, and it already had substantial exchanges with Asia before and was a big continent with diverse biomes in its own right. It was not nearly as isolated as Africa, South America, and Australia were.
The invasion of North America from Asia (with a little migration from North America to Asia), while important, was not as dramatic as what happened in Africa a few million years later. About 24 mya, Africa and the attached Arabian Peninsula began colliding with Eurasia. The once-vast Tethys Ocean had finally been reduced to a strait between the continents, and one of Earth’s most dramatic mammalian migrations began. By about 18 mya, proboscidean had migrated from Africa and they reached North America by 16.5 mya. An left Africa but stayed in Asia. As with the North American interchange with Asia, however, the greater change came the other way. Rodents, deer, cattle, antelope, pigs, rhinos, giraffes, dogs (including the ), and cats came over, along with small insectivores and shrews. Most of the iconic large fauna of today’s African plains originated from elsewhere, particularly Asia. Asian animals invaded and dominated Europe and Africa, and became abundant in North America. In general, Asia had more diverse biomes and was the largest continent, so it developed the most competitive animals. That principle, which Darwin remarked on, became very evident when the British invaded Australia in the 18th century: imports such as rabbits and foxes quickly prevailed, and . The most important Miocene development for humans was African primate development, but that is a subject for a later chapter.
NASA Images Discover Ancient Bridge between India …
Huge mammals persist to this day, although the spread of humans was coincident with the with the exception of those in Africa and, to a lesser extent, Asia. The five-to-seven-metric-ton browser formed a guild common to dinosaurs mammals, and is probably related to metabolic limits and the relatively low calorie density that browsing and foraging affords. Sometimes, the similarity between dinosaurs and mammals could be eerie, such as and , which is a startling example of , which is the process by which distantly related organisms develop similar features to solve similar problems. They were even about the same size, at least for the most common ankylosaurs, which were about the size of a car. Ankylosaurs appeared in the early and succeeded all the way to the Cretaceous’s end. Glyptodonts appeared in the and prospered for millions of years.