The second greatest difference would be in the history of global climate, still not completely understood. We know that different ice ages came and went—but we do not know why. We know that the polarity of the Earth has changed in the past, with the north magnetic pole where the south is now—but we do not know why. It seems a certainty that if the meteor had not hit and the incredible atmospheric change had not occurred, that the same progression of ice ages and accompanying continent building would not have occurred in precisely the same manner.

Look at our world as it might have been.

The rule of the dinosaurs is unbroken. The world is theirs and they are dominant on every continent—and the Yilanè rise above them all.

Except in the western hemisphere. Although South America is dominated by reptiles this is not completely true to the north. The land bridge of Central America, that connects North and South America, has been sunk beneath the ocean at different geological times. At one crucial time the break coincided with the spread of the vast sea that covered most of North America. The ice sheet of the glaciers that next came south stretched almost to the edge of this inland sea so that for millions of years the climate was northern, barely temperate in midsummer. The cold-blooded species died out and the warm-blooded species became dominant. They expanded and developed and became the dominant life-forms of this land mass.

In time, as the ice sheets withdrew, the mammals expanded north. By the time the land bridge of Central America rose from the sea again the warm-blooded creatures ruled the continent between the oceans. Yet they could not stand against the slow return of the reptiles. There is no defense, other than retreat, from armored creatures weighing 80 tons or more.

Only in the north, in the foothills and the mountains, could the mammals survive. Among them were the New World primates, from whom the Tanu are descended.

There are no Old World mammals here because the Old World is saurian. There are no bears or canines. But the New World deer abound, from small species to immense ones as large as a moose. The mastodons are here as are many marsupials including saber-tooth tigers. Mammalia in rich diversity live in the fertile band south of the ice and north of the cold-blooded saurians.

Most of the Tanu, imprisoned by a harsh environment, have never developed beyond the hunter-gatherer stage. But at this they are immensely successful. There are some exceptions, like the Sasku, who have moved on to a stable existence of neolithic farming. They have developed the settled skills of pottery and weaving, as well as a more complex and stratified society. But this does not mean that they are superior in any way to the hunting Tanu who have a rich language, simple art forms, many survival skills and a basic family group relationship.