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. An ice sheet stretched south 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 expanded, 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 mastodon 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.

ZOOLOGY

BANSEMNILLA (Metatheria: Didelphys dimidiata): A reddish-gray marsupial with three deep black bands down its back. It has a prehensile tail and opposable toes on its hind feet. It is carnivorous, favoring rats and mice, and is bred by the Sasku to eliminate these vermin from their corn-cribs.

BOAT (Cephalopoda: Archeololigo olcostephanus mutatus): Yilanè surface water transport. Propulsion is obtained by a strong jet of water expelled to the stern. The creatures have only rudimentary intelligence like their ancestral squids, but can be trained to follow certain simple commands.

CLOAK (Selachii: Elasmobranchus kappe mutatus): Used by the Yilanè for warmth during the night or inclement weather. These creatures have absolutely no intelligence, but if they are well-fed they will maintain a body temperature of approximately 102° F.