“The sixth day of creation,” said Will. “Tomorrow, the God of Genesis rests. Today… well, today is a long day indeed for Him. Tough to cram all that creating into twenty-four hours. In science’s terms an even longer day, stretching from the late Paleozoic a bit over 300 million years ago to this evening’s mighty reckoning in this little room.”
Another hint, thought Dante, that Will had returned knowing Raptor was going to be waiting for him.
“Genesis: ‘And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earth after his kind: and it was so.’
“That’s it, folks. Shazam! Cattle, creepings things, beasts of the earth. Everything except His final creation, man, made and then instructed during the balance of the sixth day.
“But we need the fossil time frame, not a few minutes of a single twenty-four-hour day, to explain what went before to shape us with all our terrible and glorious complexities and contradictions.
“As vertebrates we had gained a bony skeleton, a jointed spine, muscle and nerve systems that oxygenated and circulated the blood. As amphibians we became tetrapods: air-breathers with no more than five digits on each of our paired limbs.
“The amphibians were most successful for their day, some getting to be a few feet long and shaped like a silly-looking crocodile drawn by a five-year-old. In less than 100 million years they developed into the earliest reptile, proto-reptile, what we could call the base reptile, so successful that the amphibians today have been reduced to barely enough frogs and newts, as William Howells notes, ‘to keep a witch in brew.’
“By changing to proto-reptile, what did we gain over the amphibian ancestors we so closely resembled? We became amniotes. Only mammals, reptiles, and birds-which wouldn’t appear for sure until the flying feathered dinosaur, archaeopteryx, in the late Jurassic 170 million years ago-are amniotes.
“Amniotes have their fetal development either in an egg or in a womb. The amnion, and other protective membranes, supply the fetus with food and oxygen.
“Successively more advanced models followed that base reptile of 300 million years ago. They became the first of four ‘Megadynasties’ that Robert Bakker, a maverick dinosaur guru who has stood paleontology on its ear a score of times, suggests have existed during the history of life on land.
“Megadynasty One, the proto-reptiles, had great staying power-these early reptiles ruled for 20 million years with two types of beasts. Big quick predators, dimetrodons-popularly, ‘sail lizards’ because of tall webbed spines on their backs-and big slow vegetarians.
“Near the very end of the Paleozoic era, maybe 260 m.y. ago, one line of these sluggish and decidedly cold-blooded proto-reptiles split into two basic new vertebrate life-forms. One, called thecondonts, became the modern reptiles, the dinosaurs, and their descendants, the birds.
“The other became mammal-like reptiles called therapsids-some call them synapsids, although I doubt they had very many synapses to help them along-that formed the second of Bakker’s Megadynasties. They dominated the thecodonts from the late Permian through the Triassic, ranging from early bone-headed proto-mammals to, at the end of their reign, very advanced dog-faced cynodonts just a knife blade away from true mammals.
“They had become warm-blooded-mammal-like bony palates separating the mouth and nose cavities in some of them suggest this-but the mass extinction 249 m.y. ago at the Paleozoic/Mesozoic boundary finished them. They already had spawned the true mammals, however, tiny mouse-like things that had to wait their turn because the reptiles moved first, evolved faster, to grab all major Mesozoic ecological niches.
“These Archosauria-true reptiles-the most successful early model being the so-called crimson crocodiles, were soon weighing in at a half-ton or so, and the third Megadynasty, the Age of Reptiles, was under way. Through the Jurassic and Cretaceous right up to the end of the Mesozoic 65 m.y. ago, dinosaurs and other reptiles reigned supreme. Their story is not our story, but they were a tremendous success.
“They ruled the earth as tyrannosaurs, as stegosaurs, as ceratopsians, as massive sauropods like diplodocus and brontosaurus who reached eighty tons in weight and a hundred feet in length. Truly thunder lizards. They reentered the sea as plesiosaurs, ichthyosaurs, and mosasaurs. Soared the skies as pterodons, pterosaurs, and pterodactyls, in sizes ranging from a robin to a jet fighter.
“Archosauria seemed destined to control the world forever. Why didn’t it? Because of the infamous mass extinction at the K/T (Cretaceous-Tertiary) boundary 65 m.y. ago, often called the Great Dying. The dinosaurs went extinct not through bad genes, but through bad luck. Environmental catastrophe overtook them. Three-fourths of all living species on the earth, in the sea, in the sky, were abruptly terminated.
“The current Megadynasty Four, the Age of Mammals, was about to begin. At first it didn’t look like much. During the dinosaurs’ reign the mammals essentially were limited to two major sorts of what Bakker called little furballs: the rodent and the shrew. These little guys played out their tiny, apparently insignificant destinies down around the dinosaurs’ toenails, but they bore the marks of the mammal-live birth, warm blood, flexible skeleton.
“Live birth means mammary glands-the young are nursed and receive maternal care.
“Warm blood means hair and fur, a four-chambered heart, two sets of specialized teeth (milk teeth to grow with, permanent teeth to live with) essential for true warm-bloodedness, with variously shaped hard enamel crowns adapted to the animal’s diet.
“Flexible skeletons mean a free lumbar spine, and a unique bone growth pattern called epiphyses whereby the bone grows in the middle, not at the ends. It is this that gives the mammals their tight, flexible, very usable joints.
“Early rodent-let’s call him proto-rat-had very big teeth to chew the roots and plants of the day: tree ferns, horsetails, cycads, conifers, sequoias, araucarias (monkey puzzle trees), and the spanking new flowering plants called angiosperms.
“And proto-rat used those sharp teeth on proto-shrew, forcing the little scuttler to become tree shrew by taking to the trees where proto-rat wouldn’t-couldn’t? — follow. Also, since nocturnal proto-rat controlled the night and the ground, tree shrew became diurnal and claimed the day and the trees.
“When the dinosaurs finally galloped and leaped and plodded off in the Great Dying, our little squirrel-like ancestors were waiting in the trees just as proto-rat’s descendants were waiting on the ground. During 30 million years in their arboreal world, the tree shrews had evolved, had begun developing and coordinating our three major features-hand, eye, and brain. They had started to become monkeys.
“In the process, our eyes moved to the front of our heads, giving us the tremendous advantages of binocular and Technicolor vision. Our muzzles shrank as eye became more important than nose, the claws on the digits of our hands and feet became nails, and we developed opposable thumbs and friction skin (fingerprints) on hands and feet to help us grab useful things like tree branches or a piece of fruit.
“All of this new activity was making our brain bigger and bigger in relation to our size and weight. Which, for some, kept getting bigger also.
“Some of the monkeys got so large and slow, in fact, that they had to confine themselves to lower branches that could support them. As we move to about 28 million years ago, remember that heaviness: it is forcing some of them to develop into… loud movie music here… apes…”
A lean, fast-walking man was passing across the windows on the walk outside. Dante quit listening. The man looked in, saw Will behind the podium, and faltered for a moment before going on. Dante waited, tense, until he had gone up the stairs to the Theological Union. It was a while before he settled back against the wall, and then he kept his hand close to his gun, in case that other fast-moving man should appear out of nowhere.