In the clever orniths, though, the diplos faced a new peril, a danger for which evolution had not prepared them. Nevertheless, after more than a century of life, the matriarch had absorbed a certain deep wisdom, and her eyes, deep red with age, betrayed an understanding of the nimble horrors that pursued her kind.

Now the patient orniths had their best opportunity.

The diplos still crowded around the wrecked ginkgo grove, their great bodies in a starburst formation. Their heads on their long necks dipped over the scattered foliage like cherry picker mechanical claws. Youngsters clustered close, but for now they were excluded by the giant adults.

Excluded, forgotten, exposed.

Stego ducked his head toward one of the diplo young. She was a little smaller than the rest — no larger than the largest African elephant, a genuine runt. She was having trouble forcing her way into the feeding pack, and she snapped and prowled at the edge of the formation with a massive birdlike twitchiness.

There was no real loyalty among the diplos. The herd was a thing of convenience, not a family grouping. Diplos laid their eggs at the edge of the forest, and then abandoned them. The surviving hatchlings would use the cover of the forest until they had grown sufficiently massive to take to the open land and seek a herd.

The herds made strategic sense: Diplos helped protect each other by their presence together. And any herd needed new blood for its own replenishment. But if a predator took one of the young, so be it. In the endless Pangaean forests, there was always another who would take her place. It was as if the herd accepted such losses as a toll to be paid for its continuing passage through the ancient groves.

Today it looked as if this runty female would pay that toll.

Listener and Stego took their whips of diplo leather from around their waists. Whips raised, spears ready, they crept through the rough scrub of saplings and ferns that crowded the edge of the forest. Even if the diplos spotted them they would probably not react; the diplos’ evolutionary programming contained no alarm signals for the approach of two such diminutive predators.

A silent conversation passed in subtle movements, nods, eye contacts.

That one, said Stego.

Yes. Weak. Young.

I will run at the herd. I will use the whip. Try to spook them. Separate the runt.

Agreed. I will make the first run…

It should have been routine. But as the orniths approached, coelurosaurs scuttled away and pterosaurs flapped awkwardly into the air.

Stego hissed. Listener turned.

And looked into the eyes of another ornith.

There were three of them, Listener saw. They were a little larger than Listener and Stego. They were handsome animals, each with a distinctive crest of spiny decorative scales running down the back of its head and neck; Listener felt her own spines rise up in response, her body obeying an unbidden, ancient instinct.

But these orniths were naked. They had no belts of woven bark around their waists like Listener’s; they carried no whips, no spears; their long hands were empty. They did not belong to Listener’s hunting nation, but were her remote cousins — wild orniths — the small-brained stock from which her kind had arisen.

She hissed, her mouth gaping wide, and strode into the open. Get away! Get out of here!

The wild orniths stood their ground. They glared back at Listener, their own mouths gaping, heads bobbing.

A tinge of apprehension touched Listener. Not so long ago three like these would have fled at her approach; the wild ones had long learned to fear the sting of weapons wielded by their smarter cousins. But hunger outweighed their fear. It had probably been a long time since these brutes had come across a diplo nest, their primary food source. Now these clever opportunists probably hoped to steal whatever Listener and Stego managed to win for themselves.

The world forest was getting crowded.

Listener, confronted by this unwelcome reminder of her own brutish past, knew better than to show fear. She continued to stalk steadily toward the three wild orniths, head dipping, gesturing. If you think you are going to steal my kill you have another think coming. Get out of here, you animals. But the mindless ones replied with hisses and spits.

The commotion was beginning to distract the diplodocus. That runty female had already ducked back into the mass of the herd, out of reach of the hunters. Now the big matriarch herself looked around, her head carried on her neck like a camera platform on a boom crane.

It was the chance the allosaurs had been waiting for.

The allos stood like statues in the forest’s green shade, standing upright on their immense hind legs, their slender forearms with their three-clawed hands held beneath. This was a pack of five females, not quite fully grown but nevertheless each of them was ten meters long and weighed more than two tons. Allosaurs were not interested in runtish juveniles. They had targeted a fat male diplo, like themselves just a little short of full maturity. As the herd milled, distracted by the commotion of the squabbling orniths, that fat male got himself separated from the protective bulk of the herd.

The five allos attacked immediately, on the ground, in the air. With hind claws like grappling hooks they immediately inflicted deep, ugly wounds. They used their strongly constructed heads like clubs, battering the diplo, and teeth like serrated daggers gouged at the diplo’s flesh. Unlike tyrannosaurs they had big hands and long, strong arms they used to grab on to the diplo while dismembering him.

Allosaurs were the heaviest land carnivores of all time. They were like upright, meat-eating, fast-running elephants. It was a scene of immense and ferocious carnage.

Meanwhile the diplo herd was fighting back. The adults, bellowing in protest, swung their huge necks back and forth over the ground, hoping to sweep aside any predator foolish enough to come close. One of them even reared up on her hind legs, a vast, overpowering sight.

And they deployed their most terrible weapon. Diplo tails lashed, all around the herd, and the air was filled with the crackle of shock waves, stunningly loud. A hundred and forty-five million years before humans, the diplos had been the first animals on Earth to break the sound barrier.

The allosaurs retreated quickly. Nevertheless one of them was caught by the tip of a supersonic whip-tail that crashed into her ribs. Allosaurs were built for speed and their bones were light; the tail cracked three ribs, which would trouble the allosaur for months to come.

But the attack, in those few blistering moments, had been successful.

Already one great leg had collapsed under the male diplo, its ripped tendons leaving it unable to sustain its share of the animal’s weight. Soon his loss of blood would weaken him further. He raised his head and honked mournfully. It would take hours yet for him to die — the allosaurs, like many carnivores, liked to play — but his life was already over.

Gradually the crackle of whiplash tails ceased, and the herd grew calmer.

But it was the big matriarch who delivered the last whiplash of all.

When the allosaurs had attacked, the orniths, suddenly united in terror, had fled the clearing. Now Listener and Stego skulked side by side in the forest-edge scrub, their unused weapons in their hands, their hunt thwarted. But it wasn’t all bad news. When the allos were done feeding there might be meat to be scavenged from the fallen diplo.

Then came that last whiplash. The huge diplo’s tail landed clean across Stego’s back, laying his skin open to the bone. He screamed and fell, tumbling out into the open, his mouth agape. The slit pupils in his eyes pulsed as he gazed up at Listener.