Darren Naish, a vertebrate palaeontologist in Southampton, UK, says that perhaps in our alternative timeline the speedy, grass-mowing dinosaur equivalents would be descendants of horned relatives of Triceratops or bipedal, beaked herbivores akin to Hypsilophodon.
“Dinosaurs already come with a huge set of evolutionary advantages that it took mammals a long time to evolve,” he adds, and would have a head start at adapting to grasslands. Duck-billed hadrosaurs had ‘batteries’ of up to 1000 teeth in their jaws, as opposed to the 40-odd teeth a horse has, so could have made short work of grinding grasses.
Dinosaurs also had better eyesight than mammals, with increased colour vision, and may have been more adept at spotting danger. Horses and cows have flattened muzzles useful for cropping tough, low-lying vegetation, so duck-bills and sauropods might also have developed squared off snouts, and sauropod necks might have shortened to aid grazing at their feet.
Even closer to the present day, dinosaurs would have had to deal with the various ice ages of the past 2.6 million years. But we know that Cretaceous dinosaurs were living above the Arctic Circle. “Maybe in cooler places you would see things with thick and elaborate pelts, covered in fuzz and feathers all the way down to the tips of their toes and tails,” says Naish.
“It wouldn’t have been difficult for a ‘woolly’ tyrannosaurus or dromaeosaur relatives of Velociraptor to evolve,” adds armoured dinosaur expert Victoria Arbour of the Royal Ontario Museum in Canada. “Maybe we could have even had shaggy and woolly ceratopsians, ankylosaurs, or hadrosaurs.”
There are other adaptations common today but rare in dinosaurs. Burrowing for example, says Paul Barrett, a palaeontologist at the Natural History Museum in London. “It’s odd that dinosaurs didn’t really do it, as it’s a common way of life among lizards and snakes.” Given more time, some dinosaurs might have become subterranean specialists – the scaly or feathery equivalent of mammalian moles.