What if dinosaurs were still alive? You asked Google – here’s the answer | Brian Switek

Dinosaurs dominated terrestrial life on this planet for over 130m years. If it hadn’t been for a wayward asteroid, the reign of Tyrannosaurus rex and its ilk could have lasted for at least another 66m. In fact, let’s presume for a moment that the cosmic boulder that ended the Cretaceous period totally missed Earth and allowed dinosaurs to survive to the present. What would life be like now?

‘Even though mammals thrived in the shadow of the dinosaurs, they did so at small size.’ An artist’s impression of a rodent-like multituberculate.

A dino-maniac wouldn’t be able to ask for a better scenario. Like many young fossil fans, I used to daydream about riding an Apatosaurus to school or having a Triceratops friend in the backyard, grocery bills and destruction to public property be damned. But I am sorry to now tell my inner child that such a scenario would never be possible for two very important reasons.

Life evolves. It has ever since the very first living thing originated on the planet, and it continues even now. Dinosaurs were no exception to this. How else could we have got such a fantastic diversity of strange shapes, from the armour-clad ankylosaurs – practically living tanks – to the fearsome tyrannosaurs, long-necked sauropods, fleet-footed raptors, duck-faced hadrosaurs, and all the rest?

Given a 66m year stay of execution, dinosaurs would have continued to evolve. The species that thrived at the end of the Cretaceous – think Triceratops and its neighbours – would have left descendants that would have kept changing with time. So if dinosaurs survived to the time we know as 2017, they would be totally different than anything we know from the fossil record. There might even be new groups of dinosaurs that didn’t exist during the Mesozoic era. The present Earth wouldn’t be a hodgepodge of old favourites, but an entirely different mix of unknown dinosaurs.

The sad thing is that we wouldn’t be around to see it.

Our fossil ancestors and relatives make the point clear. Even though mammals thrived in the shadow of the dinosaurs – evolving into forms similar to beavers, flying squirrels, aardvarks, and more – they did so at small size. The largest Mesozoic mammal was about the size of a badger. And even though the very first primates had evolved by the end of the dinosaurian reign, they had more in common with a tree shrew than with you or me. If dinosaurs had somehow been able to keep their claw grip on the global ecology, they would have undoubtedly continued to influence mammalian evolution, too. The evolutionary story of our ancestors would have been irrevocably altered by the change, and it’s a near-certainty that humanity would never have come to exist. We simply wouldn’t be around to see the new dinosaurs.

But this is all speculation. The fact is that we already know what life would be like if dinosaurs were still alive. Birds are living dinosaurs. They originated in the Jurassic and flourished with their non-avian relatives. The only reason we think of birds as different is because they are the dinosaurs that survived. A sparrow or starling may not be as dramatic as a 33-metre Supersaurus or as strange as a trundling Stegosaurus, but they truly are dinosaurs that have made it to the present and will likely still be here when we’re gone. For now, we have the best of both worlds. We are here, and so are the dinosaurs.

‘We already know what life would be like if dinosaurs were still alive. Birds are living dinosaurs.’ A red kite.