By Georgie Hatt-Cook
The extinction of the dinosaurs was most probably caused by an asteroid hitting the Earth - but what would have happened if the giant space rock had missed?
For a long time it was thought that dinosaurs were a lumbering, cold-blooded extinction just waiting to happen. Even the word dinosaur has come to mean something that has outlived its time.
The scientific argument was that as cold-blooded creatures, dinosaurs would not have stood a chance of surviving an ice age.
"According to the first imaginings of palaeontologists and the general public about dinosaurs, we thought of them as reptiles," says Kristi Curry-Rogers, from the Science Museum of Minnesota.
"'Reptile' is a word which comes with a lot of other connotations, like cold-blooded, slow-moving, sprawling, scaly skins, kind of stupid."
But more recent discoveries, such as dinosaur fossils in both polar regions, reveal that these animals were far more adaptable than previously thought.
Dr Curry-Rogers has analysed fossilised bones from Late Cretaceous (65-99 million years ago) dinosaurs and found them to have more in common with mammals and birds than reptiles.
The evidence points to them being fast-growing and, crucially, that at least some of them were warm-blooded to some degree.
"They were perfectly well-adapted to deal with the problems of maintaining a body temperature," Dr Curry-Rogers told the BBC's Horizon programme.
In other words, some of the dinosaurs were more than equipped to survive almost anything that the evolving planet had to throw at them.
"They were the superlatives; they were the biggest, the heaviest, the meanest, the longest. You name it, dinosaurs were it," says fellow palaeontologist Phil Currie, from the University of Alberta in Canada, who has access to one of the richest areas of dinosaur research in the world.
"The badlands of Alberta clearly show that at the end of the Cretaceous, dinosaurs were extremely successful still," says Professor Currie, who points to dozens of different dinosaur species living in that one environment at the same time.
Had the asteroid missed, he believes, dinosaurs would have continued to dominate.
"We wouldn't have the modern animals that we're used to. Giraffes and elephants and so on; they just wouldn't have evolved because dinosaurs would still be here," says Professor Currie.
Instead of elephants, there would be large plant-devouring sauropods. In place of lions on the plains of Africa would be tyrannosaurs.
Adaptable dinosaurs had it all covered. Dinosaurs could have comfortably colonised many environments, from polar conditions to regions of rivers and forests, jungle and deserts.
A world with dinosaurs in it would be at the expense of most, if not all, of the mammals that we are familiar with today - and all that we rely on them for. No cows, no sheep, no cats equal no milk, no leather, no wool, no domestic companionship.
But milk aside, there could be perfectly suitable dino-substitutes of all kind. A Protoceratops could be as farmable as a pig with the bonus of providing eggs. And an amenable Heterodontosaurus might make a perfect pet. Great with children.
They could even have adapted to current-day habitats, dining on suburban dustbins.
Something like us
Perhaps the most advanced dinosaur at the time of the extinction was the Troodon which was "as cunning as a fox", according to palaeontologist Larry Witmer of Ohio University.
They were small, upright, bi-pedal dinosaurs which lived in large groups. By studying the brain cavity, Witmer has found evidence they possessed good vision and even potentially had a brain structure compatible with problem-solving.
"If Troodon were around today, co-existing with humans, we'd probably call it a pest," says Professor Witmer.
With its substantial brain, long grasping hands and big eyes, could Troodon have evolved to become more intelligent?
It's unlikely mammals and dinosaurs could have shared power
Evolutionary palaeo-biologist Dr Simon Conway Morris believes they could even have evolved along the lines of primates or humans.
"The human is extraordinarily well designed," he says. The whole arrangement is actually designed for a particular mode of life, which, as you can see looking around us, is incredibly successful.
"If it's such a good solution for us, is it so difficult to imagine it could be a good solution for a dinosaur, therefore a 'dinosauroid'?"
But most palaeontologists see the dinosauroid as an insult to dinosaurs.
"Dinosaurs probably would have continued along their dinosaurian trajectory, getting bigger brains and bigger eyes," says Kristi Curry-Rogers.
"But I doubt seriously that any dinosaur would ever end up looking like a person, and it is fairly arrogant to think that the end point of all evolutionary trajectories should sort of emulate human beings."
If the asteroid had missed, there probably wouldn't be humans here today either to find out how it would have turned out.
The impact that ended the golden age of the dinosaurs 65 million years ago made for an extremely bad dinosaur day but it was also a very good mammal day.
Horizon: My Pet Dinosaur is broadcast on BBC Two on Tuesday 13 March at 2100GMT