A quarter of a century ago, Dale Russell depicted an ‘intelligent dinosaur’ to get people thinking, and succeeded far beyond his wildest expectations. The large-eyed, eerily reptilian “dinosauroid” caught the attention of media around the world. So many reporters called the softly-spoken palaeontologist that he stopped answering his phone at the Canadian Museum of Nature in Ottawa. Today the sculpture is stored away in the recently renovated museum, but the idea lives on.
The dinosauroid began as a thought experiment at a time when scientists recognised that dinosaurs were not as dumb as early palaeontologists had thought. Russell noted that measurements of fossil dinosaurs showed steady increases in the encephalisation quotient (EQ) over millions of years. The EQ is a relative measure of an animal’s brain weight compared to that of an average animal of a related species and same body weight — so an EQ of 2.0 means that animal has a brain twice the weight of other similar animals its weight. Russell pondered how the trend might have affected non-avian dinosaurs had they survived to the present day. Could they have become intelligent, like us?
We tend to think intelligence is a good thing that contributed to the evolutionary success of our species. What’s good for humans should then have been good for dinosaurs. Indeed, recent research has revealed intelligent behaviour in birds, the closest living relatives of dinosaurs. Yet some palaeontologists echo the late U.S. evolutionary biologist Stephen Jay Gould, who doubted natural selection has any inherent preference for what we call intelligence. As is typical in palaeontology, both sides make a strong case when it comes to the dinosauroid.
Russell’s starting point was a fleet, 60 kg, two-legged predator called Troodon (Troodon formosus), which lived about 75 million years ago in Canada. He discovered the first Troodon skull, which revealed that its brain, relative to its body size, was unusually large for a dinosaur. To ascertain just how big its brain was compared to other dinosaurs, he calculated its EQ. What he found was telling.
Russell calculated that Troodon had an EQ that was small compared to modern humans, but was nearly six times larger than the known dinosaur average. Russell extrapolated that if Troodon had survived and retained the same body size, its modern-day descendants might have a brain volume of 1,100 cm3 — comparable to that of a small human.
Troodon also had a couple of the advanced traits that may have given ancestral primates a leg-up in the mammalian evolutionary race. The placement of its large eyes suggests that it had binocular vision, and the outer two of its three fingers also appear to be opposable.
Russell decided that evolving a big brain would have reshaped the dinosauroid. The back of its skull would have expanded to house the enlarged, bird-shaped brain. The snout would have shrunk and the teeth would have disappeared, leaving a short, turtle-like beak. To support the heavy head, Russell replaced the dinosaur’s long, horizontal neck with a short, upright one. That, in turn, required an upright posture, which would have made plausible the use of tools and weapons.
As the body became upright, he expected the tail to diminish until it disappeared, as it did with our great-ape relatives. He also anticipated that the dinosauroid would retain reptilian traits of scaly skin and the lack of external genitals, but to have evolved live birth for its large-headed young.
Wanting others to ponder the possibilities, Russell commissioned artist and taxidermist Ron Sequin to sculpt a 1.3-metre-tall dinosauroid for display beside a life-sized model of Troodon. Now at the North Carolina Museum of Natural Sciences in Raleigh, U.S., Russell looks back on his thought experiment and says “it was fun”. At the time though, he was overwhelmed by media attention. He never expected the dinosauroid to be remembered for such a long time.
A younger generation of palaeontologists remain intrigued by the idea, but think Russell’s dinosauroid needs updating. “The main problem was that it was much too human,” says Thomas Holtz, a dinosaur palaeontologist at the University of Maryland in College Park, U.S.
“I think it would have retained its tail,” and the largely horizontal body posture of a dinosaur even with a large head, he says. Holtz also maintains there’s no evidence to suggest Troodon-like dinosaurs increased in brain size during the tens of millions of years between their evolution and extinction.
On the other hand, a group closely related to Troodon not only survived but did increase their brainpower. We call them birds. And despite their reputation as birdbrains, advanced thinking has been observed in parrots and corvids. Grey parrots seem able to grasp aspects of number theory. Caledonian crows use sticks as tools. And most recently, western scrub jays were found to plan for the future by caching food when they expected to find nothing to eat the next morning.
These birds may have evolved intelligence to cope with living in complex 3-D environments (trees), like our primate ancestors, says Holtz. “They needed to process a lot of complex information. One consequence is that you have the ability to make lots of other connections.” However, he adds, “intelligence probably wasn’t the thing initially being selected for”.
Furthermore, while we might assume intelligence represents the pinnacle of an evolutionary tree, this may not be the case. “There is nothing inevitable about the evolution of big brains and/or intelligence,” says Darren Naish, a palaeontologist at the University of Portsmouth in England.
“If non-avian dinosaurs had continued to evolve, they probably wouldn’t have evolved human-sized brains,” Naish says. And even if they had evolved large brains, he thinks that, unlike Russell’s dinosauroid, smart dinosaurs would have retained feathers, powerful jaws or beaks, a horizontal body, and bird-like feet.
Holtz proposes that a Troodon descendant might have sacrificed some speed to evolve a big brain. “Otherwise I don’t think you would have to change terribly much.” The Troodon already had forelimbs with grasping hands, and Holtz expects it would have kept its tail and near horizontal body posture, in the way pachycephalosaur dinosaurs did, despite their big heads and skulls laden with solid bone.
So even if Troodon, or one of its dinosaur descendents, had evolved intelligence, they may not have looked much like humans at all. Yet it’s easy to imagine that the world would have been very different — and conspicuously devoid of humans — had the dinosaurs been given a chance to extend their evolutionary history rather than having it snuffed out
65 million years ago.