If dinosaurs weren't actually that heavy, what else don't scientists know? | Paul Barrett

We paleontologists shouldn't be afraid to admit that we are still in the dark when it comes to some aspects of dinosaur life

Jurassic Park fans of all ages are in for a bit of a shock: experts from Manchester University have found that dinosaurs, usually portrayed as enormous, earth-shaking monsters, may have been much lighter than previously thought.

But this is merely the latest in a long history of palaeontologists admitting that there is a speculative element to their field. Dinosaurs have fascinated us since the first tantalising fragments of their bones emerged from the quarries of southern England in the early 1800s, but the scientists working on these remains were faced with a perplexing, difficult task: how to reconstruct the appearance and behaviour of animals that had been dead for hundreds of millions of years, with no obvious living equivalents.

Nearly 200 years after these initial discoveries, palaeontologists are still trying to answer this same question. Our views on dinosaurs have evolved dramatically in that time, incorporating new finds and technologies beyond the wildest imaginings of the early frock-coated savants who, working by candlelight, had eagerly chipped away at their latest discoveries with hammer and chisel.

Initially, dinosaurs were viewed as scaled-up iguanas, a view perpetuated by Hollywood before the advent of CGI: who can forget the poor lizards dressed up in fake frills and horns, chasing an outraged Claude Rains in The Lost World? Based on only individual bones, Victorian scientists calculated that if dinosaurs had the same proportions as iguanas, then monsters over 200ft long were once roaming the Cotswolds and South Downs. This view held sway until the first complete dinosaur skeletons were found, first in Europe and then in staggering quantities from the American west.

A dinosaur bone rush in the 1870s had a lasting effect on all subsequent impressions of dinosaur appearance, revealing for the first time a set of animals that were to become familiar from movies and museum displays, including Stegosaurus, Allosaurus and Diplodocus. These complete skeletons showed that dinosaurs possessed an amazing variety of body shapes and sizes, from lithe, two-legged meat-eaters to ponderous long-necked herbivores, but that none rivalled the colossal, nightmarish visions imagined only a few years earlier. However, although no longer reconstructed as giant lizards, the biology of the "new" dinosaurs was still viewed through the lens of living reptiles, and they were reconstructed as lumbering brutes, an evolutionary sideshow, doomed to ultimate extinction.

For much of the 20th century, this perception invaded scientific and public imaginations. Dinosaurs were the ultimate example of hubris, icons of failure, their faded glory eclipsed by those smart little mammals that were our own early ancestors. However, the 1970s marked the onset of a revolution in our understanding of dinosaurs, the so-called "dinosaur renaissance". This gave us our modern view of dinosaurs as highly successful and dynamic social creatures with complex behaviours. Far from being an evolutionary cul-de-sac, dinosaurs gave rise to the birds, and we now have fossils showing that dinosaurs were the first to sprout those most avian of features – feathers. All of these changes come from the efforts of palaeontologists scouring the rocks for new discoveries and leading the way in applying advanced technologies like CT-scanning and engineering analyses to old bones in order to look deeper and in more detail than ever before.

These advances mean that we can now deduce how well some dinosaurs could hear or smell, and in other cases even what some of the original colours of dinosaurs might have been. Mammals and birds are now viewed as more appropriate models for dinosaur biology, offering many new insights into their evolution and behaviour.

We are still in the dark when it comes to some aspects of dinosaur life: how exactly did they die out? Why did some of them prosper while others were short-lived? What were the functions of bizarre features, like Spinosaurus's "sail". And which factors led to their runaway evolutionary success? For now, there are still plenty of things we know nothing about – and scientists shouldn't be afraid to say so.

• This article was amended on 11 June 2011. The original referred to a stegosaurus's sail. This has been corrected. It was further amended on 21 June 2011, correcting the headline and subheading, which originally read: "If dinosaurs weren't actually that big, what else don't scientists know? News that dinosaurs were not the lumbering beasts that Jurassic Park led us to believe shows that science is not infallible"

Contributor

Paul Barrett

The GuardianTramp

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