What is called dinosaur?

Dinosaur, (clade Dinosauria), the common name given to a group of reptiles, often very large, that first appeared roughly 245 million years ago (near the beginning of the Middle Triassic Epoch) and thrived worldwide for nearly 180 million years. Most died out by the end of the Cretaceous Period, about 66 million years ago, but many lines of evidence now show that one lineage evolved into birds about 155 million years ago.

Abundant fossil bones, teeth, trackways, and other hard evidence have revealed that Earth was the domain of the dinosaurs for at least 230 million years. But so far, not a single trace of dinosaur remains has been found in rocks younger than about 66 million years. At that point, as the Cretaceous period yielded to the Paleogene, it seems that all nonavian dinosaurs suddenly ceased to exist.

Along with them went fearsome marine reptiles such as the mosasaurs, ichthyosaurs, and plesiosaurs, as well as all the flying reptiles known as pterosaurs. Ancient forests seem to have flamed out across much of the planet. And while some mammals, birds, small reptiles, fish, and amphibians survived, diversity among the remaining life-forms dropped precipitously. In total, this mass extinction event claimed three quarters of life on Earth.

(Read E.O. Wilson’s Britannica essay on mass extinction.)

The name dinosaur comes from the Greek words deinos (“terrible” or “fearfully great”) and sauros (“reptile” or “lizard”). The English anatomist Richard Owen proposed the formal term Dinosauria in 1842 to include three giant extinct animals (Megalosaurus, Iguanodon, and Hylaeosaurus) represented by large fossilized bones that had been unearthed at several locations in southern England during the early part of the 19th century. Owen recognized that these reptiles were far different from other known reptiles of the present and the past for three reasons: they were large yet obviously terrestrial, unlike the aquatic ichthyosaurs and plesiosaurs that were already known; they had five vertebrae in their hips, whereas most known reptiles have only two; and, rather than holding their limbs sprawled out to the side in the manner of lizards, dinosaurs held their limbs under the body in columnar fashion, like elephants and other large mammals.

The premise of the Jurassic Park film franchise is an elegant one: that dinosaur DNA, preserved in the guts of ancient mosquitoes trapped in amber, could be used to clone these animals and bring them back to life using the latest genetic technology. It's an ingenious idea, but one that remains deeply within the realms of science fiction, at least for now.

So, given that we're unlikely to see dinosaurs roaming our zoos and safari parks anytime soon, how do scientists determine how these amazing animals fed, ran, bred and died

How old is that dinosaur?

By carefully cutting thin sections through dinosaur bones and putting them under the microscope, we can age dinosaurs and work out how fast they grew to adulthood. This is done by counting the growth lines in the bone walls which, much like tree rings, were laid down each year.

How do we know what dinosaurs looked like?

Some dinosaur fossils are so spectacularly preserved they include evidence of soft tissues like skin, muscle and internal organs. These give vital clues on dinosaur biology and appearance.

Birds are dinosaurs

The recognition that birds are dinosaurs is an idea that has been proven beyond reasonable doubt in the last 20 years, and also gives us new clues on what extinct dinosaurs might have been like.

Recreating ancient dinosaur features in birds

Some scientists are currently attempting to switch on long-dormant genes in living birds that might have been responsible for producing the teeth, characteristic skull shapes and long tails of their dinosaur ancestors.

Early birds had teeth, as shown here in this palaeoart reconstruction of Patagopteryx, which lived around 80 million years ago. Scientists have worked out which genes were responsible for forming the teeth. They are still present in birds today, but are dormant. © FunkMonk (Michael BH), licensed under CC BY-SA 3.0, via Wikimedia Commons

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These efforts are already producing impressive findings, such as genes that can transform bird beaks back into more dinosaur-like snouts and those that can stimulate hens to form teeth.

This work is undoubtedly interesting - and it has implications for human health. Some of the key genes are also important in regulating various strains of human cancer, so this pure science project on dinosaur genes is providing insights that could improve human health too.

Moreover, this type of genetic manipulation, based on the DNA of living dinosaurs, is probably the closest we will ever get in reality to a Jurassic Park scenario.