An early illustrated reconstruction of Megalosaurus

In this early reconstruction of two Megalosaurus, drawn by English artist and sculptor Benjamin Waterhouse Hawkins, the dinosaurs are depicted as having postures similar to that of large modern mammals, such as hippopotomuses.

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Dinosauria: how the 'terrible lizards' got their name

Until 1842, no one had heard of the word 'dinosaur'.

But when acclaimed anatomist Richard Owen grouped three pre-historic animals with curious features in common, he changed the way the world thought about fossil reptiles.

Humans everywhere have probably been stumbling upon dinosaur bones for millennia without knowing what they were. These rogue fossil discoveries may even have been one of the inspirations for dragons.

It hasn't been an easy road for dinosaurs - for about 80 years they were dismissed by science as not a real group. But since the 1970s the 'terrible lizards' have clawed their way back in favour with palaeontologists.

Where did dinosaurs come from?

Discovering Dinosauria

Sir Richard Owen (1804-1892) was one of the most famous comparative anatomists of his time. Not only did he instigate the separation of the British Museum and its expanding natural history collection, thus founding the Natural History Museum, he also tutored the children of the royal family in science and was famed for feuding with scientific contemporaries, most notably Charles Darwin. 

Sir Richard Owen was the first Superintendent of the Natural History Museum, from the day it first opened its doors in 1881 until he retired in 1883.

In the early 1800s a number of fossil discoveries were made in southern England, including Megalosaurus (described by William Buckland in 1824) and Iguanodon and Hylaeosaurus (described by Gideon Mantell in 1825 and 1833 respectively). On analysing this trio of finds, Owen noticed shared characteristics.

In Iguanodon and Megalosaurus, he could see that vertebrae at the base of the spine - now known as the sacrum - had fused together during the animals' lifetimes. From fossil fragments, Owen determined that Hylaeosaurus also had this characteristic. 

Richard Owen's diagram of Megalosaurus, showing the fused sacral vertebrae. This illustration was published in Geology and Inhabitants of the Ancient World in 1854.

From this observation and other similarities, he placed the animals in a new group, as detailed in his Report on British Fossil Reptiles. His initial speech to the British Association, on which the report was based, was delivered in July 1841 and allegedly lasted two hours.

It was in his report published in 1842 that Owen first used the term Dinosauria. 

The holotype of Hylaeosaurus, described by Gideon Mantell in 1833. This was one of the three reptiles on which Richard Owen based Dinosauria. © Sven Sachs, Jahn Hornung/ Wikimedia Commons (CC BY 2.5)

A dinosaur designer

'Dinosauria' is rooted in Greek and frequently quoted as meaning 'terrible lizard'. But in coining the term in his report, Owen refers to dinosaurs instead as 'fearfully great', acknowledging their large size - significantly surpassing that of any living reptile.

Although the fossil skeletons were far from complete, palaeontologists of the time attempted to work out the size of dinosaurs by scaling up living lizards. According to their estimates, some dinosaurs were 60 metres long.

Owen was sceptical of these massive sizes. Instead he measured individual vertebrae and estimated their total number based on those of living crocodiles. This yielded more realistic lengths - around nine metres for Megalosaurus and Iguanodon

A watercolour illustration of three ancient reptiles by Benjamin Waterhouse Hawkins


While other scientists continued to use modern-day lizards as a model, with dinosaurs featuring legs that splayed out from the sides of their bodies, Owen was sure that the animals' legs would have been directly under their bodies to support their large sizes. He depicted them in a similar fashion and proportion to modern quadrupedal mammals.

Subsequent research based on Owen's idea for dinosaur posture is now one of the key features used to differentiate them from non-dinosaurian reptiles.

In his proclamation of the new group Dinosauria, although referring to the animals as fossil lizards, Owen stated they were similar to pachydermal mammals. Though this taxonomic group is no longer used, it represented a group of large animals with thick skin, such as elephants and hippopotamuses.

This goes some way to explain why the stocky 1850s dinosaur models at Crystal Palace, for which Owen was a scientific advisor, have a hint of rhinoceros about them. 

One of the reptile sculptures at Crystal Palace. Richard Owen was a scientific advisor on the form the models should take, resulting in the mammalian look of these nineteenth century dinosaur reconstructions.

The first dinosaur discovery

Megalosaurus is thought to be the first dinosaur described in scientific literature. But based on a fossil uncovered in the seventeenth century, it could have been known by a different name.

In the mid-1600s, a fossil bone was acquired by Dr Robert Plot, the first keeper of Oxford's Ashmolean Museum. He noted that it looked almost exactly like the lower part of a human femur. He included an illustration of the peculiar fossil in his 1677 book The Natural History of Oxford-shire - but the piece lacked a name.

The fossil was uncovered in the Oxfordshire parish of Cornwell. Although Plot didn't detail the rock type that the fossil was found in, quarries in that part of the UK consist of limestone dating to the Mid Jurassic.

Dr Robert Plot (1640-1696) was an English naturalist and the first keeper of Oxford's Ashmolean Museum

English physician Richard Brookes reviewed Plot's work in 1763 in his compilation of books, A New and Accurate System of Natural History. In volume five he dubbed Plot's fossil Scrotum humanum, simply stating that 'stones have been found exactly representing the private parts of a man'.

But as it was determined many years later, neither Plot nor Brookes knew what the fossil really was.

S. humanum isn't a name used today - although it could have been. The Linnaean system for scientific naming began in 1758, five years before the bone was described. Plot's fossil was later thought to be from Megalosaurus. As Scrotum had been described 60 years earlier, Megalosaurus could have been considered a synonym.

However, Plot's fossil is now lost and scientists today can't confirm whether it was Megalosaurus. In the 1990s the International Commission on Zoological Nomenclature determined that Scrotum humanum did not constitute a valid scientific name. 

Plot's illustration of the unnamed fossil that he speculated could be from a giant human (Fig. 4). It was later thought to be from Megalosaurus.

Brookes's descriptive name was therefore officially disregarded, and Megalosaurus retained its claim to fame as the first official dinosaur.

A close call for the dinosaurs

Owen's Dinosauria almost met an end in the late 1800s. Increasing fossil reptile discoveries were being made and palaeontologists began searching for ways to tie the animals together.

Two key groups emerged: the ornithischians ('bird-hipped') and saurischians ('lizard-hipped'). In 1888, palaeontologist Harry Seeley published a paper on these two new groups and denounced Owen's Dinosauria, stating that it 'has no existence as a natural group of animals'.

The concept of the clade Dinosauria drifted out of favour. It was considered nothing but a miscellany of only distantly related reptiles. 

An illustration of a Lower Jurassic Period scene (about 175 - 200 million years ago) showing an ornithiscian Megalosaurus (top) and saurischian Scelidosaurus

But evidence gathered in the 1970s, including that birds evolved from a group of dinosaurs, showed that Dinosauria was not an obsolete group after all. Led primarily by American palaeontologists Robert Bakker and John Ostrom, the 'dinosaur renaissance' began, bringing dinosaurs back into the limelight, to be considered a valid group by palaeontologists once again.

Today, Museum scientists Prof Paul Barrett and Dr Susie Maidment are among those continuing to investigate the dinosaur family tree and how dinosaurs evolved.