Mantell's eureka moment came when he saw the jaw and teeth of an modern iguana preserved in the Hunterian Museum in London. The marine plant eating reptile's teeth were remarkably similar to

Mantell's fossil teeth from Sussex.

Mantell's eureka moment came when he saw the jaw and teeth of an modern iguana preserved in the Hunterian Museum in London. The marine plant eating reptile's teeth were remarkably similar to

Mantell's fossil teeth from Sussex.

Among the bones he had amassed was the broken section of a thigh bone that was 6o cm (25 in) in circumference. With his anatomical knowledge Mantell understood the logic behind the comparative anatomy practised by Cuvier and the idea of scaling up from measures on individual bones to assess the overall size of an extinct animal. When he did the calculations with the figures from his fossil thigh bone, Mantell came up with an animal having the bulk of an elephant and an astonishing length of over 10 m (30 ft), far bigger than any other fossil creature known at the time.

The year 1822 saw the publication of Mantell's book Fossils of the South Downs, the results of his investigations into the geology of Sussex, with illustrations of strata and fossils engraved by his wife. Included was reference to 'the teeth, ribs, and vertebrae of a gigantic animal of the Lizard tribe'. Mantell hoped desperately that this book would gain him entrée into the select world of the Geological Society, but his hopes were not fulfilled. When he took the fossil teeth to a meeting of the Society, the general opinion of the 'experts' was that

Jean Baptiste Julien D'Omalius d'Halloy, 1783-1875, an aristocratic Belgian who devoted himself to geology from 1804-14 and compiled a geological map of France before becoming Governor of the province of Namur (1814), member of the Belgian Senate and President of the Belgian Academy of Sciences.

they belonged to some large fish or a more recent mammal from the Diluvium. Sales of the book were another disappointment; they did not nearly cover the cost of publication and Mantell was left with a bill for £300, which was an awful lot of money in those days.

The same year saw the Chalk strata with the older greensands and clays beneath grouped into a distinct system called the Cretaceous or rather 'Terrain Crétacé' by the Belgian geologist J. J. D'Omalius d'Halloy. The name was anglicised to Cretaceous in the same year by two English geologists, William Conybeare and William Philips. For many years different parts of the pre-Tertiary rock succession had been studied in Europe, where there are extensive outcrops extending from Sweden and Denmark through northern Germany, Poland and the low countries of the Netherlands, Belgium and into France.

D'Halloy was employed by Baron De Monbret, head of the French bureau of statistics, to gather information on the rocks in France and to make a map of their distribution. During D'Halloy's evaluation of previously known information, he concluded that of the five groups of strata recognised within the old broad division of Secondary rocks, a Terrain Crétacé could be usefully recognised. As stated in the description accompanying his map, this is 'the chalk formation, such as I have determined it ... comprising the tuffas, sands and marls, which occur beneath the true chalk, [and] constitutes the third group [of the Secondary rocks]'.

William Phillips, 1775-1828, English printer, bookseller and geologist who co-authored (with W. D. Conybeare) Outlines of the Geology of England and Wales (1822) and was one of the founder members of the Geological Society of London.

In 1823, with Charles Lyell's help, Mantell managed to get a paper containing his ideas on the Cretaceous Tilgate Forest strata read at a meeting of the Geological Society, but then its publication was held up for three years, perhaps because his ideas clashed with those of senior members of the Society. Lyell even took one of Mantell's fossil teeth to Paris to get Cuvier's opinion, only for the great anatomist to dismiss it as merely that of a rhinoceros. Although Cuvier later had second thoughts, the only message that got back to Mantell was Cuvier's singularly unenthusiastic initial one, much to Mantell's disappointment and dismay. After all his hard work, which not only took up his time but also meant neglect of his medical practice and his family, his hopes of rising in the scientific world seemed to be dashed.

When Mantell heard that Buckland was due to lecture at the Geological Society in London on some saurian fossils from Stonesfield in Oxfordshire, Mantell determined to be there. His intervention in the discussion alerted Buckland to the potential competition coming from the Sussex finds and Buckland tried to steal Mantell's thunder by incorporating discussion of the Sussex bones and an illustration of them in his own paper. Luckily for Mantell, the Society's publication committee rapped Buckland, their president, over the knuckles and stopped him from going too far in the interest of fair play. Even so, Buckland did mention that Mantell's Sussex giant must have been twice the size of the Oxford one and pumped the 'reptile from Cuckfield' up to between 'sixty to seventy feet', but he did not agree with Mantell that it was a plant eater.

Mantell determined to try his luck again with Cuvier, sending him tooth specimens and drawings of the other fossils. This time Cuvier acknowledged their curious form and at last asserted his true acuity by concluding that Mantell might have a new herbivorous reptile on his hands. Encouraged at last, Mantell visited the Hunterian museum in London to see if he could find anything resembling his fossil specimens. He found nothing among the fossils, but luckily a well-informed assistant curator, Samuel Stutchbury, saw that the fossil teeth possessed a passing semblance to those of living iguana. Stutchbury was familiar with iguana specimens from the West Indies because he had recently preserved one from Barbados in a bottle of spirit for the museum collection.

It was just the breakthrough that Mantell needed. The iguana's strange, leaf-shaped teeth with serrations along the edges and flat wear surfaces were an adaptation to its plant-eating habits. The only major difference was in the size: the fossils were some 20 times bigger than those of the living beast, which was only a metre long. Mantell quickly recalculated his sums and concluded that 'his' beast must have been at least 20 m (over 60 ft) long. He proposed that it be called Iguana-saurus, but was advised by the Reverend William Conybeare, an expert on fossils with a classical education, that Iguanoides, meaning 'like an iguana', or Iguanodon, meaning 'iguana tooth', would be better. Mantell chose the latter and so the beast has been named ever since. Cuvier's mention of Mantell and his curious new beast in a new edition of one of his books on fossils ensured that Mantell's star was at last ascending in the scientific galaxy.

In 1825 his description of Iguanodon was read at a meeting of the prestigious Royal Society, and later that year the 35-year-old Mantell was elected a Fellow, thus giving him an equivalent scientific status to the members of the Geological Society who had been so chary about recognising his work. But it was nearly 10 years before Mantell had any really significant new material with which to flesh out his Iguanodon. The basic problem was that fossils of such beasts, now known to be land-living dinosaurs, are uncommon within the predominantly shallow marine strata of the south of England. It was only because land lay not far to the north when the Wealden strata were laid down and rivers draining those landscapes occasionally washed the remains of dinosaurs and plants into the shallow coastal deposits.

Then in May 1834, Mr Bensted, a Kent quarry owner, wrote to Mantell telling him of a new find of giant bones that had been unearthed by his workers in a Wealden stone quarry near Maidstone in Kent. Mantell's luck was in again: the rock slab included some of the peculiar leaf-shaped Iguanodon teeth and a jumble of other bones belonging to the animal that he had not seen before. Mantell's first problem was the fact that Bensted, being a businessman, had realised the potential monetary value of the find and was determined to get as much as he could for it. Only through the intervention of some wealthy friends, who bought the specimen and presented it to him, was Mantell able to work on the new slab, which came to be known as the 'Mantell-piece'.

Mantell ignored his patients and spent time painstakingly preparing this rock slab to reveal the fossil bones of the giant reptile he was to name as Iguanodon, one of the first dinosaurs to be described.

Mantell spent long hours preparing the fossil, laboriously chipping the hard rock matrix away from around the petrified bones while trying not to damage them. He made quite a good job of it, considering the fractured nature of many of the bones. For the first time, he had part of an actual single skeleton with backbones, ribs, part of the pelvis, foot bones and a single conical spike or horn-shaped bone about 15 cm long.

Again, Mantell tried scaling up measures from the bones and found that the beast was getting bigger and bigger. Its shoulder blade measured some 30 in, which was 20 times bigger than that of the iguana, giving Iguanodon an estimated length of 100 ft (30 m). The Geological Society at last recognised MantelPs endeavours and awarded him its prestigious Wollaston Gold Medal in 183$; the only other recipient had been William Smith.

By this time Mantell and his family were established in fashionable Brighton and he had been doing well with his medical practice, but as he spent more and more time on his geological studies the practice began to suffer. Word was that Dr Mantell was more interested in his fossils than his patients and, whether true or not, the damage was done to such an extent that he had to sell, first his stocks

Sir Richard Owen, 1804-92, renowned English anatomist who studied in Edinburgh, became conservator in the Hunterian Museum (1827-56), its first professor of comparative anatomy, then superintendent of natural history in the British Museum (1856-83) and tutor to the Royal family (1860-4). He was knighted in 1884.

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