Dinosaur discovery: Iguanodon

Once you have found your fossil, it needs to be studied scientifically
in order to reveal its identity, its relationship to other known
organisms, as well as more detailed aspects of its appearance,
biology, and ecology. To illustrate a few of the trials and tribulations
inherent in any such programme of palaeontological investigation,
we will examine a rather familiar and well-studied dinosaur:
Iguanodon. This dinosaur has been chosen because it has an
interesting and appropriate story to tell, and one with which I am
familiar, because it proved to be the unexpected starting point
for my career as a palaeontologist. Serendipity seems to have a
significant role to play in palaeontology, and this is certainly true
for my own work.
The story of Iguanodon covers almost the entire history of scientific
research on dinosaurs and also the entire history of the science
now known as palaeontology. As a result, this animal unwittingly
illustrates the progress of scientific investigation on dinosaurs
(and other areas of palaeontology) during the past 200 years. The
story also reveals scientists as human beings, with passions and
struggles, and the pervasive influence of pet theories at times in
the history of the subject.
The first bona fide records of the fossil bones that were later to
be named Iguanodon date back to 1809. They comprise, among
indeterminable broken fragments of vertebrae, the lower end of a
large, very distinctive tibia (shin bone) collected from a quarry at
Cuckfield in Sussex (Figure 6). This particular fossil was collected
by William Smith (often referred to as the ‘father of English
geology’). Smith was then researching the first geological map of
Britain, which he completed in 1815. Although these fossil bones
were clearly sufficiently interesting to have been collected and preserved (they are still in the collections of the Natural History
Museum, London), no further study was made of them. The bones
languished unrecognized until I was asked to establish their
identity in the late 1970s.
Yet 1809 was a remarkably opportune moment for such a discovery
to be made. Things were happening in Europe in the branch of
science concerned with fossils and their meaning. One of the
greatest and most influential scientists of this age, Georges
Cuvier (1769–1832), was a ‘naturalist’ working in Paris and
an administrator in the Emperor Napoleon’s government.
‘Naturalist’ was, in these times, a broad category denoting the
philosopher-scientist who worked on a wide range of subjects
associated with the natural world: the Earth, its rocks and minerals,
fossils, and all living organisms. In 1808, Cuvier redescribed a
renowned gigantic fossil reptile collected from a chalk quarry at
Maastricht in Holland; its renown stemmed from the fact that it
had been claimed as a trophy of war during the siege of Maastricht
in 1795 by Napoleon’s army. The creature, originally mistaken for a
crocodile, was identified correctly by Cuvier as an enormous marine
lizard (later named Mosasaurus by the English cleric and naturalist
the Revd William D. Conybeare). The effect of this revelation – the
existence of an unexpectedly gigantic fossil lizard of a former time
in Earth history – was truly profound. It encouraged the search for,
and discovery of, other giant extinct ‘lizards’; it established, beyond
reasonable doubt, that pre-biblical ‘earlier worlds’ had existed; and
it also determined a particular way of viewing and interpreting such
fossil creatures: as gigantic lizards.
Following the defeat of Napoleon and the restoration of peace
between England and France, Cuvier was finally able to visit
England in 1817–18 and meet scientists with similar interests. At
Oxford he was shown some gigantic fossil bones in the collections
of the geologist William Buckland; these seemed to belong to
a gigantic, but this time land-living, lizard-like creature, and
they reminded Cuvier of similar bones that had been found in Normandy. William Buckland eventually named this creature
Megalosaurus in 1824 (with a little help from Conybeare).
However, from the perspective of this particular story, the really
important discoveries were not made until around 1821–2 and at
the same quarries, around Whiteman’s Green in Cuckfield, visited
by William Smith some 13 years earlier. At this time, an energetic
and ambitious medical doctor, Gideon Algernon Mantell
(1790–1852), living in the town of Lewes, was dedicating all his
spare time to completing a detailed report on the geological
structure and fossils in his native Weald district (an area
incorporating much of Surrey, Sussex, and part of Kent) in
southern England. His work culminated in an impressively large,
well-illustrated book that he published in 1822. Included in this
book were clear descriptions of several unusual, large reptilian teeth
and ribs that he had been unable to identify properly. Several of
these teeth were purchased by Mantell from quarrymen, while
others had been collected by his wife, Mary Ann. The next three
years saw Mantell struggling to identify the type of animal to which
these large fossil teeth might have belonged. Although not trained
in comparative anatomy (the particular specialism of Cuvier), he
developed contacts with many learned men in England in the hope
of gaining some insight into the affinity of his fossils; he also sent
some of his precious specimens to Cuvier in Paris for identification.
At first, Mantell’s discoveries were dismissed, even by Cuvier, as
fragments of Recent animals (perhaps the incisor teeth of a
rhinoceros, or those of large, coral-chewing, bony fish). Undeterred,
Mantell continued to investigate his problem, and finally found a
likely solution. In the collections of the Royal College of Surgeons in
London he was shown the skeleton of an iguana, a herbivorous
lizard that had recently been discovered in South America. The
teeth were similar in general shape to those of his fossils and
indicated to Mantell that they belonged to an extinct, herbivorous,
giant relative of the living iguana. Mantell published a report on the
new discovery in 1825 and the name chosen for this fossil creature
was, perhaps not surprisingly, Iguanodon. The name means, quite literally, ‘iguana tooth’ and was created yet again, at the suggestion
of Conybeare (clearly the latter’s classical training and turn of mind
gave him a natural facility in the naming of many of these early
discoveries).
Not surprisingly, given the comparisons then available, these early
discoveries confirmed the existence of an ancient world inhabited
by improbably large lizards. For example, a simple scaling of the
minute teeth of the living (metre-long) iguana with those of
Mantell’s Iguanodon yielded a body length in excess of 25 metres.
The excitement, and personal fame, engendered by the description
of Iguanodon drove Mantell to greater efforts to discover more
about this animal and the fossil inhabitants of the ancient Weald.
For several years after 1825, only fragments of Weald fossils
were discovered; then, in 1834, a partial, disarticulated skeleton
(Figure 8) was discovered at a quarry in Maidstone, Kent.
Eventually purchased for Mantell, and christened the
‘Mantel-piece’, it proved to be the inspiration behind much of
his later work and resulted in some of the first visualizations of
dinosaurs ever produced (Figure 9). He continued probing the
anatomy and biology of Iguanodon in his later years, but much of
this was, alas, overshadowed by the rise of an extremely able,
well-connected, ambitious, and ruthless personal nemesis:
Richard Owen (1804–1892).