The discovery of ‘terrible claw’

In the summer of 1964 John Ostrom was prospecting for fossils
in Cretaceous rocks near Bridger, Montana, and collected the
fragmentary remains of a new and unusual predatory dinosaur.
Further collecting yielded more complete remains, and by 1969
Ostrom was able to describe the new dinosaur in sufficient detail
and to christen it Deinonychus (‘terrible claw’) in recognition of
a wickedly hooked, gaff-like claw on its hind foot.
Deinonychus (Figure 16) was a medium-sized (2–3 metres in
length), predatory dinosaur belonging to a group known as the
theropods. Ostrom noted a number of unexpected anatomical
features; these prepared the intellectual ground for a revolution
that would shatter the then rather firmly held view of dinosaurs
as archaic and outmoded creatures that plodded their way to
extinction at the close of the Mesozoic world.
However, Ostrom was far more interested in understanding the
biology of this puzzling animal than in simply listing its skeletal
features. This approach is far removed from the pejorative epithet
‘stamp-collecting’ that palaeontology had attracted, and echoes the
method of Louis Dollo in his earlier attempts to understand the
biology of the first complete Iguanodon skeletons (Chapter 1). As an approach, it has more in common with modern forensic pathology,
driven as it is by a need to assemble broad ranges of facts from a
number of different scientific areas in order to arrive at rigorous
interpretation, or hypothesis, on the basis of the available evidence;
this is one of several driving forces behind today’s palaeobiology.

Dinosaur palaeobiology: a new beginning

It was not until the 1960s and early 1970s that the study of fossils
began to re-emerge as the subject of wider and more general
interest. The catalyst for this re-awakening was a younger
generation of evolutionarily minded scientists eager to demonstrate
that the evidence from the fossil record was far from being a
Darwinian ‘closed book’. The premise that underpinned this
new work was that while evolutionary biologists are obviously
constrained by working with living animals in an essentially
two-dimensional world – they are able to study species, but they do
not witness the emergence of new species – palaeobiologists, by
contrast, work in the third dimension of time. The fossil record
provides sufficient time to allow new species to appear and others to
become extinct. This permits palaeobiologists to pose questions
that bear on the problems of evolution: does the geological
timescale offer an added (or different) perspective on the process of
evolution?; and, is the fossil record sufficiently informative that it
can be teased apart to reveal some evolutionary secrets?
Detailed surveys of the geological record began to demonstrate
rich successions of fossils (particularly shelled marine creatures) –
considerably richer than Charles Darwin could ever have imagined,
given the comparative infancy of palaeontological work in the
middle of the 19th century. Out of this work emerged observations
and theories that would challenge the views of biologists over the
modes of biological evolution over long intervals of geological
time. Sudden massive, worldwide extinction events and periods
of faunal recovery were documented which could not have been
predicted from Darwinian theory. Such events seemed to reset the
evolutionary timetable of life in a virtual instant, and this prompted
some theorists to take a much more ‘episodic’ or ‘contingent’ view
of the history of life on Earth. Large-scale, or macroevolutionary,
changes in global faunal diversity over time seemed to be
demonstrable; these again were not predicted from Darwinian
theory and required explanation.

Most notably, however, Niles Eldredge and Stephen Jay Gould
proposed the theory of ‘punctuated equilibrium’. They suggested
that modern biological versions of evolutionary theory needed to be
expanded, or modified, to accommodate patterns of change seen
repeatedly among species in the fossil record. These consisted of
prolonged periods of stasis (the ‘equilibrium’ period) during which
relatively minor changes in species were observable, and contrasted
with very short periods of rapid change (the ‘punctuation’). These
observations did not fit well with the Darwinian prediction of slow
and progressive change in the appearance of species over time
(dubbed ‘evolutionary gradualism’). These ideas also prompted
palaeobiologists to question the levels at which natural selection
might function: perhaps it could operate above the level of the
individual in some instances?

As a consequence, the whole field of palaeobiology became more
dynamic, questioning, and also outward-looking; it was also
prepared to integrate its work more broadly with other fields of
science. Even highly influential evolutionary biologists such as
John Maynard Smith, who had had little truck with fossils at all,
were prepared to accept that palaeobiology had valuable
contributions to make to the field.
While the general field of scientific palaeobiology was
re-establishing its credentials, the mid-1960s was also a time
of important new dinosaur discoveries; these were destined to
spark ideas that are still important today. The epicentre of this
renaissance was the Peabody Museum at Yale University, the
original workplace of ‘bone-fighter’ Othniel Charles Marsh.
However, this time it was in the person of John Ostrom, a young
professor of palaeontology with a strong interest in dinosaurs.

Reconstructing Iguanodon

In 1878 remarkable discoveries were made at a coal mine in the
small village of Bernissart in Belgium. The colliers, who were mining
a coal seam over 300 metres beneath the surface, suddenly struck a
seam of shale (soft, laminated clay) and began to find what
appeared to be large pieces of fossil wood; these were eagerly
collected because they seemed to be filled with gold! On closer
inspection, the wood turned out to be fossil bone, and the gold
‘fool’s gold’ (iron pyrites). A few fossil teeth were also discovered
among the bones, and these were identified as similar to those
described as belonging to Iguanodon by Mantell many years before.
The miners had accidentally discovered not gold, but a veritable
treasure trove of complete dinosaur skeletons.
Over the next five years, a team of miners and scientists from the
Royal Belgian Museum of Natural History in Brussels (now the Royal Institute of Natural Sciences) excavated nearly 40 skeletons
of the dinosaur Iguanodon, as well as a huge number of other
animals and plants whose remains were preserved in the same
shales. Many of the dinosaur skeletons were complete and fully
articulated; they represented the most spectacular discovery that
had been made anywhere in the world at the time. It was the good
fortune of a young scientist in Brussels, Louis Dollo (1857–1931), to
be able to study and describe these extraordinary riches, and this he
did from 1882 until his retirement in the 1920s.
The complete dinosaur skeletons unearthed in Bernissart proved
finally that Owen’s model of dinosaurs such as Iguanodon was
incorrect. As Mantell had suspected, the front limbs were not as
large and strong as the back legs, while the animal had a massive
tail (see Figure 12), and the overall proportions of a giant kangaroo.
The skeletal restoration, and the process by which it was arrived at,
are particularly revealing because they show how the influence of the contemporary interpretations about the appearance and
affinities of dinosaurs affected Dollo’s work. Owen’s ‘elephantine
reptile’ vision of the dinosaur had been questioned as early as 1859
by some tantalizingly incomplete dinosaur discoveries made in New
Jersey and studied by Joseph Leidy, a man of equivalent scientific
stature to Owen who was based at the Philadelphia Academy of
Natural Sciences. However, Owen was to be far more roundly
criticized by a younger, London-based, and ambitious rival:
Thomas Henry Huxley (1825–95).

By the late 1860s, a series of new discoveries had been made that
added considerably to the debate over the relationships of dinosaurs
to other animals. The earliest well-preserved fossil bird (called
Archaeopteryx, or ‘ancient wing’) had been discovered in Germany
(Figure 13). It was eventually bought from its private collector
by the Natural History Museum in London, and described by
Richard Owen in 1863. The specimen was unusual in that it had
well-preserved impressions of feathers, the key identifier for any
bird, forming a halo in the matrix around its skeleton; however,
unlike any living bird, and rather disconcertingly similar to modern
reptiles, it also had three long fingers ending in sharp claws on each
hand, teeth in its jaws, and a long bony tail (some living birds might
seem to have long tails, but this is just the profile of their feathers
that are anchored in a short remnant of the tail).
Not long after the discovery of Archaeopteryx, another small,
well-preserved skeleton was found in the same quarries in Germany
(Figure 14). It bore no feather impressions and its arms were far
too short to have served as wings in any case; anatomically, it was
clearly a small, predatory dinosaur and was named Compsognathus
(‘pretty jaw’).
These two discoveries emerged at a particularly sensitive time
scientifically speaking. In 1859, just a year or so before the first
skeleton of Archaeopteryx was unearthed, Charles Darwin
published a book entitled On the Origin of Species. This book provided a very detailed discussion of the evidence in favour of
the ideas being put forward by the transmutationists and
progressionists referred to earlier. Most importantly, Darwin
suggested a mechanism – natural selection – by which such
transmutations might occur and how new species appear on Earth.
The book was sensational at the time because it offered a direct
challenge to the almost universally accepted authority of biblical
teachings by suggesting that God did not directly create all the species known in the world. Darwin’s ideas were vigorously
opposed by pious establishment figures such as Richard Owen.
In contrast, the radical intellectuals reacted very positively to
Darwin’s ideas. Thomas Huxley is reputed to have declared, after
reading Darwin’s book, ‘How very stupid of me not to have thought
of that!’


While not wishing to become too involved in Darwinian matters, it
is nevertheless the case that dinosaurian discoveries featured
in some of the arguments. Huxley was quick to realize that
Archaeopteryx and the small predatory dinosaur Compsognathus
were anatomically very similar. By the early 1870s, Huxley was
proposing that birds and dinosaurs were not only anatomically
similar, but used this evidence to support the theory that birds had
evolved from dinosaurs. In many ways, the stage was set for the
discoveries in Belgium. By the late 1870s, Louis Dollo, as a bright
young student, would have been fully aware of the Owen–Huxley/
Darwin feuds. One burning question must have been: did these new
discoveries have any bearing on the great scientific controversy of
the day?

Careful anatomical study of the full skeleton of Iguanodon revealed
that it had a hip structure known as ornithischian (‘bird-hipped’);
furthermore, it had long back legs that ended in massive, but
decidedly bird-like, three-toed feet (very similar in shape to the feet
of some of the biggest known land-living birds such as emus). This
dinosaur also had a rather bird-like curved neck, and the tips of its
upper and lower jaws were toothless and covered by, yet again, a
bird-like horny beak or bill. Given the task of description and
interpretation faced by Dollo in the immediate aftermath of these
exciting discoveries, it is intriguing to note that, in the early
photographs taken at the time of the reconstruction of the first
skeleton in Brussels, just beside the huge dinosaur skeleton can be
seen skeletons of two Australian creatures: a wallaby (a small
variety of kangaroo) and a large, flightless bird known as a
cassowary.
The influence of the debate raging in England cannot be doubted.
This new discovery pointed to the truth implicit in Huxley’s
arguments and made it clear that Mantell had been on the right
track in 1851. Iguanodon was no lumbering, scaly rhinoceros
lookalike as portrayed by Owen in his grand models of 1854; rather
it was a huge creature with a pose similar to that of a resting kangaroo, but with a number of bird-like attributes, just as Huxley’s
theory predicted.
Dollo proved to be tirelessly inventive in his approach to the fossil
creatures that he described – he dissected crocodiles and birds in
order to better understand the biology and detailed musculature of
these animals and how it could be used to identify the soft tissues
of his dinosaurs. In many respects, he was adopting a decidedly
forensic approach to understanding those mysterious fossils. Dollo
was regarded as the architect of a new style of palaeontology that
became known as palaeobiology. Dollo demonstrated that
palaeontology should be expanded to investigate the biology, and by
implication ecology and behaviour, of these extinct creatures. His
final contribution to the Iguanodon story was a paper he published
in 1923 to honour the centenary of Mantell’s original discoveries.
He succinctly summarized his views on the dinosaur, identifying it
as the dinosaurian ecological equivalent of the giraffe (or indeed
Mantell’s giant ground sloth). Dollo concluded that its posture
enabled it to reach high into trees to gather its fodder, which it was
able to draw into its mouth by using a long, muscular tongue; the
sharp beak was used to nip off tough stems, while the characteristic
teeth served to pulp the food before it was swallowed. So firmly
was this authoritative interpretation adopted, based as it was on a
set of complete articulated skeletons, that it stood, literally and
metaphorically, unchallenged for the next 60 years. This was
reinforced by the distribution of replica, mounted skeletons
of Iguanodon from Brussels to many of the great museums
around the world during the early years of the 20th century,
and also by the many popular and influential textbooks written
on the subject.