Reptiles On The Rocks by William T. Blows

Chapter 1. Iguanodon Island

"Between Brook and Brixton, in the submerged Wealden bed, near low-water mark, indications of the entire skeleton of a young, perhaps half-grown, Iguanodon were detected. The bones of the foot which were most within reach had been very little disturbed. The metatarsus was extracted in one piece;. the phalanges of an outer toe were extracted in a second piece: they had been somewhat distorted at the time of imbedding, for the matrix had hardened around, and preserved them in that state. The phalanges of the toe of the opposite side of the foot were extracted similarly cemented together by the matrix, but in their natural juxtaposition. Three of the phalanges of the middle toe were also joined together by the matrix; the fourth, or ungual phalanx of this toe, was extracted separately; but Mr. Beckle's attention having been, unluckily, diverted to another subject at this time, the fossil got into the hands of an idle looker-on, who cast it into the sea."

Thus wrote Professor Richard Owen in Part IV of his monograph on "The Fossil Reptilia of the Wealden Formation" published in 1857. He continues: "These fossils, moreover, were not fortuitously acquired, but were the fruit of special researches, assiduously carried on by Mr. Beckles on the south-west coast of the Isle of Wight, with a view to materials for completing our knowledge of the great Wealden reptiles." This is a fascinating account of early palaeontology (and its frustrations) in which the Isle of Wight is already playing a vital role. Professor Owen has also this to say about Mr. Beckles's find: "This most interesting and instructive framework of the foot of the great Dinosaurian herbivorous reptile was, moreover, found in a formation and at a locality where unequivocal vertebrae and other parts of the Iguanodon were common;........."

Richard Owen was a true professional in every sense of the word. He gave us the word Dinosaur, coined from his classification Dinosauria which he proposed would include all these ancient beasts. However, his famous monograph gives ample evidence that he was very much indebted to many amateur collectors who supplied much of the fossil material that made his work possible. Things have changed little, for a large bulk of fossil hunting today is carried out by the enthusiast during his spare hours. In Part II of his monograph, Professor Owen writes: "Every collection, public and private, to which I could command access, was ransacked for a specimen that might agree with the suspected characters of the great desideratum towards completing the vertebral anatomy of the Iguanodon. Some years passed away, leaving fruitless this research; until, in 1840, in the course of a systematic examination of the private collections in this metropolis, and whilst engaged in the comparison of the reptilian fossils in the well-stored museum of J. Devonshire Saull, Esq., F.G.S., in Aldersgate Street, City, my attention was arrested by a bulky and weighty mass of anchylosed and fossilized vertebrae, with a long and rather flattened bone attached to one side, the examination of which left a conviction of their agreement in general form and characters with the supposed sacral vertebrae and iliac bones of the Iguanodon in the British Museum."

The specimen to which Professor Owen refers actually comes from Brook, a notable site for dinosaur bones on the Isle of Wight. So why the Isle of Wight? This is a question I am so often asked, and I shall now try and bring this beautiful island into focus as an important source of fossils of all kinds. But we must start at the beginning, which in our story goes back some 120 million years.

At the beginning of the Cretaceous period, when our story begins, Eurasia and North America formed one large land mass called Laurasia. The geography in the area which is now southern England was very different from that of the present day. A large lagoon lay over what is now the Weald of Kent and Sussex and this connected via a narrow inlet with a sea occupying part of what is now the North Sea. The lagoon was surrounded by low-lying land across which numerous, sluggish rivers flowed. The Isle of Wight area was crossed by one of these rivers which flowed northeastwards from a source somewhere in what is now the western end of the English Channel. The climate was evidently subtropical judging from the plant remains which are found with the dinosaurs. There also appear to have been pronounced wet and dry seasons rather like the modern Mediterranean. For much of the time the area was a large swamp, partly covered with water during the wet seasons but drying out in the dry seasons. It was in this swampland that the mottled red and purple clays which make up much of the Wealden Marls were laid down. Periodically the climate became much wetter and meandering river channels were cut by fast flowing water through the swamp muds and it was in these channels that sands and the so-called plant debris beds (grey sandy clays with abundant plant remains) were deposited. Altogether some 170 metres (about 550 feet) of these Wealden Marls were laid down and it is in this part of the Wealden Beds that the majority of dinosaur bones were found on the Isle of Wight.

Towards the end of Wealden times the lagoon spread southwestwards and deposited a sequence of blue-black clays, which we call the Wealden Shales. As the lagoon deepened and spread, the northern sea began to penetrate southwards. At the close of the Wealden the sea reached southern England and a long period of marine deposition started. This long period of time, between 110 and 65 million years ago, is represented by the Lower Greensand, Gault, Upper Greensand and Chalk. Throughout this time the sea gradually inundated more and more of the land areas until by the time that the Chalk was being laid down only the highlands of Scotland and perhaps a few mountain peaks in Ireland and Wales remained above sea level. This situation continued until the end of the Cretaceous.

Map of Geography of Southern England in Wealden Time
Figure 1 — Geography of Southern England in Wealden Time

At the beginning of the Tertiary the sea retreated and there was extensive erosion of the old Chalk sea-bed. Some 55 million years ago at the Figure 1 — Geography of Southern England in Wealden Time beginning of the Eocene the sea once more came back into the area, although it never fully established itself. Throughout the Eocene and into the early Oligocene, when the sea retreated once more, a complex sequence of river, estuarine and marine deposits were laid down, a total of nearly 700m (about 2250 feet) in all.

Diagram of Cross Section of the Geology of Southern England
Figure 2 — Cross Section of the Geology of Southern England
Map of Wealden Outcrops on Isle of Wight
Figure 3 — Map of Wealden Outcrops on Isle of Wight

Thus by the middle of the Tertiary, some 35 million years ago, the dinosaur-bearing Wealden Marls were buried beneath 1.5 kilometres (nearly 1 mile) of later deposits. How then did they become visible at the surface again? To understand this we must go back to the beginning of the Tertiary again since it was at this time that profound changes began to occur. Firstly Europe and America began to split apart and the North Atlantic Ocean began to form between them. Secondly immense upheavals were occurring around the world, upheavals that were eventually to produce the high mountain chains of the world such as the Alps and the Himalayas.

Although southern England was not directly involved in these events, it did experience some localised buckling or folding of the rocks. Today we can recognise these folds as the Thames and Hampshire Basins and the broad domes of the Weald and English Channel. These structures seem to have assumed their present form about 30 million years ago. In the succeeding aeons of time the combined forces of wind, rain and river steadily eroded the land surface. Since the end of the last Ice Age, the sea has also played an important part in shaping the geography of the area, eventually cutting its way through the rocks to separate the Island from the mainland, perhaps as little as 7000 years ago. The combined result of folding and erosion has been to reveal for inspection rocks which would otherwise be inaccessible. Thus today we can see the dinosaur-bearing Wealden Marls in two areas on the Isle of Wight, one in Sandown Bay and the second larger one along the south coast between Compton Chine and Atherfield. The same processes have also revealed Wealden rocks in the Weald of Kent and Sussex. However, although it was in Sussex that the first remains of Iguanodon were discovered in 1822, few good exposures exist today. Hence it is on the Isle of Wight that Wealden dinosaurs must be sought, where rapid erosion causes frequent cliff falls and thus a constant turnover of material to be searched.

The question is often asked what fossils occur with the dinosaurs in the Wealden Marls? Well, in fact, we find exactly the types of animals which would be found in subtropical swamps today, namely freshwater mussels and snails, fish, crocodiles and turtles. More rarely the bones of flying reptiles (pterodactyls) turn up and very recently the teeth of early mammals have been discovered. Of the flora the most common remains found are those of fossil wood which at some horizons, the plant debris beds, occurs in abundance. Most of this wood is too compressed to be identifiable but some better preserved specimens show that the land bore a forest of conifers, cycads and tree ferns. Fossil cones, leaf fragments, seeds and fern fronds can also be found.

Many fossil bones end up on the beach after erosion from the cliff, and unfortunately become subject to destruction by the sea. Individual bones get very waterworn as they roll up and down the beach along with the shingle at the mercy of storms and tides. Pieces of dinosaur bone can often be found among the stones on the beach worn as smooth as a pebble. Such specimens can only be identified by a knowledge of bone structure and the process of fossilisation. Richard Owen noted this waterworn nature of Isle of Wight specimens when he wrote in Part IV of his monograph in 1857: "Athird portion of the sacrum of the Hylaeosaurus is the specimen No.28,936, British Museum. It is from the submerged Wealden of the Isle of Wight, and has been subject, like many of the fossils from that locality, to a certain degree of attrition by sea-waves on the beach."

Fortunately not all the dinosaur bones are found on the beach. Careful searching and excavation can reveal bones still in place in the cliffs and it is from the way in which these bones occur that we can get some idea of how they became preserved. The majority of the bones have been recovered from the plant debris beds, or, less commonly, from the sandstones; in other words those depo3its which are thought to represent flooding. Most of the material consists of single bones, often broken and battered. It seems likely that skeletons of dinosaurs which died in the swamps during droughts were broken up and scattered by rising floodwaters before being swept, along with plant debris, into the river channels where burial occurred. This process accounts not only for the damaged condition of the specimens but also for the relative abundance of the different bones, for example vertebrae are common but skulls are extremely rare. In the individual dinosaur skeleton there would have been for example, some seventy or so vertebrae, two of each limb bones and only one skull. Thus when the skeleton was broken up one would expect vertebrae to be far the most abundant remains to become buried whereas skulls would be extremely rare, and this is exactly what we find in the Wealden Marls. However, this is not the whole story, since, although each bone was a potential fossil, some are more capable than others of surviving the battering which they would have received as they were transported from swamp to river channel. The vertebrae were particularly resistant in this respect because the centrum (the main body of the bone) could withstand considerable abrasion. On the other hand skulls, being hollow and constructed mostly of this bone, were very fragile and easily destroyed.

Thus few skulls would have survived to become buried. Teeth must be considered separately from bones in terms of their potential for preservation. Teeth are harder than bone and are thus able to survive after the rest of the skull has been destroyed. There is a further complication because dinosaurs shed their worn teeth and replaced them with new ones throughout their lives and one animal could, therefore, produce very many teeth. For this reason teeth are relatively more numerous than some other parts of the skeleton.

In the years that I have been collecting, I have found many dinosaur bones but only on two occasions have I located two partial skeletons, the story of these finds forming later parts of this book. These rare partial skeletons and the even rarer complete skeletons represent the odd animal which had only just died when the floods came so that decomposition had not proceeded very far. It is known from modern observations that under these circumstances even a large carcass can be washed intact into a river and may float a considerable distance downstream before getting buried or disintegrating.

The material belonging to the small dinosaur Hypsilophodon constitutes the one exception to the foregoing comments since the preservation of these specimens is very different in style from that found elsewhere in the Wealden Marls. Virtually all the specimens of this animal have been recovered from one sandstone bed in a very small area on the south coast of the Island. This locality has yielded well-preserved and naturally articulated bones representing twenty individual animals. Three of these are nearly complete skeletons and it is thought likely that several of the others were originally more complete before the sandstone blocks that contained them fell down the cliff. We still cannot account for the unusual preservation of these specimens or why only Hypsilophodon occurs in this bed.

Once the bones were buried the process of fossilisation began. Bone is a spongy material consisting basically of calcium phosphate, calcium carbonate and various organic materials. During fossilisation the organic constituents are removed and the bone is gradually altered into a complex phosphate mineral. At the same time the cavities in the bone become filled with minerals, calcite (calcium carbonate) and/or pyrite (iron sulphide), brought in by water percolating through the rock. In this way the bone becomes a heavy, solid structure but retains its original texture. Of course we must remember that much of the potential fossil material never gets preserved; some is destroyed at each stage from the death of the animal through to fossilisation. Thus we get only a very biased view of the living organisms which lived so long ago.

Island residents have found many dinosaur bones along the coasts and small collections exist in private homes as well as museums. On my earlier visits I saw several such small private collections and heard of others. A tea-room at Brook had individual dinosaur vertebrae and bones in the front room, and I examined more at Calbourne Mill. A small collection of bones were kept in a cafe next to a petrol station at Brighstone, but the cafe has since closed. A group of fossils, including the leg bones of a dinosaur, existed outside a coach station booking office in Ventnor when I was a child. A few fossil bones exist in Blackgang Chine museum, where the large models of dinosaurs attract holiday-makers each summer. A more serious collection of dinosaur remains is in the Museum of I.O.W. Geology in Sandown. Here a fine accumulation of fossils from all parts of the Island are housed, including the collections of amateurs who have generously donated their finds to the museum. In their modern display programme, these specimens will provide a valuable contribution to public entertainment and education. This is the most important collection on the Island, providing useful comparative material along with geological and palaeontological information.

Collections of Isle of Wight fossils, both public and private, have sprung up on the mainland as well. The vast national collection held at the British Museum (Natural History) in London is a comprehensive account of prehistoric life from all corners of the world. Among the many dinosaur specimens housed here the Isle of Wight is well represented. Several unique remains of rare creatures have found a place in the palaeontological department, some of which are the direct result of hard labours of the Reverend William Fox who I mentioned in the introduction. He was a clergyman whose spare time was spent roaming the cliffs of the Isle of Wight on a donkey. His observations led to the discovery of Polacanthus, a peculiar armoured dinosaur, at Barnes High near Atherfield; of Hypsilophodon, a small but fascinating bipedal dinosaur; and of Ornithopsis, a giant sauropod with enormous vertebrae. As one enters the dinosaur gallery in the South Kensington museum, a practically complete Iguanodon skeleton stands beside the cast of the larger form from Belgium. This smaller animal is also from the Island's south coast. It is specimens like this that inspired the title of this chapter, for Iguanodon remains are by far the most abundant of the dinosaur material from this locality.

After discussing many aspects of this fascinating subject, we have now turned full circle. The animals themselves are the subject of the next chapter, and the techniques of fossil hunting and preparation really the subject of another book. An inexpensive little book on this topic is "Fossil Collecting" by Mr. R.L.E. Ford. This is one of a series of short practical guides published by the natural history suppliers Watkins and Doncaster. Perhaps I mention this book out of pride for I was asked to draw the cover illustration — the skeleton of Hypsilophodon. Nevertheless it is of great value to the beginner in developing his practical skills in palaeontology.

The Island will be the subject of years of palaeontological observations and many new and interesting finds will be made. Many of these finds will be made by amateurs who frequent these cliffs and who contribute much to our knowledge of the reptiles on the rocks.

This page was last edited on: 4th March, 2015 06:16:20

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