Introduction
All the Isle of Wight fossils come from the Weald Group, an area of rock that is also found on mainland Britain. The Wessex Formation and the Vectis are the two prominent members of the group on the Isle. The Isle is rich in fossils for two reasons. The first is the hot, wet climate provided an excellent habitat for dinosaurs (explained below). This climate also have helped dry the clay around the fossils. The second is the composition of the Weald rock formations. The formations are comprised of sandstone and clay. These rocks would have collected debris like a magnet, particularly from the rivers and floods of the region (see Plant Debris beds, below). After the Mesozoic era, the Wealden group was buried by later rocks, including chalk. This preserved the group from erosion by the elements. When the Alps were formed in Europe (3-10 million years ago), tectonic plate movements brought the Wealden rocks back to the surface. 10,000 years ago, the Isle of Wight was formed from a rise in sea level, and the Wealden rocks became exposed in the Isle's cliffs via erosion.
The Wessex Formation is 130 million years old, while the Vectis Formation is 125 million years old. This places both formations in the Early Cretaceous Period, an Era which was formally a black spot for scientists. The exposed Wealden rock on the cliffs makes fossil excavation simple - storms and sea erosion naturally bring fossils to the surface. This combination makes the Isle a valuable insight into a previously unexplored ecological system. Here I will attempt to detail this ecological system, based on the Isle of Wight fossil evidence.
Climate of the Isle
Alfred Wegner proposed his "Origins of Continents and Oceans" Theory in 1912, but it wasn't widely accepted until the 1960s, when it developed into the Plate Tectonic Theory. It argues that the Earth's crust is broken up into 10 plates. These plates float on the Earth's upper mantle, which is a partially molten layer. The plates are constantly moving imperceptible distances each year. The theory proposes that the Earth was originally one large land mass he named Pangaea ("all-earth"). Eventually, Pangaea split to form two super continents, Laurasia (in the north) and Gondwanaland (in the south). The split happened through Jurassic era, and changed the location of the continents, notably England. They shifted away from the equator to a new northern location. England would have been on the tip of this new Laurasia continent, and so would have benefited from a wetter climate closer to the sea.
There is also evidence supporting that the global climate warmed substantially during this period. Black shales from the Cretaceous period suggest low oxygen in that water as a result of high temperatures. Oxygen isotope studies on Cretaceous carbonates suggest a warm ocean, with surface waters warmer then present ocean waters, 12K-15K warmer in some places. Crocodilian fossils were found as far as 50o N, suggesting a warmer climate. (Many cretaceous crocodilian teeth have been found on the Isle of Wight) In addition, the sea level was 100-200 meters higher then present, possibly due to a lack of polar ice.
The clays and sandstones of the Wessex Formation were deposited by a series of river systems; the clays gain their mottled color from repeated wetting and drying in a seasonally semi-arid environment. Grey clay bands found in the formation packed with organic debris are known as "plant debris beds". They are thought to be the result of rivers swollen by monsoonal rain bursting their banks causing flash floods. Whatever was caught in the flood was deposited into a muddy clay bed. Ian Harding mentions this phenomenon; "the flash floods .. triggered catastrophic mud flows which tumbled dinosaurs, crocodiles and plants together into massive chaotic log jams - the sedimentary deposits in which we find the dinosaur remains today." Material from these plant debris beds include burnt plants, which are thought to have been caused by forest fires - common during periods of drought when temperatures were high. Harding states that "Sporadic electric storms would have ignited the dry vegetation, with spectacular wildfires sweeping the plain". Plants from the Wessex and Vectis formations have been found with growth rings preserved, indicating that the plants growth often slowed or stopped for long periods of time. These rings have been found in modern climates where it may not rain for years.
So we have evidence of a highly seasonal climate on the Isle during the Cretaceous period - monsoons combined with forest fires and drought. Micheal Munt of the Museum of Isle of Wight Geology, added that the land would have been cris-crossed with rivers and pools, making the Island an "ideal habitat for dinosaurs".
Flora of the Isle
Ian Harding from the University of Southampton was looking at the paleontology (study of organic microfossils) of the island in a documentary with the BBC. He said; "The plant microfossil record indicates vegetation that is diverse. We have discovered spores produced by club mosses, quillorts and water ferns growing in damp conditions, possibly around water bodies, and ferns and tree ferns growing on slightly drier ground. The pollen of cycad-like plants and conifers (although bearing tough and apparently rather indigestible leaves) indicate that trees would have flourished on higher, better drained soils". Ed Jarzembowski, a palaeoentomologist from Maidstone Museum, mentioned that he had found amber from a primitive conifer, most likely a monkey-puzzle tree. Ian Harding later adds that "there is now general agreement" that flora of the Isle would consist of "higher ground clad in tree ferns and conifers which gave way to scrub consisting of the peculiar fern Weichselia, and ephemeral ponds."
Ferns (such as Weichselia) and water ferns are part of the Polypodiophyta branch of the Pteridophyta family. Some of these reproduce with spores that germinate only in moist areas, some reproduce via rhizomes (underground stems). Water ferns that existed in the Mesozoic era include the Marsileales and Salviniales species. The later was fully floating, the former has roots. The polypodiophyta family were fast-growing and resilient. Their rhizomes allowed to them to reproduce quickly, and regenerate after been eaten by herbivores. They would have been popular in the rivers and pools of the Isle of Wight. Club mosses and quillworts are part of the Lycophota branch of the Pteridophyta family. They are small plants that reproduce via sexual reproduction. Club mosses are evergreen and so would have provided a constant food source for herbivores.
Cycads are members of the Cycadophyta family, with Cycadeoids. Cycads have separate male and female plants, while Cycadeoids sometimes don't. They are palm-like seed plants with long woody trunks and tough leaves. Some Mesozoic Era Cycads included: Leptocycas, Cycas, Zamia, Dioon, Bowenia, Stangeria, and Microcyas. Araucaria were slow growing evergreen trees, conifers and shrubs. They had tough bark and leaves. Mesozoic Era conifers included redwoods, yews, pines and the monkey puzzle tree (Araucaria).
Angiosperms ("flowering plants") overtook the Araucaria during the Cretaceous period as the dominant flora. They where characterized by fast growth, strong tolerance to disturbance, and rapid seed reproduction. They would have been common although not dominant in the early Cretaceous period on the Isle, and would have provided food for insects and herbivores.
Fauna of the Isle
Herbivores dominated the Isle of Wight. 13 out of the 18 recorded species found on the Isle are herbivores. This is consistent with the dinosaur genera, which shows that 65% of dinosaurs were herbivores, and 35% were carnivores. The most common fossils of the Isle - according to the Illonis state geographical survey - are the herbivore ornithropods Iguanodon, Hypsilophodon and Valdosaurus. Iguanodon was a strong-legged quadrupedal herbivore, averaging 5 meters in length. It was probably a herding animal, suggested by discoveries in Belgium where dozens of Iguanodon fossils were found together. Hypsilophodon was 2 meters long and 60 cm tall. It was a early Cretaceous period bi-pedal herbivore. A pack of 20 Hypsilophodon were unearthed together on the Isle, indicating its herd-like behavior. Valdosaurus was a 3 meter long Early Cretaceous period herbivore. It was similar to Hypsilophodon and probably lived in a similar manner. All of these are likely to have been pack animals. Polacanthus fossils have also been found on the Isle of Wight. Polacanthus remains have often been discovered together with Iguanodon herds in the past. Scientists speculate that the Polacanthus (which was a small spiky-armored herbivore) hung around groups of Iguanodon to take safety in numbers.
The second group of herbivores were the sauropods. Many sauropod species have been found on the isle; Eucamerotus, Iuticosaurus, Pelorosaurus, Pleurocoelis, and Titanosaurus (mid-late cretaceous). It was previously thought that the long necked sauropods ate the plentiful conifers of the era, much like the giraffes of today. However paleontologist Kent Stevens changed all this with his computer-generated models of dinosaur skeletons in 1987. He found that the necks of most sauropods wouldn't be able to get their heads much higher then the horizontal, let alone to the treetops. However, the neck could reach down to ground level, and this allowed it to graze on ferns, like a "huge cow of the pre-historic". Recently "gastroliths" or stomach stones have been discovered in the stomachs of some sauropods. These were supposed to have been deliberately swallowed to aid digestion. Modern reptiles, such as crocodiles, do this today. Another fact about sauropods is that they are thought to lay their eggs in a circle. Sauropod eggs found in southern France showed that they had been laid in a trench, in circular arcs. The radius of the circle is the same length as a sauropod revolving on its hind legs. Around one hundred eggs were laid per circle.
The outnumbered carnivores on the Isle consisted of Aristosuchus, Eotyrannus, Neovenator and Baryonyx. Aristosuchus was discovered on the Isle of Wight by Seeley in 1866. There is some confusion about classification with this species, Calamospondylus and Calamosaurus. It was a light, graceful, 2 meters long carnivore. Eotryannus was found in 1997 by Naish on the Isle of Wight. A 40% complete skull was found. It was a 4.5 meter long fast running carnivore that was a relative of T. Rex. Neovenator was 8 meters long and had a 'puffin-like' skull. The number of teeth found and the shape of the jaw have led scientists to conclude that Neovenator was "the major flesh-eater around in the UK" in its period. Baryonyx is a rarity amongst dinosaurs - it was a fish eater. 9 meters in length, it fed on fish such as Lepidotes (which was found in the stomach of a Baryonx specimen found in Sussex). It had a high EQ (brain weight to body weight ratio) which may have helped it catch fish.
Pterosaurs are distinct from dinosaurs in that they are flying reptiles - dinosaurs never flew. The Pterosaurs found on the Isle are Ornithocheirus and Istiodactylus. Ornithocheirus was a fish-eating carnivore with a wingspan of a small plane - 12 meters. The carnivorous Istiodactylus was only recently named in 2001, and was for a long time confused with Ornithocheirus. It has a duck-billed mouth, a 5 meter wingspan, and is thought to have eaten carrion as well as fish.
As England would have been surrounded by sea during the Cretaceous, and because of the large number of rivers on the Isle, much fossilized aquatic life has been found. Fossils of ammonites (cephalopods with complex shells) ostracods, corals, sponges and fish including the shark Lamna appendiculata are recorded. Ostracods or Ostracoda are crustacean like crabs and lobsters. They has 7 pairs of appendages, specialized for different tasks. The animal lives inside a carapace made of two valves. They shed the carapace seven times during life growing a new larger one each time. They are sexually dimorphic - males and females are different shapes. Ammonite fossils are so common that local schools organize fossil hunting trips to the Island beaches to search for them.
In 1994 Twitchett discovered a lot of insect remains in the Wealden group of the isle. They all came under the orders Celeoptera (beetles), Blattodea (cockroaches), Diptera (flies), Hermiptera (true bugs) and Trichoptera (caddisflies). Beetles were the most abundant, but as specimens were probably transported in streams to the salient water where they were fossilized, there were no complete specimens. Tougher elements could therefore be expected to make up a disproportionate amount of the sample.
Flora and Fauna Interaction
The landscape of the Cretaceous Isle would have comprised of tree ferns and conifers on higher ground, with water ferns such as Weichselia on the lower ground. Some angiosperms may have been seen in sparse patches. On these plants would have grazed large packs of herbivore dinosaurs such as Iguanodon, Hypsilophodon and Valdosaurus. The occasional sauropod such as Eucamerotus would have joined them. Small predators such Neovenator and Eotyrannus would have worked alone, or perhaps in a pack, picking off the weaker members of the herd like modern tigers. The waters would have been home to many ammonites, and perhaps the odd ostracod or shark. Fishing these waters would have been the Pterosaura Istiodactylus, Ornithocheirus and perhaps the dinosaur Baryonyx. Scattered here and there (particularly around the angiosperm) would have been beetles such as Celepotera, flies such as Diptera and cockroaches such as Blattodea. These would have been feeding on the plant life and may have constituted a quick stack for a small carnivore.
According to Tiffney, an important evolutionary process in dinosaur-plant interaction took place during the Cretaceous period, brought on by the rapid spread of the angiosperm]s (flowering plants). Angiosperms evolved from the earlier first stage gymnosperms, and possess several common features. They are more "weedy" and less "woody" then the angiosperms, and as a consequence are able to regenerate more quickly. They possess the ability to reproduce via horizontal stems or root sprouting, like vines. This allows them to dominate an area without sexual reproduction. Some Angiosperms possess weaker defensive mechanisms then the earlier gymnosperms, and so - coupled with their explosive growth rate - represent a better food source. The diversification of these angiosperms are closely mirrored by the radiation of small herbivores. On the Isle of Wight, these herbivores would include the Valdosaurus, the Hypsiophodon, and the Iguanodon - the three most common dinosaurs. This link is notable for two reasons:
A. Over 50% of all dinosaur diversity stems from this radiation, which occurred exclusively in the last 40 million years of the dinosaur's history.
B. Evidence (such as the find of the pack of 20 Hypsiophodon on the Isle of Wight) suggests that the individuals in each species are very numerous. This contrasts with the much lower numbers of dinosaurs found together before the mid-Cretaceous.
This radiation of dinosaurs could be related to rapid growth and higher food quality provided by the angiosperms. However there is also evidence to support that the global climate changes in the Cretaceous era contributed to a better environment for ferns and other gymnosperms, increasing the number of food sources.
During the middle to late Cretaceous period on the Isle of Wight you would find a number of large packs of (often bi-pedal) herbivores that were taking full advantage of the growth in angiosperms, small flowering plants and ferns. Evidence for this includes the large number of bi-pedal herbivore skeletons found on the Isle of Wight (particularly Iguanodon and Hypsiophodon) and the pack of 20 Hypsiophodon found together there.
Conclusion
The paleoecology of the Isle of Wight represents a rare glimpse into an ecosystem buried in our past. The geology of the Island allows us to determine the arid, semi-tropical climate woven with rivers and ponds. Flash-floods, droughts and the Wealden formations provide us with the evidence that we need to describe the flora and fauna of this ecosystem. Herds of Iguanodon and Hypsiophodon would have roamed the landscape grazing on the ferns such as Weichselia that prospered in the damp but hot climate. These herbivores would have been undergoing a slow co-evolution with angiosperms, spreading their seeds across Euroasia. The occasional carnivore such as Neovenator would have preyed on them, as the Pterosaura fished for aquareous life in the plentiful water bodies around the Isle. The Isle of Wight is so valuable to paleologists because not only does it provide us with this unprecedented picture of the Early Cretaceous period, but it paints it with such clarity, thanks to its geological canvas.
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