A Child's View of the Dinosaur's

It appears that I'm not the only member of my family with more than a passing interest in the dinosaurs. This is one of the pictures produced by my grandson!

Ammonites

Of all the fossils associated with the Jurassic Coast, the ammonite is probably the most well known. They appeared at the beginning of the Jurassic period around 200 million years ago. They are cephalopod molluscs related to the octopus and squid, although thier closest living relative is the nautilus (seen below).



Ammonites were free swimming creatures, that used the chambers in thier shells as ballast tanks to control bouancy. The soft parts of the animal itself were located in the end chamber. Judging by the number of fossils we now find, they must have been a common sight floating around the Jurassic and Cretatious seas in various shapes and sizes

Despite being common, ammonites are very special fossils, of enormous use to geologists trying to work out the history of ancient times. Ammonites evolved very quickly and so are important in helping to identify rocks as being from a particular age. To understand this, is so important, to remember that the type of rock that forms depends on its geopgraphical location. Different sediments are now forming in the English Channel and North Sea. In millions of years time, after these sediments have compacted to form rocks, they may look totally different. It may be that the skeletal remains of cod, plaice and herrings etc will confirm that they originated at around the same time. However if all these fish survive for millions of years, it may not help the geologists of the future at all



Ammonites are valuable becUAE Individual species did not last long before they evolved into different species. When we find them in two different rocks therefore, they tell us that those rocks are of the same age. For example, the ammonite Titanites, seen in many garden walls on the Isle of Purbeck, lived at the time when the Portland rocks were being deposited. Find an example of Titnates in a rock and you know how old that rock is

What makes ammonites even more fascinating to the amateur geologist is that the evolutionary trends are relatively easy to pick out. It seems that as ammonites evolved they developed more and more ornamentation on the outside of thier shells, so generally speaking the ones with smooth shells are earlier that those with spikes and nobbly bits on. Another trend involved the walls that seperated the chambers in the ammonite shell. These gradually became more and more elaborate and form beautifully intricate patterns on the outside where the shell has worn away

At the end of the Creatateous (around 60 million years ago), the ammonites, like the dinosaurs, mysteriously dissapear. By that time they had gone into evolutionary reverse, with some forms beginning to uncoil, eventually resulting in forms that were almost straight

The Jurassic seas, where much of Dorset originated, must have once swarmed with these beautifull creatures with thier elaborate ornamentation and possibly vibrant colours. They proliferated in rich, tropical seas, and due to thier free-swimming lifestyle have left thier imprint in a variety of rocks

Source

Graphics: Wikipaedia
Text: Fossils and Rocks of the Jurassic Coast by Robert Westwood

Dinosaurs on the Jurassic Coast

About 225 million years ago, the first dinosaur appeared in the forests of what is now South America. It was a small two-legged animal about the size of a chicken. It was quick and agile on its two strong legs, and probably a very effective hunter. Within about 30 million years its dinosaur relatives had become the dominant creatures on the planet; they were to reign for about 165 million years



Most people know the dinosaur is a reptile, but many erroneously think the term applies to all giant reptiles. In fact dinosaurs came in all shapes and sizes; but certainly some of the larger ones were the biggest, fastest and most ferocious animals that have ever walked the Earth. The main distinguishing feature of a dinosaur is that it is a reptile that developed an upright gait. This gave it an immediate advantage over other reptiles with thier awkward sideways gait

At the beginning of the Triassic period there was a mass extinction of many species. These events have happened a number of times during geological history and have continued to puzzle geologists. Certainly much competion to the emerging dinosaurs was removed by this global catasrophe. The dinosaurs diversified rapidly during the Triassic and, with little competition, got bigger and bigger. Other reptiles also evolved, some taking to the air

During the Jurassic dinosaurs diversified further and became truly dominant. Huge plant eating varieties evolved along with ferocious predators. Other forms of life also flourished and, in the sea, other reptiles grew to immense size. The shallow, tropical seas in which Dorset's rocks were deposited must have been home to a fantastic array of life

The Cretatious period saw dinosaurs continue to dominate. Some of the most well known dinosaurs like Tyrannosaurus lived in this period and the shallow lagoons where the Purbeck rock was formed have helped preserve thier bones for us to study. At Durlston Bay and Worbarrow Bay it is possible to sea the footprints of these massive creatures. The most likely example you will find is the three pronged footprint of the Iguanadon (pictured above), a plant eater that was up to 10 metres long and 5 metres high. At the end of the Cretatious period (about 65 million years ago) the dinosaurs died out.

Whether or not it was the impact of a huge meteorite as has been suggested is still open to debate. The evidence is strong, but it should be remembered that mass extinctions have taken place at other times

Source:

Text: Fossils and Rocks of the Jurrasic Coast by Robert Westwood
Graphic: Wikipaedia

Fossils at Charmouth

I was on holiday in Charmouth a few weeks ago, its a beautifull little gateway town to the Jurassic Coast which I reccomend. Its beauty lies in the fact that it makes many towns, beaches and cliffs on the Jurassic Coast very accessable

While I was there, I went fosiiling on Charmouth beach with my son, so we duly rented a fossil hammer, and we were off. Fossils are the remains of animals and plants that have been preserved in stone. they are the raw material for the science of paleantology, providing direct evidence of past life on Earth and the way it has changed over millions of years. The rocks that make up the cliffs at Charmouth are rich in the fossils of animals that swam in the Jurassic seas. The coast erodes rapidly resulting in thousands of fossils being fed onto the beaches from the landslides in surrounding cliffs, especially after the winter storms. The remains that have been found here since the eighteenth century represent one of the richest slices of life in Jurassic times anywhere in the world



It had been raining the night before, so that should have given the cliffs the ideal conditions to offer up a few fossils. We were total novices, never having been fossiling before, so we were learning as we went along. As you can see, we found some ammonites, some better than others, so if we can do it, so can you! If the cliffs arent offering up fossils, there is a local shop that sells them!

There is a code of conduct relating to the collection of fossils, which operates between Lyme regis and Burton Bradstock:

• the best and safest place to look for fossils is on the beach where the sea has washed away soft clay and mud
• do not collect or hammer into the cliffs, fossil features or rocky ledges
• keep collecting to a minimum - avoiding the removal of in-situ fossils, rocks or minerals
• the collection of actual specimens should be restricted to those places where there is a plentifull supply
• only collect what you need, leaving some for others
• never collect from walls or buildings
• take care not to undermine fences, bridges or other structures
• be considerate and dont leave a site in an unsightly or dangerous condition
• some landowners do not wish people to collect, please observe notices
• report any important fossil finds at the Charmouth Heritage Coast centre

Source: some text from 'The Official Guide to the Jurassic Coast'

The Rock beneath our feet!

Rock can be broadly classified into three types. Igneus, metamorphic and sedimentary, with the Jurassic Coast being of the sedimentary type

Igneus, is the rock that originates from magma within the earth's crust, produced by volcanic activity, when it is found on the earths surface
Metamorphic is the rock that is transported into the depths of the earth by geological processes, where it is heated and compressed. This process eventually changes its composition

Sedimentary rock is created by processes that occur on the surface of the earth, by the weathering of existing rock by water, ice and wind. Sedimentary rocks may consist of the organic remains of marine organisms (limestone), land plants (coal) or chemical reactions and evaporation (salt). Sedimentary rocks that constitute the Jurassic Coast are formed largely of the remains of marine animals. Sedimentary rock is often created by the weathering and re-deposition of pre-existing rock, with the parent rock being of igneus, metamorphic or sedimentary type. Rock particles, once created, are generally carried to distant locations by water, wind or ice, before sedimentation occurs

In past times of high sea levels, shallow seas have flooded deep inland and produced vast continent-wide limestone deposits. Chalk is a form of limestone, that developed in the Cretatious era. This rock was formed by millions of tiny plates of single-celled microorganisms called coccoliths. Over a few million years thier calcite plates piled up on the seabed to form a carbonate mud, which is now a form of limestone, up to 300 metres thick. This chalk forms the spectacular white cliffs of Southern England and North Western France

Any fossil content within a sedimentary rock will indicate its age and the type of environment in which it was deposited. Sedimentary rock often contains organic and inorganic materials. For example, early Jurassic black mudstone, found in the cliffs of Lyme Regis, contains organic material in the form of fish teeth and ichthysaurus bones. The mud itself is made of small inorganic rock particles, but its black colour suggests a high carbon content, the result of decomposition of the soft parts of organisms

Most sediment is deposited underwater, and is then buried further before it becomes rock. The exposure of marine sediment above sea level is due either to tectonic plate processes such as earthquakes and volcanic activity or to a general decrease in sea levels such as is associated with glaciation. Once sedimentary rock is exposed, weathering begins, particles are transported, and the cycle begins again

Fossils

I have wanted an ammonite for many a long day now, and as you can see from this picture, I am now the proud owner of one. However, all is not as it seems ... I bought this one for a few pounds in Lyme Regis. It is a Promicroceras Planicosta and was found at Lower Lias, Lyme Regis ... it is approximately 190 million years old!



Ammonites are an extinct member of the molusc family, possessing an external shell, coiled in a flat spiral and divided into chambers. They appear in the Carboniferous period and mysteriously died at the end of the cretatious era

Geologists are able to use fossils to help them identify rocks of similar age. Rocks which are hundred of miles apart can be recognised as being of the same age due to the fossils that they contain. Ammonites are especially good for the purpose as many evolved and changed rapidly (in geological terms), producing different species with distinctive shell forms. The Jurassic has been divided into a series of zones based on the appearance and disappearance of different ammonites

Source: The Official Guide to the Jurassic Coast