The Dead at Castle Rushen EarthCache

The listed coordinates will bring you to a little garden area located just outside the walls of Castle Rushen (you don't need to pay to enter, it's in a public area). However, the dead we seek here at the castle for this EarthCache are not commemorated with statues - nor are they connected with the many that died during the long history of Castle Rushen. The dead you are seeking are found in the limestone rocks of the castle itself and died about 330 million years before anyone even thought about building the castle...

Castle Rushen is well known for the limestone from which it is constructed. The attractive, light coloured blocks are used throughout the thick towering walls and have stood up well over the life of the castle. The Isle of Man is often thought of as an island of slate, but in fact there is a wonderful range of geology in different parts of the island and in this area limestone is easily found - you can find the old quarries in the local area from where the stone was taken. Limestones in the South of the Island were formed, in the Carboniferous period, around 330 million years ago.

When Limestones were formed the Isle of Man was positioned close to the equator with much of the Island submerged beneath a shallow, tropical sea. This sea was inhabited by organisms such as corals, crinoids (a type of brittle star), numerous shellfish, primitive sharks and algae. The algae would grow together as clumps of slime on the sea bed. The slime would accrete calcium carbonate and trap mud, building up a solid mound of limestone representing an early form of reef. Courtesy of Manx Geology.

Sharks Teeth

Shark teeth are a common type of fossil for a number of reasons. First, shark teeth, like most teeth, are made of dentin, a hard calcified tissue that does not easily decompose. Dentin is harder and denser than bone. In a tooth, the Dentin is surrounded by a very hard enamel shell.

An example of a shark tooth fossil (centre)

Secondly, to maintain a sharp smile, shark teeth are designed to regularly fall out and be replaced. If a shark has 40 or 50 teeth in its front dentition, and that dentition is replaced every few weeks, it takes no leap in logic to realize a shark can go through tens of thousands of teeth in a lifetime. Different estimates for different sharks range anywhere from 25,000 to 50,000 teeth lost in a lifetime. Now multiply that by millions of generations of sharks over tens of millions of years, and presto, shark teeth are the most common fossil. 

Crinoids

Because many crinoids resemble flowers, with their cluster of waving arms atop a long stem, they are sometimes called sea lilies. But crinoids are not plants. Like their relatives--starfishes, sea urchins, sea cucumbers, and brittle stars - crinoids are echinoderms, animals with rough, spiny surfaces and a special kind of radial symmetry based on five or multiples of five. Crinoids have lived in the world's oceans since at least the beginning of the Ordovician Period, roughly 490 million years ago. They may be even older. Crinoids came close to extinction towards the end of the Permian Period, about 250 million years ago. The end of the Permian was marked by the largest extinction event in the history of life. The fossil record shows that nearly all the crinoid species died out at this time. The one or two surviving lineages eventually gave rise to the crinoids still populating the oceans today.

Three different types of crinoid fossil you might spot

In general, crinoids have three main body parts. The first, the stem, attaches the animal to the ocean floor and consists of disk-shaped pieces stacked on top of each other. These stem pieces come in a variety of shapes - round, pentagonal, star-shaped, or elliptical - and each stem piece is perforated in its center. Rarely are crinoids preserved in their entirety: once the soft parts of the animal decayed, sea currents generally scattered the skeletal segments. By far the most common crinoid fossils are the stem pieces.

Brachiopods 

Brachiopods are marine animals that secrete a shell consisting of two parts called valves. Brachiopods have an extensive fossil record, first appearing in rocks dating back to the early part of the Cambrian Period, about 525 million years ago. They were extremely abundant during the Paleozoic Era, reaching their highest diversity roughly 400 million years ago, during the Devonian Period. At the end of the Paleozoic, however, they were decimated in the mass extinction that marks the end of the Permian Period, about 250 million years ago. This event, known as the Permo-Triassic mass extinction, may have killed more than 90 percent of all living species. It was the largest of all extinction events (larger than the major extinction at the end of the Cretaceous that killed off the dinosaurs). Although some brachiopods survived the end-Permian extinction, and their descendants live in today's oceans, they never achieved their former abundance and diversity. Only about 300 to 500 species of brachiopods are exist today, a small fraction of the perhaps 15,000 species (living and extinct) that make up the phylum Brachiopoda.

A brachiopod fossil

Brachiopod shells come in a variety of shapes and sizes. Sometimes the bottom valve is convex like the top valve, but in many species the bottom valve is concave or occasionally conical. The outer surface of the valves may be marked by concentric wrinkles or radial ribs. Some brachiopods have prominent spines, but usually these are broken off and are found as separate fossils. The shells of living brachiopods typically range in size from less than 0.25 inches to just over 3 inches in length or width. Fossil brachiopods generally fall within this same range, though some adults have shells that are less than 0.04 inches in diameter, and an exceptional few have shells that are 15 inches across.

Because of their worldwide abundance, diversity, and rapid evolution in the Paleozoic, brachiopod fossils are useful indicators of the ages of different rock layers. By matching the brachiopod species contained within rocks deposited in different locations, paleontologists can determine that the rock units were deposited at the same time.

Coral

Corals are made up of small invertebrate animals, known as zooids, that look like tiny sea anemones. They feed on small food particles they find in the water around them. Together, many zooids form colonies, many colonies form reefs. Coral reefs can be massive structures, stretching hundreds of miles. The Great Barrier Reef in northern Australia can be seen from space. The oldest coral fossils are over 500 million years old. The earliest forms were different from those we see today and they died out 225 million years ago. Modern corals are still common in tropical oceans.

A coral fossil

Corals are very important fossils. Many corals have a hard exoskeleton made of calcium carbonate. It is this exoskeleton that is usually fossilised. When the coral dies, the skeleton can be broken down to form limestone, the important building stone you see here. Fossil corals also tell us about the past. Since many corals live in warm, shallow sea water, their fossils are good indicators of environmental conditions. This tells us that the area where the fossils were found must have had a much warmer, tropical environment at certain periods in its history.

The listed coordinates are in a little garden area in front of the castle. There was a statue of Captain John Quilliam here but as of September 2020, this has been relocated. I've left the original photo I took but also included a new one kindly provided by the Wombles so it should still be easy to identify the right place. This is in a public area outside the castle walls and there is no need to pay to enter the castle to complete the EarthCache. If you do go inside, keep a look out for more stones though, who knows what you might see!

There not fossils in all the stones of the castle, just certain ones. Clearly the stone used in the construction of the castle came from more than one quarry and it was probably just one particular quarry that will have provided the fossil stones. There are however a number of stones containing fossils to be found and here at Castle Rushen, the fossils are often spotted in the slightly darker (navy) coloured limestone. Please use the old and new spoiler photos to find a particular stone packed with fossils to ensure you don't leave disappointed and this should be the one you use to answer the questions. However, please feel free to expand your search. I spotted several other stones with fossils in the wall between the bench and the entrance into the square, and there will be many more. If you can't see the photo for any reason, the stone you are looking for is about 1 metre about the right hand end of the bench. 

Please answer the questions by sending me a message or email via my profile. Please try to send the answer at the same time as submitting your log, or soon afterwards. If your answer is not received within a reasonable timeframe, your log may be deleted. Please note when using the official app in the field, you need to see 'message sent' appear after you've sent the message - please check it has been successfully sent by checking the message center as it doesn't always work if the signal is low. Do not post answers in your online log, thank you.

1) From the types of fossil outlined above, what is the predominant type of fossil you see here?

2) Look for the biggest fossil in the stone and give me the approximate size (length/height). Where in the stone is it located? (E.g. middle, top left, top right etc)

3) Describe the general appearance of the predominant fossils.

4) How many fossils (approximately) do you think might be in this one stone? Choose either 10, 100, 1000, 10,000. Remember you can only see one side of a stone that is much bigger and the fossils will be continious throughout the block.

Now have a walk towards the main square and look for other fossil stones between the statue and the tower (and in the bottom of the tower). Question 5 is optional as I don't want to put you off if you can't find the stones but it's a fun task and worth a look.

5) Find some other fossil stones. How are they different? Are there more or less fossils in the other stones you see? Are the fossils the same type - how are they different? Have you identified any other types of fossil whilst examining the stones? This last question is an optional task, not required for logging, so I'm going to leave it to you as to how much detail you wish to share. I have included it because the other stones are a little different and are worth a look, but don't worry if you can't find them.

Optionally, please include a photo of yourself or GPSr with in the gardens as additional proof of your visit. Ideally, please avoid spoiler photos of the fossils that might give away the answers.

Please note, on rare occasions, the gardens may be locked due to works in progress, dangerous masonry/trees etc. Signs are not always put up with an explanation. Whilst unfortunately, it is unavoidable and a consequence of the times we live in with people complaining and organisations concerned about their liabilities. If you cannot access the EarthCache this is unfortunate but just one of those things. Please just post a note to alert others to the situation.