What happened here? A Silurian mystery.

Look carefully at the rock pictured below. What can we find out from it?

Use your mouse to explore the picture and do some close-up investigation. Hint: There are seven areas to investigate.

There is also a more accessible version of this page available. Higher resolution and printable versions of this image are also available here.

When you've made your observations, consider the facts and questions listed below.

Wenlock fossil assemblage
area 1
solitary rugose coral This cone-shaped fossil is a solitary rugose coral. The coral skeleton is strong and compact, so is not easily broken by storm currents. The coral would live with the point of the cone buried in the sediment - so it has been moved from its life position.
area 2
net-like bryozoans Net-like bryozoans were fragile colonies of tiny creatures which lived standing upright to fan the water for food. They could not have fed lying on the muddy sea floor or living so close together. The shell is upside down. We know this because brachiopods usually live with their curved-edged shell resting on the mud.
area 3
colonial coral This colonial coral liked to live in clean sunlit water - it cannot live where there is too much sediment in the water, which would have clogged its tentacles.
area 5
fragments of broken bryozoans, brachiopods and a small piece of crinoid stem Here are many fragments of broken bryozoans, brachiopods and a small piece of crinoid stem. They are fragile and easily broken by currents. They are also relatively light, so may have been moved from where they were living. The brachiopods, corals and crinoids may not even have been living close to each other.
area 6
fragment from a crinoid stem In the centre of this picture is a fragment from a crinoid stem. The flattened cylinders articulate to form a long stem-like structure which holds the head of the crinoid above the sea floor.
trilobite At the very centre of this picture is a Calymene trilobite. Look closely to see its large "nose" (glabellum) and eyes. The smooth fossil just above it is the top part of a cystoid.
brachiopod shell This tiny brachiopod shell is complete. Brachiopod shells have two parts (valves) which fit closely together and hinge open to feed. We can see both valves of the shell are still joined together, although it is lying on its side. If it was in its life position we would only be able to see the uppermost valve.

First, think about the facts - things that we can know and see.

  • The rock is a limestone, made up from fine-grained calcium carbonate mud and lots of remains of the shells and skeletons of creatures.
  • Many of the fossilised creatures look the same as or very similar to creatures which build or live in and on reefs today.
  • Some of the fossils look broken.
  • The fossils are all jumbled up together in the sediment.

The last two observations are very interesting and lead us to ask some more questions - a more detailed investigation is needed here ...

Are all of the fossils broken?

Why are some of the fossils broken?

Did the animals live in the positions that we find them in now as fossils?

Wenlock Creatures