An extinct life form , is an animal, or plant with is no longer physicallly alive on our planet. Extinction has been going on for millenia, though we tend to associate it with the effects of man at present.
So what is limestone?
There are many EarthCaches which talk about this rock, but basically it is a rock and is rich in the remains of other organisms which lived in a shallow tropical sea. We have come to look at a certain type of fossil which is found in this limestone. Namely an extinct nautilus.
An artist's impression of a simplified cross-section through a ‘living‘ nautilus
Nautiloids were marine animals. They had a coiled external shell similar to that of the modern nautilus. In other living cephalopods, e.g. octopus, squid and cuttlefish, the shells are small and internal, or absent.
The nautiloid's shell was divided into chambers separated by walls known as septa (singular septum). These strengthened the shell and stopped it from being crushed by the external water pressure. Nautiloids could probably not withstand depths of more than 100 metres.
The creature lived in only the last chamber, the body-chamber; earlier ones were filled with gas or fluid which the nautilus was able to regulate in order to control its buoyancy and movement, much like a submarine.
There is a visible example of a nautilus in the stone of the Castle Howe Memorial
In order to log a find against this EarthCache you will need to answer some questions and send your answers to me via the Messenger facility or through my my profile .
1) You will find the nautilus on the same side of the memorial as the inscription plaque, directly below the lip. Please describe the nautilus to me. What colour is it? Which way is its orientation? Is it a complete fossil showing the chambers?
2) Please measure the precise diameter of the nautilus shell.
3) Please include a photo of yourself or your GPS at site as proof of visit.