It is the impression of a cidaroid club spine in flint. Cidaroids are regular (displaying radial symmetry, not bilateral symmetry) sea urchins from the cretaceous period.
Yes, a lovely cidaroid spine. If you want to know more about sea urchins you might like to visit the Echinoid Directory at: http://www.nhm.ac.uk/research-curation/research/projects/echinoid-directory/index.html
Thank you for the helpful responses.My daughter will be thrilled to know what it is but I have a couple of other questions: how old is it likely to be and where and how would it have formed?
It looks similar to the club spine of Tylocidaris known from the Upper Chalk (Cretaceous) about 100-65 million years ago.
Chert and flint
What are chert and flint? Chert is a mineral formed of micro-cystalline siica, which is extremely small crystals of quartz (silica) tightly packed together.
Flint is a type of chert that formed in one particular time and place, in the soft white limestone rock called the Chalk during the Late Cretaceous period, 100 to 65 million years ago, towards the end of the time of the dinosaurs.
How and when was flint formed? The Chalk rock was formed in a sea which covered most of Northern and Central Europe and Britain. Tiny plankton called coccolithophores lived in the water column and over millions of years their accumulated calcium carbonate skeletons formed the Chalk.
Simple filter-feeding animals called sponges were also very common on the sea floor Natural bath sponges are the skeletons of sponges composed of flexible protein material containing no mineral matter. Many sponges have a different skeleton formed of tiny needles of silica called spicules.
After death, siliceous sponges were buried by later sediments, and the silica spicules dissolved under the higher pressure and temperature of burial. Chemical conditions later caused this dissolved silica to be redeposited. The redeposited silica formed the flint that replaced the Chalk rock in the layers (tabular flint) and rows of scattered lumps (nodular flint) that can be seen in white Chalk cliffs such as those at Dover.
Chalk crops out at the surface in a swathe across Britain from Dover to the Yorkshire coast, but flint from the Chalk can be found all over Britain. Flint is hard and insoluble, so that when the Chalk has been dissolved or washed away by weathering the flint remains behind. Flint nodules are broken up by frost, stream or wave action, and the last two of these wear the fragments into round pebbles. Flint has been transported all over the country by the sea, rivers, glaciers in the past and by people.
I suggest you keep all this information together with your specimen. If you would like me to send you specimen labels for your collections please email me at IAS2@nhm.ac.uk
All the best,
Fiona, thank you very much for this information. Would I be correct to think the spine would've been buried by sediments and then decomposed, having left its impression on the forming flint, then, through weathering, the flint was eroded and the impression revealed? Do you know how long would this process have taken?
Thanks again, it's great to finally get an understanding of what this is!
Absolutely .... well done. The length of time for this process to take place is a tricky question - other than a very long time.
Thanks Fiona. I'm guessing we're talking millions of years but impossible to know for certain I presume. The wiki page for flint says, "Certain types of flint, such as that from the south coast of England, contain trapped fossilised marine flora." How appropriate!
This pebble has been a mystery to us for years and I'm glad I finally made the effort to find out about it. When my daughter comes home from uni I'll fill her in on what I've discovered about her find, which she made when she was 11, on her Year 6 school journey to Osmington Bay, near Weymouth, Dorset in 2005. She was on a beach walk with her class when they stopped for a rest; she picked up a pebble and was about to throw it into the sea when she turned it over and saw this beautiful little fossil impression. When she showed it to me I was amazed and resolved to find out what it was but it's taken me this long to get round to it. I'm glad I did!
I will email you as you suggested for some labels and will keep this information with the find. I am very grateful to you and quagga for solving the mystery of the little fossil pebble for me and my daughter. Thank you
You are very welcome - I am glad the mystery has finally been solved. Thank you for telling us about the find which could so easily have been lost in the sea - a treasure for a lifetime!