The best way to do this, for me, is a visit to the east
coast of England and the search for shark’s teeth. This is one of those pursuits
best reserved for the winter time and a trip soon after the holidays is a great
way to unwind and get some air in those lungs. There are many sites to choose
from and I tend to pick one that is a little off the beaten track and not over
exposed. I will not be revealing where this site is since it is relatively
little known, does not suffer from over hunting and, as a result, usually
provides a few teeth. So many exposures these days are virtually exhausted
until a rock fall or a spring tide comes in to scour the beds.
All of the east coast beds are Eocene age – around 50
million years old and are representative of a rich marine life. All of these
various sites are part of the London Clay Formation of which the most famous,
the Isle of Sheppey, has yielded the most extensive fauna of all. The large and
varied invertebrate fauna that is found consists mainly of animals that lived
on the sea floor or attached themselves to rocks in the surf. Marine turtles
have been found as well as a large fauna of fish. The rarest fossils are those
of land animals such as crocodile, hippo, birds such as Prophaethon and that most iconic of fossils – the dawn horse Hyracotherium (Eohippus).
The sea during this time was a warm, highly oxygenated low
energy shelf environment and the London Clay was deposited over a period of
five transgression events. During this period, which covered around 4 million
years, the fish were masters of the seas and chief amongst those were the
sharks and their teeth can be locally abundant at some localities. Just why are
sharks teeth so abundant as fossils anyway?
Well it is, of course due to the amount of sharks that were
present during this time and the amount of teeth that were constantly being
shed throughout their lifetime. We have to realise that there were no vast
fishing fleets depleting the seas of fish and sharks and, just as any ocean
throughout prehistory, a sea teeming with life must have been a sight to
behold.
Sharks have a living conveyor of teeth which constantly
replace those that are lost. It is a remarkable mechanism which most people do
not appreciate and the fact that the teeth are set in the gums of the shark in
layered rows, as opposed to being fixed in the jaw, often catches people out by
surprise. But despite the abundance of teeth lost, not all are fossilised and
there is still an element of luck required to ensure fossilisation.
When teeth are shed or lost, just like any other fossil,
they have to be buried quickly to stand any chance of fossilisation. Have you
ever wondered why there are hardly any modern day shark teeth found on the
beaches of the world? Because shark teeth are essentially made up of calcium
phosphate and, without a quick burial, would disintegrate over a period of
time.
Burial prevents decomposition of the tooth by oxygen and
bacteria and the slow process of fossilisation takes place. Gradually mineralisation
occurs and the teeth absorb these minerals from the sediments they are buried
in.
Those of you who are familiar with fossil sharks teeth will
be familiar with their beautiful colours. Some are blue, some are green, a few
on occasion are red and others can be ivory but the most common colour, by far,
is black. How do these teeth end up in these colours when, at time of deposition,
they are all white? Well the minerals that are absorbed are instrumental in
influencing the colour of the tooth simply because the chemical composition
dictates the colour as it replaces the calcium. This is the same with all kinds
of fossil teeth all over the world – including dinosaur teeth.
Finding sharks teeth is not as simple as you may think. Sure
there are occasions when a nice specimen will be sitting on some sand and you
can just walk up and pick it up and you think “hell this is easy”. The truth is
that you often have to really work for your teeth but if you are patient and
get your eye in then the rewards are there.
My last trip was on the back end of a gale and I arrived an
hour or so after high tide so that I could search on a falling tide. The sea
was crashing in to the shore with some ferocity and I was excited at the
prospect of finding some nice specimens. However, despite the fact that the
tide had turned, the rough sea ensured that there was still no way onto the
shore and I had to be patient and wait. Unfortunately, this was the only day
that I could get here with the tide in my favour and even then I only had a few
hours prospecting before dark.
Eventually the tide relented and I was able to start
looking. The majority of sharks teeth at this particular site are black in
colour and the shore is particularly “noisy” when you are trying to
differentiate teeth from everything else. “Noisy” is my way of describing a bed
where there is a lot of collateral material such as seaweed, algae, sand,
shingle, a selection of man-made bits and copious amounts of shell debris. The
Oxford Clay is also “noisy” in some beds due to the amount of fossil debris
that accumulates and finding material of consequence can be difficult.
The best way to search, unquestionably, is to get on your
hands and knees and get intimate with the beds. This is best done with some
form of knee protection of which the best things to use are knee pads and these
are readily available at any hardware store. Do not neglect your back though
since bending over for long periods can have consequences if you are not use to
such exertion or if you have had back issues in the past.
Other than that, you just have to get your eye in and once
you have found a couple of teeth then they can turn up at regular intervals.
Light levels can be important too and sometimes morning light is often
preferable to other periods of the day as the sun is lower and tends to bounce
off the enamel of the teeth betraying their presence although, in truth, you
can find them at any time of the day. Indeed, on this trip, I found two in quick
succession when it was virtually dark and the sun had disappeared – there was
just enough reflection for me to spot them.
Despite what I thought were good conditions, larger teeth
were largely absent although I managed to find 18 smaller teeth of which a few
examples are quite delightful. Fossil sharks teeth are stunning and are often
beautiful to look at and are a proper Nature’s gem which I believe are often
taken for granted. Please don’t since it is still a form of miracle that they
fossilise in the first place and, in the case of these teeth, are over 50 million years old. Wonderful.
So this is how I beat the Christmas blues and have done so
for a few years now. It does not compare with digging for marine reptiles or
excavating dinosaur remains in the south but it still fascinates and I love
doing it as much now as I did the first time I searched for sharks teeth.
Searching for sharks teeth is not just for Christmas and I do a few trips every
year but if you want dust off the cobwebs and fill those lungs with ozone after
the festivities, then I can think of nothing better.
 |
| Just look at this stunning preservation |
0 comments:
Post a Comment