Burren and Cliffs of Moher UNESCO Global Geopark - Geology

Fossil crinoids – finding the ‘new’ in
the old
The limestone of the Burren is packed with fossils. It is
reasonable to say it is made of fossils. A lot of the time
we don’t see them because the surface of the limestone
is covered by algae or lichen but just below the surface
lie the remains of animals that lived in a tropical shallow
sea, 330 million years ago. And of all the fossils in the
limestone, bits of fossil crinoids are the most abundant.
Crinoids come in a variety of forms, the most typical
being a long narrow stem, with a globular body or ‘calyx’
on top and multiple long feathery-looking arms extending
upwards from that. They look a bit like ferns and are
also known as ‘sea-lilies’ or ‘feather stars’. Crinoids were
abundant in the Carboniferous shallow seas and they are
still found in the world’s oceans today although generally
in deeper water, so they are rarely seen. Crinoids belong
to the echinoderms, so they are closely related to sea
urchins, sand dollars, starfish and even sea cucumbers.
Like many sea creatures, crinoids make their hard parts
out of the mineral calcite. It is the hard parts that survive
to become fossils. For crinoids, their hard parts are a
series of discs stacked on top of each other that make up
the skeleton of the stem and arms of the animal. During
life, these are attached together by ligaments giving the
animal a degree of flexibility to wave around in ocean
currents, where they use their arms to collect food from
the water.
Unfortunately, most fossil crinoids in the Burren
limestone are not complete, they were separated into
their individual pieces shortly after they died, when the
connecting tissues had decomposed or were eaten. These
pieces of crinoid were then moved around on the seafloor
by waves and currents and broken up even further by
burrowing organisms or scavengers before being buried
and turned to rock. These individual circular sections of
stem are known as ‘ossicles’ and vary in size from 1mm
to about 20mm in diameter. When alive, the stems can
be over 1m long but after death they break up, however,
sometimes short sections of stem survive intact. While
finding a complete fossil crinoid in the Burren is unlikely,
because each crinoid has hundreds of individual pieces,
this means there are a lot of crinoid pieces to be found.
When palaeontologists find ‘new’ species, they are of
course finding old fossils and just giving them a new
name. My Geopark research with Dr. Steve Donovan on
fossil crinoids has already identified a ‘new’ 326 million
year old species (Heloambocolumnus harperi) from
Doolin, a crinoid unknown anywhere else in the world.
As I find more specimens, this ‘new’ material should
provide even more ‘new’ fossil discoveries in the coming
years.
Figure caption: Fossil crinoids from the Burren. Left, fossil crinoid ossicle unique to Doolin; centre, typical preservation of crinoid bits; right,
short section of intact stem.