IrIsh FossILs serIes
Plaster cast of the two cm long Phillipsia kellii, an Irish Carboniferous trilobite from Ardipodien, Co. Kildare. Courtesy, TCD Geological Museum. Since trilobites are now extinct, the only way to study them is through fossil evidence. As with any organism, it is extremely rare for any soft parts to be preserved as fossils and it is the dorsal surface of trilobites that is usually fossilized. In fact, any discarded moult found on the sea floor would have represented a potential fossil. In Ireland, trilobite fossils have been reported in the following localities, among them Portrane shore, Co. Dublin, Hook Head, Co. Wexford, and Tramore, Co. Waterford. Just look for the gleaming eye in that shale! Trilobites certainly hold a special appeal in the imagination of palaeontologists and fossil enthusiasts alike. For instance, take a stroll through the streets of Prague, the city where Joachim Barrande, French palaeontologist, made pioneering discoveries on trilobites in the 19th century, and you will find the “Trilobit Restaurant”, named and decorated in honour of these curious arthropods and serving delicious dishes such as “Mr.Barrand’s meat” and “Trilobit feast.” Trilobites first appeared in the Early Cambrian (c. 542 million years ago) and became extinct at the end of the Permian (c. 250 million years ago). The Permian mass extinction was also responsible for the demise of many other taxa, such as rugose and tabulate corals, and its cause is still a matter of debate. Perhaps, had this extinction event not occurred, trilobites would have lost their allure by now, and we would consider them nothing more than common pests, to be fished out of rock pools by children and carefully avoided by scuba divers! Then again, the magic of palaeontology lies in its ability to evoke lost worlds. Some say trilobites do it best. Anthea Lacchia, a TCD geology graduate is working on a two-year research masters in palaeontology. To find ouT MorE Irish Fossils by Patrick Gaffikin, Appletree Pocket Guides. Trilobite!: Eyewitness to Evolution by Richard Fortey.
Terrific TrilobiTes
Anthea Lacchia introduces us to some Irish fossils
rilobites are an extinct group of marine organisms, superficially resembling present day woodlice. They are classified as arthropods, a group that also includes crustaceans and insects. Turn back the clock to Ordovician times, circa 488 to 443 millions years ago, and look into the murky waters and there you would witness trilobites crawling on the sea floor, burrowing their way into ancient sediments, or eerily floating in swirling water masses. What were these creepy crawlies of the deep really like? A lot is in the name; trilobites had a body divided into 3 lobes, specifically one axial and two lateral lobes, and they can also be divided into head, thorax and abdomen, known in scientific circles as cephalon, thorax and pygidium. They possessed a tough exoskeleton, which they periodically moulted as they grew, and their eyes and limbs are complex enough to fill the pages of many scientific papers. Both shallow and deep-water forms existed and it is generally thought that trilobites which were either blind or had reduced vision dwelled in deep waters, below the photic zone. They Triarthus eatoni from Beecher’s Trilobite Bed, certainly colonised a range of different ecological environments and reproduced Ordovician, New York, which shows appendages preserved in iron pyrites. sexually by laying eggs. Some fossil trilobites have been found with associated Ptychoparia striata, a Cambrian trilobite from brood chambers, a discovery, to the Ginetz, Bohemia, Czech Republic. palaeontologist, akin to that of a cowboy striking gold. The limbs were sometimes used for swimming and some trilobites developed spines that may have been used to aid floating. interestingly, when danger loomed, trilobites could “enrol” or curl up into a ball or capsule and await safer conditions.
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