The ‘trident’ trilobites of Morocco
Dr Kendal Martyn (UK)
Spectacular “spiny” adaptations of the Devonian (about 380Ma) trilobites of Morocco are well known. Free-standing spines, sometimes up to one hundred on a single specimen, make for spectacular (if fragile) specimens. Historically, similar species were first recognised way back in the 1880s by the classic work of Barrande on the fossils of Bohemia (in what is now the Czech Republic).
More recently, the large-scale commercial digging of trilobites in the Anti-Atlas of Morocco, coupled with improved preparation techniques, has produced a wealth of information and new forms. As the digging around Djebel Issimour got tougher during the mid-late 1990s, this lead to people digging further afield. Near Foum Zguid, they found something new – a trilobite with a trident.
Now called Walliserops trifercatus (Morzadec, 2001), many features relate this trilobite to more widespread asteropygid trilobites such as Comura bultynki and Quadrops flexuosa (also known as Phyllonix phyllonix).
Walliserops trifurcatus is hard to find: one person, one week (full time) for one specimen (often incomplete). In fact, getting hold of a complete specimen is hard: getting it out of the rock without butchering it is harder still (see an unprepared trilobite and you’ll see what I mean).
Debate started almost immediately on the purpose of the trident: hood ornament; antler; defensive spear; sensory organ or feeding aid. Discovery of a smaller, short-trident form at the same locality, Walliserops sp., suggested sexual dimorphism: a male/female difference in form, for example, antlers on deer. Discovery of yet another small, short trident form put paid to sexual dimorphism: three separate species seem to be represented. But then, any male/female adaptation in fossils is hard to prove.
Speculation is likely to continue for some time. Most of the uses proposed seem to revolve around behaviour, evidence of which is notoriously hard to find, demonstrate or associate with a specific species in the fossil record. Feeding or defence seem to have the edge at the moment.
Trident trilobites were once thought to be examples of a highly peculiar fauna limited to one location. Erbenochil – “the trilobite with eyeshades” – comes from the same location. Once again, however, the rocks surprised those in the know. Around the classic locality of Djebel Issimour, yet another species was found, Walliserops “issimourensis”, now in the collection of the Royal Ontario Museum in Canada, which is a short, fat, trident form this time.
The rocks could well surprise us again … It is worth noting that it took 20 years after the first specimen of W. trifurcatus was found before its description was properly published. So, we might need to keep an open mind for quite some time.
Further reading
Trilobites of the World: An atlas of 1000 photographs, by Pete Lawrance and Sinclair Stammers, Siri Scientific Press, Manchester (2014), 416 pages (Paperback), ISBN: 9780957453036.
Trilobite!, by Richard Fortey, Flamingo (2001), 256 pages (Paperback), ISBN-13: 978-00065513-6.
Palaeontigraphica Abt. A. 162:53-85.
Reference
Morzadec, P. (2001): Les Trilobites Asteropyginae du Devonien de l’Anti-Atlas (Maroc).