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Trilobites to arms!

With lance and sword

The most interesting and sought-after (and therefore the most expensive) trilobites are those that – thanks to their bizarre appearance – stand out from the crowd. Spiny trilobites! This term, of course, is not a scientific one, but one most commonly used by enthusiasts. The term includes all trilobites that have an armour with spines attached to them or have parts of armour that may resemble anything down from a sword to a trident or even a fork. Not only trilobites of the order Lichida may look like the well-armed knights of the Palaeozoic, but also other taxa were represented in this exotic-looking bunch of arthropods.Which functions could these spectacular bodily extensions have fullfilled?

Drotops armatus When commercial fossil hunters in Morocco exposed a whole series of the utmost unusual looking trilobites, people first thought of them to be fakes - and not entirely without reason. As time passed by specialists and collectors got on their toes when dealing with any Moroccan trilobites. Yet as more and more of these fossils entered the market, even scientists took some of these to examine them and could soon conclude that authentic specimens were among them as well. Of course many pieces were partially restored, retouched or reconstructed, but the question whether all these exotic species actually existed in Morocco was answered.

Naturally, even before these events, spiny trilobites from Morocco and other parts of the world were known. The double-horned trilobite Dicranurus, for example, which also occurs in the USA, or the sword-bearing Psychopyge. And Joachim Barrande had described spiny trilobites like Selenopeltis buchii as early as the 19th century. From Germany the species Ceratarges had been long known, with it's characteristical curled backwards-pointing spines. No doubt existed that spiny trilobites were represented in many different taxa.

About the function and meaning of these morphologic features, scientists can still not entirely agree. In my opinion one could divide the different groups of bodily extensions into several different types.

cranidial forward pointing extensions, like swords (Psychopyge) and forks (Philonyx, Walliserops)
cranidial upward and backward pointing extensions like horns on the head. (Dicranurus, Ceratarges)
genal, backward pointing extensions, extended genal spines. (Cyphaspis and many others)
Pleural, mostly backward pointing extensions in the form of extended Pleurae. (Selenopeltis etc.)
Extensions in the form of many long spines across the entire thorax. (Terataspis, Drotops armatus)
Pygidial, backward pointing extensions in the form of extended pygidial ribs or telson. (Kettneraspis and others)

Mrakibina cattoi Forward pointing extensions, especially when very long, were up till recently considered to be tools or weapons of some sort. It was extensively spectaculated that the trilobite Walliserops with it's long fork dug through sediment in order to catch small soft-bodied creatures or other nutrition.The same was thought of Psychopyge's sword-like extension. I personally don't hold this interpretation to be very logical, because these as these extensions were preserved, they were made up out of the same rigid chemical composition as the other parts of armor of trilobites, and thus barely manoeuvrable. Extensions like these seem to be more likely to be part of a tool of increased mobility.

From the cranidium backwards-pointing extensions like those in the species Dicranurus and Ceratarges were often only said to be part of their defense mechanism, to scare off predators. This function would although not make much sense as part of their defensive enrollment, because the spines would not be positioned at such an angle that it would effectively be able to discourage a predator to leave it's prey. It is more likely other more logical explanations are in place, which I will explain further, later on.

Comura sp.Comura sp.
The functionality of a combination of extended genal spines and pygidial spines at the time of enrollment. (This text belongs to Sam Gon III's drawing of Comura)

Extended genal spines however, seem to have taken on some less disputable functions. For a starters they were helpful with taking off from the oceanfloor, this action in particular was also useful in the molting process for many different species of trilobites. Furthermore, when enrolled, they offer an effective protection, in this case positioning the genal spines pointing outwards resulting in an unpleasant surprise for any potential attackers looking to eat this trilobite as an afternoon snack.

Eoredlichida intermedia The same barely disputable conclusions can be drawn for pleural spines and pygidial extensions. They probably have fullfilled mainly defensive funtions. Undoubtfully this function also exists with trilobites which had clear rows of straight-standing spines (varying in lengths) divided in rows or different patterns across the thorax region of their exoskeletons (Drotops armatus, Terataspis or the Russian Hoplolichas). With other observations, different secundary meanings were attached to these spines. This was the result of a discovery that these spines were actually hollow, and would have probably served as extensions to which sensatory hairs which could have served for sensing things like currents and vibrations in the water. Ofcourse this interpretation is not watertight either, but to me it seems to be both credible and logical.

Walliserops trifurcatus Recently, Richard Fortey mentioned a new way of interpreting the previously described swords, forks, tridents and horns. The same interpretation had seemed logical to me since I first laid my eyes upon Dicranurus. I am although not even argueing my way of thinking was ahead of this true master of trilobites. Yet my general interest in nature and environment and the comparison to recent lifeforms led me to this conclusion from the very start on, and it was only acknowledged by other sources: That these extensions served as nothing more then attributes in fights that would have occured among trilobites.

In 2005 a cooperation between Richard Fortey and Robert Knell led to the article “Trilobite spines and beetle horns: sexual selection ni the Palaeozoic?” - this article is available in our external data archive – and had thus come to the following conclusion relating to a certain trilobite familiy:

"Raphiophorid trilobites commonly bore median cephalic protuberances such as spines or bulbs, showing a remarkable variety of form. It is unlikely that their primary function was for protection or in hydrodynamics. A case is made that they were secondary sexual features, by comparison with similar morphological structures developed on rhinoceros beetles and other arthropods. This interpretation is supported by four lines of evidence: their ontogeny, their diversity, the existence of plausible examples of sexual dimorphs in some cases and the fact that they show positive allometry."

Ceratarges spinosus Recent stag beetles primarily use their pincers for earning breeding rights, as do deers' antlers or marlin's bills. Insects, mammals and fish share this characteristic, and there is no argument against it that this could at least have been the case with some trilobite species. Ofcourse the question remains whether these armed trilobites were mainly males? Was it nothing more then sexual dimorphism, and how do the females look? Could it be that different described trilobite species were nothing more then the same trilobites of a different gender? Think of the extreme differences between certain birds like wild ducks or tropical parrots! Question after question arises.

Many of these questions are discussed about in our forum. Enthusiasts can join in on the the thread regarding this subject here: Deutungsversuche von Glabellafortsaetzen (The potential functions of glabellar extensions).

In any case spiny trilobites form a fascinating part of their hobby for many collectors. Thanks to the delicate nature of these spiny fossils, they require a great deal of patience and skill in order to get a succesful result from the preparation, consequently leading to expensive fossils, unless you do it yourself. In addition to that they often belong to the preferred objects of dubious preparators, who through large-scale reconstructions or more or less completely fake examples hope to earn a quick dollar or euro. That should although not scare off thecollectors to acquaint themselves with these magnificently fascinating trilobites.

Spiny trilobites, in all their many forms, are not only desired objects for their difficult and beautiful preparation, but also for the scientifically interesting functional meaning behind their morphology. This leaves us to hope that in the future, through further professional research on trilobites from Morocco and elsewhere, we will be able to gain more knowledge about these bizarre and interesting trilobites of the world.

Ptychopyge elegans

© Image of Walliserops trifurcatus on this page courtesy of PaleoDirect.

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Last Update : 01/30/2010 5:07 PM