exotic phacopid trilobite of Family Acastidae comes from the Devonian
limestones in trhe Anti-Atlas Mountains of Morocco near Foum Ziguid,
where a huge diversity of other trilobites are collected. Some years
ago now it was known in the commercially
trade as Trident Comura, and was highly sought by collectors. The “trident” trilobite
nickname persists today. Recent years have seen trilobite workers expend
a huge effort on the trilobites of Morocco, as they are some of the
finest to be found, highly diverse, and usually are preserved in life-like
three dimensions (as often is the case in limestone as opposed to shale).
is illustrative of the hard work in Morocco with many publication appearing
over the past 15 years. As work proceeded, Morzadec (2001) named the
species Walliserops trifurcatus at a time when but one species of walliserops
was known. Soon thereafter, Brett and Chatterton (2001) erected the
new genus Parabolops, with two species, Parabolops neptunis with a
longer trident, and Parabolops hammi, another trident having a shorter
forked trident; Morzadec’s work won out and the Walliserops genus
name stuck. By the time of Chatterton et al.’s 2006 paper, the
long-forked species shown here was named Walliserops trifurcatus, and
two shorter-forked species named Walliserops tridens and Walliserops
hammi. Other variations of Walliserops have been discovered (e.g.,
Walliserops lindoei and Walliserops hammi), some as yet undescribed.
is unprecedented among more than 20,000 trilobite species, an evolutionary
enigma, and a functional mystery. Many hypotheses have
been put forth regarding why the adaptation took place and the purpose.
The appearance of such a prominent phenotypic trait would ostensibly require
considerable “evolutionary energy”, for which some substantial
selective advantage would be expected for its possessors. Energy would
also be expended to grow, and possibly regrow, the protuberance which might
have made shedding its exoskeleton more difficult, and it hardly benefitted
the trilobites steamlining. Moreover, the trident itself lacks the bilateral
symmetry, curving away from the body axis, and distinctive trait among
most animals, arthropods and trilobites. Further, there is variability
in the trident curvature, with shorter tridents more curved. Several uses
of the trident have been discussed: 1) a means of levitating above the
3) a mechanism for hiding or defending; 4) a mere adornment of sexually
(dimorphic) selection as in the staghorn beetle; 5) sexual or caste polymorphism
as in social insects. Of course, a combination is plausible, for example,
sexually selected armament.
As with many
other Devonian trilobites, Walliserops sported an impressive array
than 50 spines as protection in a
sea where predator skills and
weapons were also evolving. And then, of course, there the trilobite
has crystal Schizochroal eyes that were only in trilobites of Order
Phacopida, Suborder Phacopina, and which are beautifully preserved
in this specimen.
Morzadec P (2001). "Les Trilobites Asteropyginae
du Dévonien de l'Anti Atlas (Maroc)". Palaeontographica.
Abteilung A (in French) 244 (1–3): 53–85.
B, Fortey RA, Brett K, Gibb S & McKellar
R (2006). Trilobites from the Lower to Middle Devonian Timrhanrhart
Formation, Jbel Gara el Zquilma, southern Morocco. Palaeontographica
- Knell RJ & Richard A. Fortey RA (2005). "Trilobite
spines and beetle horns: sexual selection in the Palaeozoic?".
Biology Letters 1: 196–199.
see: Moroccan Trilobites;
Images provided by Fossil
Mall, where you can also see other
Walliserops species: Walliserops
hammi ; Walliserops
n. sp aff. lindoei ; Walliserops n. sp aff. tridens