Trimerocephalus
Trimerocephalus is a genus of eyeless trilobites from the order Phacopida, family Phacopidae. It lived during the final stage of the Devonian, the Famennian, and became extinct at the end of this stage, together with all other trilobites with the exception of some Proetida. It can be found in Australia, the Czech Republic, France, Germany, Iran, Kazakhstan, Morocco, Poland, the Russian Federation, Spain, and the United Kingdom.
Distribution
Species belonging to the genus Trimerocephalus have been found in Europe, Morocco, Iran and Australia. T. caecus has been found in the Upper Devonian of Poland, Germany, the Russian Federation, North Africa, and France.T. lentiginosus has been excavated from the Upper Devonian of the Russian Federation. T. cryptophthalmoides is present in the Upper Devonian of Kazakhstan, and the Russian Federation.T. dianopsoides occurs in the Upper Devonian of Poland. T. interruptus is deposited in the Upper Devonian of Poland.T. lacunosus has been identified in the Upper Devonian of Germany. T. lelievrei was collected in the Upper Devonian of Morocco.T. mastophthalmus is known from the Upper Devonian of Germany, Poland, England, southwestern Asia, and Kazakhstan.T. mimbi has been found in the Upper Devonian of West-Australia.T. nigritus is present in the Upper Devonian of France.T. polonicus occurs in the Upper Devonian of Poland.T. procurvus has been identified in the Upper Devonian of Spain and Germany. T. shotoriensis was excavated from the Upper Devonian of Eastern Iran. T. sponsor has been identified in the Upper Devonian of the Czech Republic and Spain. T. steinachensis is known from the Upper Devonian of Germany. T. tardispinosus has been found in the Upper Devonian of Australia.T. trifolius occurs in the Upper Devonian of Poland.T. vodorezovi is present in the Upper Devonian of Kazakhstan.
Taxonomy
Acuticryphops is probably ancestral to Trimerocephalus, and mainly differs from its descendants in having an eye lobe with a small number of lenses. Crônier, 2003, erected the subgenus Trimerocephalus containing T. trifolius and T. nigritus. In order not to be polyphyletic, T. would need to include at least T. steinachensis, and preferably T. dianopsoides as well. These species are in the same clade as T. mastophtalmus however, which is the type of the genus Trimerocephalus, which would by definition be in the nominal subgenus Trimerocephalus . This in turn would prompt the erection of another subgenus with all remaining species shown in the cladogram.
Description
Trimerocephalus is one of several phacopid genera that is eyeless. The dorsal facial sutures are not functional, so cranidia and free cheeks are not found separated. The marginal ridge bordering the cheeks is wide and convex. The part of the margin that is tucked-under and only visible when viewing the cephalon from the belly, is short and flat. The vincular furrow, a groove that fits the margin of the tailpiece or pygidium when the animal was enrolled, is wide and deep. The pygidium is about 3 times wider than long.