Elliptocephala is an extinctgenus from a well-known class of fossil marine arthropods, the trilobites. It lived from the later part of the Tommotian to the upper Botomian. Elliptocephala can easily be confused with Ellipsocephalus, a trilobite genus of the Ptychopariida order.
Etymology
The species E. walcotti was named in honor of Charles Doolittle Walcott, a renowened early paleontologist, that described many trilobite species.
According to Lieberman E. sequomalus is an early species, close to the common ancestor of the genus. The rest of the species fall into two distinct groups. The first consists of the closely related E. bicensis and E. asaphoides, with E. walcotti and twin species E. praenuntius slightly less close and E. mediocris near the basis of this group. The second group consisting of the closely related E. mirabilis and E. lundgreni, with E. logani and E. parvifrons slightly further removed, followed by E. paraoculus, and E. laxocules near the basis of this second group.
Relationship within the Olenelloidea
Elliptocephala is the sistergroup of the clade comprising Wanneria walcottana, the Holmiidae, Fritzolenellus, Mummaspis, Laudonia, the Biceratopsinae and the Bristoliinae. Including Elliptocephala, this clade is the sistergroup of the Olenellidae.
E. logani was excavated from the Middle Olenellus-zone of the Northwest Territories.
E. lundgreni is present in
E. mediocris was collected in Northwestern Greenland, questionably from the Olenellus-zone.
E. mirabilis is found in Northwestern Greenland, questionably from the Olenellus-zone.
E. paraoculus is present in the Middle Olenellus-zone of the Northwest Territories.
E. parvifrons was excavated from the Middle Olenellus-zone of the Northwest Territories.
E. praenuntius occurs on the eastern Ellesmere Island, Canada, in what possibly belongs to the Lower Olenellus-zone.
E. sequomalus is found in the Middle Olenellus-zone of the Northwest Territories.
E. walcotti was collected in the Middle Olenellus-zone of the Northwest Territories (type section of the type section of the Sekwi Formation.
Description
As with most early trilobites, Elliptocephala has an almost flat exoskeleton, that is only thinly calcified, and has crescent-shaped eye ridges. As part of the Olenellina suborder, Elliptocephala lacks dorsal sutures. Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe of the central area of the cephalon, that is called glabella. The head shield of Ellipticephala carries backwards directed spines at the corner between the halfcircle shaped frontal and side margin and the backmargin that is roughly perpendicular to the midline. The frontal lobe of the glabella is roughly 1½× the length of the backward ring-shaped lobe and the most backward set of side lobes taken together, measured along the midline. L4 is also much wider than L0. Side lobes L2 and L3 do not merge with each other. The line between the backward tip of eye lobe and the junction of the back margin of lobe with glabella with the midline is 10-20°. L3 touches the eye ridge. L0 carries a node at the midline. The third thorax segment from the front is not larger than the neighboring segments and does not carry larger spines. Thoracic pleural furrows extend onto spines. Long backward directed spine on the midline of T15, and this spine is broad at its base.
