Elliptocephala

Not to be confused with Ellipsocephalus.
Elliptocephala
Temporal range: late Lower Cambrian (Upper Tommotian to Upper Botonian) 531–518.5 Ma
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita
Order: Redlichiida
Suborder: Olenellina
Superfamily: Olenelloidea
Family: “Wanneriidae”
Subfamily: “Wanneriinae”
Genus: Elliptocephala
Emmons, 1844
Species
  • E. asaphoides Emmons, 1844 (Type)[1]
  • E. bicensis (Walcott, 1910)[1] synonym Callavia bicensis
  • E. laxocules (Fritz, 1972)[1] synonym Olenellus laxocules
  • E. logani (Walcott, 1910)[1] synonyms Olenellus logani, Wanneria logani
  • E. lundgreni (Moberg, 1892)[1] synonyms Wanneria lundgreni, Kjerulfia lundgreni, Holmia lundgreni
  • E. mediocris (Poulsen, 1958)[1] synonyms Wanneria mediocris, W. ruginosa, W. subglabra, W. troelseni
  • E. mirabilis (Poulsen, 1958)[1] synonyms Holmia mirabilis, Wanneria mirabilis
  • E. paraoculus (Fritz, 1972)[1] synonym Olenellus paraoculus
  • E. parvifrons (Fritz, 1972)[1] synonym Wanneria parvifrons
  • E. praenuntius (Cowie, 1968)[1] synonym Olenellus praenuntius
  • E. sequomalus (Fritz, 1972)[1] synonym Olenellus sequomalus
  • E. walcotti Lieberman, 1999[1] synonym Olenellus truemanni pro parte

Elliptocephala is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived from the later part of the Tommotian (upper Schmidtiellus mickwitzi-zone) to the upper Botomian (early middle Olenellus-zone). Elliptocephala can easily be confused with Ellipsocephalus, a trilobite genus of the Ptychopariida order.

Etymology

Elliptocephala is the contraction of ellipse (from Greek ἔλλειψις elleipsis, "falling short") and cephalus (Greek: κέφαλος kephalos, "head") for the rounded headshield that is wider than long.

Taxonomy

Relations within Elliptocephala

According to Lieberman[1] 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.[2]

Distribution

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 (L4) of the central area of the cephalon, that is called glabella. The head shield (or cephalon) 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 (L4) is roughly 1½× the length of the backward ring-shaped lobe (also called occipital ring or L0) and the most backward set of side lobes (L1) taken together, measured along the midline (or sagittally). 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 (T3) 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.[1]

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Lieberman, B.S. (1999). "Systematic Revision of the Olenelloidea (Trilobita, Cambrian)" (PDF). Bulletin of the Peabody Museum of Natural History 45.
  2. Lieberman, B.S. (1998). "Cladistic Analysis of the Early Cambrian Olenelloid Trilobites" (PDF). Journal of Paleontology 72 (1): 59–78.
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