''Elliptocephala'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

from a well-known class of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

marine

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s, the

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s. It lived from the later part of the Tommotian ( upper ''Schmidtiellus mickwitzi''-zone) to the upper

Botomian Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission ...

( early middle ''Olenellus''-zone). ''Elliptocephala'' can easily be confused with '' Ellipsocephalus'', a trilobite genus of the

Ptychopariida Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. The earliest species occurred in the second half of the Lower Cambrian, and the last species did not survive the Ordovician–Siluria ...

order.

Etymology

The species ''E. walcotti'' was named in honor of

Charles Doolittle Walcott Charles Doolittle Walcott (March 31, 1850February 9, 1927) was an American paleontologist, administrator of the Smithsonian Institution from 1907 to 1927, and director of the United States Geological Survey. He is famous for his discovery in 19 ...

, a renowned early paleontologist, that described many trilobite species.

Taxonomy

Relations within ''Elliptocephala''

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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

comprising ''Wanneria walcottana'', the

Holmiidae Holmiidae is a family of trilobites, that lived during the Lower Cambrian (Atdabanian). The Holmiidae is a diverse family of eight genera containing at least 17 species. It includes some of the earliest trilobites of Baltica. Holmiidae occur thro ...

, '' Fritzolenellus'', '' Mummaspis'', '' Laudonia'', the

Biceratopsinae The Biceratopsinae is an extinct subfamily of redlichiid trilobites within the family Biceratopsidae, with species of small to average size. Species belonging to this subfamily lived during the Toyonian stage (Upper ''Olenellus''-zone), 516-51 ...

and the

Bristoliinae The Bristoliinae is an extinct subfamily of trilobites, fossil marine arthropods, with species of small to average size. Species belonging to this subfamily lived during the Botomian and Toyonian stage (''Olenellus''-zone), 522-513 million years ...

. Including ''Elliptocephala'', this clade is the sistergroup of the

Olenellidae Olenellidae is an extinct family of redlichiid trilobite arthropods. Olenellids lived during the late Lower Cambrian (Botomian/ Toyonian) in the ''Olenellus''-zone in the former paleocontinent of Laurentia and parts of what became the Famatin ...

Distribution

* ''E. asaphoides'' was collected in the Middle ''Olenellus''-zone of eastern New York State (Greenwich Formation). * ''E. bicensis'' is found in Quebec, Canada and believed to be from the ''Olenellus''-zone (limestone boulder found in a conglomerate that has probably formed during the Lower Ordovician). * ''E. laxocules'' occurs in the Middle ''Olenellus''-zone of the Northwest Territories (type section of the

type section In geology, a stratotype or type section is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the ...

of the Sekwi Formation, 0.2 miles Southeast of June Lake, Mackenzie Mountains). * ''E. logani'' was excavated from the Middle ''Olenellus''-zone of the Northwest Territories (type section of the

of the Sekwi Formation, 0.2 miles Southeast of June Lake, Mackenzie Mountains, and the Illtyd Formation, Wernecke Mountains). * ''E. lundgreni'' is present in * ''E. mediocris'' was collected in Northwestern Greenland, questionably from the ''Olenellus''-zone (Wulff River Formation, Marshall Bugt,

Inglefield Land Inglefield Land is an unglaciated area along the northwestern coast of Greenland. It was named after English explorer Edward Augustus Inglefield. History Inglefield Land is noted for its archaeological sites, which show evidence of occupation by ...

). * ''E. mirabilis'' is found in Northwestern Greenland, questionably from the ''Olenellus''-zone (Wulff River Formation, Marshall Bugt,

). * ''E. paraoculus'' is present in the Middle ''Olenellus''-zone of the Northwest Territories (type section of the

of the Sekwi Formation, 0.2 miles Southeast of June Lake, Mackenzie Mountains). * ''E. parvifrons'' was excavated from the Middle ''Olenellus''-zone of the Northwest Territories (type section of the

of the Sekwi Formation, 0.2 miles Southeast of June Lake, Mackenzie Mountains, and the Illtyd Formation, Wernecke Mountains). * ''E. praenuntius'' occurs on the eastern

Ellesmere Island Ellesmere Island (; ) is Canada's northernmost and List of Canadian islands by area, third largest island, and the List of islands by area, tenth largest in the world. It comprises an area of , slightly smaller than Great Britain, and the total ...

, Canada, in what possibly belongs to the Lower ''Olenellus''-zone (430 feet above the basis of the Kane Formation, 6 miles Northwest of the head of Scoresby Bay). * ''E. sequomalus'' is found in the Middle ''Olenellus''-zone of the Northwest Territories (type section of the

of the Sekwi Formation, 0.2 miles Southeast of June Lake, Mackenzie Mountains). * ''E. walcotti'' was collected in the Middle ''Olenellus''-zone of the Northwest Territories (type section of the

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 (L4) of the central area of the cephalon, that is called

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior ...

. 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.

References

{{Taxonbar, from=Q5365812 Cambrian trilobites Extinct animals of North America Olenelloidea Taxa named by Ebenezer Emmons