''Eoredlichia'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

of average to large size (up to long, or when including the spine on the ninth thorax segment pointing horizontally to the back, that itself equals the main body length). It lived during the early

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

(late Atdabanian) in the Chengjiang fauna of Yunnan, China, and in Australia and Thailand. ''Eoredlichia'' is compounded of the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

(''eos'',

dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's ho ...

) and '' Redlichia'', a later but related genus, so it means "early ''Redlichia''". The species

epithet An epithet (, ), also byname, is a descriptive term (word or phrase) known for accompanying or occurring in place of a name and having entered common usage. It has various shades of meaning when applied to seemingly real or fictitious people, di ...

''intermedia'' means intermediate, indicating it is morphologically intermediate between other species. '' Eofallotaspis'' gives rise to '' Lemdadella'', and thence to ''Eoredlichia'' and the other Redlichiidae.

Description

Dorsal exoskeleton

Like most early trilobites, ''Eoredlichia'' was very flat, was thinly calcified and had sickle-shaped eye ridges. Like all other Redlichiina it had opistoparian sutures, and a small tailshield or pygidium. The headshield or ( cephalon) is about twice as wide as long (along the midline), spindle-shaped, bluntly pointed at the base of the genal spines, and straight where it connects with the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the ...

. The central area of the cephalon, that is called glabella, is tapering forward and has three crossing furrows. The genal spines grow from the cephalon at about mid-length outwards and backwards at an angle of about 30° at base, gradually bending till parallel to the midline at its tip approximately perpendicular to where thorax and pygidium meet. The thorax has fifteen segments, with number 9 (counted from the front) carrying a spine approximately as long as the entire main body.

Appendages

This species is one of the few for which antennae, legs and gills (together the so-called biramous appendages), and the alimentary tract are known. The unbranched, slim, whip-like (or setaceous) antennae are about ⅓ of the body length, and consist of 46–50 rings of gradually decreasing width. Each ring carries a fine hair on the side of the midline. Like in all other adult trilobites for which the appendages are known, each consists of a common basis (hip or coxa), a leg (or endopod) and a gill (or exopod), in ''Eoredlichia'' 21 pair in all. The coxa carries spines towards the midline and each pair of opposing coxae is presumed to have functioned as jaws (or gnathobases). The endopod consists of seven leg segments (called podomeres), the last of which is forked to form a claw, that would help it to keep its footing. The basal podomere of the exopod was connected along its entire length with the coxa through a

hinge joint A hinge joint (ginglymus or ginglymoid) is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane. According to one classification system they are said to be uniaxial (having ...

. To the back, each exopod carries about forty thin long filaments, that probably acted as gills, and short setae along the rounded distal lobe. Three pairs of appendages were connected to the underside of the cephalon, one pair connected to each of the fifteen thorax segments and presumably three diminutive pairs under the pygidium. The gut is a straight tube, with nine pairs sacs (or diverticulae), four in the cephalon and five in the thorax. ''Eoredlichia'', like many other Cambrian trilobites, is best interpreted as a scavenger/

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

References

External links

''Photo of E. Intermedia''Trilobite information
{{Taxonbar, from=Q5381858 Redlichiidae Redlichiida genera Cambrian trilobites Fossils of China Cambrian trilobites of Australia Cambrian genus extinctions