''Cirquella'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

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 preserved ...

marine

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s, the

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 At ...

s. It lived during the

Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxim ...

stage, in the former

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although ...

Description

Only the thin and lightly calcified headshields (or

cephalon Cephalon, Inc. was an American biopharmaceutical company co-founded in 1987 by pharmacologist Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont Company. Baldino s ...

) of ''Cirquella'' have ever been found. It is very flat, almost oval in outline, the length about 85% of the width. The central area of the cephalon (or

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 to ...

) is moderately tapered forward. The furrows dividing the glabella are only weakly developed. The back of the eye ridge is opposite the first lobe (L1) of the glabella in front of the band (or occipital ring) at the back of the glabella. In ''Cirquella espinata'' there is no genal spine but a slight angularity of margin opposite first lobe in front of the occipital ring. In ''Cirquella nummularia'' the rim of the cephalon is entirely rounded.W.H. Fritz (1993). The Lower Cambrian Olenelloid Trilobite Genera ''Cirquella'' and ''Geraldinella'' from Southwestern Canada. Journal of Paleontology, 67/5:856-86

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Distribution

''C. nummularia'' is known from the earliest half of the Lower ''Nevadella'' Zone, in the Dogtooth Mountains, British Columbia, Canada, and in Nevada.
''C. espinata'' lived at the same time in the Southern Canadian Rocky Mountains.
''C. nelsoni'' is reported from the ''Fallotaspis''-''Judomia'' Faunule, ''Fallotaspis'' Biozone, Campito Formation, Inyo-White Mountains, Eastern California.Western Trilobite Association website
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Habitat

''Cirquella'' species were probably marine bottom dwellers, like all Olenellina.

References

Sources

Lieberman, B.S. (2002). Phylogenetic analysis of some basal early Cambrian trilobites, the biogeographic origins of the Eutrilobita, and the timing of the Cambrian radiation. Journal of Paleontology, 76(4):692-708. olenellina Cambrian trilobites Fossils of British Columbia Fossils of the United States {{redlichiida-stub