''Meniscuchus'' 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 Botomian stage, which lasted from approximately 522 to 516 million years ago. This faunal stage was part of the

Cambrian Period The Cambrian Period ( ; sometimes symbolized C with bar, 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 ...

. ''Meniscuchus'' has been found in the USA (Alaska, New York), Canada (Newfoundland, Quebec), Russia (Siberian Platform, Gorno-Altayskaya) and Australia (New South Wales).Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997

Distribution

* ''M. helena'' has been found in the Lower Cambrian of Canada (Newfoundland). * ''M. menetus'' is known from the Lower Cambrian of Australia (Cymbric Vale Formation, New South Wales). * ''M. nanus'' was collected in Alaska.

Description

Like all Eodiscina, the headshield (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 ...

) and tailshield (or

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

) are approximately equal in size. Like all Weymouthiidae, ''Meniscuchus'' is eyeless and lacks free cheeks. The axis 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 wide at its base (that is, where it would touch 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 cre ...

) and is rounded at the front, where it touches the border furrow. The glabella is divided by two furrows crossing the glabella, creating a frontal lobe (L4) more than twice as long (along the axis) as its narrow neighbour (L3). Further lobes (L2 and L1) may be suggested by a faint dent in the furrow defining the outline of the glabella. At the back the glabella is terminated by a narrow occipital ring (L0), extended backwards at midline with its margin a semicircle. The cephalic border is almost as wide as L4, but is only half as wide laterally while becoming slightly wider again further back. Thorax probably with three segments. Its pygidium is relatively long. Its axis is tapering and reaching the border furrow at midline, and is deeply segmented with 4 to 10 axial rings. The pleural areas are unfurrowed. The border of the pygidium is uniformly narrow. The doublure is wide and almost vertical.

References

Weymouthiidae Agnostida genera Cambrian trilobites of North America Cambrian trilobites of Australia {{agnostida-stub Cambrian genus extinctions