''Ovatoryctocara'' is a

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 ...

of small corynexochid

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 from the

Cambrian 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 ...

, that lived in what now are Siberia, China, Greenland and Canada (Newfoundland). ''Ovatoryctocara'' can be recognised by the combination of the following characters: the central raised 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 approximately cylindrical and has two rows of four triangular or round pits. 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 ...

only has 5 or 6 segments. The 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 ...

) has an axis (or rhachis) of 6 to 12 rings, the pleural furrows are well developed and the border is absent or narrow as a hair.

Etymology

The name of the genus is derived from its type ''Oryctocara ovata''. Ovata refers to its oval overall shape, the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

ὀρύκτης (oryctos) means "digger", and the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

cara is a word for "head" or "face".

Biostratographic significance

The species of the genus ''Ovatoryctocara'' occur near the lower limit of the Middle Cambrian in Siberia. The

first appearance datum First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying the geologically oldest fossil discovered, to date, of a particu ...

(FAD) of ''Ovatoryctocara granulata'' was proposed as the defining marker for the lower limit of the

Wuliuan The Wuliuan stage is the fifth stage of the Cambrian, and the first stage of the Miaolingian Series of the Cambrian. It was formally defined by the ICS in 2018. Its base is defined by the first appearance of the trilobite species ''Oryctocephalu ...

. ''O. granulata'' is moderately widespread (East Siberia, South China, Greenland, and Newfoundland).

Distribution

* ''O. ovata'' was found in the early Middle Cambrian of the Russian Federation (''Ovatoryctocara granulata'' zone, Nekekit, Malaya Kuonamka, Olenek, Amyday, and Muna rivers, and into the lower ''Kounamkites'' zone, Molodo River, East Siberia). * ''O. angusta'' ssp. ''angusta'' is present in the early Middle Cambrian of the Russian Federation (lower part of the ''Ovatoryctocara granulata'' zone, Malaya Kuonamka, and Torkukuy rivers, East Siberia). * ''O. angusta'' ssp. ''snegirevae'' has been encountered in the early Middle Cambrian of the Russian Federation (''Ovatoryctocara granulata'' zone, Molodo and Malaya Kuonamka Rivers; Amaday Horizon, Maya River, East Siberia). * ''O. doliiformis'' has been collected from the early Middle Cambrian of the Russian Federation (upper part of the ''Ovatoryctocara granulata'' zone, Molodo River, East Siberia) * ''O. granulata'' occurs in the early Middle Cambrian of the Russian Federation (''Ovatoryctocara granulata'' zone, Nekekit, Malaya Kuonamka, Olenek, Amyday, and Muna rivers, and into the lower ''Kounamkites'' zone, Molodo River, East Siberia), China (''O. granulata''–'' Bathynotus holopyga'' zone, late Duyunian, Kaili Formation), latest Lower Cambrian of Greenland (upper ''Olenellus'' zone, Henson Glacier Formation) and of Canada (top of the ''Cephalopyge notabilis'' zone, Branche Cove Marl Member, Eastern Cove Branche, Newfoundland).

Description

Very small to small trilobite (maximum length approximately ) of more or less oval overall shape. The head shield (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 ...

) has natural fracture lines that end at the tip of the genal angle or the rear margin (or it has gonatoparian or proparian facial sutures). The central area of the cephalon (or

) is cylindrical or slightly expanded midlength and/or at the frontal lobe. The furrows that show the segmented origin, are most distinct in the form of four sets of rounded or triangular pits, sometimes with a shallow depression between them at the midline. The glabella is almost touching the front of the cephalon (or the pre-glabellar field is short). Narrow eye ridges emerge from the back of the frontal lobe outward and slightly backward (± 20°). Thorax of 5 or 6 segments. Pygidium approximately the same size (isopygous) or larger (macropygous) than the cephalon, with an axis of 6 to 12 rings, and clear pleural furrows. The border is lacking or hair thin. The surface may be smooth or has granules.

References

{{Taxonbar, from=Q15614549 Cambrian trilobites Corynexochida genera Oryctocephalidae Fossils of Greenland