''Anabaraspis'' 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 ...

redlichiid Redlichiida is an order of trilobites, a group of extinct marine arthropods. Species assigned to the order Redlichiida are among the first trilobites to appear in the fossil record, about halfway during the Lower Cambrian. Due to the difficulty ...

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 ...

. ''A. splendens'' occurs in the uppermost Lower Cambrian and lowest Middle Cambrian of Russia (

Toyonian 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 on ...

and lower

Amgan 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 ago (m ...

, ''A. splendens'' and ''Oryctocara'' Zones, northwestern and southeastern

Yakutia Sakha, officially the Republic of Sakha (Yakutia),, is the largest republic of Russia, located in the Russian Far East, along the Arctic Ocean, with a population of roughly 1 million. Sakha comprises half of the area of its governing Far Eas ...

). In ''Anabaraspis'' there is a long area in front of the glabella which is not differentiated in a border and a preglabellar field. This is a unique character in the family Paradoxididae. The frontal lobe of the central raised area (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 ...

) of 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 ...

) is slightly pointed, rather than rounded or truncate, a character shared with ''

Plutonides ''Plutonides'' is a genus of Middle Cambrian trilobite in the family Paradoxididae with species ''Plutonides sedgwickii'' and possibly ''Plutonides? illingi''. Several other species and subspecies were at times placed in ''Plutonides'' but have s ...

'', though, in ''Plutonides'' it hangs over the short anterior border.

Description

The

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...

of ''Anabaraspis'' is relatively flat, oval to inverted egg-shaped. The glabella subpentagonal with a blunt frontal tip, and widest near the back of the frontal lobe. The glabella is divided into three rings by furrows that cross the midline, although the most frontal of these is shallow in the middle. In front of that may be two faint sets of furrows that do not cross-over. The area in front of the glabella is relatively long (about ⅓× the length of the glabella), and not differentiated into a preglabellar field and the anterior border. The facial suture in front of the eye is long and strongly divergent, while the portion behind the eye isshort. The genal spine is short and stout. The articulate middle part of the body (or

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 ...

) has 15 to 18 segments with long, sickle-shaped spines. The inner part of the ribs is about as wide as the axis. The tailshield (or pygidium) is longer than wide, slightly hexagonal, with a long, flat posterior area. The rear margin of the pygidium is truncate or indented. The pygidial axis is short, with 1 axial ring. The surface is smooth.

References

Cambrian trilobites Paradoxidoidea Fossils of Russia Fossil taxa described in 1951 {{redlichiida-stub