''Anabaraspis'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of redlichiid

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

, ''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 ...

and lower

Amgan The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

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

Yakutia Sakha, officially the Republic of Sakha (Yakutia), is a republics of Russia, republic of Russia, and the largest federal subject of Russia by area. It is located in the Russian Far East, along the Arctic Ocean, with a population of one million ...

). In ''Anabaraspis,'' there is an extended area in front of the glabella which is not differentiated in a border and a preglabellar field. It 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 ...

) of the headshield (or

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

) is slightly pointed rather than rounded or truncate, a character shared with '' Plutonides'', though, in ''Plutonides,'' it hangs over the short anterior border.

Description

The

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

of ''Anabaraspis'' is relatively flat, oval to inverted egg-shaped. The glabella is subpentagonal with a blunt frontal tip and is 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 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 in short. The genal spine is short and stout. The articulate middle part of the body (or

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of 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 di ...

) 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 The pygidium (: 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 compos ...

) is longer than wide, slightly hexagonal, with a long, flat posterior area. The rear margin of the pygidium is truncated or indented. The pygidial axis is short, with one axial ring. The surface is smooth.

References

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