''Olenelloides armatus'' 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 ...

, small sized (about long) olenelloid

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 ...

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 ...

. It lived during the later part of the Botomian stage, which lasted from approximately 524 to 518.5 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 ...

. The most conspicuous feature is the hexagonal head shield that carries 6 ray-like spines..

Etymology

The genus is named after its originally supposed close relationship with '' Olenellus''. The species epithet , a

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 ...

adjective meaning 'armoured', is a reference to the fierce looking spines of the head shield.

Occurrence

''Olenelloides armatus'' lived during the late Lower Cambrian deposits presumably contemporary with the middle ''Olenellus''-zone (''Wanneria'' subzone), that probably represents the late

Botomian 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 ...

, approximately between 519 and 516 million years ago.

Distribution

''Olenelloides armatus'' has been collected from the Fucoid Beds, Northern slopes of the Meall a'Ghiubhais, County

Ross and Cromarty Ross and Cromarty ( gd, Ros agus Cromba), sometimes referred to as Ross-shire and Cromartyshire, is a variously defined area in the Highlands and Islands of Scotland. There is a registration county and a lieutenancy area in current use, the latt ...

, Scotland, UK.

Description

As with most early trilobites, ''Olenelloides'' has an almost flat exoskeleton, that is only thinly calcified, and has crescent-shaped eye ridges. As part of the Olenellina suborder, ''Olenelloides'' lacks dorsal sutures. Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe (L4) of the central area of the cephalon, that is called

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 ...

. The exoskeleton of ''Olenelloides armatus'' is small (up to ) and narrow (less than as wide as long, measured between the base of the outermost spines). Its 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 ...

) is hexagonal, with three pairs of spines extending from each of the corners of the cephalon, all almost as long as the diameter of the cephalon. The frontal pair (or procranidial spines) have an angle of about 25° to the axis, the middle pair (or genal spines) of about 100°, and the rear pair (or intergenal spines) of about 150°. The intergenal spines do not emerge from the cephalic border, but rather from the sides of the 2nd lobe of the

from the back - the scientific convention is to count glabellar lobes back to front, giving them the following names: occipital ring or lobe (OR or OL), 1st lobe (L1), 2nd lobe (L2), 3rd lobe (L3), and anterior lobe (AL or L4) -. The front side of the cephalon is slightly bulging out forward to accommodate the frontal lobe (L4) of the raised central area called glabella. The eye lobes are short, wide and strongly curved, occupying most of the middle rd of the area outside the glabella (the 'cheeks' or

genae This glossary of entomology describes terms used in the formal study of insect species by entomologists. A–C A synthetic chlorinated hydrocarbon insecticide, toxic to vertebrates. Though i ...

). The occipital ring is wider than the other glabellar lobes, and carries a node on the rear edge at midline. 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 ...

has a wide axis of about of the total width of the thorax, not including the spines, and consists of 9 segments. The frontal 3 are equal in size, but segments further back get smaller at an increasing rate. The thorax segments carry a node on the rear edge at midline, that diminishes towards the back. The 1st, 2nd, 4th and 5th thorax segments (counting front to back) do not carry spines, the frontal edge of the outer lobes (or pleurae) suddenly angles back at 150° ending in a blunt tip. The 3rd segment ends laterally in a straight spine that angles back at about 150° and extending backwards beyond the axis. The 6th-10th segments carry spines that curve backwards and increasingly inwards to the midline and extending increasingly less far backwards, the 6th ending parallel to the midline and extending as far back as the spine of the 3rd segment.

Taxonomic history

Ben Peach described the species as ''Olenellus (Olenelloides) armatus'', assigning it to a new subgenus of '' Olenellus''. Other early scholars regarded ''Olenelloides armatus'' as a separate genus closely related to '' Olenellus''. McNamara argued that ''O. armatus'' developed from ''Olenellus'' ancestry through retention of juvenile features ( paedomorphosis), and regarded the original ranking more appropriate. More recent scholars however suggest to treat ''Olenelloides'' as a peculiar but valid genus within the

Olenellidae Olenellidae is an extinct family of redlichiid trilobite arthropods. Olenellids lived during the late Lower Cambrian (Botomian/Toyonian) in the so-called ''Olenellus''-zone in the former paleocontinent of Laurentia plus parts of what became the ...

, and assign it provisionally to the subfamily Laudoniinae. They argue that the absence of a preglabellar field and the presence of advanced genal spines are not immature features, but are shared with ''Laudonia''. Lieberman does not support assignment to the Laudoniinae, and alternatively proposes inclusion in the Biceratopsinae.

Habitat

''Olenelloides armatus'' probably was a fast-moving low-level epifaunal

detritivore Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

.Paleobiology Database
/ref>

References

{{Taxonbar, from=Q7086379 Redlichiida genera Biceratopsidae Cambrian trilobites Monotypic arthropod genera Cambrian trilobites of Europe Cambrian genus extinctions