''Olenelloides armatus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

, small sized (about long) olenelloid 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 ...

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

. 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 ( ) 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 ...

. 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 ''Olenellus'' is an extinct genus of redlichiida, redlichiid trilobites, with species of average size (about long). It lived during the Botomian and Toyonian stages of the Lower Cambrian (''Olenellus''-zone), , in what is currently North America ...

''. The species epithet , a

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

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

Occurrence

''Olenelloides armatus'' lived during the late

Lower Cambrian 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 ...

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 ...

, 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 (), is an area in the Highlands and Islands of Scotland. In modern usage, it is a registration county and a Lieutenancy areas of Scotland, lieutenancy area. Between 1889 and 1975 it was a Shires of Scotland, county. Historical ...

, 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 ...

. 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., Frank Baldino, Jr., neuroscientist Michael Lewis, and organic chemist James C. Kauer—all three former scientists with the DuPont ...

) 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 ...

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

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 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 Benjamin Neeve Peach (6 September 1842 – 29 January 1926) was a British geologist. Life Peach was born at Gorran Haven in Cornwall on 6 September 1842 to Jemima Mabson and Charles William Peach, an amateur British naturalist and geologis ...

described the species as ''Olenellus (Olenelloides) armatus'', assigning it to a new subgenus of ''

''. Other early scholars regarded ''Olenelloides armatus'' as a separate genus closely related to ''

''. McNamara argued that ''O. armatus'' developed from ''Olenellus'' ancestry through retention of juvenile features (

paedomorphosis Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the Physiology, physiological, or Somatic (biology), somatic, development of an organism, typically an animal. Neoteny i ...

), 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 ''Olenellus''-zone in the former paleocontinent of Laurentia and parts of what became the Famatin ...

, 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 trilobite genera Cambrian trilobites of Europe Cambrian genus extinctions