Olenelloides
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Olenelloides armatus Temporal range: Late Botomian 519–516 Ma |
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| artist's reconstruction | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Trilobita |
| Order: | Redlichiida |
| Suborder: | Olenellina |
| Superfamily: | Olenelloidea |
| Family: | Biceratopsidae |
| Subfamily: | Biceratopsinae |
| Genus: |
Olenelloides (Peach, 1894) |
| Species: | O. armatus |
| Binomial name | |
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Olenelloides armatus (Peach, 1894) |
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| Synonyms | |
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Olenellus (Olenelloides) armatus Peach, 1894 |
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Olenellus (Olenelloides) armatus Peach, 1894
Olenelloides armatus is an extinct, small sized (about 1 centimetre or 0.39 inches long) olenelloid redlichiid trilobite arthropod. 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 most conspicuous feature is the hexagonal head shield that carries 6 ray-like spines..
The genus is named after its originally supposed close relationship with Olenellus. The species epithed armatus, a Latin adjective meaning 'armoured', is a reference to the fierce looking spines of the head shield.
Olenelloides armatus lived during the late Lower Cambrian deposits presumably contemporary with the middle Olenellus-zone (Wanneria subzone), that probably represents the late Botomian, approximately between 519 and 516 million years ago.
Olenelloides armatus has been collected from the Fucoid Beds, Northern slopes of the Meall a’Ghiubhais, County Ross and Cromarty, Scotland, UK.
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 exoskeleton of Olenelloides armatus is small (up to 1 cm) and narrow (less than ½× as wide as long, measured between the base of the outermost spines).
Its head shield (or cephalon) is hexagonal, with three pairs of spines extending from each of the corners of the cephalon, all almost ⅔× 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 glabella 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 ⅓rd of the area outside the glabella (the 'cheeks' or genae). The occipital ring is wider than the other glabellar lobes, and carries a node on the rear edge at midline.
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