''Nephrolenellus'' 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 ...

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 ...

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 ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

marine

arthropods 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 ...

, of relatively small size (sagittal length of cephalon rarely exceeds 11 mm). Currently two species are attributed to it. ''Nephrolenellus'' lived at the end of the

Lower Cambrian 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 ...

. Species are known from the

Great Basin The Great Basin is the largest area of contiguous endorheic basin, endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California ...

of California, Nevada and Arizona, with one specimen from Canada.

Taxonomy

''N. geniculatus'' may have been a direct descendant of ''N. multinodus''.

Distribution

''Nephrolenellus multinodus'' occurs in the late Lower Cambrian of California (Toyonian, Pyramid Shale Member, Carrara Formation, Inyo County, 35.8° N, 116.2° W). and of Nevada (Toyonian, Lincoln County; and C-Shale Member, Pioche Formation, Ruin Wash, Chief Range, 37.8° N, 114.6° W).

Description

As with most early trilobites, ''Nephrolenellus'' has an only thinly calcified

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 ...

. Although most of the body is rather flat, the frontal lobe (L4) of the central area of the cephalon (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 ...

) is raised, but not bulbous, and does not overlap the border at the front in dorsal view. It also has the crescent-shaped eye ridges typical for the earliest trilobites. As part of the Olenellina suborder, ''Nephrolenellus'' 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 glabella. Typically for ''Nephrolenellus'' the eyeridges are pointing backwards and significantly (45°) outwards (along the tangent between the base and termination). The glabella is strongly hourglass-shaped, very much constricted at the second pair of side lobes (L2). The furrow between the second and third pair of lobes (S2) is transverse or gently convex anteriorly. S3 is pit-like and isolated from furrow defining the glabella (or axial furrow). The spine at the outer backside of the cephalon is longer than the most backward lobe of the glabella (also called occipital ring or L0), and it is based at point the cephalon is at its widest. The prothorax consist of thirteen segments, and the third segments has enlarged side lobes (or pleural lobes) that each carry trailing spine at the side that is comparable in length to the entire exoskeleton. It lacks the long axial spine where prothorax ends. The portion of the thorax where the pleural lobes are reduced (or opisthothorax) consist of at least 23 segments.

References

Cambrian trilobites of North America Redlichiida genera Biceratopsidae {{Redlichiida-stub Cambrian genus extinctions