''Emigrantia'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

trilobites 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 ...

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 segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, oft ...

, of small to average size. It lived during the

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 Commissi ...

stage (last phase of the Upper ''Olenellus''-zone), in what is today the South-Western United States. ''Emigrantia'' can easily be distinguished from other trilobites by the sturdy but not inflated genal spines, that are attached at midlength of the cephalon, in combination with effaced features of the raised axial area of the head shield (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 ...

Etymology

The name of the genus is derived from Emigrant Pass, Nopah Range, California, near the collection site of many of the last of the Lower Cambrian Olenellina.

Description

As with most early trilobites, ''Emigrantia'' has an almost flat

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 ...

, that is only thinly calcified. As part of the Olenellina suborder, ''Emigrantia'' 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

. The exoskeleton of ''Emigrantia'' is inverted egg-shaped in outline and up to 3 cm in length, disregarding the genal spines and the pleural spines of the 3rd thorax segment. The 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 ...

) is approximately pentagonal, with the right and left frontal margin together forming a circle segment. It has a distinct cephalic border that is developed as a raised ridge. The genal spines are stout, up to 2 mm in diameter near the base and appear to be massive. They are attached about half length of the cephalon and bend quickly to proceed to their tip parallel to the midline. Intergenal angle strongly rounded, from perpendicular to the midline angling to 135°-150°. The glabella is of approximately constant width along its length, and the furrows are indistinct. The thorax has at least 12 segments, but probably a few more. The tips of the pleural lobes point backwards, but except for the third segment, these are not spiny. The 3rd segment is macropleural.

Differences with some other Biceratopsinae

'' Biceratops nevadensis'' and ''

Peachella ''Peachella'' is an extinct genus of trilobites, fossil marine arthropods, with species of average size (about long). It lived during the Toyonian stage (Upper ''Olenellus''-zone), , in what is today the southwestern United States. It can easily ...

'' share extremely effaced cephalic features with ''Emigrantia''. ''Biceratops'' however lacks genal spines. In ''Peachella'' the genal spines are short and bloated, in contrast with being longer than the cephalon and attached halfway down its side (or lateral margin). ''

Eopeachella ''Eopeachella'' is an extinct genus of trilobites, fossil marine arthropods, with species of probably small size (largest headshield (or cephalon) long), entire, articulate specimens have not yet been found. It lived during the Toyonian stage ...

'' has short genal spines with only the basis inflated and less effaced cephalic features.

Distribution

''Emigrantia'' is known only from the Lower Cambrian of California (Carrara Formation, Thimble Limestone Member,

Nopah Range The Nopah Range is a mountain range located in Inyo County, California, United States, near the eastern border with Nevada. Geography The mountain range lies east of the adjacent Resting Spring Range, the Owlshead Mountains and lower Death Valle ...

Inyo County Inyo County () is a county in the eastern central part of the U.S. state of California, located between the Sierra Nevada and the state of Nevada. In the 2020 census, the population was 19,016. The county seat is Independence. Inyo County is ...

References

Cambrian trilobites Redlichiida genera Biceratopsidae {{Redlichiida-stub