''Emigrantia'' 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 ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

trilobites Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, ...

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 preserve ...

marine

arthropods 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 ...

, 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 Commission ...

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 ...

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 () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

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

) 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'' 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'' 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 Vall ...

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