''Kangacaris'' 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 ...

of soft-shelled

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 ...

-like

arthropod 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 the

nektaspid Nektaspida (also called Naraoiida, Nektaspia and Nectaspida) is an extinct order (biology), order of non-Mineralized tissues, mineralised artiopodan arthropods. They are known from the mid-Cambrian to the upper Silurian. Originally classified as t ...

order from 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 ...

(Botomian). ''K. zhangi'' is known from

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

, and ''K. shui'' from South-West China.

Etymology

The generic name is derived from "Kanga", a contraction of Kangaroo Island, and

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

' ("shrimp"). The specific name of the type species honors the Chinese

palaeontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Xingliang Zhang.

Description

The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

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 ...

of ''Kangacaris'' is inverted egg-shaped, about long and wide. The axis is ⅓× as wide as the body and only slightly raised. The semi-circular headshield (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 s ...

) is about ⅔× as long as the tailshield (

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

), and in between them three short

thoracic The thorax or chest is a part of the anatomy of humans, 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 divisions of the crea ...

body segments (

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide in ...

s). The lateral margin of the pygidium is progressively angling towards the axis, ending in the slightest hint of a point. Twelve to thirteen furrows are most distinct on the axis, and becoming indiscernible near the border. The border of the cephalon is about ¼× as long (axially) as the thoracal somites, and the border of the pygidium is about ½× as long as the somites. This border has about 17 regularly spaced ridges perpendicular to the rim. ''K. shui'' has a better defined and narrower axis, more arched posterior margin of the cephalic shield, more posterolaterally deflected pleural areas of the thoracic segments, and smaller pygidium than ''K. zhangi''.

Differences from ''Emucaris fava''

''Kangacaris'' differs from ''

Emucaris fava ''Emucaris fava'' is an extinct species of soft-shelled trilobite-like arthropod of the nektaspid order from the Lower Cambrian (Cambrian Stage 4) of South Australia. It is the only species classified under the genus ''Emucaris''. Etymology ...

'' in having three thorax segments, while ''Emucaris'' has four. When disregarding the border, ''Kangacaris'' has an inverted egg-shape, while the pygidium of ''Emucaris'' is a triangle with a rounded termination. The axis of the pygidium of ''Kangacaris'' is ⅓ of the width of the body and clearly segmented, while in ''Emucaris'' it is one fifth and has a pattern of polygons of approximately equal area. The axis of the pygidium of ''Emucaris'' terminates in a spine that ends at the outer rim of the border, while ''Kangacaris'' lacks a terminal spine.

Distribution

Fossils of ''K. zhangi'' were collected from the

Emu Bay Shale The Emu Bay Shale is a geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätte (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilobites. The Emu Bay Shale is ...

Kangaroo Island Kangaroo Island, also known as Karta Pintingga (literally 'Island of the Dead' in the language of the Kaurna people), is Australia's third-largest island, after Tasmania and Melville Island. It lies in the state of South Australia, southwest ...

, South Australia. Remains of ''K. shui'' have been found at the

Maotianshan Shales The Maotianshan Shales are a series of Cambrian, Early Cambrian deposits in the Chiungchussu Formation, famous for their ''Lagerstätte, Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized organisms or traces. ...

Yunnan Yunnan , () is a landlocked Provinces of China, province in Southwest China, the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is ...

, South-West China.

References

{{Taxonbar, from=Q16983865 Nektaspida Prehistoric arthropod genera Prehistoric arthropods of Australia Emu Bay Shale