''Markuelia'' is a

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 ...

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 ...

worm-like bilaterian animals allied to

Ecdysozoa Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerates (including arachnids), crustaceans, and myriapods), Nematoda, and several smaller phylum (biology), phyla. The grouping of these animal phyla into a single ...

and known from strata of Lower Cambrian to Lower Ordovician age containing five

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. An advanced

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

imaging technique called X-ray tomographic microscopy has been applied to splendidly preserved, uncrushed ''Markuelia'' fossils found in

Hunan Hunan is an inland Provinces of China, province in Central China. Located in the middle reaches of the Yangtze watershed, it borders the Administrative divisions of China, province-level divisions of Hubei to the north, Jiangxi to the east, Gu ...

province in southern

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

and in eastern

Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...

. When details in features smaller than one

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

across can be observed, these fossils are seen to represent many developmental stages, from the first cell divisions to the time of hatching; therefore they offer a unique opportunity to study the development of

Lower Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

animals. The features observed indicate that the genus had a mouth surrounded by a ring of teeth, an

alimentary canal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...

, and an

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

. However the characters preserved are inconclusive regarding the genus' taxonomic affinity; it can at best be placed in the scalidophoran total group, since it is currently impossible to ally it with the Priapulids or other

scalidophora Scalidophora is a group of marine pseudocoelomate ecdysozoans that was proposed on morphological grounds to unite three phyla: the Kinorhyncha, the Priapulida and the Loricifera. The three phyla have four characters in common — chitinous cuti ...

References

''Geotimes''"Fossil embryos exposed in 3-D"
October 2006

Prehistoric protostome genera Cambrian invertebrates Cambrian first appearances Ordovician extinctions Fossils of China Fossils of Russia {{Protostome-stub

Further reading

References