Kunmingella
| Kunmingella | ||||||||
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| Cambrian (2nd series) | ||||||||
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China, Siberia |
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| Scientific name | ||||||||
| Kunmingella | ||||||||
| Huo , 1956 | ||||||||
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Kunmingella is a genus of extinct arthropods . The species Kunmingella douvillei is the most common fossil-preserved arthropod species in the Chengjiang Fauna Community of China, which is assigned to the second series of the Cambrian .
description
Kunmingella fossils are about 3.5 to 6 millimeters long and are among the smallest Cambrian arthropods. The most striking feature is a two-lobed carapace , which consisted of two shell elements that could be folded together at a central joint , which in life was probably held together by a ligament , and then enveloped the animal, similar to the recent ostracods or mussel crabs. The carapace was smooth or slightly granular, only weakly mineralized and thin, it did not consist of calcite . The animals can be preserved with their shells folded or, more rarely, in the unfolded state (so-called "butterfly" shape). In the living and active animal, the carapace was on top (dorsal), with the extremities sticking down, they could probably walk on the surface of the sediment and also swim freely over it. On the top of the carapace, a series of elevations can be seen as special structures. A bulge-shaped or knot-shaped structure in the front (anterodorsal) was perhaps used to prevent the shell halves from opening too far, or even over-folding. At the edge, the bowls had a raised, reinforced edge that was set off by a shallow furrow. In the back of the bowls sat a straight or sickle-shaped curved lobe.
From the underside (ventral side), the actual body of the animal, hidden dorsally by the carapace, can only be seen in particularly well-preserved specimens, it was only a maximum of 1.5 millimeters wide. This consisted of ten segments , five of which are assigned to the head and five to the trunk section . Each segment carried a pair of limbs, with the head pointing forward and the trunk pointing back. The trunk was closed at the rear by a small triangular point without extensions. The head had a pair of very large eyes that sat on the underside at the level of the anterodorsal bumps of the carapace. The first limbs (extremities), which were homologous to the first antennae of the crustaceans , were single-branched, the following pairs of extremities of segments two to eight typical, two-branched split legs , and the last two pairs again single-branched. The antennae consisted of five members, of which the front three could be pushed forward out of the carapace, they were rather short. The split legs on the head and trunk were constructed similarly to each other, they consisted of a five-part inner branch (endopodite) used for walking and a broad leaf-shaped outer branch (exopodite), which had a wide hairline at least on the trunk limbs and could be used for swimming. The last two pairs of legs were designed differently. The penultimate one was long and could be stretched back over the carapace, it had a claw-like structure at the end. The tenth pair of legs between them were considerably shorter.
development
We know from some exceptionally well-preserved fossils, on whose legs the attached eggs are still visible, that Kunmingella was engaged in brood care . The eggs were attached to the three front (two-branched) trunk extremities, presumably along the outer edges of the exopodites. According to the length of the carapace of small specimens, which can be classified into five size classes, one deduces five larval stages for further development. The first two stages had a simple and undivided dome-shaped shield and were only 200 to 230 micrometers long, the later were, like the adults, two-lobed. Some animals found, which are interpreted as fourth instar larvae, had not ten, but only seven pairs of extremities. So new segments were formed during the Laval phase of development ( anamerism or anamorphosis).
ecology
It is assumed that Kunmingella individuals crawled around on the substrate surface with a wide open, spreading carapace or swam in free water close to the ground, i.e. they belonged to the benthal to benthopelagic fauna. Little is known about nutrition, but due to the less specialized extremities one usually suspects a detritus eater . Kunmingella itself was obviously often prey to Cambrian robbers ( predators ), as can be assumed from numerous fragments in fossilized feces ( coprolites ). Which predator hunted the animals, of course, cannot be stated, but many suspect the Anomalocarididae .
distribution
Kunmingella is known almost exclusively from China, where fossils of the genus are common in numerous deposits. Outside of China there is only one indication of the genus, without any species assignment, from Siberia. Both areas were close to the equator in the early Cambrian, and both the Siberian and the South Chinese craton formed their own small continents.
Systematics
Kunmingella douvillei (Mansuy, 1912) is the type of the genus and by far the most common . Although about two dozen other species have been described by numerous editors over the decades , almost all of them were synonymous with this in a revision of the Chinese Bradoriids , so that today only a second species is recognized, Kunmingella typica Huo & Shu, 1985. This differs from the type species in that it has a long, straight or slightly curved thorn on each half of the carapace, which sits at the back and points downwards. The genus Kunmingella forms with three other genera, also known only from the second series of the Cambrian in China, Emeiella , Hanchiangella and Nanchengella , the family Kunmingellidae. This is one of the seven families of Bradoriida , an extinct, formerly globally extended order of arthropods. Bradoriida were common in the Cambrian, they occur suddenly at the beginning of the second series, probably immediately before the first trilobites , became rare at the end of the Cambrian and died out around the middle of the Ordovician , possibly due to the competition of the mussel crabs, which around this time appear in the fossil record.
Individual evidence
- ↑ Hou Xian-guang, David J. Siveter, Mark Williams, Feng Xiang-hong (2002): A monograph of the Bradoriid arthropods from the Lower Cambrian of SW China. Transactions of the Royal Society of Edinburgh: Earth Sciences 92 (3-4): 347-409. doi : 10.1017 / S0263593300000286
- ↑ a b c Xianguang Hou, Mark Williams, David J. Siveter, Derek J. Siveter, Richard J. Aldridge, Robert S. Sansom (2010): Soft-part anatomy of the Early Cambrian bivalved arthropods Kunyangella and Kunmingella: significance for the phylogenetic relationships of Bradoriida. Proceedings of the Royal Society London Series B 277: 1835-1841. doi : 10.1098 / rspb.2009.2194
- ↑ Yanhong Duan, Jian Han, Dongjing Fu, Xingliang Zhang, Xiaoguang Yang, Tsuyoshi Komiya, Degan Shu (2014): Reproductive strategy of the bradoriid arthropod Kunmingella douvillei from the Lower Cambrian Chengjiang deposit, South China. Gondwana Research 25 (3): 983-990. doi : 10.1016 / j.gr.2013.03.011
- ↑ Ludmila M. Melnikova, David J. Siveter, Mark Williams (1997): Cambrian Bradoriida and Phosphatocopida (Arthropoda) of the former Soviet Union. Journal of Micropalaeontology 16: 179-191. doi : 10.1144 / jm.16.2.179
- ↑ Mark Williams, David J. Siveter, Leonid E. Popov, Jean MC Vannier (2007): Biogeography and affinities of the bradoriid arthropods: Cosmopolitan microbenthos of the Cambrian seas. Palaeogeography, Palaeoclimatology, Palaeoecology 248: 202-232. doi : 10.1016 / j.palaeo.2006.12.004
- ↑ Mark Williams, David J. Siveter, María José Salas, Jean Vannier, Leonid E. Popov, Mansoureh Ghobadi Pour (2008): The earliest ostracods: the geological evidence. Senckenbergiana lethaea 88 (1): 11-21.
Web links
- Xian-guag Hou, Richard Aldridge, Jan Bergström, David J. Siveter, Derek Siveter, Xiang-Hong Feng: The Cambrian Fossils of Chengjiang , China: The Flowering of Early Animal Life. Wiley, 2008. ISBN 978-0-470-99994-3 ( limited preview in Google Book Search)