Tuesday, 1 December 2015

Eokinorhynchus rarus: A Kinorhynch from the Early Cambrian of Sichuan Province, China.

Kinorhynches are tiny (at most 3 mm) worm like animals found in marine sediments, with segmented tube- or barrel-shaped bodies, separate head and neck regions and evertable pharynxes. They are relcated to Pripulid Worms (large unsegmented Worms with evertable pharyxes and Loriciferas (small unsegmented animals with cup-shaped rigid bodies and evertable pharynxes), the three groups being grouped together as the Scalidophora. Molecular clock estimates have suggested that the three groups diverged during the Eidacaran, but while Priapulids are well documented from the Cambrian onwards, and a large, Loricifera-like animal (Sirilorica) is also known from the Cambrian, to date no Kinorhynches have been found in the fossil record from any period.

In a paper published in the journal Nature:Scientific Reports on 26 November 2015, a team of scientists led by Huaqiao Zhang of the Key Laboratory of Economic Stratigraphy and Palaeogeography of the Chinese Academy of Sciences, at the NanjingInstitute of Geology and Palaeontology, describe a series of Kinorhynch fossils from the Early Cambrian Xinli Member of the Dengying Formation in Nanjiang County in Sichuan Province, deposits that form part of the Small Shelly Fauna at the beginning of the Cambrian (the Small Shelly Fauna marks the beginning of the Cambrian in deposits around the world; in these beds numerous small shells and shell-elements are found, but not larger mineralized shells) and are dated to about 535 million years ago.

Several of the best preserved specimens are described together as Eokinorhynchus rarus, where 'Eokinorhynchus' means 'dawn-Kinorhynch' and 'rarus' means 'rare', though Zhang et al. record the presence of fragmentary specimens that apparently belong to other species. Eokinorhynchus rarus is essentially similar to modern Kinorhynches, with a segmented tubulaer trunk, a neck region and head with an evertable pharyx, but while modern Kinorhynches invariably have 11 segments, Eokinorhynchus rarus appears to have a minimum of 20.

SEM images of Eokinorhynchus rarus. (a–c) Dorsal, ventral, and left lateral views, respectively. (d–f) Close-up views of zones 2 and 3 to show the arrangement pattern of pharyngeal teeth (numbered in the two basal circlets), with white arrows denoting the 3rd and black arrows denoting the 4th circlet of pharyngeal teeth. Abbreviations: A1–A20, 1st to 20th trunk annulus; an, anus; cs, caudal spine; hsc, head scalid; ls, large sclerite; 1ls–5ls, 1st to 5th pair of large sclerites; mg, midgut; nsc, neck scalid; spl, small plate; ss, small spine; vls, ventral large sclerite. Scale bar beneath (c) applies to (a–c), and scale bar beneath (d) applies to (d–e). Zhang et al. (2015).

The presence of Eokinorhynchus rarus in deposits dating to the earliest Cambrian supports the idea that the Scalidophoran groups diverged in the Ediacaran, but does not explain the absence of Kinorhynch fossils from other deposits, particularly notable Cambrian drposits such as the Burgess Shale, which preserve numerous non-mineralized taxa. Zhang et al. suggest that the microscopic size and interstitial lifestyle of Kinorhynches makes them unsuitable for Burgess Shale type preservation, but suitable for preservation as phosphatic microfossils; a type of preservation that has only been discovered and studied in recent years, as computerized scanning and modeling methods have enabled palaeontologists to study fossils that would either have been destroyed or overlooked using traditional techniques.

Reconstruction of Eokinorhynchus rarus. (a–c) Dorsal, ventral, and right lateral views, respectively. Dinghua Yang in Zhang et al. (2015).

See also...

http://sciencythoughts.blogspot.co.uk/2015/05/yuganotheca-elegans-early-cambrian.htmlYuganotheca elegans: An Early Cambrian Lophophorate Animal with affinities to Brachiopods and Phoronids.                   Lophophorates are animals which feed using a filter called a...
http://sciencythoughts.blogspot.co.uk/2015/05/priapulid-worms-from-middle-cambrian-of.htmlPriapulid Worms from the Middle Cambrian of Canada.                                                                      Priapulid Worms are a form of marine worms with denticle-covered pharynxes which can be everted to form proboscises. They are a minor element of modern marine faunas, largely restricted to deep marine...
http://sciencythoughts.blogspot.co.uk/2014/11/a-new-species-of-vetulicolian-from.htmlA new species of Vetulicolian from the Early Cambrian of Kangaroo Island, South Australia.                                                                    Vetulicolians are an enigmatic group of Cambrian fossils known from the Chengjiang and Guanshan biotas of South China, Sirius Passet in...

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