Chuandianella ovata Maotianshan Shales Arthropod

Description: This unusual arthropod is known as Waptia ovata. The species is known mostly from the distinctive wrinkled carapace, but this one has much soft tissue preserved. The discovery of the Chengjiang Biota by Hou Xian-guang in 1984 opened a window onto a remarkable array of life forms from what is termed the Cambrian Explosion. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

The systematic position of this taxon has undergone several revisions. It was originally placed within the Ostracodiform genus Mononotella, then later referred to a new genus Chaundianella. More recent finds of remains other than the carapace have shown it to be similar to the Burgess Shale arthropod Waptia fieldensis. However, Chuandianella has notably different features, including classic arthropod biramous limbs. While the species is known from other Lower Cambrian locations in Yunnan, Sichuan, Guizhou, and Shaanxi Provinces, only those from the Chengjiang Biota are known to show soft part preservation. This one shows the antennae preserved as well. The negative image makes the antennae more apparent. Note as well the threedimensional nature of the shells, a most unusual preservation occurrence.

Discovered in 1984, the Chengjiang Biota now ranks as the most diverse faunal fossil assemblage of all the Burgess Shale like deposits. It is also some 10 million years older than the Burgess Shale, and like the Burgess Shale, non-mineralized soft tissue parts are often extraordinarily well preserved with high resolution as aluminosilicate films, sometimes with oxidized iron content. Various taphonomic processes leading extensive preservation of soft tissue have been proposed, including rapid death by asphyxia followed by rapid burial in anoxic sediment undisturbed by turbidity. The Chengjiang biota is dominated by the phyla Arthropoda and Porifera. There are seven lobopodians, more than any other Lagerstätte that some scientists elevate to phylum rank, and seven members of the extinct phylum Vetulicolia. Members or potential members of phyla Priapulida, Nematomorpha, Hyolitha, Hemichordata, Echinodermata, Ctenophora, Chordata, Cnidaria, Chaetognatha, and Brachiopoda are found. A large number of enigmatic animals of uncertain affinity are found as well, some of which may represent failed evolutionary experiments, or even new phyla that did not persist for long in the early to middle Cambrian, or were rapidly replaced by more derived forms. Among the diverse Maotianshan Shales fauna, of utmost important are the putative early chordates, particularly Haikouella, potentially an ancestor to or the earliest craniate chordate. Myllokunmingia and Haikouichthys are interpreted as early Craniata, and possibly very primitive agnathids, the progenitor of the fishes and all vertebrates.

References:

• Hou, X. G.; Bergstrom J, (1991) The arthropods of the Lower Cambrian Chengjiang fauna, with relationship and evolutionary significance, p. 179-187. In A. M. Simonetta and S. Conway Morris (eds.), The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press, Cambridge.
• Hu-Qin Liu & De-Gan Shu (2004). "New information on Chuandianella from the Lower Cambrian Chengjiang Fauna, Yunnan, China". Journal of Northwest University (Natural Science Edition) (in Chinese) 34 (4): 453–456.

Also see: Chengjiang Maotianshan Shales, Chengjiang Biota, Chengjiang Fossils, Cambrian Explosion