Alalcomenaeus Opabinid Arthropod from Maotianshan Shales


Alalcomenaeus sp

Phylum Arthropoda, Class Dinocaridida, Order Radiodonta, Family Opabiniidae

Geological Time: Early Cambrian (~525 million years ago)

Size: Fossil is 26 mm long

Fossil Site: Chengjiang Biota, Qiongzhusi Section, Yu'anshan Member, Heilinpu Formation, Maotianshan Hill, Yuxi, Chengjiang County, Yunnan Province, China


Alalcomenaeus, Unusual Opabinid Arthropod Fossil ChengjiangAlalcomenaeus is thought by some scientists to be one of the great appendage arthropods known as the opabinids, named after Opabinia from the Burgess Shale Fauna. Other opabinids from Chengjiang are Jianfengia and Leanchoilia. The long antenna and exceptional detail of the appendages are readily apparent in this fine specimen. The taxon is unknown outside the Chengjiang Biota. This is a truly exceptional specimen and representative of the Cambrian explosion.

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. 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 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 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

Also see: Chengjiang Biota, Chengjiang Fossils, Cambrian Explosion

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