Isoxys paradoxus, a Shelled Arthropod from Chengjiang

Name: Phylum Arthropoda: Isoxys paradoxus (Chengjiang Biota)

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

Size: 44 mm long by 11 mm tall on a 47 mm by 25 mm matrix

Fossil Site: Chengjiang Biota - Quiongzhusi Section, Yu’anshan Member, Heilinpu Formation, Mafang Village, Haikou County, Kunming, Yunnan Province, China

Isoxys paradoxusThis unusual primitive arthropod is known as Isoxys paradoxus. The species is mostly identified by a distinctive, pointed, bivalved carapace. The Isoxys genus is only rarely found with any soft parts preserved, and only then in the species Isoxys auritus. Based upon the few known examples, it possessed a long segmented body, stalked eyes that projected forward, Isoxysand short antennae. The swimming appendages and most other soft parts only protruded only a short distance from their protective shell. The other two species of the genus: Isoxys paradoxus and Isoxys curvirostratus have an elongated posterior projection. The fossil shown here is Isoxys paradoxus. This taxon is known only from the Chengjiang Biota, but other members of the genus are found in deposits in Europe, Australia, and North America.

Vannier, J. and Chen, J-Y, 2000. The Early Cambrian colonization of pelagic niches exemplified by Isoxys (Arthropoda). Lethaia, 33, 295-311.

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