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
|  This
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,  and
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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