Isoxys

Genus of extinct arthropods

Isoxys Temporal range: Atdabanian to Paibian PreꞒ Ꞓ O S D C P T J K Pg N
Isoxys curvirostratus from the Chengjiang Biota
Fossil of Isoxys acutangulus from the Burgess Shale
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Order:	†Isoxyida
Family:	†Isoxyidae
Genus:	†Isoxys Walcott, 1890
Species
See text

Isoxys (meaning "equal surfaces") is a

extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators.^[1] It had a pair of large spherical eyes (which are the most commonly preserved feature of the soft-bodied anatomy),^[2] and two large frontal appendages used to grasp prey.^[1]

Description

biramous appendages (c,d) (c) and (d) represent first four limb pairs and remaining posterior limbs, respectively

Species of Isoxys have roughly semicircular bivalved carapaces, which vary in morphology between species. The front and rear edges of the carapaces bear forward and posterior facing spines, respectively which in some species are greatly elongated.^[3] The carapaces of Isoxys are typically 1.1 to 3.3 centimetres (0.43 to 1.30 in) in length, excluding the spines, though some species are known to reach over 6 centimetres (2.4 in). In long-spined species when including spine length, some specimens exceed 10 centimetres (3.9 in).^[4] The opening angle of the carapace was close to vertical, giving it a narrow profile when viewed from above.^[3]

Isoxys is thought to be one of the

20 species of Isoxys have been described,[3] which have a global distribution, having been found in North America, Siberia, Australia, China and Europe, spanning from Cambrian Series 2 into the Miaolingian.^[11]

• Isoxys chilhoweanus Walcott, 1890 (type) Tennessee, USA, Cambrian Series 2
• Isoxys acutangulus (Walcott, 1908) Balang Formation, Guizhou, China, Cambrian Stage 4, Burgess Shale, Canada, Miaolingian
• Isoxys auritus (Jiang, 1982)
  Chengjiang Biota, Yunnan, China, Cambrian Stage 3
  , Balang Formation, China, Cambrian Stage 4
• Isoxys curvirostratus Vannier & Chen, 2000 Chengjiang Biota, China, Cambrian Stage 3
• Isoxys paradoxus Hou, 1987 Chengjiang Biota, China, Cambrian Stage 3
• Isoxys zhurensis Ivantsov, 1990 Sinsk Formation, Siberia, Cambrian Series 2
• Isoxys bispinatus Cui, 1991 Shuijintuo Formation, Sichuan, China, Cambrian Series 2
• Isoxys glaessneri García−Bellido, Paterson, Edgecombe, Jago, Gehling & Lee, 2009 Emu Bay Shale, Australia, Cambrian Stage 4
• Isoxys communis Glaessner, 1979 Emu Bay Shale, Australia, Cambrian Stage 4
• Isoxys guanduensis Wang et al., 2012 Guanshan Biota, Yunnan, China, Cambrian Stage 4
• Isoxys minor Luo et al., 2008 Guanshan Biota, Yunnan, China, Cambrian Stage 4
• Isoxys wudingensis Luo & Hu, 2006 Guanshan Biota, Yunnan, China, Cambrian Stage 4
• Isoxys globulus Liu et al., 2018 Balang Formation, Guizhou, China, Cambrian Stage 4
• Isoxys jianheensis Liu et al., 2018 Balang Formation, Guizhou, China, Cambrian Stage 4
• Isoxys volucris Williams, Siveter & Peel, 1996, Sirius Passet, Greenland, Cambrian Stage 3
• Isoxys mackenziensis Kimmig & Pratt 2015 Rockslide Formation, Canada, Miaolingian
• Isoxys longissimus Simonetta & Delle Cave, 1975 Burgess Shale, Canada, Miaolingian
• Isoxys carbonelli Richter & Richter, 1927, Pedroche Formation, Spain, Cambrian Series 2
• Isoxys shandongensis Wang and Huang, 2010, Mantou Formation, Shandong, China, Miaolingian

Indeterminate species are also known from the Spence Shale of Utah, dating to the Miaolingian, as well as the Kaili Biota in Guizhou, China, which also dates to the Miaolingian.^[11]

See also

• Arthropod
• Cambrian explosion
• Chengjiang biota
  • List of Chengjiang Biota species by phylum
• Paleobiota of the Burgess Shale

References