Temporal range: Atdabanian to Paibian
|Isoxys sp., 24mm|
Isoxys was a bivalved arthropod, which was probably a free-swimming predator. It had a pair of large spherical eyes (which are the most commonly preserved feature of the soft-bodied anatomy), and two large appendages, which have led to speculation that it may be related to the great appendage arthropods.
Isoxys was abundant in tropical seas, and may have had a global distribution. Eyes of different specimens appear to have been adapted to different light intensities; one specimen of I. auritus was either crepuscular in shallow water, or lived in waters around 140 m below the sea surface; whereas another was morphologically adapted to a diurnal light intensity in shallow waters. It is likely that Isoxys was a visual predator that hunted swimming above the seafloor. It had powerful prehensile frontal appendages and large spherical eyes. Isoxys could propel itself by the beating possibly 14 flippered swimming legs (setose exopods) and steer with a flap-like tail (or telson).
There are a number of species of Isoxys. I. volucris is the most abundant in the Sirius Passet locality; I. auritus is found in China. In addition to a single specimen of I. longissimus, 163 specimens of I. acutangulus – making a total of 164 specimens of Isoxys are known from the Greater Phyllopod bed, where they comprise 0.31% of the community.
- "Isoxys acutangulus". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011.
- García-Bellido, D.; Vannier, J.; Collins, D. (2009). "Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada". Acta Palaeontologica Polonica 54 (4): 699. doi:10.4202/app.2009.0024.
- Liu, Q.; Luo, H.-L.; Chen, L.-Z.; Lu, S.-X. (2006). "Panlongia, a new trilobitomorph genus from the Lower Cambrian, Kunming, Yunnan". Acta Palaeontologica Sinica 45: 384–392.
- Vannier, J.; Garcia-Bellido, C.; Hu, X.; Chen, L. (Jul 2009). "Arthropod visual predators in the early pelagic ecosystem: evidence from the Burgess Shale and Chengjiang biotas". Proceedings. Biological sciences / the Royal Society 276 (1667): 2567–2574. doi:10.1098/rspb.2009.0361. ISSN 0962-8452. PMC 2686666. PMID 19403536.
- Stein, M.; Peel, J. S.; Siveter, D. J.; Williams, M. (2009). "Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland". Lethaia 43 (2): 258. doi:10.1111/j.1502-3931.2009.00189.x.
- Schoenemann, B.; Clarkson, E. N. K. (2010). "Eyes and vision in the Chengjiang arthropod Isoxys indicating adaptation to habitat". Lethaia 44 (2): no. doi:10.1111/j.1502-3931.2010.00239.x.
- Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS 21 (5): 451–65. doi:10.2110/palo.2003.P05-070R. JSTOR 20173022.