Yawunik is a representative of the megacheiran family Leanchoiliidae (Aria, Caron, & Gaines, 2015). Megacheirans are basal true arthropods with a frontal appendage pointing upward and made of multiple claws (the cheira, or “great appendage”). Megacheirans are generally considered to be among the first true arthropods (that is, arthropods with segmented bodies and appendages), and possibly the earliest representatives of the extended chelicerate lineage (Aria, 2022).
Yawunik – Latinized spelling of Yawu?nik’, the fierce monster of the Ktunaxa First Nation’s creation story.
kootenayi – After the name Kootenay National Park, representing the area where the fossil was found, a territory previously inhabited by the Ktunaxa First Nation among others.
Burgess Shale and vicinity: None
Other deposits: None
Marble Canyon, Kootenay National Park, British Columbia.
Along with Surusicaris elegans (Aria & Caron, 2015), Yawunik kootenayi is one of the first two arthropods described from the Marble Canyon locality of the Burgess Shale (Aria et al., 2015). The original study was based on 42 specimens from the 2012 Royal Ontario Museum expedition, the same year the new fossil deposit was found. Dozens more specimens have since been collected, making Yawunik one of the most abundant arthropods of the Marble Canyon quarry, next to Sidneyia (Nanglu, Caron, & Gaines, 2020). As the largest and one of the best preserved megacheiran arthropod, Yawunik has since been referenced in many studies.
Yawunik kootenayi was a large predator, stouter than its closest relatives. The body lacks any biomineralization. Like other leanchoiliid megacheirans, it is characterized by flagellate frontal appendages (cheirae) made of three long claws, and a body divided into two regions (tagmata): the cephalon, covered by a single shield, and the segmented trunk. At the front of the head, leanchoiliids bore a pair of large unstalked lateral eyes and a pair of smaller, mushroom-shaped median eyes. The megacheiran appendages were of similar simple morphology throughout the body, reflecting the typical arthropod biramous limb: sub-cylindrical basis with teeth for mastication (basipod), relatively strong walking legs (endopods), and paddle-like, semi-rigid flaps (exopods) fringed with lamellae. The tail is a single element called a telson, having the shape of spear’s tip (lanceolate).
Known through more than 180 specimens, Yawunik is one of the most abundant arthropods of Marble Canyon, and is also known from Tokumm Creek.
Like other leanchoiliid megacheirans the frontal appendages of Yawunik likely combined both sensing and grasping functions to detect and catch prey items. Food caught was brought under the body where it was rudimentarily masticated between the bases of limbs (basipods), before being channeled back to the mouth. As a leanchoiliid, Yawunik also had large glands atop its gut, presumably involved in digestion. The megacheiran body appendages, made of relatively strong walking legs (endopods) as well as paddle-like, semi-rigid flaps (exopods), would have allowed for both locomotion on the sea floor and swimming. The exopods likely served for gas exchanges (like breathing) as well, but recent studies showed that megacheirans and other Cambrian arthropods also possessed dedicated gills (Liu et al., 2021).