Unranked clade (stem group arthropods)
The affinity of Tuzoia is unknown because key information about its body structure and appendages is missing. It has been suggested that it is a crustacean (Briggs et al., 1994), specifically a phyllocarid (Lieberman, 2003). However, these affinities cannot be substantiated until further details of the morphology are revealed. Tuzoia shares similarities in carapace and eye structure with Isoxys (Vannier et al., 2007), another arthropod of uncertain affinity.
Tuzoia – from Mount Tuzo, in the Valley of the Ten Peaks, named in 1907 after Henrietta Tuzo, who was the first to climb this mountain.
burgessensis – from Mount Burgess (2,599 m), a mountain peak in Yoho National Park. Mount Burgess. The name was given in 1886 by Otto Klotz, the Dominion topographical surveyor, after Alexander Burgess, a former Deputy Minister of the Department of the Interior.
Holotypes – USNM 80477b (T. burgessensis),USNM 57720 (T. retifera),USNM 80478b (T. canadensis) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale: T. retifera and T. canadensis from the the Tuzoia layer above the Raymond Quarry, the Raymond and Walcott Quarries on Fossil Ridge, and other sites on Mount Field and Stanley Glacier. (See Vannier et al., 2007 for references).
Other deposits: T. guntheri from the Middle Cambrian Marjum and Pioche Formations of Utah and Nevada; T. bispinosa from the Middle Cambrian Kaili Formation of South China; T. polleni from the Lower Cambrian Eager Formation of British Columbia; and T. australis from the Lower Cambrian Emu Bay Shale of Australia as well as a number of poorly documented species from China. (See Vannier et al., 2007 for references).
Middle Cambrian, Glossopleura Zone to Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott and Raymond Quarries, the Tuzoia layer above the Raymond Quarry and the Collins Quarry on Fossil Ridge. The Tulip Beds (S7) on Mount Stephen.
Brief history of research:
Tuzoia was first described by Charles Walcott (1912) based on a single carapace specimen from the Burgess Shale. He collected many more specimens after this publication that were later described in detail by Resser (1929). Resser designated ten different species of Tuzoia, including specimens from the Burgess Shale, the Eager Formation of British Columbia, the Kinzers Formation in Pennsylvania and the Tangshih Formation of China. Tuzoia was also described from other regions in the United States, including Utah (Robison and Richards, 1981) and Nevada (Lieberman, 2003), Australia (Glaessner, 1979), the Czech Republic (Chlupáč and Kordule, 2002), and other localities in China (Yuan and Zhao, 1999; Pan, 1957; Shu, 1990; Luo et al., 1999). At one point, there were over 20 described species of Tuzoia, all described from carapace morphology only, but a major redescription of all available material undertaken by Vannier et al., (2007) validated only 7 of these species. Vannier et al. (2007) also provided a more in-depth analysis of the morphology, including the first description of soft parts such as eyes, antennae and gut structures. The first description of frontal appendages in Tuzoia is documented in Caron et al. (2010).
The most prominent feature of Tuzoia is its large, bivalved carapace. The two dome-shaped carapace valves have convexly rounded ventral margins and are joined along a straight dorsal margin that extends at the front and back into pointed spines, or cardinal processes. There are two pairs of spines present in the mid-posterior and posteroventral locations of the carapace, and several smaller spikes may be present along the ventral margin. There are also spines along the dorsal margin, varying in number, size and orientation between species. A lateral ridge passes horizontally through the carapace, and is lined by frills in T. burgessensis. The carapaces are covered in a polygonal pattern. A pair of large, spherical eyes on stalks project forward from underneath the carapace, and a pair of thin antennae may also be present. The head bears a pair of robust frontal appendages with at least six segments each. In some specimens, a long, straight gut with digestive glands is preserved. Overall T. retifera and T. canadensis differ from T. burgessensis by having less and more spines respectively.
As the name suggests, the Tuzoia beds between the Raymond and Collins Quarries on Fossil Ridge yield abundant Tuzoia burgessensis specimens, with over 160 specimens found so far. T. burgessensis is also found rarely in Raymond Quarry, where T. retifera is more common, with 87 known specimens. Tuzoia is also found rarely in other sites on Mount Field and Mount Stephen.
Tuzoia is suggested to be free-swimming animal, based mainly on the morphology of the carapace. The midposterior and posteroventral spines probably acted as a keel to provide directional stability to the animal while swimming, and the lateral ridge may have allowed directional control to improve the streamlining of the animal while preventing sinking. The reticulate pattern of the carapace is interpreted as a way of strengthening the carapace without adding so much weight that the animal would be unable to swim. Spines and the lateral ridge may also have provided protection from predation. The eyes had a wide field of vision, further suggesting that Tuzoia was a swimmer. The antennae would have been used to sense the environment, and the frontal appendages could have been used to obtain food.