Outlines of Tuzoia canadensis (left), Tuzoia burgessensis (middle) and Tuzoia retifera (right).
© MARIANNE COLLINS
Tuzoia is known as one of the most diverse and widespread hymenocarines, but, besides isolated carapaces, other soft-tissues are scarce. Tuzoia may represent one of the earliest hymenocarine representatives.
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.
Burgess Shale: T. retifera and T. canadensis from 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. australis from the Lower Cambrian Emu Bay Shale of Australia (Glaessner 1979; García-Bellido et al. 2009). T. bispinosa from the Lower Cambrian Balang Formation of China (Wen et al. 2019) and the Wuliuan Kaili Formation of China (Yuan and Zhao 1999; Wen et al. 2015). T. guntheri from the Middle Cambrian Marjum and Pioche Formations of Utah and Nevada (Robison and Richards 1981; Lieberman 2003). T. jianheensis from the Lower Cambrian Tsinghsutung Formation of China (Chen et al. 2017). T. lazizhaeiensis from the Lower Cambrian Balang Formation of China (Wen et al. 2019). T. polleni from the Lower Cambrian Eager Formation of British Columbia (Resser 1929), the Lower Cambrian Kinzers Formation of Pennsylvania (Resser 1929; Vannier et al. 2007), the Lower Cambrian Parker Quarry in Vermont (Pari et al. 2022) and the Wuliuan Pioche Formation of Utah and Nevada (Resser and Howell 1938). Other species of Tuzoia are known (e.g., T. manchuriensis), albeit poorly documented or with open nomenclature. (See Lieberman 2003; Vannier et al. 2007; Wen et al. 2019; Izquierdo-López and Caron 2022a for references).
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. Marble Canyon and Stanley Glacier in Kootenay National Park.
Tuzoia was first described by Charles Walcott (1912) based on a single carapace specimen from the Burgess Shale, which was later expanded in more detail by Resser (1929). Since then, Tuzoia has been described from multiple other Cambrian sites: Utah (Robison and Richards 1981) and Nevada (Lieberman 2003) in the USA, Australia (Glaessner 1979; Luo et al. 1999; Yuan and Zhao 1999; Wen et al. 2015, 2019; Wu and Liu 2022), the Czech Republic (Chlupáč and Kordule 2002), and multiple localities in China (Pan 1957; Shu 1990; Luo et al. 1999; Yuan and Zhao 1999; Wen et al. 2015, 2019; Wu and Liu 2022) ), making it one of the geographically most widespread arthropod species of that period (Hendricks et al. 2008). Given its distribution, more than 20 species of Tuzoia have been historically defined, but major redescriptions have reduced this number to lower than 10 (Vannier et al. 2007; Wen et al. 2019). Several species, though, remain poorly known or with open nomenclature. In 2021, a new genera to the family tuzoiidae, Duplapex, was described from the Qingjiang Biota of China (Ma et al. 2021). Soft parts such as eyes, potential antennae and gut structures were first reported by Vannier et al. (2007), and were followed by new information on the anatomy of the head (Wen et al. 2019) and legs (Caron et al. 2010; Wen et al. 2019; Du et al. 2020), albeit generally poorly preserved. A re-study of Tuzoia, including new material from the Marble Canyon and adjacent outcrops at the Burgess Shale (Caron et al. 2014) found fully-preserved legs and a tailpiece, as well as new details of the head, allowing for a first comprehensive reconstruction of its anatomy and evaluation of its affinities (Izquierdo-López and Caron 2022).
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 usually extends at the front and back into pointed spines, or cardinal processes. Most species of Tuzoia have two main spines on the mid-posterior and posteroventral margin of the carapace. Smaller spines are usually present along the posterior, ventral and dorsal side of the carapace; they vary in number, size, and orientation between species. A lateral ridge passes horizontally, perpendicular to the surface of the carapace valves, which is often spinose. The carapaces are covered in a polygonal pattern. The head bears a pair of large, spherical eyes on short stalks, and projects forwards from underneath the carapace and bears a pair of antennae and a pair of lobes between the eyes. The trunk is short, and is completely covered by the carapace. It bears a total of 12 thick biramous legs. Each leg is divided into a base (basipod), which is elongated and bears a few isolated spines and an inner branch (endopod), divided into seven segments, with the terminal one having a claw-like shape. The basipod of the first anterior legs may bear dentate projections (endites), and all segments of the endopod bear spines. The remaining, more posterior legs do not show these projections, and spines are limited to a couple of segments. The legs may also have a paddle-like outer branch (exopod), although its shape is not clear. The body terminates into two pairs of broad fan-like appendages (caudal rami). Besides the carapace, anatomical details are a composite between different species of Tuzoia from the Burgess Shale formation, mainly T. burgessensis and T. retifera. Possible anatomical differences across species are currently unknown.
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 also found at Stanley Glacier and in the Marble Canyon and Tokumm Creek localities, albeit not highly abundant.
Tuzoia is suggested to be free-swimming animal. 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 legs end in claw-like structures, suggesting that Tuzoia may have also been able to walk on the benthos or anchor itself to structures such as carcasses. If that was the case, the carapace must have been able to open partially. The large, frontally-directed eyes, as well as the spines on the anterior legs, also reinforce the idea that it was a predator or scavenger. The spines present on the more posterior legs could have also been used to attach to surfaces or manipulate food.
http://www.bioone.org/doi/abs/10.1666/pleo05070.1