Arthropod appendages from the Weeks Formation Konservat-Lagerstätte: new occurrences of anomalocaridids in the Cambrian of Utah, USA RUDY LEROSEY-AUBRIL, THOMAS A. HEGNA, LOREN E. BABCOCK, ENRICO BONINO & CARLO KIER The Guzhangian Weeks Formation (House Range, Utah, USA) contains a virtually unstudied but diverse assemblage of “soft-bodied” organisms. This fauna includes several enigmatic appendages of arthropods that are described in this con- tribution. Six appendages (two isolated and four paired appendages) are interpreted as frontal appendages of a probably new species of Anomalocaris. They are characterized by a slender morphology, 14 podomeres, ventral spines alternating in size, up to three auxiliary spines per ventral spine, and only two dorsal spines. Another isolated appendage is also ten- tatively assigned to Anomalocaris, but it exhibits a more robust morphology, a stronger distal tapering, and apparently simple ventral spines, suggesting that it may represent a distinct taxon. These frontal appendages represent the youngest occurrence of anomalocaridids in Laurentia and demonstrate the persistence of older, Burgess Shale-type taxa in the Weeks Formation. An assemblage of four antenniform and six robust and heavily-armed appendages is also described. These are interpreted as the serially arranged, anterior appendages of a single individual of an undetermined arthropod species. This association of three pairs of robust, spiny appendages with two pairs of antenniform structures in a Cam- brian arthropod is unique. • Key words: Arthropoda, Anomalocarididae, Weeks Formation, Konservat-Lagerstätte, Cambrian, Guzhangian. LEROSEY-AUBRIL, R., HEGNA, T.A., BABCOCK, L.E., BONINO, E. & KIER, C. 2014. Arthropod appendages from the Weeks Formation Konservat-Lagerstätte: new occurrences of anomalocaridids in the Cambrian of Utah, USA. Bulle- tin of Geosciences 89(2), 269–282 (5 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript re- ceived April 19, 2013; accepted in revised form September 5, 2013; published online March 4, 2014; issued XXX XX, 2014. Rudy Lerosey-Aubril, Laboratoire de géologie de Lyon: Terre, Planètes, Environnement (UMR 5276, CNRS), Université Claude Bernard Lyon I, Campus de la Doua, 2 rue Raphaël Dubois, 69622 Villeurbanne, France; leroseyaubril@gmail.com • Thomas A. Hegna, Department of Geology, Western Illinois University, Tillman Hall 113, 1 University Circle, Macomb, IL 61455, USA; ta-hegna@wiu.edu • Loren E. Babcock, School of Earth Sciences, The Ohio State University, Columbus, Ohio 43210, USA, and Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden; loren.babcock@geol.lu.se • Enrico Bonino & Carlo Kier, Back to the Past Museum, Carretera Cancún, Puerto Morelos, Quintana Roo 77580, Mexico; e_bonino@yahoo.it, kierc@cancun.com.mx The Weeks Formation is one of at least nine Cambrian Konservat-Lagerstätten in the Great Basin region (Utah, Nevada, and California) of the western United States (e.g. Gunther & Gunther 1981, Robison 1991 and references therein, Lieberman 2003, English & Babcock 2010, Robi- son & Babcock 2011). Fossils from the Weeks Formation have been known for more than a century (Walcott 1908a, b) but many remain to be thoroughly studied. Until recently (Adrain et al. 2009, Robison & Babcock 2011), the trilo- bite fauna had received little scientific attention since Wal- cott (1916a, b), with the exception of a couple of unpublis- hed Ph.D. theses (Beebe 1990, Peters 2003). This trilobite fauna is remarkable for the high proportion of articulated specimens (Adrain et al. 2009, Robison & Babcock 2011) and for the rare but exquisite preservation of digestive structures (Robison & Babcock 2011, Lerosey-Aubril et al. 2012). The shelly fauna also includes abundant inarticulate brachiopods (Walcott 1908b, Rowell 1966, Streng & Hol- mer 2006), hyolithids (Walcott 1908b), sponge spicules, and rare echinoderms (Ubaghs & Robison 1985). The upper part of the Weeks Formation has produced a rather diverse as- semblage of both weakly-biomineralised and soft-bodied organisms dominated by arthropods and worms (e.g. paleo- scolescids). This includes the oldest aglaspidid (Lerosey- Aubril et al. 2013), the enigmatic aglaspidid-like arthropod Beckwithia (Raasch 1939, Hesselbo 1989), and the arthro- pod appendages described herein. Although fragmentary, these new fossils give important insights into the composi- tion of the Weeks Formation fauna and its relationships with older, better-known Cambrian soft-bodied assemblages. 269 DOI 10.3140/bull.geosci.1442