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Journal of Paleontology 91(5):987–993
antenna extends forward from the anterior cephalic tergite. No limb setae have been observed. Raised, elliptical structure present immediately posterior to
PCT; widest part of structure coincides with S1, narrows posteriorly; infill coarser than surrounding matrix. Postabdomen not preserved; holotype preserved in ventral aspect.
Remarks.—Antarcticarcinus pagoda n. gen. n. sp. is assignable to the Euthycarcinoidea by possession of a greater number of ventral sternites than dorsal tergites, uniramous appendages, possession of anterior and posterior cephalic tergites with a pair of spherical eyes located near the juncture of these plates, and a pair of mandibles. However, a direct comparison with other euthycarcinoid taxa is extremely difficult owing to the incom- plete nature of the holotype of A. pagoda n. gen. n. sp. Overall, A. pagoda n. gen. n. sp. bears the greatest gross similarity with members of the family Euthycarcinidae Handlirsch, 1914 (i.e., genera Euthycarcinus, Kottixerxes, Schramixerxes, Smithixerxes, and Synaustrus). Problems with this placement include preservation of apparently only four dorsal tergites (T1–T4 in Fig. 2.2), although this is likely due to the incomplete nature of the holotype. Apparent limb podomeres beneath the preabdomen (LMB in Fig. 2.2) appear to be flattened; whether this flattening is due to taphonomy or to original morphology cannot be determined. Additionally, no limb setae have been observed. Within the family Euthycarcinidae, all members of the genera Euthycarcinus, Kottixerxes, and Synaustrus have slender, non-flattened, antennaeform appendages with setae (Gall and Grovagel, 1964; Schram and Rolfe, 1982; Schneider, 1983; Schultka, 1991; Edgecombe and Morgan, 1999). Of the remaining genera currently within Euthycarcinidae, Schramixerxes possess no setae on the limbs (Racheboeuf et al., 2008) and no information on limbs exists for Smithixerxes (Schram and Rolfe, 1982). Without any postabdominal infor- mation, and considering the incomplete nature of the holotype, we prefer to retain Antarcticarcinus pagoda n. gen. n. sp. in open nomenclature within the class Euthycarcinoidea. Antarcticarcinus pagoda n. gen. n. sp. was originally
described and interpreted as a freshwater decapod crustacean (crayfish) by Babcock et al. (1998). This attribution was based largely upon the texture of the single specimen that was known at that time (a single lateral processes as interpreted herein, PRI 68572, Fig. 3.1, 3.2) that was interpreted as a crayfish propodus or fixed finger (Babcock et al., 1998). Those authors further based their attribution upon burrows that were interpreted as having been constructed by crayfish that occur in the lower Triassic Fremouw Formation, which occurs several formational units above the Pagoda Formation (Babcock et al., 1998, fig. 2). Moreover, Fremouw traces occur in a completely different depositional setting—crevasse splay deposits laterally adjacent to floodplain deposits (Babcock et al., 1998). Babcock et al. (1998) dissected crayfish and interpreted the
rod-like, or closely spaced linear texture of the fossil lateral processes (Fig. 3.1, 3.2) as being similar to the cuticle of the modern crayfish genus Procambarus, but they did not indicate if further dissections were done with other groups of claw-bearing arthropods. Also, there was no indication in PRI 68572 of the ‘teeth’ mentioned in Babcock et al. (1998) when examined under a stereomicroscope, but the margin of the preserved
Figure 3. Disarticulated and isolated lateral process of Antarcticarcinus pagoda n. gen. n. sp. This specimen, which occurs on a small slab with no other remains present, was previously interpreted by Babcock et al. (1998) as a crayfish claw; compare with lateral process (LP) in Figure 2. (1) PRI-68572, showing texture. Photographed immersed in ethanol under polarized light. Scale bar = 1 cm. (2) interpretive drawing of PRI-68572.
portion of the cuticle does appear to have an irregularly fractured edge. Because of the articulated state of the anterior portion of the holotype of A. pagoda n. gen. n. sp. (PRI 68571), including the lateral processes, the decapod crustacean inter-
pretation of the single isolated specimen (Babcock et al., 1998, fig. 3A) is no longer supported, and that specimen is transferred to A. pagoda n. gen. n. sp. herein. Antarcticarcinus pagoda n. gen. n. sp. appears to have been
well adapted for a lacustrine environment,with grossmorphology consistent with a nektobenthic lifestyle. The large wing-like processes extending laterally from the trunk dorsal surface may have aided in stabilizing the animal on softmuds at the sediment- water interface, or in swimming for steering or lift rather than propulsion. Although many other euthycarcinoid taxa possessed spine-like extensions of the dorsal segments (McNamara and Trewin, 1993; Wilson and Almond, 2001; Racheboeuf et al., 2008), no other taxon has advancement of these features forward of the posterolateral corner of tergite, or the greatly exaggerated size of the lateral processes in A. pagoda n. gen. n. sp. A probable three-dimensional gut trace in the holotype is partially filled with sediment coarser than the surrounding matrix, indicating a possible deposit-feeding lifestyle.
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