Judomia absita Fritz 1973

Judomia absita Fritz, 1973

(Fig. 7.1–7.6)

Judomia? absita FRITZ, 1973, p. 14, pl. 8, figs. 1–11.

Material examined. PWNHC-2009.20.23-2009.20.46, KUMIP-320714-320737, from Nevadella zone, Early Cambrian, Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada (Section 1, 196.1– 378 m above base of formation and in float; Section 2 in float; Section 3, lower 100 m of formation; Section 4, 195– 215 m above base of formation; Section 14 in float).

Diagnosis. Glabella cylindrical; strongly incised SO conjoined adaxially; S1, S2, and S3 not conjoined adaxially; extraocular area shows some relief; posterior cephalic border length (sag.) increases adaxially.

Discussion. Nelson (1976, 1978) commented on the presence of various species he referred to Judomia in the Lower Cambrian of the White-Inyo region of California. However, his definition of Judomia did not always accord with a phylogenetically constrained, monophyletic conception of the genus [see Lieberman (2001) for more detailed discussion]. For this paper a total of 20 taxa within the Olenellina were subjected to phylogenetic analysis; these were chosen to best consider the phylogenetic placement of J. absita. The two outgroups used were Nevadella mountjoyi Fritz, 1992 and N. perfecta (Walcott, 1913); these were shown by Lieberman (2001) to be basal to the 18 ingroup taxa. Phylogenetic patterns were determined by parsimony analysis of 57 holaspid exoskeletal characters and character states based on Lieberman (2001). Character states for J. absita are presented in Table 1; the complete list of characters and character states is otherwise identical to that used by Lieberman (2001). The resulting tree from this phylogenetic analysis is presented in Figure 8.

The present study provides additional evidence that species of Judomia are indeed present in Laurentia; the genus was originally described from Siberia. This indicates the potential for a biostratigraphic link between Siberia and Laurentia. Specifically, J. absita occurs in the Nevadella zone in Laurentia and other species of Judomia occur in the Judomia zone of the Atdabanian stage of Siberia (Palmer & Repina 1993); thus, these biostratigraphic divisions might be coeval. Based on the higher-level phylogeny presented in Figure 8, the Laurentian J. absita is sister to the Siberian J. tera. This provides further support for the close biogeographic and tectonic relationship between these two cratons in the late Proterozoic and early Cambrian (see also McKerrow et al. 1992; Pelechaty 1996; Lieberman 1997; and Meert & Lieberman 2004, 2008).

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Judomia absita

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