New information on olenelline trilobites from the Early Cambrian Sekwi Formation, Northwestern Canada

This is the author's accepted manuscript, the published version is available at http://www.nrcresearchpress.com/doi/abs/10.1139/E10-073#.U21JO4FdXUL .A new species of olenelline trilobite, Nevadella keelensis, is described from the Early Cambrian (Cambrian Series 2, Stage 3) in the Sekwi Formation, Mackenzie Mountains, Canada. The difficulty in discerning between Nevadia Walcott, 1910 and Nevadella Raw, 1936 is discussed, and a revision of the two genera is suggested, particularly with the addition of Nevadella keelensis n. sp. A holmiid trilobite, perhaps conspecific with Esmeraldina rowei (Walcott, 1910), was also confirmed from the same locality. The E. sp. aff. rowei represents the narrow form of a species known for great variability in cephalic form. The trilobite material comes from a low diversity, shallow water, peritidal facies that was not sampled in previous studies of Cambrian fossils in the area, and could prove useful in facilitating biostratigraphic correlation across the Selwyn Basin and with other parts of Laurentia as well

New olenelline trilobites from the Northwest Territories, Canada, and the phylogenetic placement of Judomia absita

This is the author's accepted manuscript, the published version is available here http://www.mapress.com/zootaxa/2011/f/z02918p028f.pdfThe Early Cambrian olenelline trilobites are a diverse clade that have been the subject of several phylogenetic analyses. Here, three new species of Bradyfallotaspis Fritz, 1972 (B. coriae, B. nicolascagei, and B. sekwiensis) and one new species of Nevadia Walcott, 1910 (N. saupeae) are described from the Sekwi Formation of the Mackenzie Mountains, Northwest Territories, Canada. In addition, new specimens potentially referable to Nevadia ovalis were recovered that may expand that species’ geographic range, which was thought to be restricted to Sonora, Mexico. A phylogenetic analysis incorporating several olenelline taxa, including Judomia absita from the Sekwi Formation, is also presented herein. This species has been assigned to various olenelline genera, including Judomia Lermontova, 1951 and Paranevadella Palmer & Repina, 1993. Phylogenetic analysis suggests this species is closely related to Judomia tera Lazarenko, 1960 from Siberia. This phylogenetic relationship provides further support for the hypothesis that a close biogeographic relationship existed between Laurentia and Siberia during the Cambrian

Bradyfallotaspis sekwiensis Gapp, Lieberman, Pope & Dilliard, 2011, n. sp.

<i>Bradyfallotaspis sekwiensis</i> n. sp. <p>(Fig. 5.1–5.7)</p> <p> ? <i>Bradyfallotaspis</i> sp. 3 FRITZ, 1973, p. 11, pl. 6, figs. 25–27.</p> <p> <b>Type material.</b> Holotype PWNHC-2009.20.18. Paratypes KUMIP 320708-320710 and PWNHC-2009.20.19- 2009.20.20. From <i>Nevadella</i> zone, Early Cambrian, Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada (Section 1, 175.6– 288 m above base of formation; Section 2 in float). There are a total of six specimens.</p> <p> <b>Etymology.</b> Named after its occurrence in the Sekwi Formation.</p> <p> <b>Diagnosis.</b> Anterior cephalic border (sag.) equal to length (sag.) of LO and L1; preglabellar area absent; ocular lobes not in contact with posterior border furrow.</p> <p> <b>Description.</b> Width of cephalon (tr.) is greater than or equal to twice the cephalic length (sag.); anterior cephalic border length (sag.) is long approximately equal to length (sag.) of LO and L1; preglabellar field is absent; a pit-like structure is visible where ocular ridge contacts L3 and LA in some specimens; width (tr.) of the extraocular area varies from 0.75–2 times the width (tr.) of the interocular area; a strongly incised SO is present, often yet not always conjoined adaxially; a node is present on the posterior margin of LO in the one specimen that has a well preserved margin.</p> <p> <b>Discussion.</b> This species differs from all other species of <i>Bradyfallotaspis</i> by its possession of the anterior cephalic border (sag.) equal to twice length (sag.) LO and its lack of a preglabellar area. It differs from <i>B. fusa</i> and <i>B. patula</i> by having the ocular ridges connected to the glabella at L3 and having the genal spine length (exsag.) greater than the length (sag.) of the cephalon. Finally, its ocular lobes do not contact the posterior border furrow, unlike <i>B. coriae</i> and <i>B</i>. <i>fusa</i>. <i>Bradyfallotaspis</i> sp. 3 of Fritz (1973) is questionably placed within <i>B. sekwiensis</i> based on its glabella with high relief, its wide (tr.) cephalon with a broad anterior cephalic border, and its posterior cephalic border that tapers to a point adaxially. However, the material of <i>B</i>. sp. 3 is limited, not well preserved, and some of it is based on early ontogenetic stages. Therefore, it is not possible to definitively ascertain whether it is conspecific with <i>B. sekwiensis</i>.</p>Published as part of <i>Gapp, Wesley, Lieberman, Bruce S., Pope, Michael C. & Dilliard, Kelly A., 2011, New olenelline trilobites from the Northwest Territories, Canada, and the phylogenetic placement of Judomia absita Fritz, 1973, pp. 15-28 in Zootaxa 2918</i> on pages 19-22, DOI: <a href="http://zenodo.org/record/202343">10.5281/zenodo.202343</a&gt

Judomia absita Fritz 1973

<i>Judomia absita</i> Fritz, 1973 <p>(Fig. 7.1–7.6)</p> <p> <i>Judomia? absita</i> FRITZ, 1973, p. 14, pl. 8, figs. 1–11.</p> <p> <b>Material examined.</b> PWNHC-2009.20.23-2009.20.46, KUMIP-320714-320737, from <i>Nevadella</i> 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).</p> <p> <b>Diagnosis.</b> 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.</p> <p> <b>Discussion.</b> Nelson (1976, 1978) commented on the presence of various species he referred to <i>Judomia</i> in the Lower Cambrian of the White-Inyo region of California. However, his definition of <i>Judomia</i> 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 <i>J. absita</i>. The two outgroups used were <i>Nevadella mountjoyi</i> Fritz, 1992 and <i>N. perfecta</i> (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 <i>J. absita</i> 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.</p> <p> The present study provides additional evidence that species of <i>Judomia</i> 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, <i>J. absita</i> occurs in the <i>Nevadella</i> zone in Laurentia and other species of <i>Judomia</i> occur in the <i>Judomia</i> 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 <i>J. absita</i> is sister to the Siberian <i>J. tera</i>. 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 <i>et al.</i> 1992; Pelechaty 1996; Lieberman 1997; and Meert & Lieberman 2004, 2008).</p> <p>0 0 0 0 0 0 0 0 0 111111111122222222222333333333444444444455555555 123456789012345678901234567890123456789012345678901234567</p> <p> <i>Judomia absita</i></p> <p>111X000122100101 Y 111011001211000012?23011????????????????</p>Published as part of <i>Gapp, Wesley, Lieberman, Bruce S., Pope, Michael C. & Dilliard, Kelly A., 2011, New olenelline trilobites from the Northwest Territories, Canada, and the phylogenetic placement of Judomia absita Fritz, 1973, pp. 15-28 in Zootaxa 2918</i> on pages 23-27, DOI: <a href="http://zenodo.org/record/202343">10.5281/zenodo.202343</a&gt