Lotagnostus, Whitehouse, 1936

Taylor, John F., Loch, James D. & Repetski, John E., 2024, Taxonomy and stratigraphic distribution of Lotagnostus (Agnostida: Agnostidae) and associated trilobites and conodonts in the Upper Cambrian (Furongian) of Laurentia, Zootaxa 5422 (1), pp. 1-66 : 37

Lotagnostus cf. L. obscurus Palmer, 1955

( Plate 7.1–7.3, 7.7–7.9, 7.13–7.15 )

cf. 1955 Lotagnostus obscurus, Palmer , p. 92, pl. 19, figs 5–7 only [fig. 10 = L. sp. indet].

non 2011 Lotagnostus cf. L. obscurus Palmer, 1955 ; Westrop et al., p. 24, figs 10A-Q.

Material and occurrence. Lotagnostus nolani Fauna : collection 5/22/08B (4-3), D3362-CO (2-0) from the Windfall Formation at Ninemile Canyon, Nevada.

Discussion. Ludvigsen & Westrop (in Ludvigsen et al., 1989) placed Lotagnostus obscurus in synonymy with Lotagnostus americanus ( Billings, 1865) , a decision perpetuated in a few subsequent papers ( Westrop, 1995; Peng & Babcock, 2005). However, Westrop et al. (2011) restudied and re-illustrated the type specimens of L. obscurus and resurrected L. obscurus as a separate, largely effaced species. Peng et al. (2015) agreed with this decision as do we. However, unlike previous authors, we exclude the second pygidium illustrated by Palmer (1955, pl. 19, fig. 10) from Lotagnostus obscurus . This pygidium has well-impressed furrows, displays evidence of trisection of the pygidial axis, and lacks the conspicuous elevation and strong sagittal convexity at the anterior end displayed by the holotype. It strongly resembles a pygidium of Lotagnostus sp. from the Hales ( Plate 16.16 ), but displays a narrower intranotular axis, narrower border furrow of more constant width, and lacks the constriction of the acrolobe displayed by that species.

Two nearly effaced cephala in collection D3362-CO resemble Lotagnostus obscurus in the outline of their acrolobe, very strong transverse convexity, elevated and very strongly convex (sag.) posterior end, and the shape of the anteroglabella. They differ, however, in possessing longer basal lobes and a prominent occipital band that extends posteriorly well behind the glabellar culmination. Additionally, while the structure of the axis in the associated Windfall pygidia appears consistent with Lotagnostus obscurus ( Westrop et al., 2011, fig. 7D–F, reillustrated the holotype pygidium) the pygidial outline appears more quadrate, the border widens opposite the posteroaxis as the margin of the pleurae appears to straighten, the convexity is less (although the specimen looks dorsoventrally compressed resulting in the longitudinal fracture), and the posterior margin looks more quadrate than rounded. Given the small number of specimens available to evaluate the significance of these differences, we consider the assignment of our material to that species uncertain.

Westrop et al. (2011) similarly reported an effaced species of Lotagnostus from the Windfall Formation in the Cherry Creek Range in eastern Nevada as Lotagnostus cf. L. obscurus . It differs from the species identified by that name herein from the Antelope Range in numerous features of both the cephalon and pygidium. The species from the Cherry Creek Range has smaller basal lobes and a longer (sag.) preglabellar field, which constitutes 26% of the length of the cephalon, as compared with only 20% in the species from the Antelope Range. The former species also has a proportionally shorter posteroaxis that makes up only 50% of the length (sag.) of the pygidial axis, in contrast to that of the Antelope Range species which composes 60%. Consequently, the axial node on the species from the Cherry Creek Range lies very near the midlength of the pygidial axis, rather than well in front of it. It also displays a smoothly rounded anterior margin on the cephalon and posterior margin on the pygidium, whereas those margins on the Antelope Range species are more transverse, and the sclerite shape slightly quadrate.

Figures

PLATE 7. Miscellaneous Windfall taxa.Each white scale bar represents 2mm. 1-3. Lotagnostus cf. L. obscurus. USMN 775722, cephalon, from D3362-CO, dorsal, anterior, and left lateral views. 4-6. Rhaptagnostus cf. R. convergens. Cephalon, CM 41350, from 5/22/08B, dorsal, anterior, and right lateral views. 7-9. Lotagnostus cf. L. obscurus. Cephalon, CM 41351, from 5/22/08B, dorsal, anterior, and right lateral views. 10-12. Homagnostus?. Pygidium, CM 41356, from 5/22/08B, dorsal, posterior, and left lateral views. 13-15. Lotagnostus cf. L. obscurus. Pygidium, CM 41353, from 5/22/08B, dorsal, posterior, and left lateral views. 16. Homagnostus? sp. Pygidium, CM 41401, from 5/22/08B, dorsal view. 17-18. Micragnostus cf. M. intermedius. Cephalon, CM 41358, from 5/22/08B, left lateral and dorsal views. 19. Hedinaspis sp. Fragmentary thoracic and/or pygidial fragment, CM 41359, from 5/22/08C, dorsal view. 20. Machairagnostus cf. M. corrugatus. Pygidium, CM 41349, from 5/22/08B, dorsal view. 21-22. Homagnostus? sp. Cephalon, CM 41357, from 5/22/08B, dorsal and anterior views.

PLATE 16. Taxa from Hedinaspis-Charchaqia Fauna in the Hales Formation, Hot Creek section. Each white scale bar represents 2mm. 1. Lotagnostus nolani n. sp. Carapace (latex peel of external mold), USMN 775754, with Mendoparabolina nyensis, cephalon (counterpart of holotype), USMN 218571 (= Taylor, 1976, pl. 3, fig. 16), from D7130-CO, dorsal view, x7.8. 2, 3. Lotagnostus nolani n. sp. Cephalon, USMN 775755, from D7133-CO, dorsal and anterior views, x11.0. 4-5. Lotagnostus nolani n. sp. Cephalon, USMN 775756, from D7130-CO, dorsal and lateral views, x9.7. 6. Lotagnostus nolani n. sp. Pygidium, USMN 775757, from D7130-CO, dorsal view, x12.2. 7. Lotagnostus nolani n. sp., pygidium, USMN 775758, from D7130-CO, dorsal view, x10.3. 8. Pseudagnostus? sp., carapace, USMN 775759, from D7130-CO, dorsal view, x8.0. 9. Pseudagnostus? sp., carapace, USMN 775760, from D7133-CO, dorsal view, x8.3. 10. Mendoparabolina nyensis (Taylor, 1976), small cranidium, USMN 775761, from D7133- CO, dorsal, x14.3. 11. Mendoparabolina nyensis (Taylor, 1976), pygidium, USMN 775762, from D7130-CO, dorsal view, x7.5. 12. Lotagnostus sp., cephalon, USMN 775763, from D7130-CO, dorsal view, x16.8. 13. Ceratopygid undet., cranidium, USMN 775764, from D7129-CO, dorsal view, x3.9. 14. Lotagnostus sp., cephalon, USMN 775765, from D7130-CO, dorsal view, x8.6. 15. Lotagnostus sp., pygidium, USMN 775766, from D7131-CO, dorsal view, x4.4. 16. Lotagnostus sp., pygidium, USMN 775767, from D7130-CO, dorsal view, x6.5. 17. Ceratopygid undet., pygidium, USMN 775768, from D7129-CO, dorsal view, x2.6.