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 : 43

Lotagnostus aff. L. nolani

( Plate 8.18–8.19 )

Material and occurrence. Lotagnostus rushtoni Fauna : collection D3381-CO (2-1); 5-22-08D (1-1) from the Windfall Formation at Ninemile Canyon, Nevada.

Discussion. Strongly scrobiculate Lotagnostus sclerites are rare in collections of the L. rushtoni Fauna , and all but two cephala were too small or fragmentary for meaningful comparison with L. nolani and similar species. However, those cephala differ from those of L. nolani in having a more posteriorly positioned glabellar node situated at the rear of M2, centered in line with or just in front of the anterior tips of basal lobes. The largest and best preserved cephalon also displays a significantly lower ratio ( Figure 10.3 ) between preglabellar field length (PFL) and anteroglabella length (AAL). In L. nolani the PFL/AAL ratio averages 0.81, with the lowest recorded value being 0.63. That of the best L. aff. L. nolani cephalon is 0.62.

Figures

PLATE 8. Cephala of Lotagnostus nolani n. sp. and Lotagnostus aff. L. nolani. Each white scale bar represents 2mm. 1-17. Lotagnostus nolani n. sp. 1-4. Holotype, CM 41360, from 5/22/08B, dorsal; anterior, left lateral, and anterior oblique views. 5. CM 41361, from 5/22/08B, dorsal view. 6. CM 41362, from 5/22/08B, dorsal view. 7-9. USMN 775724, from D3362-CO, anterior, right lateral, and dorsal views. 10. CM 41301, from 5/22/08B, dorsal view. 11. CM 41302, from 5/22/08B, dorsal view. 12-14. CM 41363, from 5/22/08B, dorsal, anterior, and right lateral views. 15. CM 41364, from 5/22/08B, dorsal view. 16. CM 41365, from 5/22/08B, dorsal view. 17. USMN 775725, from D3362-CO, dorsal view. 18-19. Lotagnostus aff. L. nolani. USMN 775726, from D3381-CO, dorsal and anterior oblique views.

FIGURE 10. Morphometric comparisons of some Lotagnostus species. (1) Dimensions measured on cephala. Abbreviations: AAL, Axial Anteroglabella Length; APL, Axial Posteroglabella Length; EBL, Exsaggital, Basal lobe Length; PFL, Preglabellar Field Length. (2) Scatter plot of EBL/APL ratio versus length of the cephalon for 3 species of Lotagnostus. L. “trisectus” refers to species identified by that name from Sweden in previous studies. (3) Scatter plot of PFL/AAL ratio versus length of the cephalon for 4 species of Lotagnostus. (4) Graphic comparison of posteroaxis length/length of axis as a function of pygidial length (excluding articulating half ring) for 3 species of Lotagnostus.