Lotagnostus americanus ( Billings, 1860 )

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 : 35-36

Lotagnostus americanus ( Billings, 1860)

( Plate 6, figs 1–3)

1860 Agnostus americanus ; Billings, p. 303, fig. 1a only [fig. 1b = L. aff. L. clarki ].

1865 Agnostus americanus Billings, 1860 ; Billings, p. 395, fig. 372a only [fig. 372b = L. aff. L. clarki ].

1944 Agnostus americanus Billings, 1860 ; Rasetti, p. 233, pl. 36, fig. 2 only [fig. 1 = L. aff. L. clarki ].

1989 Lotagnostus americanus ( Billings, 1860) ; Ludvigsen & Westrop in Ludvigsen et al., p. 12, pl. 1, fig. 15, only [fig. 16 = L. aff. L. clarki , fig. 17 = L. sp. indet.].

non 1995 Lotagnostus americanus ( Billings, 1860) ; Westrop, p. 15, pl. 1, figs 17–20 [= L. sp. indet.]

2005 Lotagnostus americanus ( Billings, 1860) ; Peng & Babcock, p. 110–113, figs 2.2, 2.4 only [2.3 = L. aff. L. clarki ].

non 2008 Lotagnostus americanus ( Billings, 1860) ; Lazarenko et al., pl. 23, figs 1, 2, 5, 5a.

non 2009 Lotagnostus americanus americanus ( Billings, 1860) ; Rushton, p. 276, fig. 1J–O.

2011 Lotagnostus americanus ( Billings, 1860) ; Westrop et al., p. 578–584, fig. 5A–C only [figs. 5D-G, 6 = L. cf. L. clarki ]. non 2012 Lotagnostus americanus ( Billings, 1860) ; Ahlberg & Terfelt, fig. 4a–f.

2015 Lotagnostus americanus ( Billings, 1860) ; Peng, Babcock, Zhu, Ahlberg, Terfelt, & Dai, fig. 5H–J only [fig. 5G = L. aff. L. clarki ].

Discussion. Rushton (2009) discussed the selection of Billings’ (1860) pygidium as the holotype. Only eleven specimens identified as L. americanus from the Lévis Formation have been illustrated: the holotype and two other pygidia, six cephala, and one enrolled skeleton. All but three of the eleven specimens came from one boulder, designated Boulder 37 by Rasetti (1944). Unfortunately, those three specimens are the holotype ( Plate 6.1-6.3) and two topotype cephala. They came from elsewhere in the Lévis Formation and, in describing the species, Billings (1860) noted that he could not say for certain that the cephala represented the same species as the holotype. What is even more problematic with respect to the type material for L. americanus is that none of the pygidia illustrated from Boulder 37 displays the pitted surface texture on the distal areas of the pleural fields, the short scrobiculae on the proximal areas, or the very steep slope of the pitted distal areas that characterize the holotype. One pygidium ( Rushton, 2009; fig. 1M) is nearly the same size as the holotype, making it implausible to attribute those differences to ontogenetic variation. In fact, the steep slope of the pitted distal areas of the pleural field gives the holotype an appearance unlike that of any other pygidium assigned to L. americanus , with the proximal, scrobiculate part of the pleural field appearing wider (tr.) than the pitted distal portion at the level of F 2 in dorsal view. This can be clearly seen in Peng & Babcock (2005, fig. 2) where the holotype is one of sixteen pygidia included in the collage. On all other pygidia attributed to L. americanus in that figure, the pitted distal part of the pleural field appears as wide or wider than the scrobiculate inner part at F2. The uniqueness of the holotype, combined with the uncertainty of association with the topotype cephala or any other sclerites from the Lévis Formation, renders it unsuitable as a standard in our opinion and we here restrict Lotagnostus americanus to the holotype.

The affinities of the remaining Lotagnostus americanus specimens from the Lévis are uncertain.They most closely resemble Lotagnostus clarki n. sp. from the Windfall Formation.While the pygidia are indistinguishable from those of L.clarki , there are noteworthy differences in the shapes and relative proportions of the glabellar lobes in the two species. Therefore,the Lévis specimens are left in open nomenclature here as Lotagnostus aff. L.clarki ,which is discussed below.

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