Lotagnostus nolani, Taylor & Loch & Repetski, 2024

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 : 39-40

Lotagnostus nolani n. sp.

( Plate 1.1–1.5, 1.11–1.16 , Plate 8.1–8.17 , Plate 9 , Plate 16.1–16.7 )

1976 Lotagnostus trisectus ( Salter, 1864a) ; Taylor & Cook, text-fig. 29F.

Diagnosis. Strongly scrobiculate Lotagnostus with M2 lateral lobes depressed and subdivided, long basal lobes (EBL/APL ratio greater than 0.45; Figure 10.2 ), and elongate, slightly asymmetrical glabellar node anteriorly positioned on the front half of M2; median preglabellar furrow in larger specimens weakly impressed, shallowing anteriorly, and does not intersect the border furrow; posteroaxis conspicuously trisected with notular axis bounded by faintly to moderately impressed notular furrows that connect deep notulae; pleural field divided into a subcircular, nearly horizontal proximal area with widely spaced, radially oriented short scrobiculae that is surrounded by more downsloping distal areas with densely spaced, irregular pits.

Etymology. Named after Thomas B. Nolan in recognition of his accomplishments as former Director of the United States Geological Survey (see Leopold & Baker, 1996).

Material and occurrence. Holotype CM 41360 is a cephalon from collection 5/22/08B: assigned specimens include 10 cephala CM 41301–41305 , 41361–41365 and 11 pygidia CM 41306–41309 , 41366–41372 from collection 5/22/08B; and 2 cephala USNM 775724–775725 and 2 pygidia USNM 775727–775728 from collection D3362-CO. Lotagnostus nolani fauna : collections 5/22/08B (267-255) and D3362-CO (17-15). from the Windfall Formation at Ninemile Canyon, Nevada; Hedinaspis-Charchaqia Fauna : collections D7130-CO (13-13), D7132- CO (0-2) and D7133-CO (6-2) from the Hales Limestone at the Hot Creek section, Nevada.

Description. Cephalon semiovate in outline; sagittal length approximately equal to maximum width (93- 105%); moderately convex (sag., tr.). Genae slightly convex (sag., tr.), moderately inclined in anterior view. Axial furrows moderately impressed; nearly straight, moderately convergent from posterior margin to F2, bowed outward slightly along M3, gently convergent along anterior lobe. Glabella long (sag.) 73% of cephalic length (69–79%), approximately one-third of cephalic width at M3 (29-35%); stands in low relief above adjacent genae in larger specimens, more strongly convex (tr.) and stands higher in relief in smaller specimen. Basal lobes subtriangular; long (exsag,), approximately one third (27–37%) of glabellar length; anterior ends lie at or behind posterior end of glabellar node, posterior ends extend slightly beyond glabellar culmination; basal furrow angled to appear concave adaxially. Narrow (sag.) occipital band visible closely behind glabellar termination in dorsal view. F1 a slight expansion of axial furrow or very short, anterolaterally directed notch extending inward from axial furrow just posterior to anterior end of basal lobes. M1 hexagonal on specimens with slot-like F1; glabellar culmination bluntly pointed with small terminal node. M2 trisected; lateral lobes depressed, subdivided into multiple, small, subelliptical lobes separated by faint furrows; elongate, slightly asymmetrical axial node centered on front half of lobe. F2 a short (tr.) and wide (exsag.) notch in side of glabella extending adaxially half way to midline. M3 trisected on larger specimens by faintly impressed, anteriorly convergent, longitudinal furrows extending from F2 to F3; longer (exsag.), lateral lobes subelliptical and slightly inflated. F3 transglabellar, moderately impressed, straight to gently concave anteriorly in smaller specimens, tripartite in larger specimens with transverse central segment and lateral segments in front of lateral lobes of M2 directed anterolaterally abaxially to intersection with axial furrow. Anteroglabella accounts for slightly less than a third (29–34%) of glabellar length (sag.); broad, length equals only 83% (75–93%) of maximum width (tr.); subpentagonal with anterolateral corners rounded; bluntly pointed anteriorly. Median preglabellar furrow faintly impressed, shallowing anteriorly, failing to reach border furrow in some larger specimens; straight in small specimens, more irregular, blending with scrobiculae in larger sclerites. Anterior cephalic margin typically as even curve although several specimens slightly indented medially. Convex border of very gently tapered from midline to posterolateral angle; border furrow well impressed, equal in width to border. Scrobiculae distributed uniformly across genae, well impressed distally in all specimen sizes shallowing adaxially to appear less strongly impressed adjacent to axial furrows, particularly in small specimens.

Pygidium semiovate in outline, nearly equant, width at M2 slightly greater (97–107%) than length; moderately convex (sag., tr.); axis stands in low relief above pleural field in posterior view; pleural field separated into a subhorizontal circular area adjacent to axial furrow from F1 to slightly behind posteroaxis marked by widely spaced, short, radially arranged scrobiculae, surrounded by more steeply inclined area with closely spaced, deep, irregular pits; boundary between scrobiculate and pitted areas sharp. Slope of pitted area very steep posterior to F2, more moderately inclined along anteroaxis.Articulating half-ring short, crescentic.Articulating furrow broad (sag.), well-impressed, narrowed distally; curved backward slightly medially. Axis long, 84% (77–92%) of pygidial length exclusive of articulating half-ring; slightly convex (sag., tr.) with exception of axial node, slightly constricted at M2. Axial furrows slightly sinuous, moderately impressed along anteroaxis, slightly shallower around posteroaxis. Anterior axial lobe strongly trisected; M1 lateral lobes slightly inflated, M2 lateral lobes very slightly inflated, slightly shorter than M1; medial lobe confluent from M1 to M2, narrower than lateral lobes, bearing axial node posteriorly. F1 well impressed, slightly curved, directed slightly anteromedially; discontinuous, interrupted medially by confluent central lobes of M1 and M2. Transaxial F2 moderately impressed, nearly straight, transverse; moderately impressed subsidiary furrows extend from F2 to connect with F1 to circumscribe M1-M2 medial lobe. Posteroaxis long (sag.), 57% (52–62%) of axial length, slightly convex, slightly declined (sag.), broadest (tr.) slightly anterior to lobe midlength, maximum width variable, average 105% (94–113%) of posteroaxis length; trisected by faintly impressed notular furrows, very faint along anteriormost 20% of lobe; furrows diverge slightly from F2 to approximately a third of the length of lobe, intranotular axis achieving its maximum width at this point, converge slightly posteriorly; intranotular axis slightly convex, stands in low relief above extranotular areas; well impressed notulae present, best expressed along posteriormost 80% of lobe; terminal node commonly absent. Border short (sag.), convex. Short posterolateral spines level with or behind the terminus of posterior lobe. Border furrow uniformly well impressed, broad, slightly narrower at anterolateral corners; wider and shallower in largest specimens.

Discussion. Strongly scrobiculate species with virtually identical pygidia to that of Lotagnostus nolani have been reported, by various species names (e.g. L. punctatus and L. trisectus , among others), from Asia, Australia, South America, and Sweden. L. nolani is set apart from all these species by its higher (>0.45) EBL/APL ratio ( Figure 10.2 ), and more anterior placement of the asymmetrical glabellar node, which is centered on the anterior half of M2 such that the base of its steeper anterior slope lies in line with the posterior ends of the anterolateral lobes of M3. Similarly high EBL/APL ratios have been confirmed only in Lotagnostus trisectus , which is now restricted to Avalonian Britain, and L. aff. L. nolani from the Lotagnostus rushtoni Fauna in the Windfall (discussed below). Although L. trisectus cephala yield comparably high EBL/APL ratios, none of the topotype pygidia of L. trisectus illustrated by Rushton (2009) displays prominent scrobiculae and pits on the pleural fields like those of L. nolani . It is possible that what Rusconi (1951b) described as Goniagnostus verrucosus from Argentina, and Shergold et al. (1995) subsequently re-assigned to L. trisectus has a similarly high EBL/APL ratio, but matrix concealing the posterior margin of the single cephalon on which this species is based makes accurate measurement of the ratio impossible. Moreover, the well-preserved glabellar node is centered at the midlength of M2, rather than on the front half as on L. nolani . Comparison of pygidial morphology between the two species is not possible at present because the pygidium of L. verrucosus is unknown. Until additional material can be described and illustrated, we feel it is best to treat Lotagnostus verrucosus and L. nolani as separate species. Despite some flattening and resultant fractures, the specimens from the Hales Limestone assigned here to Lotagnostus nolani retain the defining features of this species, fortifying correlation of the L. nolani and Hedinaspis-Charchaqia Faunas. The three figured cephala ( Pl. 16 , figs 1-5) all display the forwardly placed glabellar node, depressed and subdivided lateral lobes of M2, and long basal lobes that yield an EBL/ABL ratio over.45.

The flattened condition of the holotype of Lotagnostus punctatus ( Lu, 1964, pl 5, fig. 5; Peng et al. 2015, fig. 9B) precludes recovery of some critical features, such as shape and position of the glabellar node. However, uncompacted cephala recovered from limestone in the same formation ( Peng et al., 2015, figs 9D, 9H) confirm a more posterior placement of the node and lower EBL/APL ratios than in L. nolani . The sclerites from Sweden identified as L. trisectus by Westergård (1922), and used to illustrate that species by Shergold & Laurie (1997), actually compare more closely with L. punctatus in position of the glabellar node and EBL/APL ratio ( Fig. 10.2 ).

Two of the four species of Lotagnostus reported by Westrop & Landing (2016) from Avalonian strata in Nova Scotia also strongly resemble L. nolani but are readily distinguished by their lower EBL/APL ratios, less elongate and more posteriorly positioned glabellar node, and several other features. The cephalon of Lotagnostus salteri differs in having the glabellar node situated opposite the anterior tips of the basal lobes, more weakly impressed and usually discontinuous longitudinal furrows on M3, and fewer and shallower scrobiculae on the genal fields than L. nolani . Although the pygidia of the two species are very similar, most L. salteri pygidia display a proportionally shorter posteroaxis and slightly broader (tr.) intranotular axis. Lotagnostus ponepunctus ( Matthew, 1901) differs from L. nolani in having fewer and more weakly impressed scrobiculae on the genal fields and a deeper and more continuous median preglabellar furrow that intersects the anterior border furrow. Its pygidium has much shallower scrobiculae and pits on the pleural fields, and a constricted acrolobe in larger specimens.

Figures

PLATE 1. Ontogenetic comparison of Lotagnostus nolani and L. clarki n. sp. All images at same scale and all from collection 5/22/08B. 1-5, 15. L. nolani cephala. 1. CM 41301. 2. CM 41302. 3. CM 41303. 4, 15. CM 41304. 5. CM 41305. 6-10, 21. L. clarki cephala. 6. CM 41310. 7. CM 41311. 8. CM 41312. 9, 21. CM 41313. 10. CM 41314. 11-14, 16. L. nolani pygidia. 11. CM 41306. 12. CM 41307. 13. CM 41308. 14,16. CM 41309. 17-20, 22. L. clarki pygidia. 17. CM 41315, 18. CM 41316. 19. CM 41317. 20. CM 41318. 22. CM 41319.

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.

PLATE 9. Pygidia of Lotagnostus nolani n. sp. Each white scale bar represents 2mm. 1-4. USMN 775727, from D3362-CO, dorsal, posterior, right lateral, and posterior oblique views. 5. CM 41366, from 5/22/08B, dorsal view. 6. CM 41367, from 5/22/08B, dorsal view. 7. USMN 775728, from D3362-CO, dorsal view. 8-10. CM 41368, from 5/22/08B, dorsal, posterior, and left lateral views. 11. CM 41369, from 5/22/08B, dorsal view. 12. CM 41370, from 5/22/08B, dorsal view. 13. CM 41371, from 5/22/08B, dorsal view. 14-16. CM41372, from 5/22/08B, dorsal, posterior, and left lateral 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.

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.