Laneites polydorus ( Billings, 1865a )

Adrain, Jonathan M. & Pérez-Peris, Francesc, 2021, Middle Ordovician (Darriwilian) cheirurid trilobites from the Table Cove Formation, western Newfoundland, Canada, Zootaxa 5041 (1), pp. 1-73 : 8-11

Laneites polydorus ( Billings, 1865a)

Plates 1–4

1865a Cheirurus polydorus Billings , p. 286, fig. 274.

1865b Cheirurus polydorus Billings ; Billings, p. 374.

1890 Ceraurus polydorus Billings ; Vogdes, p. 103.

1893 Ceraurus polydorus Billings ; Vogdes, p. 290.

1910 Ceraurus polydorus Billings ; Raymond, 1910, p. 240.

1915 Cheirurus polydorus Billings ; Barton, p. 134.

1930 Ceraurinus polydorus Billings ; Bradley, p. 178.

1963 “ Cheirurus ” polydorus Billings ; Whittington, p. 85, pl. 25, fig. 10.

1963 “ Cheirurus ” polydorus Billings ; Whittington and Kindle, fig. 3.

1965 Ceraurinella polydorus (Billings) ; Whittington, p. 408, pl. 60, figs. 1-11.

1967 Ceraurus polydorus (Billings) ; Ross, p. D23.

1971 Ceraurinella polydorus (Billings) ; Lane, p. 18, text-fig. 10.

1973 Ceraurinella polydorus (Billings) ; Čugaeva, p. 76.

1977 Ceraurinella polydorus (Billings) ; Ludvigsen, p. 960.

1980 Ceraurinella polydorus (Billings) ; Fortey, p. 78.

1981 Ceraurinella polydorus (Billings) ; Bruton and Harper, p. 171.

1985 Laneites polydorus (Billings) ; Přibyl and Vaněk in Přibyl et al., p. 161, pl. 5, figs 1, 2, text-figs. 8, 9.

1997 Ceraurinella polydorus (Billings) ; Adrain and Fortey, p. 99.

2003 Laneites polydorus (Billings) ; Jell and Adrain, p. 395.

2019 Sycophantia polydora (Billings) ; Adrain and Karim, fig. 4.10.

Material. The lectotype, selected by Whittington (1965, p. 408), is an incomplete cranidium, GSC 685 (Whittington, 1963, pl. 25, fig. 10). Whittington (1965, pl. 60, figs. 1–11) illustrated three more cranidia and a pygidium. Silicified material illustrated herein, GSC 135161–135169, 135171–135189, 135353 is all from horizon TCM 18.

Diagnosis. As the genus is monotypic, see genus diagnosis.

Description. Cranidial measurements are based on the specimens of Plate 1 , figures 1, 2, 15, 21. Cranidium subtrapezoidal in outline, broad (tr.) posteriorly with maximum width across genal angles (excluding genal spines), narrowing forward, slightly vaulted dorsally in medial part, fixigenal field flat in anterior view; anterior border short (sag.), shorter medially, subtly lengthened laterally, describing broad anteriorly directed arch with the medial part completely transverse and lateral part curving strongly posteriorly, forming rounded anterolateral corners (e.g., Pl. 1, figs 2, 3), distal tip set slightly anteriorly to the intersection of S3 and the axial furrow, sculpture of dense, tiny granules equally distributed over all the surface; anterior border furrow deeply incised, short (sag.), describing an anteriorly directed arch similar to the anterior border; glabella with length (sag.) 116% (97.2–135.8%) maximum width (tr.), sub-rectangular in outline, sub-parallel lateral margins, maximum width across L3, narrower at the base of L1, subtly expanded forward, anterolateral corners gently rounded, posterolateral corners rounded but more pointed than the anterolateral corners, anterior margin transverse with distal part slightly bowed posteriorly, posterior border transverse in the median portion with distal part across L1 slightly bowed posteriorly, weakly dorsally inflated, in lateral view anteriorly to S2 slightly sloped downward from the horizontal (e.g., Pl. 1, fig. 9); glabella with densely distributed tiny tubercles on entire surface; S1–S3 well defined, narrow (tr.), extending about one quarter of the glabellar width; S1 longest, extending slightly further adaxially than S2/S3, running adaxially and curving posteriorly, deeply incised distally, continued posteriorly as a faint depression that connects with SO and separates L1 from the median glabellar lobe (e.g., Pl. 1, figs 1, 16); S2 and S3 parallel, narrower (tr.) than S1, with marked posterior deflection medially, less posteriorly directed than S1; SO similar in depth and length (sag., exsag.) to S1–S3, shallowing medially; LO subrectangular in outline, long sagittally, shorter exsagittally with anterolateral and posterolateral corners angular, anterior margin transverse medially, posterior margin gently bowed posteriorly with the medial part almost transverse; L1 subquadrate, similar in size to L2 and L3, posterior margin subtly bowed posteriorly; L2 and L3 equal sized, quadrate in outline, L3 with lateral margin with light lateral bow; frontal lobe semicircular in outline, longer (sag.) than the rest of glabellar lobes; axial furrow similar in depth and width to glabellar furrows; fixigenal field sub-triangular in outline, narrow (tr.) anteriorly, wider posteriorly, with dense sculpture of tiny pits and small granules; anterior fixigenal field triangular in outline, short (exsag.), narrow (tr.), broader posteriorly, tapering forward, with small area in front of the eye ridge (e.g., Pl. 1, fig. 2); posterior fixigena subrectangular in outline, with similar length (exsag.) but wider (tr.) than anterior fixigenal field; posterior border furrow short (exsag.), deeply incised, distally slightly curving anteriorly, at the genal angle strongly curved anteriorly; lateral border furrow deep, directed anteriorly and adaxially; posterior border short (exsag.) with posterior margin transverse and anterior margin slightly curved anteriorly, expanding distally with maximum length (exsag.) at the genal angle, extended at genal angle by a broad-based genal spine (see Whittington, 1965, pl. 60, fig. 4), directed posterolaterally; lateral border wider (tr.) next to genal angle, narrowing forward, directed anteriorly and adaxially; palpebral lobe relatively large, margin gently arched laterally (e.g., Pl. 1, fig. 1), posterior end set opposite to the posterior part of L2, anterior part is continuous with a broad eye ridge; eye ridge tapering forwards, running inward and forward from the palpebral lobe to the intersection with axial furrow slightly posterior to S3 (e.g., Pl. 1, fig. 2); palpebral furrow narrow, deeply incised, running from the posterior tip of the palpebral lobe forward along the eye ridge finishing in the intersection with the axial furrow.

Librigenal measurements were made on specimens of Plate 2 , figures 17, 19, 21, Plate 4 , figure 14. Librigena subtrapezoidal in outline; eye relatively large, bulbous, elongate, differentiated from the field by a narrow and shallow furrow (e.g., Pl. 3, fig. 31), elevated from the field; eye tilted forward, with the anterior end of the furrow set more abaxially than the posterior end; field subquadrate in outline, width 69.6% (65–72.7%) of exsagittal length along lateral border furrow, slightly expanding from the inner margin to the outer margin next to the border furrow, in lateral view laterally convex, dense sculpture of tiny granules and less densely arranged small pits equally distributed across the surface of the field, more scarce in the area close to the border furrow; small slightly inflated area sub-triangular in shape anterior to the eye (e.g., Pl. 2, figs 19, 21, Pl. 3, fig. 31, Pl. 4, fig. 14), with smoother sculpture differentiated from the rest of the field; border furrow deep, narrow; border elongated, exsagittal length of the librigenal field along the lateral border furrow 37.1 % (35.8–38.1%) length of the border, slightly bowed outwards; border elongate, broad (similar in width to the field), broader in medial portion, tapering anteriorly and posteriorly, slightly vaulted dorsally, internal and external margin arched outwards, dense sculpture of tiny granules equally distributed across entire external surface; posterior projection of the border elongate, triangular in outline, narrowing posteriorly, longer than anterior projection; anterior projection short, triangular in outline, narrowing anteriorly; anterior facial suture short, concave, describing a slightly curved outward arch, subtle change in slope opposite to border furrow with the suture across the field slightly steeper than across the border (e.g., Pl. 2, fig. 17); posterior facial suture long, posteriorly convex through the border, changing in slope opposite to border furrow to almost transverse inwards; doublure smooth, beneath the border half the width of border, beneath anterior projection triangular in outline tapering anteriorly, beneath posterior projection prominent, visible in dorsal view (e.g., Pl. 2, fig. 17).

Rostral plate unknown.

Hypostomal measurements were made on specimens of Plate 2 , figures 1 and 12. Hypostome subcircular in outline, with sagittal length 88.7% (87.6-88.7%) maximum width (tr.), maximum width across anterior wings, slightly vaulted medially; anterior border gently arched anteriorly, very short (sag.) in medial area, expanding slightly laterally, merging smoothly with anterior wings; anterior border furrow shallow, short (sag.), slightly lengthened (exsag.) distally, anteriorly bowed; anterior wings prominent, subtriangular in outline, slightly extended beyond lateral shoulder, ventral pits expressed dorsally as large strongly dorsally deflected wing process (e.g., Pl. 2, fig. 10); lateral notch well defined, prominent, broadly concave dorsoventrally (e.g., Pl. 2, figs 4, 7, 9, 10); posterior wings smaller than anterior wings, deflected dorsally and inwards; middle body long (sag.), ovoid in outline, with sagittal length 133.6% (131.8–135.3%) width, anterior lobe much larger than posterior lobe, slightly vaulted medially and anteriorly (e.g., Pl. 2, fig. 9); anterior lobe ovoid in outline, anterior margin highly arched anteriorly, posterior margin arched posteriorly, maximum width anteriorly, slightly tapering posteriorly; posterior lobe of middle body U-shaped, short (sag.) with maximum length medially, tapering laterally, less inflated than anterior lobe and almost flat; middle furrow separating anterior and posterior lobes of the middle body, very shallow, especially medially where it is almost effaced, arched posteriorly; maculae reduced, elongate, ovoid in shape; border furrow deeply incised, deeper anteriorly and slightly shallower posteriorly, narrow, slightly wider across the anterior part of the posterior lobe; lateral border highly expanded anteriorly across the shoulder, narrower posteriorly, arched outwards at shoulders (e.g., Pl. 2, fig. 1); posterior border short (sag.), gently arched posteriorly, smooth margin; small pair of spines at the posterolateral corner of the border (e.g., Pl. 2, figs 12, 14); densely sculptured with tiny granules equally distributed around entire ventral surface; doublure slightly directed inwards dorsally, smooth, expanded beneath lateral border, slightly tapering backwards, shorter beneath posterior border.

Total number of thoracic segments unknown; articulating half-ring broad (tr.), slightly shorter (sag) than the axial ring, vaulted dorsally as the axis, semicircular in outline, anterior and posterior border anteriorly arched; articulating furrow shallow across most of its course, slightly shorter (sag.) than the articulating half-ring and arched anteriorly but with distal apodemal pits deeply incised, narrow (tr.), running forward; axial ring subrectangular in outline, dorsally vaulted, long (sag.), lengthened laterally, slightly widerthan articulating half-ring (tr.), anterior margin almost transverse, turning forward in distal position, posterior margin almost transverse, slightly bowed posteriorly, distal tips pointed; axial furrow short, deep; articulating flange present along anterior and posterior margin of the pleurae, running transversely from the intersection with the axial furrow to the fulcrum, short (exsag.), slightly expanding distally and longest next to the fulcrum, flange curving dorsoventrally in the distal tip forming anteriorly the fulcral process and posteriorly the fulcral socket (e.g., Pl. 3, figs 13, 24, 26); flange separated from pleural ridge by a short (exsag.), relatively shallow articulating furrow; furrow visible in dorsal view laterally; pleurae constricted across the fulcrum dividing the pleura into a proximal part (adaxial to the fulcrum) and a distal part (abaxial to the fulcrum); proximal part rectangular in outline, flat in anterior view, same length proximally as the distal part of the axial ring, anterior and posterior margin almost transverse along proximal three quarters, running slightly posteriorly and anteriorly respectively, in the most distal quarter; both margins curve posteriorly and anteriorly forming a sagittal constriction in the pleura; in anterior view the constricted area of the pleura forms a small dorsally concave depression (e.g., Pl. 3, figs 3, 19); distal part extending in a pleural spine, running ventrolaterally, curved posteriorly, proximal part long (exsag.), narrowing distally, ending in a pointed tip, flat in cross section; proximal part of the pleura bears a pleural furrow (e.g., Pl. 3, figs 1, 8, 21), narrow, deeply incised, proximally connected with the axial furrow, running straight from the anterior part of the pleura posteriorly obliquely, shallowing at the pleural constriction (almost effaced), change direction running anteriorly, slightly directed outwards connecting with the anterior articulating furrow; raised rim visible ventrally marking the termination of segment with the pleural spine extended beyond; densely sculpted by tiny granules more densely arranged distally and in the anterior and posterior margin of the pleural spine (e.g., Pl. 3, figs, 17, 24, 25).

Pygidial measurements were made on the best preserved specimens of Plate 4 , figures 1, 3, 8, 16. Pygidium broad (tr.) with sagittal length (excluding articulating half-ring and pygidial spines) 38.5% (36–40.5%) maximum width; fulcrum set close to the axis, with pleura directed posteriorly; articulating flange straight along the anterior margin of the first pleural segment (e.g., Pl. 4, fig. 3), anterolaterally ending at fulcrum with a fulcral process visible in dorsal view; articulating half-ring long (sag.) with sagittal length 33.3% total sagittal length of the pygidium, tapering distally, highly vaulted dorsally, anterior margin anteriorly bowed, posterior margin transverse, sculpted with tiny granules; articulating furrow deeply incised, short (sag.), slightly broader medially; axis triangular in outline (e.g., Pl. 4, figs 1, 3, 8), vaulted anteriorly and less vaulted, almost flat, posteriorly, narrow with maximum width (across the first segment) 37.9% (36–39.1%) maximum width of the pygidium; axis consists of three axial rings and a terminal piece; first axial ring trapezoidal in shape, slightly longer (sag.) and broader (tr.) than the second axial ring, with anterior margin slightly broader than posterior margin, anterior margin straight, posterior margin slightly bowed anteriorly, almost transverse, posterolateral corner slightly rounded; second axial ring trapezoidal in shape, with anterior margin broader (tr.) than posterior margin, both margins slightly bowed anteriorly, posterolateral corner merged with second pygidial pleural band; third axial ring slightly shorter (sag.) and narrower (tr.) than second axial ring, anterior margin slightly bowed anteriorly, posterior margin curved anteriorly, abaxial extent not defined by axial furrow, smoothly merged with pleural field; terminal piece small, anterior margin anteriorly bowed, posteriorly almost effaced, not distinguishable from the pygidial pleural field; first inter-ring furrow as long (sag.) as articular furrow and slightly narrower (tr.), slightly longer in medial part, deeply incised becoming shallower in medial part, almost running transverse subtly bowed anteriorly; second inter-ring furrow similar to the first interring furrow, slightly narrower; third inter-ring furrow narrower than the rest, equal length (sag.), shallower in medial part, arched anteriorly; axial furrows only present anteriorly (e.g., Pl. 4, fig. 8), running from the intersection with the articulating furrow to the intersection with the first interpleural furrow, slightly narrower and shallower than articulating furrow, curved laterally; two interpleural furrows, both similar in width to inter-ring furrows, running in posterolateral direction, deeply incised proximally, shallowing distally, almost effaced next to the pleural margin; first pleural segment longer (sag.) than the rest, extended by a long, thick, conical, pleural spine, spine directed dorsally, laterally and posteriorly (e.g., Pl. 4, fig. 1, 6, 10), slightly curving abaxially, circular in cross section, thick proximally, tapering distally; pleural furrow in the first pleural segment located in the adaxial part (e.g., Pl. 4, fig. 8), running laterally and posteriorly from the axial furrow ending slightly beyond the pygidial margin; second and third pleural segments smaller than first, without pleural furrow, extended in short pleural spines, triangular in outline, second pleural spine slightly longer than third; pygidial border expressed ventrally as a narrow rim (e.g., Pl. 4, fig. 4, 5, 19), describing a posteriorly directed arch, only the anterolateral tips visible dorsally where the rim merges with the anterior flange; dense sculpture of small tubercles equally distributed across entire surface; doublure short, slightly longer sagittally, smooth, dorsally directed (e.g., Pl. 4, fig. 7, 12).

Discussion. Whittington (1965) revised the species and provided excellent photographs of some incomplete crackout specimens from Table Cove. Our silicified material is important in that it provides the first information on the morphology of the librigena, hypostome, and thoracic segments, additional cranidia and pygidia, as well as ventral/internal morphology. The species was compared with relevant taxa in the genus discussion above.

Figures

PLATE 1

PLATE 2

PLATE 3

PLATE 4