Cydonocephalus tiffanyae, Adrain & Pérez-Peris, 2021

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 : 23-25

Cydonocephalus tiffanyae n. sp.

Plate 6 , figs 11–13, 16–23, Plate 7 , Plate 8 , figs 1-17, 19, 20

2019 Cydonocephalus n. sp. 2; Adrain and Karim, fig. 4.6.

Material. Holotype, cranidium, GSC 135225 (Pl. 7, figs 9–11, 15), and assigned specimens GSC 135217–1352224 , 135226–135231 , 135352 , all from horizon TCM 2.

Etymology. For Tiffany Adrain.

Diagnosis. S1 long and transverse in dorsal view, barely turned posteriorly at most adaxial point; L1 large; S2 and S3 not visible in most specimens; cranidial sculpture of dense but subdued tubercles of multiple sizes; librigena with lateral border developed into adaxial raised ridge and an abaxial furrow, bounded by a a second small ridge along the lateral margin; librigenal lateral border furrow broad and shallow, with tubercles only on the adaxial half of the librigenal field; hypostome elongate, with long middle body and long bilobate posterior border; pygidium with densely tuberculate sculpture, distal parts of spines separate from one another and coming to sharp distal point.

Description. Cranidial measurements were made on the largest and best preserved specimens of Plate 7 , figures 2, 10, and Plate 8 , figures 1, 2. Cranidium highly vaulted dorsally, bulbous, maximum width across the genal angles (excluding genal spines), slightly tapering anteriorly, extremely downturned fixigenal field (e.g., Pl. 7, fig. 16), anteriorly sloping downwards from horizontal; anterior border short (sag., exsag.), describing a broad, anteriorly directed, arch, in dorsal view completely overhung by the glabellar frontal lobe, dense sculpture of medium-sized granules over entire surface; anterior border furrow short (sag, exsag.), deeply incised, describing an anteriorly directed arch similar to that of the anterior border, completely overhung dorsally by the glabella; glabella subcircular in outline with sagittal length 100.75% (93.8–104.3%) maximum width (tr.), maximum width across anterior part of L1, highly inflated dorsally with the most inflated part anteriorly S1 (e.g., Pl. 7, fig. 5, 15), anterior margin highly arched anteriorly, anterolateral corners completely rounded, posterolateral corners more pointed, subtly rounded; posterior border slightly bowed anteromedially, sloped downward from horizontal in lateral view, with sculpture of a mixture of tiny and slightly larger tubercles evenly scattered across the surface; S1 short (exsag.), deeply incised, running posteromedially, describing wide “S” shape, short distal part running anteriorly, long medial part almost transverse, slightly sloped, terminal proximal part very short, strongly curved posteriorly (e.g., Pl. 7, fig. 2); S2 and S3 expressed as weak, obliquely set lineations (most obvious on Pl. 7, fig. 7, but also visible on Pl. 7, figs 5, 6), not visible on all specimens; SO similar in depth and length (sag., exsag.) to S1, anteriorly bowed medially, most distal part slightly running forward; LO subrectangular in outline, slightly wider than the base of L1, broad (sag., exsag.), slightly broader medially, anterior margin slightly bowed anteromedially, posterior margin almost transverse, distally slightly curved anteriorly, distal anterior and posterior corners slightly rounded, sculpture similar to glabella with a mix of smaller and larger granules; L1 broad and long, rectangular in outline, wider than long; L2 and L3, in specimens in which S2 and S3 are expressed, comprise undifferentiated area of glabella between faint furrows, with no independent inflation; fixigenal field with dense sculpture of tiny granules and less dense larger granules; interocular fixigena long and extremely narrow; posterior fixigena short and wide, rectangular in outline, sloping sharply downwards at a near-vertical angle (e.g., Pl. 7, fig. 16); posterior border furrow running transversely, proximally short (exsag.) and as deeply incised as SO, gradually lengthening (exsag.) and shallowing distally; lateral bor- der furrow very short, as shallow and wide as the distal part of the posterior border furrow; posterior border shortest (exsag.) proximally opposite LO, lengthening abaxially, reaching maximum length at genal angle before changing course from transverse to anterolaterally directed, sculpture of densely scattered tiny granules and less dense larger tubercles; genal spine set at genal angle, relatively short and narrow (e.g., Pl. 7, fig. 17), directed posterolaterally, ending in a pointed tip; lateral border extremely short, widest at genal angle but narrower than length of posterior border; palpebral lobe very narrow, elongate (exsag.), in lateral view describing a dorsally directed arch, posterior end set opposite proximal end of S1, anterior end set slightly anterior to proximal end of S1, no eye ridge present (e.g., Pl. 7, fig. 11); palpebral furrow narrow, deeply incised, running entire length of lobe; doublure beneath LO long (sag.) slightly shorter than LO.

Librigenal measurements are based on specimen of Plate 6 , figure 22. Librigena subtriangular in outline; eye relatively large, bulbous, set anteriorly; visual surface set directly atop field, no furrow or socle present; librigenal field narrow, elongate, with dense sculpture of medium tubercles; lateral border furrow very broad (e.g., Pl. 6, fig. 22), shallow, slightly tapering anteriorly and posteriorly, bowed laterally; lateral border with width 30.9% (28.6– 33.3%) total librigenal width (excluding eye), describing a laterally directed arch, with maximum curvature in posterior part, posteriormost part directed adaxially, tapering anteriorly; lateral border consists of a narrow, swollen, adaxial ridge bounded laterally by a shallow concave furrow and a second, less inflated ridge along lateral margin; anterior projection triangular in shape, short (exsag.), directed anterolaterally, covered with fine granules; posterior branch of facial suture long, arcuate; anterior branch facial suture nearly straight; both posterior and anterior sutures with small sutural ridge developed on field; doublure beneath lateral border of same width as border, narrower posteriorly and slightly widening anteriorly, anteriorly curving inwards, tapering in the most anterior part, smooth.

Rostral plate unknown.

Hypostomal measurements were made on the specimens of Plate 6 , figures 11 and 16. Hypostome elongate, with maximum width across anterior wings, slightly vaulted anteriorly in medial region; sagittal length 90.3% (88.2–92.3%) maximum width across the anterior wings; anterior border highly bowed anteriorly, short sagittally, slightly longer (exsag.) exsagittally, merging smoothly with anterior wings; anterior border furrow verg short (sag.), deeply incised, slightly shallower in medial region; anterior wings prominent, directed anterolaterally, extended beyond the lateral shoulder, elongate pits expressed dorsally; lateral notch well defined, relatively short (exsag.), dorsally concave (e.g., Pl. 6, fig. 13); posterior wings reduced, deflected dorsomedially; middle body subcircular in outline with similar sagittal length and maximum width, anterior lobe larger than posterior border, anterior portion ventrally vaulted (e.g., Pl. 6, fig. 13); anterior lobe suboval in outline, anterior margin broadly arched anteriorly, maximum width across anterolateral corners, anterolateral corners rounded, tapering (tr.) posteriorly; posterior lobe of middle body U-shaped, slightly narrower (tr.) than anterior lobe, short (sag.) with maximum length in medial region, tapering distally, almost flat dorsally, separated from the anterior lobe by a middle furrow; middle furrow very shallow, almost effaced medially, arched posteriorly; maculae elongate, ovate in outline; border furrow deep anteriorly across the anterior lobe of the middle body, posteriorly shallow and wide, shallower and wider in medial region; lateral border relatively narrow (tr.), wider posteriorly, lateral shoulder subtle and not prominent; posterior border bilobate in outline (e.g., Pl. 6, figs 11, 16, 17), highly expanded (exsag.) with medial part shorter, distally broad with margin broadly arched posteriorly, in lateral view slightly directed ventrally (e.g., Pl. 6, fig. 13), in posterior view posterior margin of distal lobes dorsally concave (e.g., Pl. 6, figs 12, 21); anterior border, middle body and lateral border with dense sculpture of mediumsized granules, posterior border less densely sculptured; doublure beneath the lateral and posterior border with same width, slightly directed dorsally, smooth.

Thorax unknown.

Pygidial measurements were taken on specimen of Plate 8 , figure 11. Pygidium broad (tr.) with sagittal length (excluding articulating half-ring) 67.6% maximum pygidial width, slightly inflated dorsally in the anterioromedial part; fulcrum set next to axial region; articulating half-ring with sagittal length 12.5% maximum pygidial length (sag.), longer medially and tapering laterally, vaulted dorsally, anterior margin lightly anteriorly arched, posterior margin almost transverse, slightly bowed posteriorly; articulating furrow short (sag.), deeply incised, slightly shallower medially; axis with sagittal length 70.0% maximum width and width 48.6% maximum width of pygidium, composed of three axial rings and a reduced terminal piece (e.g., Pl. 8, fig. 11, 15), sub-triangular in outline, broader across the first axial ring and tapering posteriorly, dorsally vaulted with the highest inflation anteriorly and flattened posteriorly; first and second axial rings subrectangular in outline, similar in shape, first axial ring slightly wider and longer than the second; first axial ring shorter medially, lightly tapering laterally, anterior and posterior margins subtly bowed posteriorly and anteriorly respectively, corners squared off; third axial ring slightly narrower and shorter, subtrapezoidal in outline, anterior margin wider than posterior, anterior corner pointed and posterior corner more rounded; terminal piece very small, almost effaced, flat; first inter-ring furrow with same length and width as articulating furrow, deep, slightly shallower medially; second inter-ring furrow similar to the first inter-ring furrow, slightly narrower; third inter-ring furrow not developed, third ring confluent with terminal piece; axial furrow narrow, deeply incised anteriorly and shallowing posteriorly; three pleural segments extended by pleural spines, separated by a pair of relatively wide and shallow interpleural furrows; pleural spines directed backwards, first pair slightly longer than others, curving posteriorly, broader proximally, tapering distally in the last portion, ending in a pointed tip, dorsoventrally flat with the distal tip slightly curving upwards in lateral view; pygidial border expressed ventrally as a narrow rim (e.g., Pl. 8, fig. 20), describing a posteriorly directed arch, not visible dorsally; doublure relatively long (sag.), strongly flexed upwards (e.g., Pl. 8, fig. 9), smooth; dense sculpture of tiny tubercles equally distributed over surface and more sparsely distributed larger tubercles.

Ontogeny. Anterior border develops greater arch anteriorly; the glabella expands transversally and dorsoventrally (the sagittal length remains similar), especially anterior to S1 where the inflation is greater (e.g., Pl. 6, figs 18, 19); L1 becomes longer (sag.) and larger; S1 lengthens and becomes more transverse; LO lengthens (sag.) and widens (tr.) (e.g., Pl. 6, fig. 18), the medial part of the anterior margin becomes more anteriorly curved; the palpebral lobe moves closer to the glabella and backwards, reducing the width of the anterior part of the fixigenal field and the length (exsag.) of the posterior fixigenal field; the fixigenal field is strongly deflected ventrally; the genal spines decrease in length (e.g., Pl. 6, fig. 18) and become almost absent in large holaspids; the tuberculate sculpture increases in density and size of the tubercles, and in large holaspids the tubercles become flatter.

Discussion. Cydonocephalus tiffanyae is strikingly similar to the species from the Dapingian of the Antelope Valley Formation, California, illustrated by Ross (1972, pl. 7, figs 17–19) as “ Cydonocephalus scrobiculus Whittington. ” One of us (JMA) has collected abundant well preserved silicified specimens of this species and it will be described in a separate work. The California taxon is clearly distinct from C. scrobiculus and represents a new species, though Ross’s comparison was accurate. Detailed comparison of the California species with C. tiffanyae will be deferred until description of the former, but the species share an extended hypostome, longer than it is wide with a long, bilobate posterior border. This contrasts markedly with the hypostome of C. griphus (Whittington, 1963, pl. 27, fig. 19), which is wider than it is long and has a narrow posterior border with no sign of bilobate structure. The hypostome of C. torulus (Whittington, 1963, pl. 29, fig. 6), however, has a more elongate middle body, and while the posterior border remains short, it does appear to be slightly bilobate.

Among presently named species, C. tiffanyae is most similar to C. scrobiculus . The species share a nearly transverse S1 with little posterior deflection adaxially and a librigena with a very broad lateral border furrow and tubercles on the field restricted to a region below the eye. The librigena lateral border furrow of C. scrobiculus (Whittington, 1963, pl. 29, fig. 14) also appears to show the adaxial ridge and median furrow seen in C. tiffanyae (Pl. 6, fig. 22). Of the unassigned acanthoparyphine pygidia in the Shallow Bay formation (Whittington, 1963, pl. 31, figs 1–17, 19–20), those of C. tiffanyae are most like a tuberculate specimen with thoracic segments attached (Whittington, 1963, pl. 31, figs 13, 14, 17), and this may represent the thorax and pygidium of C. scrobiculus . The species differ in that C. scrobiculus has plainly visible, though weakly impressed, S2 and S3, and has a a more subdued cephalic tuberculate sculpture (though this could partly be due to calcareous preservation and mechanical preparation). Further comparison is deferred until a forthcoming revision of C. scrobiculus , when larger photographs will be available.

Figures

PLATE 6

PLATE 7

PLATE 8