Kawina stougei, 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 : 26-28

Kawina stougei n. sp.

Plate 6 , figs 10?, 14?, 15?, Plates 9 , 10

2019 Kawina n. sp. 2; Adrain and Karim, fig. 4.12.

Material. Holotype, pygidium, GSC 135250 (Pl. 10, figs 10, 13, 15, 17), and assigned specimens GSC 135233– 135236 , 135241 , 135243 , 135245–135247 , 135251–135254 , 135355 , and questionably assigned specimen GSC 135215 , all from horizon TCM 2, GSC 135244 from TCM 14, GSC 135239 , 135240 , 135242 , 135248 , 135249 , from TCM 18, and GSC 135237 from TCM 20.

Etymology. After Svend Stouge.

Diagnosis. Librigenal field narrow, with fine caecal pitting and subdued, scattered tubercles; eye large; librigenal lateral border furrow narrow; pygidium with axis relatively large, subtriangular; pygidial spines very short, with subdued dorsal tubercles.

Description. Cranidium trapezoidal in outline, broad posteriorly with maximum width across genal angles, narrowing anteriorly, highly vaulted, fixigena downturned abaxially (e.g., Pl. 9, fig. 9), in lateral view sloping downwards from the horizontal; anterior border broad (tr.), arched anteriorly, short (sag.) with medial part almost overhung by the frontal part of the glabella, slightly expanding abaxially, distally curving strongly backwards, forming rounded corners, lacking sculpture; anterior border furrow anteriorly bowed, medially overhung by glabella, deeply incised, short (sag., exsag.), longer abaxially; glabella subovoid in outline, with maximum with across L1, lateral margins subparallel, tapering slightly forwards, anterior margin rounded (e.g., Pl. 9, figs 7, 8), posterolateral corners gently rounded, anterolateral corners rounded; posterior margin opposite medial glabellar area transverse, slightly bowed posteriorly opposite L1, highly vaulted dorsally, sloping downwards anteriorly from the horizontal, with sculpture of medium-size, flat tubercles (e.g., Pl. 9, figs 1, 3), some of them almost effaced, scarcely distributed across entire surface; S1–S3 well defined, short (exsag.), extended about one third of the glabellar width; S1 slightly longer (exsag.) and deeper than S2/S3, extended adaxially slightly beyond S2/S3, distal tip turned slightly anteriorly, middle part transverse to slightly posteriorly directed, proximal tip curved posteriorly; S2 and S3 subparallel, curved gently posteriorly, S2 extended inwards slightly beyond S3, shorter (exsag.) and shallower than S1; SO short (sag., exsag.), deeply incised, similar in length and depth to S1, medially opposite medial glabellar area transverse, abaxially behind L1 describing a subtle posteriorly directed arch (e.g., Pl. 9, fig. 1); LO subrectangular in outline, relatively long (sag., exsag.), slightly longer sagittally, corners squared off with anterior and posterior corners slightly rounded, anterior margin slightly narrower (tr.) than posterior margin, anterior margin transverse medially and bowed posteriorly abaxially behind L1, posterior margin transverse, lacking sculpture; L1–L-3 subrectangular in outline, slightly wider than long; L1 slightly wider and longer than L2/L3; frontal lobe semicircular in outline, anterior margin broadly bowed anteriorly, similar in length to L3; axial furrow narrow, width posteriorly similar to that of LO, slightly tapering anteriorly, shallow; fixigenal field broad (tr.) posteriorly and very narrow (tr.) anteriorly across the interocular field, lacking sculpture; anterior fixigena subtriangular in outline, elongate (exsag.), broad (tr.) posteriorly, narrowing anteriorly, anteriorly sloping downwards from the horizontal; posterior fixigenal field subrectangular in outline, wider than long, in anterior view strongly downturned abaxially; posterior border furrow short (exsag.), shorter near LO, slightly longer distally, deeply incised, shallowing slightly distally, course transverse proximal to genal angle, distal to genal angle gently curved anterolaterally; lateral border furrow similar in width to length of distal part of posterior border, shallower, directed anterolaterally; posterior border shorter (exsag.) near LO, longer distally, maximum length (exsag.) at genal angle, genal angle with posterior margin posteriorly pointed and gently curved (e.g., Pl. 9, fig. 5), anterior margin transverse, posterior margin running slightly posteriorly, lacking sculpture; lateral border short (exsag.) and narrow (tr.), triangular in outline, directed anteriorly and slightly laterally, wider (tr.) near the genal angle, tapering forward, lacking sculpture; palpebral lobe very narrow (tr.), elongate (exsag.), posterior end set opposite anterior region of L1, anterior end set opposite L3, just anterior to S2 (e.g., Pl. 9, figs 5, 12), curved posteromedially with posterior part nearly transverse; palpebral furrow running along entire palpebral lobe, narrow, deeply incised, slightly shallower anteriorly; doublure beneath LO short (sag.) with approximately half of the sagittal length of LO; beneath the posterior border short (sag.) doublure proximally, longer distally, forming an expanded area beneath the genal angle.

Librigenal measurements were made (where possible) on specimens of Plate 9 , figures 19, 20, Plate 10 , figures 1, 7. Librigena subtriangular in outline; eye large, bulbous, subspherical in shape, set anteriorly, dorsally elevated; narrow, deep furrow around the base of the eye separating it from the librigenal field (e.g., Pl. 9, fig. 20), furrow interrupted by small sutural ridge along anterior branch of facial suture; librigenal field subtrapezoidal in shape, maximum width of field 33.9% (30.8–36.9%) length along the lateral border furrow, maximum width opposite the posterior half of the eye lobe, tapering anteriorly and posteriorly; posteriorly region of field forming elongate narrow area, triangular in outline, sloped downward distally from the horizontal; field with dense sculpture of tiny granules and sparse medium-sized, somewhat effaced, tubercles, along with large but shallow caecal pits; lateral border furrow relatively wide, slightly narrower anterior and posteriorly, deeply incised, with gentle lateral arch; lateral border relatively narrow, width of the border 47.1% (44.0–50.0%) width of the field, anteriorly slightly more inflated (e.g., Pl. 9, fig. 22), less inflated posteriorly, outer margin laterally convex; border forming rounded ridge alongside border furrow, lateral region flat and facing ventrolaterally; anterior projection short, triangular in outline, ventrally directed; posterior projection long, curving inwards, more inflated posteriorly, dense sculpture of tiny granules; anterior branch of facial suture short, slightly anteriorly convex; posterior branch of facial suture long, slightly posteriorly convex, changing slope slightly a quarter of the way adaxially of the width of the librigenal field; doublure beneath lateral border of similar width to border, narrower anteriorly and slightly widening posteriorly (e.g., Pl. 10, fig. 5), posteriorly curving inwards, tapering in the most anterior part; lacking sculpture.

Rostral plate unknown.

Hypostome subquadrate in outline (anteriormost region is not fully preserved in any of the specimens; slightly wider than long, maximum width across anterior wings only slightly wider than across the shoulders (e.g., Pl. 9, figs 18, 25); distal part of anterior border (e.g., Pl. 9, figs 18, 25) sloping backwards to merge smoothly with lateral anterior wing; anterior wing downturned in anterior view, flexed dorsally, wing process pit not present (e.g., Pl. 9, figs 14, 27); lateral notch and posterior wing not defined; middle body ovoid in outline, longer than wide, with anterior lobe much longer (sag.) than posterior, slightly vaulted ventrally medially, with dense sculpture of small tubercles; anterior lobe ovoid in outline, maximum width across anterolateral corners, slightly tapering posteriorly, slightly vaulted ventrally, anterior margin strongly arched anteriorly, anterolateral corners rounded, posterolateral corners less rounded and more angular, posterior margin posteriorly bowed; posterior lobe reduced in size, U-shaped, short (sag., exsag.), slightly shorter distally, with approximately same width (tr.) as anterior lobe, anterior and posterior margin broadly arched posteriorly, corners rounded, subtly vaulted ventrally and nearly flat; anterior and posterior lobe separated by a middle furrow, very shallow and almost effaced medially; maculae elongate, oval in outline, posteromedially directed (e.g., Pl. 9, fig. 25); lateral border furrow narrow, deeply incised anteriorly, slightly shallower posteriorly, posteriorly confluent with the middle furrow; posterior border furrow long (sag.), very shallow, arched posteriorly with medial area almost transverse; lateral border expanded (tr.) especially across the shoulder, outer margin slightly bowed laterally; posterior corners of the margin rounded; posterior border shorter (sag.) than lateral border, transverse, medial part slightly shorter (sag.), vaulted ventrally, posterior margin divided in two by a small medial bump (e.g., Pl. 9, figs 17, 28); dense sculpture of tiny granules on all surfaces; doublure broad beneath the lateral border, tapering posteriorly, reduced beneath the medial part of the posterior border, dorsomedially directed.

Thorax unknown.

Pygidial measurements are based on the specimen of Plate 10 , figure 10. Pygidium subsemicircular in outline, wider than long, with sagittal length (excluding articulating half-ring) 68.0% maximum width, highly vaulted mainly due to downsloping pygidial pleural segments (e.g, Pl. 10, figs 13, 15, 16); fulcrum set close to the axis, with pleurae turned strongly downturned beyond the fulcrum; articulating flange short (exsag.), along the anterior margin of the first pleural segment (e.g., Pl. 10, figs 10, 11, 19), separated from the pleural segment by a shallow furrow, furrow shorter (exsag.) proximally, slightly longer distally; articulating half-ring short (sag., exsag.), with sagittal length 8.8% sagittal length of pygidium, longer sagittally, shorter exsagittally, anterior margin transverse, posterior margin subtly bowed posteriorly in medial part, with dense sculpture of small granules; articulating furrow short (sag., exsag.), deeply incised, slightly bowed posteriorly; axis triangular in outline, composed of three axial rings and a prominent terminal piece (e.g, Pl. 10, fig 10); maximum width across first axial segment, narrower posteriorly, with sagittal length 58.8% total pygidial length and width across first axial ring 44.0% maximum pygidial width, moderately dorsally vaulted, with dense sculpture of tiny granules and medium sized, effaced, tubercles; first axial ring subrectangular in outline, slightly longer (sag.) than articulating half-ring, same width as articulating half-ring, anterior and posterior margins bowed posteromedially, corners squared off; second and third axial rings similar in shape to first, similar in length (sag.), slightly narrower (tr.), each with maximum width in anterior part of the segment and slightly narrowing posteriorly, more strongly arched posteriorly than first axial ring; terminal piece prominent, triangular in outline, with sagittal length 23.5% pygidial length, anterior margin bowed posteriorly, wider anteriorly and narrowing posteriorly, ending posteriorly in a pointed tip, sloping downwards posteriorly from the horizontal; first inter-ring furrow as long (sag.) and wide (tr.) as articulating furrow, deeply incised, slightly shallowing medially, bowed posteriorly in medial part; second inter-ring furrow similar in shape to first inter-ring furrow, slightly narrower (tr.) and shallower; third inter-ring furrow slightly shorter (sag.), narrower (tr.) and shallower than the rest, describing a broad arch directed posteriorly; axial furrow with similar width and depth as first inter-ring furrow, shallower posteriorly; pleural field strongly sloping down from the horizontal, composed of three segments extended by paddle like pleural spines, spines in contact along most of length; first pleural segment running posterolaterally, anterior margin gently bowed anterolaterally, slightly expanding distally, rounded distal tip; second pleural segment running posteriorly, subtriangular in outline, widening distally, rounded distal tip; third pleural segment posteriorly directed, lateral margins parallel directed backwards, narrow (tr.) anteriorly, expanding posteriorly, beyond terminal piece same width, rounded distal tip; pygidial border expressed ventrally as a narrow rim, medial part strongly arched posteriorly (e.g, Pl. 10, figs 18, 24), distal part anterolaterally directed; pleural regions with dorsal sculpture of dense equally distributed small tubercles mixed with more sparsely distributed medium sized flat tubercles, variably effaced; doublure very short (exsag.) distally, long (sag.) medially opposite border arch, dorsally directed (e.g, Pl. 10, fig. 26).

Discussion. The very short pygidial spines differentiate Kawina stougei from all other species. The shortest spines seen in any other species are those of pygidia of K. spinigena Ancygin, 1977 , but they are still considerably longer than those of K. stougei . In addition, the terminal piece of K. spinigena ( Ancygin, 1977, pl. 3, figs 14–17) is much smaller than that of K. stougei .

Kawina stougei differs from the type species, K. vulcana , in its more transverse S1, more subdued glabellar sculpture, much narrower librigenal field, and relatively larger eye. Of described species, K. stougei most closely resembles K. arnoldi . Particularly similar are the narrow librigenal lateral borders, narrow librigenal field, and relatively large eye. Kawina arnoldi has a more anteriorly bowed S1 that turns strongly posteriorly in the adaxial part. The species share a large pygidial terminal piece, but the pygidial spines of K. arnoldi are much longer, and appear to lack dorsal sculpture.

No species of Kawina as yet has a well documented early ontogeny. At horizon TCM 2, heliomerines and Cydonocephalus tiffanyae are the most common cheirurids, and most small cheirurid growth stages that have been recovered obviously represent these taxa. Kawina stougei is quite rare at the horizon. A single cranidium (Pl. 6, figs 10, 14, 15) from TCM 2 is clearly neither C. tiffanyae (cranidia of similar size that do represent C. tiffanyae are illustrated on Pl. 6, figs 18, 19) nor a heliomerine. It is possible that it belongs to K. stougei and it is tentatively assigned. If this is correct, then there is substantial ontogenetic change in the cranidium of the species. This is far from impossible, as early cranidia of C. tiffanyae (e.g., Pl. 6, fig. 23) similarly have broad fixigenae and a relatively uninflated glabella. Alternatively, there is one pygidium from the horizon, assigned below to “ Kawina ? sp.” that the small cranidium could be associated with, or it might simply represent a rare species by itself. Only when a reasonably complete cranidial ontogeny of a species of Kawina becomes known can these possibilities be evaluated.

Figures

PLATE 6

PLATE 9

PLATE 10