Laneites Přibyl and Vaněk

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 : 6-7

Laneites Přibyl and Vaněk in Přibyl et al., 1985

Type species. Cheirurus polydorus Billings, 1865a , from the Table Cove Formation (Darriwilian) of western Newfoundland, Canada .

Other species. Monotypic.

Diagnosis. Glabellar furrows S2 and S3 with marked posteromedian deflection; palpebral lobes and eye ridge elongate; genal spine with large base and apparently directed laterally; librigenae with short (exsag.) but wide (tr.) fields; hypostome with relatively weak middle furrow; major pygidial spines elongate, divergent, and produced dorsally; no independently inflated pygidial terminal piece present.

Discussion. When Přibyl and Vaněk in Přibyl et al. (1985, p. 161) proposed Laneites , they assigned the type and, with question, the Baltic Darriwilian species Cheirurus (Cheirurus) ingricus Schmidt, 1881 . The latter was followed by Hansen and Nielsen (2003), though Klikushin et al. (2009, p. 336) referred this species to Paraceraurus Männil, 1958 . The genus name has been referred to, and hence implicitly treated as valid, by Zhou et al. (1998) and Edgecombe et al. (1999), and was listed as valid by Jell and Adrain (2003, pp. 395, 468).

The earliest formally named Laurentian cheirurine species is the Dapingian Sycophantia seminosa Fortey, 1980 , from the Profilbekken Member of the Valhallfonna Formation, Ny Friesland, Svalbard, arctic Norway (Laurentian-affinity East Svalbard Terrane). The only other species referred to Sycophantia is S. aff. seminosa of Ingham in Ingham et al. (1986, p. 498, fig. 20a–n), known from silicified material from the Dounans Limestone Formation (Dapingian), near Aberfoyle, Stirling, Scotland (Highlands Border Complex, interpreted as a peri-Laurentian island arc). Comparing the type species, the anterior border of S. seminosa is short sagittally, but is much longer exsagittally, forming a large triangular area beside the anterior glabellar lobe and in front of the fixigena, terminated against a long (exsag.), open anterior border furrow. That of L. polydorus is only a little larger exsagittally, and it curves tightly around the border furrow, which is a very narrow lineation. The eyes are much more posteriorly placed in L. polydorus , set largely opposite L2 versus largely opposite L 3 in S. seminosa . Furrows S2 and S3 have a pronounced posterior deflection in L. polydorus , but are oblique and more or less linear in S. seminosa . Finally, the pygidium of S. seminosa ( Fortey, 1980, pl. 16, figs 8, 10) seems to have a raised terminal piece behind the third axial ring whereas there is no sign of such a feature in L. polydorus . Hence, while the genera have been considered among the earliest and most basal cheirurines (e.g., by Edgecombe et al. [1999, p. 1167]), they have substantially different morphology. Note that the hypostome attributed to S. seminosa ( Fortey, 1980, pl. 16, figs 3, 6), with its obscure middle furrow, strong pitting of the middle body, and wide lateral and posterior borders which come to a posterior point, does not seem to be cheirurine, but likely represents a pliomerid. It compares very closely, for example, with the hypostome of a Dapingian species of the pliomerine Pseudomera Holliday, 1942 , illustrated by Adrain and Karim (2019, fig. 3.10).

The earliest known Laurentian cheirurine is Ceraurinella sp. of Adrain and Fortey (1997), from the Tourmakeady Formation of County Mayo, Ireland (Laurentian-affinity Northwestern Terrane). The age of the fauna was given by Adrain and Fortey (1997) as Whiterockian (i.e., Dapingian), but there are various faunal elements (e.g., the bathyurid Benthamaspis Poulsen, 1946 ; the telephinid Opipeuterella Fortey, 2005 ; the “hystricurid” Heckethornia McAdams and Adrain, 2009 ; the cheirurid Parasphaerexochus Čugaeva, 1973) that are otherwise known only from the Floian, and none that are otherwise exclusively post-Floian except for the cheirurine. Hence it seems likely the true age is Floian. Adrain and Fortey (1997, p. 99) compared the Tourmakeady species with both S. seminosa and L. polydorus . Material is sparse, but it is more like L. polydorus in the anterior cranidial border that is of similar short length sagittally and exsagittally. On the other hand, it does have an independently inflated and fairly well defined pygidial terminal piece, whereas the equivalent region in L. polydorus is flat with no triangular terminal piece defined. The Irish species also has a well defined pleural furrow on the first pygidial segment that runs for some disance posterolaterally ( Adrain and Fortey, 1997, pl. 11, fig. 5) whereas this furrow is visible only as a faint adaxial notch in most specimens of L. polydorus (the only exception is the largest specimen of Pl. 4, fig. 8, where a faint furrow is present). Librigenae are also quite different, as the Tourmakeady species has broader lateral borders and a field that is relatively longer (exsag.) but markedly narrower than in L. polydorus .

Apart from the species discussed above, the only other pre-Darriwilian cheirurine known from Laurentia is Lehua aff. L. argus of Ross (1972, p. 37, pl. 16, fig. 17), from the Dapingian of the Antelope Valley Formation, Nye County, Nevada. The species is known from a single partial cranidium, and as far as can be discerned, Ross’s comparison of it with the lower Darriwilian Newfoundland species Lehua argus Whittington, 1963 , is reasonable.

In addition to L. polydorus , there are four named Laurentian Darriwilian species, all from the Laurentian-affinity Midland Valley Terrane, South Ayrshire, Scotland, and assigned to the genera Ceraurinella Cooper, 1953 ( Ceraurinella dispersa ( Tripp, 1962) , Confinis Formation; Ceraurinella magnilobata Tripp, 1967 , Stinchar Limestone Formation), Gabriceraurus Přibyl and Vaněk in Přibyl et al., 1985 ( G. proicens ( Tripp, 1967) , Sinchar Limestone Formation), and Xylabion Lane, 1971 ( X. kirklandiensis Tripp, 1979 , Confinis Formation). Laneites polydorus is only closely similar to the species of Ceraurinella , but comparison is hampered by the distorted internal mold preservation of the Scottish material and the tiny available photographs. Both of the Scottish species seem to differ from L. polydorus in ways similar to the Tourmakeady Ceraurinella sp. discussed above. Ceraurinella dispersa , for example, has a pygidium with the first pleural furrow deep and well impressed, and Ceraurinella magnilobata has librigenae (unknown for Ceraurinella dispersa ) that are longer but narrower than those of L. polydorus .

The main question to consider in assessing the value of recognizing Laneites is whether it is sufficiently distinct from early species of Ceraurinella that it should be recognized as a monotypic (presumptive) sister genus, or simply as another early Ceraurinella species. Přibyl and Vaněk in Přibyl et al. (1985, p. 162) considered that Laneites “differs markedly from Ceraurinella ... ” and listed differences in the course of the glabellar furrows, the size, shape, and direction of the genal spine, the size of the palpebral lobes and eye ridges, the greater width of the pygidium, the wide divergence of the anterior pygidial spine pair, and the presence of a small median projection of the pygidial margin between the third spine pair. Most of these seem to be genuine. We noted above, in comparison with S. seminosa , the distinctive posterior deflection of S2 and S 3 in L. polydorus . None of the silicified specimens preserve the genal spine and in fact the only known specimen which does ( Whittington, 1965, pl. 60, figs 1, 4, 6) has just a partial spine broken near its base and preserved only on the right side of the specimen. Both it and the holotype (Whittington, 1963, pl. 25, fig. 10) do suggest a robust spine with a markedly laterally directed course. The major pygidial spines are certainly much longer and more dorsolaterally splayed than is evident in any early species of Ceraurinella . The presence of a posteromedian projection on the pygidium does seem evident on the single specimen illustrated by Whittington (1965, pl. 60, fig. 8), but is plainly absent from most of the silicified pygidia, where the margin is gently anteriorly arcuate or transverse in this region. For the time being, at least, we recognize Laneites . Better material of early (Floian to Darriwilian) species of Ceraurinella which would permit meaningful phylogenetic analysis would help to resolve the question.