Validity and composition of the Silurian trilobite genera ...€¦ · Island, Cape Phillips...

Validity and composition of the Silurian trilobitegenera Borealarges and Dicranogmus, with newspecies from the Canadian Arctic

Jonathan M. Adrain

Abstract: New silicified material from Arctic Canada demonstrates that the lichid trilobite genera Borealarges andDicranogmus, recently claimed to be synonyms, are independent groups with no close phylogenetic connection to oneanother. Dicranogmus has been known mainly from cranidia alone; prior association of librigenae and pygidia with theArctic Canadian species D. skinneri has been queried. This association is correct beyond reasonable doubt, based ondescription of new material of both D. skinneri and a new species. Three new species of Borealarges are related toB. tuckerae Adrain 1994. Cladistic analysis supports the monophyly of this species group. Pending further new information,however, the group is retained within the genus Borealarges. The stratigraphic range of the species group is extendedfrom the lower Wenlock (Sheinwoodian) to upper Ludlow (Ludfordian) by the discovery of a rare species in the DouroFormation of Cornwallis Island, Arctic Canada. New taxa from the Wenlock of the Cape Phillips Formation, ArcticCanada, include Dicranogmus wynni, Borealarges nicoae, B. warholi, and B. yulei.

Résumé : Du matériel silicifié nouvellement récolté de l’Arctique canadien démontre que les genres lichides Borealaspiset Dicranogmus sont des groupes indépendants sans lien phylogénétique proche, à l’encontre de l’assertion récentequ’ils étaient synonymes. Dicranogmus n’était connu auparavant que de cranidiums isolés; l’association de librigènes etpygidiums référés à l’espèce de l’Arctique canadien D. skinneri a été mise en doute. Cette association est exacte au-delàde tout doute raisonnable, en se basant sur la description de nouveau matériel de D. skinneri et d’une autre espèce.Trois nouvelles espèces de Borealaspis sont apparentées à B. tuckerae Adrain, 1994. L’analyse cladistique supporte lamonophylie de ce groupe d’espèces. Par contre, dans l’attente de nouvelles informations, ce groupe est maintenu dansle genre Borealaspis. La durée stratigraphique de ce groupe d’espèces est prolongée du Wenlock inférieur (Sheinwoodien)au Ludlow supérieur (Ludfordien) suite à la découverte d’une espèce rare dans la Formation de Douro de l’Île Cornwallisde l’Arctique canadien. Des taxons nouveaux du Wenlock de la Formation de Cape Phillips, Arctique canadien, comprennentDicranogmus wynni, Borealarges nicoae, B. warholi et B. yulei.

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Introduction

Trilobites of the family Lichidae Hawle and Corda, 1847,are among the most common and diverse constituents of richsilicified trilobite faunas recovered from the lower Wenlockto lower Ludlow of the Cape Phillips Formation of the CanadianArctic Archipelago (Fig. 1). Their description was begun byPerry and Chatterton (1977), who named three new lichidspecies. Adrain (1994) proposed the new trochurine genusBorealarges, while Adrain and Ramsköld (1996) have describedthe oldest known members of Radiolichas Reed 1923. Adrainand Ramsköld (1996) gave the stratigraphic ranges of allCape Phillips Formation lichid species for which at leastsome sclerites had been illustrated.

Recently, Van�k (1999) has claimed that Borealarges is asubjective junior synonym of Dicranogmus Hawle and Corda,1847, an opinion noted, if not endorsed, by Whittington(2002). Dicranogmus itself is a controversial taxon, known

mainly from species based only on cranidia. The best-knownspecies to date has been D. skinneri Perry and Chatterton1977. The association of sclerites figured as D. skinneri,however, was strongly contested by Thomas and Holloway(1988, p. 231), who considered the pygidia to belong “… eitherto a lichine or tetralichine…”. The purpose of the presentpaper is threefold: (1) to describe three well-preserved newspecies of Borealarges and to provide an explicit hypothesisof ingroup relationship for the genus based on cladisticparsimony analysis; (2) to remove any doubt about themorphology of Dicranogmus through revision of D. skinneriand description of a new species, confirming that Perry andChatterton’s association of sclerites is correct; and (3) todemonstrate that Borealarges and Dicranogmus are distinctgenera with no close phylogenetic relationship, and to reassertthe validity of the former genus.

Comprehensive locality information given by Adrain andEdgecombe (1997) is followed herein. Adrain (1994) cited

Can. J. Earth Sci. 40: 749–763 (2003) doi: 10.1139/E03-008 © 2003 NRC Canada

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Received 24 September 2002. Accepted 20 December 2002. Published on the NRC Research Press Web site at http://cjes.nrc.ca on27 May 2003.

Paper handled by Associate Editor B. Chatterton.

J.M. Adrain. Department of Geoscience, University of Iowa, Iowa City, Iowa 52242, U.S.A. (e-mail: [email protected]).

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the graptolite zonation of Lenz and Melchin (1990). Adrainand Edgecombe (1997) established a preliminary trilobitezonation calibrated against that for the graptolites. This schemewas supplemented by Adrain (1997) and Adrain and Ramsköld(1997). Trilobite occurrences are cited following this sequenceof faunas.

Dicranogmus and Borealarges

Van�k (1999, p. 33) recently challenged the validity of

Borealarges, explaining [sic] “ADRAIN [1994] not statedifferent marks from the genus Dicranogmus…” and claim-ing that the former is a junior subjective synonym of the lat-ter. The case hinges on the identity of two Bohemianspecies: Dicranogmus pustulatus Hawle and Corda, 1847(the type species of Dicranogmus) and Lichas simplexBarrande, 1846. Historically, pustulatus has been considereda junior synonym of simplex (e.g., Barrande 1852; Lane1984; Morris 1988; see list in Thomas and Holloway 1988,p. 230). Thomas and Holloway (1988, figs. 290, 291, 295),however, refigured a cast of the holotype cranidium ofpustulatus and compared it to the holotype cranidium ofsimplex, as figured by Horný and Bastl (1970, pl. 18, fig. 3),pointing out that the morphology of simplex indicatessynapomorphies with species then attributed to RichterargesPhleger 1936. They hence reassigned simplex to Richterarges,and indicated that cranidia assigned to simplex by Van�k(1959) belong in fact to pustulatus. Adrain (1994) thenerected Borealarges, which encompassed a species group pre-viously assigned to Richterarges and to which simplexshould also be assigned.

Voká� (1988), meanwhile, in a paper published in the sameyear as Thomas and Holloway’s work, figured material that heassigned to simplex, claiming that the nature of the pygidiumhe illustrated confirmed the ceratargine (i.e., trochurine) affinityof Dicranogmus. Voká�’s material included one cranidiumwhich, following Thomas and Holloway, is clearly pustulatus(cf. Voká� 1988, pl. 1, fig. 4, with Thomas and Holloway1988, pl. 13, fig. 291), and one cranidium that is clearly simplex(cf. Voká� 1988, pl. 1, fig. 2, with Horný and Bastl 1970, pl. 18,fig. 3), along with a Borealarges pygidium, which is almostcertainly that of simplex.

Adrain and Ramsköld (1996) clarified the systematic positionof Dicranogmus, showing that it bears considerable, likelysynapomorphic, similarities to Radiolichas, and that the statusof the genera as Trochurinae (of which Borealarges is clearlya member) is, in the present state of knowledge, ambiguous.

Van�k (1999) reproduced Voká�’s photographic plate, withthe addition of a single illustration of another cranidiumcollected by Voká� and belonging to simplex (Van�k 1999,pl. 1, fig. 1). Van�k recognized the cranidium of pustulatusfor what it was (terming it “Morphological type ‘Dicranogmuspustulatus’”), but claimed that it represented a late holaspidmorphology, and that the “simplex” specimens were juvenilesof the same species. As a result, he concluded that Borealargesis a junior synonym of Dicranogmus. Van�k did not citeAdrain and Ramsköld’s (1996) paper.

Even based on Van�k’s own illustrations, the case forontogeny is clearly not correct, as the pustulatus specimen isintermediate in size between the two figured simplex cranidia.Figure 2 illustrates genuine juvenile cranidia of bothDicranogmus and Borealarges, demonstrating that there islittle detailed similarity between early stages of members ofeither genus. At no stage in its known life history does thecranidium of any species of Dicranogmus resemble that ofany species of Borealarges. Instead, as shown by Fig. 2, juvenileDicranogmus cranidia closely resemble adult Dicranogmuscranidia (see Figs. 3, 4), and there is little chance of confusingthe genera.

In summary, in light of abundant new information from

Fig. 1. Map of localities around Cornwallis Island, central CanadianArctic, from which material is described herein. ABR, Abbott River,Cape Phillips Formation, late Wenlock and early Ludlow (sectionsABR 1 and ABR 3, and talus boulders ABR TTD, ABR TTC(3),ABR TTC(7), and ABR 3TT); BH, south shore of Baillie-HamiltonIsland, Cape Phillips Formation, early Wenlock through early Ludlow(sections BH 1, BHL 1, and BH 2, and locality BHH); GSC, GoodsirCreek, Douro Formation, late Ludlow (locality GSC 3); RES, townof Resolute Bay. Dashed line indicates line of facies changefrom platform carbonates to the southeast to basinal deposits tothe northwest.



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northern Canada (Adrain 1994, and herein), Thomas andHolloway’s (1988) opinion about the specific and genericdistinctness of pustulatus and simplex is almost certainlycorrect. Van�k’s (1999) claim of the synonymy of Borealargesand Dicranogmus is incorrect, as it is based on confusion ofco-occurring species belonging to either genus and theunsupportable opinion that the morphological differencesbetween pustulatus and simplex are ontogenetic.

Systematic paleontology

Terminology is as outlined by Adrain (1994). Illustratedspecimens are stored in the collections of the Department ofInvertebrate Palaeontology, Royal Ontario Museum, Toronto,with specimen number prefix ROM.

Family Lichidae Hawle and Corda, 1847Subfamily Trochurinae Phleger, 1936Genus Dicranogmus Hawle and Corda, 1847

TYPE SPECIES: Dicranogmus pustulatus Hawle and Corda, 1847.Kopanina Formation (Ludlow), Czech Republic.

OTHER SPECIES: Lichas aequalis Törnquist, 1884, Ashgill, Sweden;Dicranogmus gregalis Chugaeva, 1983, Ashgill, Russia;Dicranogmus guizhouensis Wu, 1977, Lower Silurian, Guizhou,China; Dicranogmus scabrosus Zhou and Zhou, 1982, Ashgill,Inner Mongolia; Dicranogmus skinneri Perry and Chatterton,1977, Wenlock, Arctic Canada; Dicranogmus wynni n. sp.,Wenlock–?Ludlow, Arctic Canada.

DIAGNOSIS: See Thomas and Holloway (1988, p. 230), supple-mented as follows:

Posterior and lateral librigenal border furrows shallow oreffaced; genal spine broad and short; entire librigena withdense tuberculate sculpture matching that on cranidium;librigenal lateral border with dorsal row of large tubercles;pygidium with anteriorly broad axis on which only the first

segment and ring furrow are defined; narrow and tapering,subtriangular pygidial terminal piece set off from axis byabrupt change in slope; first and second pygidial pleural andinterpleural furrows fully defined; third defined only as minuteproximal depressions; pygidium with three sets of subtriangularto pointed border spines.

REMARKS: As noted earlier in the text, Thomas and Holloway(1988) were not convinced that Perry and Chatterton’s (1977)association of sclerites in their new Dicranogmus skinneriwas correct. Adrain and Ramsköld (1996) gave reasons forconfidence in the association, and it is confirmed by revisionof D. skinneri and description of D. wynni. Briefly, cranidiaand pygidia of species of Dicranogmus occur at all sampledhorizons of the Cape Phillips Formation. They are an exactmatch in terms of sculpture and size, occur in the same(generally rare) relative abundances, and there is a completelack of any other lichid sclerite types at any horizon withwhich either the cranidia or the pygidia might be associated.Thomas and Holloway (1988) thought that the pygidia mightbelong to a lichine or tetralichine. Tetralichines, as they noted,became extinct during the Ordovician. Lichines, in the formof species of Dicranopeltis Hawle and Corda, 1847, do occurin the sections, but they are exceedingly rare and do not occurat all horizons. Their pygidia have been identified and areclearly distinct from those assigned beyond doubt toDicranogmus, differing most obviously in the ubiquitouspresence, versus absence, of a deep pleural furrow on thethird segment. As outlined by Adrain and Ramsköld (1996),Dicranogmus and Radiolichas share several potentialapomorphies, and the nature of their relationship to theremainder of Trochurinae requires further investigation.

Dicranogmus skinneri Perry and Chatterton, 1977(Figs. 3.1–3.36, 3.40–3.42)

FIGURED SPECIMENS: ROM 52401–52406 from BH 1 110 mand BHL 1 0 m, Cape Phillips Formation, Wenlock(mid-Sheinwoodian, Struszia dimitrovi Fauna); ROM52407–52428 from locality BHH, section BH 1 204 m, sectionBHL 1 92 m, Baillie-Hamilton Island, and talus boulderABR TTD, Cornwallis Island, all Wenlock (lateSheinwoodian, Struszia petebesti Fauna).

REMARKS: Dicranogmus skinneri was described fully by Perryand Chatterton (1977). With confirmation of their sclerite as-sociations, this description remains valid and is not repeatedherein. Dicranogmus skinneri is compared with the onlyother well known species, D. wynni n. sp.(see followingdescription).

The stratigraphic range of D. skinneri spans the successiveStruszia dimitrovi and S. petebesti Faunas of Adrain andEdgecombe (1997). Very few trilobite species pass from onefauna to the other, and most genera are represented by differentspecies in either fauna. A pygidium from BHH-A (Fig. 3.30)has its pygidial pleural tips extended into short, nearly tubular,spines, in contrast to the broadly triangular shape of those ofS. dimitrovi Fauna specimens (cf. Figs. 3.7, 3.17). However,a specimen from ABR-TTD (Fig. 3.31) also shows the triangularcondition. At present, this is the only observable morphologicalvariation within the sample. It is conceivable that a much

Fig. 2. Comparison of juvenile cranidia of Dicranogmus versusBorealarges, all from ABR 1 22 m, all ×12. The genera haveradically different juvenile morphologies and are easily distinguished.(Figs. 2.1, 2.4) Dicranogmus wynni n. sp., small cranidium,ROM 54054. (Figs. 2.2, 2.3, 2.5) Borealarges calei Adrain, 1994.(2.2, 2.3) small cranidium, UA 9238. (2.5) small cranidium, UA 9237.



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larger sample might reveal the presence of more than onespecies among the available material, but it seems likely thatat least most of the younger S. petebesti Fauna material isconspecific with the older S. dimitrovi Fauna taxon.

Dicranogmus wynni n. sp.(Figs. 3.37–3.39?, 3.43–3.49?; Fig. 4)

DERIVATION OF NAME: After Steve Wynn.

TYPE AND FIGURED SPECIMENS: Holotype, cranidium, ROM 52456(Figs. 4.33, 4.37, 4.39), and paratypes ROM 52438–52443,52445, 52447–52455, 52457, 52458, 52461, 54054. Assignedspecimens ROM 52437, 52444, 52446, 52459. Questionablyassigned specimens ROM 52429–52436 (lower Gorstian,Kettneraspis caldwelli Fauna).

TYPE LOCALITY AND TYPE STRATUM: Section ABR 1 22 m, CapePhillips Formation, Wenlock (upper Homerian, Strusziaharrisoni Fauna), near Abbott River, northwestern CornwallisIsland, central Canadian Arctic.

DIAGNOSIS: Longitudinal furrows subparallel, running directlyback behind bullar lobes, and nearly effaced in front of S0;hypostome broad relative to sagittal length and with coarsetuberculate sculpture, particularly on lateral border; anteriorpleural band of second pygidial segment pinched into isolatedknob proximally.

REMARKS: Dicranogmus wynni is subtly but pervasivelydifferentiated from D. skinneri. The species are so similarthat extended written description of D. wynni is consideredunnecessary. The species have nearly identical librigenae,but have clear cranidial, hypostomal, and pygidial differentiain all known specimens. In D. skinneri, the longitudinal furrowsrun strongly adaxially behind the bullar lobes (Figs. 3.11,3.12) to create a V-shaped rear to the median lobe, and thisportion of the furrow is still clearly impressed, though shorterthan the anterior portion. In contrast, the posterior part of the

longitudinal furrow runs more nearly posteriorly in D. wynni(Figs. 4.1, 4.12) and in most specimens is almost wholly effacedalong its posterior course. The median glabellar lobe expandsposterolaterally and is inflated posteriorly in D. skinneri buttotally lacks inflation in D. wynni. Hypostomes of D. skinnerihave a relatively narrow middle body and only relativelysubdued tuberculate sculpture on the lateral border. Those ofD. wynni have much broader middle bodies, are on the wholebroader relative to their length, and have much coarser anddenser tuberculate sculpture on the lateral border. Finally,pygidia of D. skinneri (Figs. 3.30, 3.31, 3.42, 3.50) have ananterior pleural band on the second segment which istransversely continuous. Those of D. wynni (Figs. 4.32,4.37, 4.40, 4.43), in contrast, have this pleural band distinctlyinterrupted by a longitudinal furrow which separates theproximal part of the band into an isolated knob adjacent tothe axial furrow.

Genus Borealarges Adrain, 1994

TYPE SPECIES: Borealarges reedi Adrain, 1994. Cape PhillipsFormation (Wenlock), Cornwallis Island, Arctic Canada.

OTHER SPECIES: In addition to those given by Adrain (1994)and new species described herein, Lichas simplex Barrande(discussed earlier in the text) and the poorly knownRichterarges convexus Tomczykowa, 1991, from the Prídolíof Poland, belong. Richterarges kielcensis Tomczykowa, 1993,from the upper Ludlow of Poland, is a member of Adrain’s(1994) Borealarges (s.l.) group.

REMARKS: When the Sheinwoodian species Borealarges tuckeraewas proposed (Adrain 1994), it was diagnosed and distin-guished from all congenerics then known by a series ofprominent autapomorphies. Since that work was completed,a further three new upper Sheinwoodian and lower Homerianspecies sharing these apomorphies have been discovered. Inaddition, a very rare upper Ludlow species from platform

Fig. 3. (Figs. 3.1–3.36, 3.40–3.42) Dicranogmus skinneri Perry and Chattertton, 1977, ×6, except where noted otherwise. (3.1, 3.8)cranidium, dorsal and left lateral views, ROM 52401, BHL 1 0 m, ×7.5. (3.2) hypostome and attached rostral plate, ventral view, ROM52402, BH 1 110 m. (3.3) hypostome, ventral view, ROM 52403, BH 1 110 m, ×7.5. (3.4, 3.10) right librigena, external andventrolateral views, ROM 52404, BH 1 110 m. (3.5) left librigena, external view, ROM 52405, BH 1 110 m. (3.6) left librigena, externalview, ROM 52406, BH 1 110 m, ×7.5. (3.7) partial pygidium, dorsal view, ROM 52407, BHH-A, ×7.5. (3.9, 3.11) cranidium, obliqueand dorsal views, ROM 52408, BHL 1 92 m, ×7.5. (3.12) cranidium, dorsal view, ROM 52409, BHH-C. (3.13) right librigena, externalview, ROM 52410, BHH-C, ×7.5. (3.14) right librigena, external view, ROM 52411, BHH-C. (3.15) right librigena, external view,ROM 52412, BH 1 204 m, ×7.5. (3.16, 3.21) left librigena, external and ventrolateral views, ROM 52413, BHL 1 92 m, ×7.5. (3.17)partial pygidium, dorsal view, ROM 52414, BHH-A, ×7.5. (3.18) hypostome, ventral view, ROM 52415, BHH-A. (3.19) hypostome,ventral view, ROM 52416, BHH-A, ×10. (3.20, 3.27) right librigena, external and ventrolateral views, ROM 52417, BHH-A. (3.22–3.24)hypostome, right lateral, ventral, and posterior views, ROM 52418, BHH-A, ×5. (3.25) hypostome, ventral view, ROM 52419, ABRTTD. (3.26) thoracic segment, dorsal view, ROM 52420, BHH-A, ×7.5. (3.28) partial pygidium, dorsal view, ROM 52421, BHH-A.(3.29, 3.30, 3.36) pygidium missing anterior pleural band of first segment, left lateral, dorsal, and posterior views, ROM 52422, BHH-A.(3.31) pygidium, dorsal view, ROM 52423, ABR TTD. (3.32, 3.34, 3.35) right librigena, ventrolateral, internal, and external views,ROM 52424, ABR TTD. (3.33) partial pygidium, dorsal view, ROM 52425, BHH-A. (3.40) right librigena, external view, ROM 52426,ABR TTD. (3.41) right librigena, external view, ROM 52427, ABR TTD. (3.42) partial pygidium, dorsal view, ROM 52428, ABR TTD, ×5.(Figs. 3.37–3.39, 3.43–3.49) Dicranogmus wynni n. sp.? (3.37, 3.38, 3.43) crushed left librigena, external, internal, and ventrolateralviews, ROM 52429, ABR 1 30 m. (3.39) left librigena and fragment of cranidium, external view, ROM 52430, ABR 1 30 m. (3.44)fragment of cranidium, dorsal view, ROM 52431, ABR 1 30 m, ×5. (3.45, 3.49), left librigena, external and ventrolateral views, ROM 52432,BH 2 42 m. (3.46) hypostome, ventral view, ROM 52433, ABR 1 30 m. (3.47) partial pygidium, dorsal view, ROM 52434, ABR 1 30.(3.48) partial pygidium, dorsal view, ROM 52435, ABR 1 30 m. (Fig. 3.50) Dicranogmus sp., partial pygidium, dorsal view, ROM 52436,BH 2 7.5 m, ×7.5.



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limestones of the Douro Formation obviously belongs to thegroup, significantly extending the known stratigraphic range.The species together appear to represent a robustly supportedclade within Borealarges.

Borealarges is by now sufficiently diverse and well enoughknown that cladistic analysis is feasible. All eight namednorthern Laurentian species were included. The British B.bucklandii (Milne Edwards, 1840) was excluded because ofthe unresolved problem of its species identity discussed byAdrain (1994). Whittington (2002) has suggested that thebucklandii species differentia outlined by Adrain (1994) areartefacts of preparation, but they are not so easily dismissed,and the British Wenlock species almost certainly representsa mixed sample of more than one taxon. Plesiomorphic stateswere determined by reference to Ordovician species currentlyassigned to Hemiarges Gürich 1901. In particular, species ofthe H. turneri group (see Rudkin et al. 1994) were consultedin accordance with the earlier suggestion (Adrain 1994, p. 1082)that these taxa represent the most primitive possible membersof the Borealarges genus group. Although a generalized“outgroup” coding is utilized, any member of the H. turnerigroup could be explicitly designated the outgroup taxon withno change to the coding. Characters used in the analysis areas follows:1. Number of prominent spine–tubercle pairs retained on

the median glabellar lobe in large holaspides: (0) 2 pairs;(1) 3 pairs.

2. Condition of the anterior parts of the longitudinal furrowin dorsal view: (0) anteriorly divergent; (1) anteriorlyconvergent.

3. Inflation of the median glabellar lobe: (0) weakly tomoderately inflated; (1) strongly inflated, longitudinalfurrows bowed laterally.

4. Size of paired median glabellar spines–tubercles in largeholaspides: (0) reduced through ontogeny to tubercles;(1) retained as short spines.

5. Anterolateral corners of cranidium: (0) smoothly rounded;(1) with sharp, subtriangular anterolateral projections.

6. Posterior extension of librigenal field: (0) definitely setposteriorly atop proximal part of genal spine; (1) terminatedin front of genal spine, at most a dorsal furrow on spine.

7. Length of genal spine: (0) very long; (1) short.8. Cross-sectional shape of genal spine: (0) dorsoventrally

flattened, broad; (1) subcylindrical, rounded.

9. Genal spine tip: (0) with same slope as lateral border;(1) dorsally upturned.

10. Eye height: (0) moderate; (1) very tall.11. Librigenal posterior border furrow: (0) shallow and evenly

curved; (1) deep and nearly straight.12. Tubercles on hypostome: (0) essentially absent; (1) sparse,

restricted to area near anterior margin; (2) dense, developedposteriorly.

13. Posterior margin of hypostome: (0) bilobate; (1) trilobate.14. Adaxial pair of pygidial border spines: (0) crowded together

medially; (1) widely spaced.15. Shape of pygidial border spines: (0) flattened, short; (1)

subcylindrical, long.16. Subsidiary pygidial spine pairs: (0) absent; (1) one pair;

(2) two pairs.17. Pygidial length/width ratio: (0) 60% or greater; (1) 50%

or less.The data matrix is given in Table 1. The data were analyzed

using PAUP version 4.0b10 (Swofford 2002). Because of thelow number of study taxa, it was possible to use PAUP’sexhaustive search algorithm, and it is hence certain that theresult is optimal and that all shortest trees have been found.The designated outgroup (all-0 coding) was employed,accelerated transformation (ACCTRAN) optimization wasselected, all characters were run unordered, and polymorphiccodings were treated as variation.

Analysis yielded two equally parsimonious results, one ofwhich is shown with character information mapped in Fig. 5.The two most parsimonious trees differ only in the placementof Borealarges calei Adrain 1994, and B. morrisoni Adrain,1994; the second tree (not shown) features these species in atrichotomy with the B. mikulicorum Perry and Chatterton,1977 – B. reedi clade.

The implications of the analysis are as follows:

(1) There is an extremely well-supported clade comprisingBorealarges tuckerae and the new taxa described later in thetext. Monophyly of this group is supported by the followingshared derived character-states: retention of three prominentspine pairs on the glabellar median lobe; development of aninflated median glabellar lobe with anteriorly divergentlongitudinal furrows; development of a subcylindrical genalspine with a strongly dorsally upturned tip; development of avery tall, nearly stalked eye; development of long, cylindrical

Fig. 4. Dicranogmus wynni n. sp., ABR 1 22m, ×6, except where noted otherwise. (4.1, 4.6, 4.7, 4.11) cranidium, dorsal,posterodorsal, left lateral, and anterior views, ROM 52437, ABR 3 24+ m, ×5. (4.2) cranidium, dorsal view, ROM 52438. (4.3, 4.8)partial cranidium, dorsal and left lateral views, ROM 52439. (4.4, 4.9, 4.14) partial cranidium, dorsal, right lateral, and anterior views,ROM 52440. (4.5) cranidium, dorsal view, ROM 52441, ×7.5. (4.10, 4.15) partial cranidium, dorsal and anterior views, ROM 52442, ×5.(4.12, 4.13, 4.17) cranidium, dorsal, left lateral, and anterior views, ROM 52443, ×7.5. (4.16) fragment of cranidium, dorsal view,ROM 52444, ABR 3 24+ m, ×5. (4.18, 4.19, 4.25) broken cranidium, dorsal, anterior of one piece, left lateral of the other piece, ROM 52445.(4.20) left librigena, external view, ROM 52446, ABR 3 24+ m, ×5. (4.21) right librigena, external view, ROM 52447, ×7.5. (4.22)right librigena, external view, ROM 52448, ×7.5. (4.23) hypostome, ventral view, ROM 52449. (4.24, 4.29) hypostome, ventral andright lateral views, ROM 52450, ×5. (4.26) thoracic segment, dorsal view, ROM 52451. (4.27) hypostome, ventral view, ROM 52452.(4.28, 4.30) left librigena, ventrolateral and external views, ROM 52453. (4.31) left librigena, external view, ROM 52454. (4.32, 4.34,4.38) pygidium, dorsal, left lateral, and posterior views, ROM 52455. (4.33, 4.37, 4.39) pygidium, holotype, left lateral, dorsal, andposterior views, ROM 52456. (4.35) hypostome, ventral view, ROM 52457. (4.36) partial pygidium, dorsal view, ROM 52458. (4.40,4.41) pygidium, dorsal and left lateral views, ROM 52459, ABR 3 24+ m, ×5. (4.42) partial pygidium, dorsal view, ROM 52460.(4.43) pygidium, dorsal view, ROM 52461.



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pygidial spines; and development of a short pygidium, withlength half or less maximum width.

(2) This clade does not form a monophyletic group to theexclusion of Borealarges (s.l.) with the other species assignedby Adrain (1994) to Borealarges s.s. Rather, B. (s.l.) caleiAdrain, 1994, shares two significant apomorphies with thetype and closely related species. All have considerablyshortened genal spines together with a hypostome showing atrilobate, versus bilobate, posterior margin. The B. tuckeraegroup retains what appears to be the primitive elongate genalspine condition, as well as the bilobate hypostome with strongmedian posterior concavity.

(3) Consequently, the B. tuckerae group may ultimately beshown to represent an independent clade for which genericrecognition is appropriate. In the present state of knowledge,the basal relationships between species assigned to Borealarges(s.l.) and to genera, such as Richterarges Phleger, 1936 andCraspedarges Gürich, 1901, are difficult to establish. In addition,there are several newly discovered and as yet undescribednorthern Laurentian species relevant to the broader problem.Pending development of these new data and cladistic analysisof the trochurines as a whole, the B. tuckerae group seemsbest retained for the present within Borealarges.

Borealarges warholi n. sp.(Figs. 6, 7.1–7.6)

DERIVATION OF NAME: After the late Andy Warhol.

TYPE SPECIMENS: Holotype, cranidium, ROM 52462 (Figs. 6.1,6.5, 6.6, 6.10), and paratypes ROM 52463–52486,53997–54000.

TYPE LOCALITY AND TYPE STRATUM: Talus boulder ABR TTD,Cape Phillips Formation, Wenlock (upper Sheinwoodian,Struszia petebesti Fauna), near Abbott River, Cornwallis Island,central Canadian Arctic.

DIAGNOSIS: Anterolateral cranidial projections large; glabellarmedian lobe inflated, but paired tubercles not extended intoshort spines; librigenal posterior border with even posteriorcurvature onto adaxial side of genal spine; librigenal fieldextended posteriorly as wedge-shaped area on proximal partof genal spine; pygidial lateral border spines very long; pygidialmedial border spines small and crowded together medially;

subsidiary pygidial border spines generally absent, at mostone very small pair.

DESCRIPTION: Cranidium with length (sagittally (sag.)) 65% ofmaximum width across posterior borders; width acrossanterolateral projections 55% maximum; across palpebral lobes80% maximum; anterior border short (sag., exsagittally (exsag.)),almost exactly flush with front of glabella in plan view,sculpture of few very sparse tubercles aligned on dorsalaspect and single anteriorly placed terrace line subparallelwith anterior margin (e.g., Fig. 6.6); anterolateral cranidialprojection extended without interruption from anterior border,with variable area but generally large and broad; anteriorfixigena reduced to narrow strip forming ridge along anteriorsection of facial suture; anterior sections of facial suture

Characters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Outgroup 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0B. calei 0 0 0 0 0 0 1 0 0 0 0 2 1 0 0 0 0

1B. mikulicorum 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 0B. morrisoni 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 0 0B. nicoae 1 1 1 1 1 1 0 1 1 1 1 1 0 0 1 1 1B. reedi 0 0 0 0 1 0 1 0 0 0 0 1 1 1 0 0 0B. tuckerae 1 1 1 1 1 0 0 1 1 1 0 1 0 0 1 1 0B. warholi 1 1 1 0 1 0 0 1 1 1 0 1 0 0 1 0 1B. yulei 1 1 1 1 1 1 0 1 1 1 1 1 0 0 1 2 1

Table 1. Data matrix for parsimony analysis of Borealarges.

Fig. 5. Preferred cladogram for phylogeny of Borealarges (length =21; consistency index = 0.905; retention index = 0.946), producedby PAUP* exhaustive search, with character support mapped usingACCTRAN optimization. Black bars are apomorphies; open barsare reversals. Polymorphic codings were treated as variation. Exceptwhere noted, character-state transformations are state 0 to state 1.



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Adrain 757

straight and anteriorly convergent from midpoint of palpebrallobe to a point opposite one-third to one-half the length ofthe bullar lobe, then very slightly anteriorly convergent,subparallel, or slightly anteriorly divergent to points ofanterolateral projections; anterior margin of glabella withbroad and even anterior convexity; longitudinal furrows laterallyconvex and parentheses-shaped; median lobe with maximumwidth one-third distance anteriorly along bullar lobe, widthacross junction of S1 and longitudinal furrows 85–90%maximum width; median lobe moderately inflated, withdense sculpture of moderately large tubercles, many smallerfine tubercles interspersed anteriorly; anterior paired tuberclesrelatively subdued but always visible, posterior two pairslarge and more prominent, but not developed into short spines;longitudinal furrows narrow and incised, widening slightlyat maximum width of median lobe; bullar lobe kidney-shaped,not markedly inflated, widest opposite anterior edge of palpebrallobe, sculpture similar to that of anterior part of medianlobe, with one or two more prominent tubercles posteriorly;palpebral lobe small, triangular, held in horizontal plane whenrear occipital ring is oriented vertically, but with considerabledorsal convexity (Figs. 6.6, 6.8), midpoint set at about 30%distance from rear of cranidium (in sagittal profile), sculptureof four to six small tubercles and small pit near center;palpebral furrow essentially absent, interocular fixigenae gradesimperceptibly into L1; posterior section of facial suture withstrong sutural ridge, bounded adaxially by deep incised furrow;L1 with even dorsal inflation, slightly less than that of bullarlobe, sculpture similar to median lobe, sparse immediatelyopposite palpebral lobe, largest tubercles clustered adaxially;rear part of median lobe set off from inflated anterior part bydistinct shallow subtransverse furrow and break in slope,with three larger tubercles transversely aligned and severalsmaller tubercles interspersed; L0 longest sag., shorteningmarkedly behind L1, sculpture of scattered, more or lesstransversely aligned tubercles smaller than those on medianlobe, with very fine row aligned along posterior margin, medianoccipital tubercle not prominent; posterior border furrow verydeeply incised, lengthening slightly near abaxial contact withsutural ridge; posterior border short behind L1, lengtheningabaxially, with subdued dorsal sculpture of fine tubercles;cranidial doublure extremely narrow; longitudinal furrow withshort, narrow, transverse accessory furrow visible ventrally(Fig. 6.10), running onto bullar lobe at about one-third distancefrom rear of lobe; fossula prominent, set on adaxially indentedplatform beneath anterior part of axial furrow.

Librigena with smooth, fairly strong lateral convexity in planview; lateral border significantly wider than posterior border,dorsal sculpture of lateral row of larger tubercles arranged insubmarginal line and smaller tubercles of various sizes scatteredon dorsal and medial aspects; ventral lateral part of borderwith fine subparallel terrace lines arranged obliquely to margin(Fig. 6.39) so as to be slightly anteriorly imbricate; lateralborder furrow shallow and trough-like; field with relativelysparse sculpture of large tubercles and interspersed finetubercles, tubercles generally denser anteriorly and beneatheye (e.g., Figs. 6.31, 6.38); field always extended posteriorlyonto dorsal aspect of genal spine; posterior border with variablemorphology, from relatively incised and straight (Fig. 6.50)to nearly as shallow as lateral border furrow and withconsiderable posterior concavity (Fig. 6.38); morphology of

eye and eye socle poorly known, but eye not prominentlystalked; genal spine with broad base, becoming moresubcylindrical distally, with strong posterior curvature andupturned tip (Fig. 6.39); doublure with strong, serrate, terracelines subparallel to lateral margin (Fig. 6.32) and much moresubdued, elliptical terrace lines on broad inner part.

Rostral plate (note: rostral plate could belong to the lesscommon co-occurring species, Borealarges nicoae n. sp.)short, of similar length sag. and exsag. (Fig. 6.26); anteriormargin with even anterior convexity; posterior margin withnearly even posterior concavity, interrupted medially by shortsubtransverse region; connective sutures forming sharp, mediallydirected chevron; anterior part of plate above connected suturesbowed anteriorly and extended laterally past posterior part;ventral sculpture of fine subparallel terrace lines, conformingto the curvature of the anterior and posterior margins.

Hypostome with length (sag.) 75–80% maximum widthacross shoulders; anterior margin with nearly even anteriorconvexity, frequently with short transverse area medially(e.g., Figs. 6.27, 6.30); hypostomal suture forming relativelybroad anterior face (Fig. 6.36); anterior wing stout andtab-shaped (Fig. 6.36); middle body occupying 50–60%sagittal length, sculpture smooth, with relatively sparse butprominent pits and subdued tubercles restricted to scatteredoccurrence near anterior margin; middle furrow impressed onlylaterally as short notch; maculae very faint swelling on ventralsurface, but often well-impressed dorsally (e.g., Fig. 6.29);shoulder flared to lateral point; lateral border posterior toshoulder with coarse, reticulate terrace lines and slight ventralconcavity; posterior border very long, with prominent medianventral convexity (Fig. 6.35); posterior margin bilobed, althoughmedian anterior indentation can be very subtle, and sometimesnearly transverse (e.g., Fig. 6.27); three median doubluralspines relatively small, lateral spines sometimes nearly effaced(Fig. 6.28); doublure with smooth sculpture, entirely lackingterrace lines.

Thorax not identified.Pygidium with width approximately twice sagittal length

excluding posteromedian spine; axis occupying about 60%of sagittal length and 35–40% maximum width anteriorly;axial furrows posteriorly convergent opposite first and secondaxial rings, subparallel opposite most of remainder of axis,converging in even arc posteriorly to circumscribe rear ofaxis, and terminating at strong post-axial ridge; axial furrownarrow but deeply incised, of similar depth everywhere; onlyfirst and second axial rings fully defined by complete ringfurrows; first ring of similar short length sag. and exsag.;second ring extended posteromedially; five or six additionalrings becoming increasingly less well defined posteriorly;first and second rings with single transverse row of small,subdued tubercles; axis posterior to second ring with prominentcoarse tuberculate sculpture; only first and second pleuraland interpleural furrows defined, all of similar length (exsag.)and depth; anterior pleural band of first segment very short(exsag.) adaxially, lengthening rapidly abaxial to fulcrum,with transverse row of very small tubercles along posterioraspect; posterior pleural band of first segment about twice aslong adaxially as anterior band, much more exsag. convex,with sparser transverse row of larger tubercles set alongmidlength; anterior band of second segment elongate, withvery reduced dorsal convexity, similar in appearance to posterior



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pleural areas, with scattered small and moderate tubercles;posterior pleural band of second segment similar in constructionto posterior band of first segment, declined about 45°fromtransverse plane; posterior pleural area lacking incised furrows,with tuberculation of varying size, largest similar in size tolarge tubercles on rear of axis; pygidial border set off frompleura posteriorly by very shallow border furrow border slightlyless dorsally convex than first and second posterior pleuralbands, with sculpture of relatively fine, scattered tubercles;all pygidial spines cylindrical in section; first and secondpairs of pygidial spines very elongate, with gradual posteriorcurvature; third pair similar in size to first two pairs, nearlyexsag. aligned, but with slight posterior curvature; medianthree pygidial spines much smaller and shorter than lateralpairs, tapering to sharp point, crowded together medially;first three spine pairs with dorsal tuberculate sculpture similarto that of first posterior pleural band; doublure not wellpreserved, with fine subparallel lineations, much morecoarsely developed near posterior margin, grading intoposteroventrally directed tubercles along margin and chevron-shaped lineations and tubercles on ventral aspect of spines.

REMARKS: Borealarges warholi differs from the slightly olderB. tuckerae in its much larger anterolateral cranidial projections;more robust dorsal cephalic tuberculation; paired glabellartubercles that are not developed into short spines; longerfirst and second pygidial marginal spine pairs; more curvedpygidial marginal spines; more medially crowded medianpygidial spines; and pygidium that is wider relative to itslength.

Borealarges nicoae n. sp.(Figs. 7.7–7.49)

DERIVATION OF NAME: After the late Nico.

TYPE SPECIMENS: Holotype, cranidium, ROM 54001 (Figs. 7.7,7.14, 7.17), and paratypes ROM 54002–54027.

TYPE LOCALITY AND TYPE STRATUM: Talus boulder ABR TTD,Cape Phillips Formation, Wenlock (upper Sheinwoodian,Struszia petebesti Fauna), near Abbott River, northwesternCornwallis Island, central Canadian Arctic.

DIAGNOSIS: Relatively long paired spines very prominent onmedian glabellar lobe; dorsal cranidial sculpture relativelysparse; librigenal posterior border furrow deep; librigenal

field terminated in front of genal spine base; pygidium verybroad; one prominent pair of subsidiary pygidial border spines.

REMARKS: Description is accomplished through extendedcomparison with Borealarges warholi, which is given fulldescription earlier in the text. Borealarges nicoae n. sp. isdistinguished from B. warholi in the possession ofanterolateral cranidial projections that are slightly smallerand more thorn-like; median glabellar lobe that is narrowerand not as inflated; much longer paired glabellar spines;generally more prominent, conical, and spinose cephalictuberculation; slightly shorter anterior border; a distinctpalpebral furrow in some specimens (e.g., Figs. 7.12, 7.26);usually deeper and less arcuate posterior librigenal borderfurrow; more elevated eye; a librigenal field terminated infront of the genal angle, versus extending posteriorly alongdorsal aspect of genal spine; a hypostomal middle body withdenser pitting and more prominent maculae; more ventrallyconcave posterior hypostomal border, posterior margin withstronger medial posterior concavity; pygidium wider relativeto its length, with the second axial ring less well defined;shorter pygidial post-axial ridge; more sparsely and finelytuberculate pygidial pleurae; major pygidial spines that aresplayed much more laterally; small pair of auxiliary pygidialspines developed on margin between second and third pairsof major spines; much less medially crowded medial spines.

Borealarges nicoae is most similar among described speciesto B. tuckerae. Much of this similarity, however, isplesiomorphic relative to the several compelling apomorphieslinking B. nicoae with the younger B. yulei. These includethe definite termination of the librigenal field in front of thegenal angle, the development of a deep and nearly straightlibrigenal posterior border furrow, and the development ofauxiliary spines on the pygidium. These features corroboratethe sclerite associations of co-occurring species in theABR-TTD boulder, which are based on the fact thatB. warholi is much more common than B. nicoae.

Borealarges yulei n. sp.(Fig. 8)

DERIVATION OF NAME: After Doug Yule.

TYPE AND FIGURED SPECIMENS: Holotype, cranidium, ROM 54028(Figs. 8.1, 8.6, 8.11, 8.17), and paratypes ROM 54029–54042,54050; assigned specimens ROM 54043, 54045–54051.

TYPE LOCALITY AND TYPE STRATUM: Talus boulder ABR 3TT,

Fig. 6. Borealarges warholi n. sp., ABR TTD, ×6, except where noted otherwise. (6.1, 6.5, 6.6, 6.10) cranidium, holotype, dorsal, leftlateral, anterior, and ventral views, ROM 52462. (6.2, 6.7, 6.11, 6.12) cranidium, dorsal, anterior, ventral, and right lateral views, ROM52463. (6.3, 6.8, 6.13) cranidium, dorsal, anterior, and left lateral views, ROM 52464. (6.4, 6.9, 6.14) cranidium, dorsal, anterior, andleft lateral views, ROM 52465. (6.15, 6.16) cranidium, dorsal and left lateral views, ROM 52466, ×7.5. (6.17, 6.18) cranidium, dorsaland left lateral views, ROM 52467. (6.19, 6.20), cranidium, dorsal and right lateral views, ROM 52468. (6.21, 6.22) cranidium, dorsaland right lateral views, ROM 52469. (6.23, 6.24) cranidium, dorsal and left lateral views, ROM 52470. (6.25, 6.33) cranidium, dorsaland right lateral views, ROM 52471. (6.26) rostral plate, ventral view, ROM 52472, ×7.5. (6.27) hypostome, ventral view, ROM 52473, ×7.5.(6.28, 6.37) hypostome, dorsal and ventral views, ROM 52474, ×7.5. (6.29, 6.30) hypostome, dorsal and ventral views, ROM 52475, ×7.5.(6.31, 6.32) left librigena, external and internal views, ROM 52476. (6.34–6.36) hypostome, ventral, posterior, and left lateral views,ROM 52477, ×7.5. (6.38) left librigena, external view, ROM 52478. (6.39, 6.40) right librigena, ventrolateral and external views, ROM 52479.(6.41, 6.42) partial pygidium, left lateral and dorsal views, ROM 52480, ×7.5. (6.43) partial pygidium, dorsal view, ROM 52481, ×7.5.(6.44, 6.46) pygidium, dorsal and right lateral views, ROM 52482, ×7.5. (6.45) partial pygidium, dorsal view, ROM 52483, ×7.5. (6.47, 6.48)pygidium, posterior and dorsal views, ROM 52484, ×7.5. (6.49) right librigena, external view, ROM 52485. (6.50) right librigena, externalview, ROM 52486.



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Cape Phillips Formation, Wenlock (lower Homerian;Pseudogerastos rossi Fauna), near Abbott River, northwesternCornwallis Island, central Canadian Arctic.

DIAGNOSIS: Anterolateral cranidial projections small but sharplypointed; median glabellar lobe relatively narrow, with shortpaired spines; librigenal posterior border nearly straight;librigenal posterior border furrow deep; librigenal fieldterminated in front of genal spine base; pygidial axis large inarea and broad; pygidial border spines relatively short andslender; two prominent pairs of subsidiary border spinesbehind the first and second major pygidial border spines.

REMARKS: Borealarges yulei new species is distinguished fromB. nicoae in the possession of slightly finer, much moredensely distributed dorsal cranidial tuberculate sculpture; shorterpaired glabellar spines; relatively smaller anterolateral cranidialprojections; a less elevated eye; a pygidial axis that is muchlarger relative to the overall pygidial dimensions; and anadditional pair of auxiliary pygidial spines.

Borealarges yulei is distinguished from B. warholi in itsmuch smaller anterolateral cranidial projections; narrow glabellawith more prominent paired spines; librigenal field that isnot extended posteriorly along dorsum of genal spine; deeper,less curved librigenal posterior border furrow; pygidium withmuch broader axis, more slender pygidial spines, and twopairs of auxiliary pygidial spines.

Borealarges n. sp.(Fig. 9)

FIGURED SPECIMENS: ROM 54052, 54053, from the DouroFormation (late Ludlow), locality GSC 3, near GoodsirCreek, eastern Cornwallis Island, central Canadian Arctic.

REMARKS: A very rare species collected from upper Ludlowplatform limestones of the Douro Formation on eastern

Cornwallis Island is important because it is obviously re-lated to the Borealarges tuckerae group and greatly extendsits known stratigraphic range. The species is most similar tothe youngest of the Wenlock group, B. yulei. A librigenafrom the Douro Formation (Fig. 9.2) differs from those as-signed to B. yulei (e.g., Fig. 8.22) mainly in the more promi-nent development of spines along the rear of the posteriorborder and inner aspect of the genal spine. A pygidium(Fig. 9.1) shows both pairs of small auxiliary spines in thesame position between the first and second, and second andthird pairs of major spines. In addition, the Douro specieshas a third pair of small spines developed adaxial to the thirdpair, but abaxial of the three medial spines.

Acknowledgments

Fieldwork was funded by Northern Science Training Grantsand Boreal Alberta Research Grants from the CanadianCircumpolar Institute, grants under the research agreementsprogram of the Department of Energy, Mines, and Resources(Canada) and the Natural Sciences and Engineering ResearchCouncil (Canada) (NSERC), a grant-in-aid from thePaleontological Society, and much logistical assistance fromthe Polar Continental Shelf Project. B.D.E. Chatterton(University of Alberta, Edmonton, Alberta) kindly made hisearlier Cape Phillips Formation collections freely availablefor study. Costs of technical preparation were met by NSERCgrants to B.D.E. Chatterton and A.C. Lenz (University ofWestern Ontario, London, Ontario). Thanks to J. Waddington(Royal Ontario Museum, Toronto, Ontario) for assistancewith specimen numbers, C. Hensley (Natural History Museum,London, U.K.) for assistance with literature, and Guan Jian(University of Iowa, Iowa City, Iowa) for translation of Chinese.I am grateful for the help of reviewers M. Campbell andG.D. Edgecombe and Associate Editor B.D.E. Chatterton.

Fig. 7. (Figs. 7.1–7.6) Borealarges warholi n. sp., ABR TTD, ×7.5. (7.1, 7.2) partial pygidium, dorsal and ventral views, ROM 53997.(7.3, 7.5) partial pygidium, dorsal and ventral views, ROM 53998. (7.4) partial pygidium, dorsal view, ROM 53999. (7.6) partial pygidium,dorsal view, ROM 54000. (Figs. 7.7–7.49) Borealarges nicoae n. sp., ABR TTD, ×6, except where noted otherwise. (7.7, 7.14, 7.17)cranidium, holotype, dorsal, left lateral, and anterior views, ROM 54001. (7.8, 7.15) cranidium, dorsal and left lateral views,ROM 54002, ×7.5. (7.9, 7.16) cranidium, dorsal and right lateral views, ROM 54003, ×7.5. (7.10, 7.11) partial cranidium, dorsal andright lateral views, ROM 54004, ABR TTC(3), ×7.5. (7.12, 7.13) cranidium, dorsal and anterior views, ROM 54005, ABR TTC(7), ×7.5.(7.18) partial cranidium, dorsal view, ROM 54006, ABR TTC(7), ×7.5. (7.19) partial cranidium, dorsal view, ROM 54007, ABR TTC(3), ×7.5.(7.20, 7.24, 7.25) left librigena, ventrolateral, external, and internal views, ROM 54008, (7.21) left librigena, external view, ROM 54009,ABR TTC(3), ×7.5. (7.22) right librigena, external view, ROM 54010, ABR TTC(7), ×7.5. (7.23) left librigena, external view,ROM 54011, ×7.5. (7.26, 7.27) partial cranidium, dorsal and right lateral views, ROM 54012, ABR TTC(7). (7.28) left librigena,external view, ROM 54013, ×7.5. (7.29, 7.35) right librigena, ventrolateral and external views, ROM 54014, (7.30) left librigena,external view, ROM 54015, ABR TTC(7), ×7.5. (7.31, 7.32, 7.36) pygidium, posterior, left lateral, and dorsal views, ROM 54016.(7.33, 7.41) hypostome, ventral and left lateral views, ROM 54017. (7.34) right librigena, external view, ROM 54018. ×7.5. (7.37)pygidial fragment, dorsal view, ROM 54019, ABR TTC(7), ×7.5. (7.38) hypostome, ventral view, ROM 54020. (7.39, 7.47) pygidium,dorsal and posterior views, ROM 54021, ×7.5. (7.40) hypostome, ventral view, ROM 54022, ABR TTC(7), ×7.5. (7.42) hypostome,ventral view, ROM 54023, ×7.5. (7.43, 7.44) hypostome, dorsal and ventral views, ROM 54024, ×.5. (7.45, 7.46) partial pygidium,ventral and dorsal views, ROM 54025, ×7.5. (7.48) partial pygidium, dorsal view, ROM 54026, ABR TTC(3), ×7.5. (7.49) pygidium,dorsal view, ROM 54027, ×7.5.



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Fig. 8. Borealarges yulei n. sp., ABR 3TT, ×6, except where noted otherwise. (8.1, 8.6, 8.11, 8.17) cranidium, holotype, dorsal, leftlateral, anterior, and ventral views, ROM 54028. (8.2, 8.7, 8.12) cranidium, dorsal, anterior, and left lateral views, ROM 54029. (8.3, 8.8, 8.9)cranidium, dorsal, anterior, and left lateral views, ROM 54030. (8.4) cranidium, dorsal view, ROM 54031. (8.5) right librigena, externalview, ROM 54032, ×7.5. (8.10) cranidium, dorsal view, ROM 54033, (8.13) rostral plate, ventral view, ROM 54034, ×7.5. (8.14) hypostome,ventral view, ROM 54035. (8.15) cranidium, dorsal view, ROM 54036. (8.16) cranidium, dorsal view, ROM 54037, ×10. (8.18) hypostome,ventral view, ROM 54038, ×7.5. (8.19) hypostome, ventral view, ROM 54039, ×7.5. (8.20) right librigena, external view, ROM 54040, ×10.(8.21) left librigena, external view, ROM 54041, ×7.5. (8.22–8.24) right librigena, internal, external, and ventrolateral views, ROM 54042.(8.25) right librigena, external view, ROM 54043, BH 2 2 m, ×7.5. (8.26, 8.28, 8.29, 8.31) pygidium, dorsal, posterior, ventral, and leftlateral views, ROM 54044. (8.27) pygidial fragment, dorsal view, ROM 54045, BH 2 3 m, ×7.5. (8.30) right librigena, external view,ROM 54046, BH 2 3 m, ×7.5. (8.32, 8.34) cranidium, anterior and dorsal views, ROM 54047, BH 2 2 m, ×7.5. (8.33) cranidium, dorsalview, ROM 54048, BH 2 3 m, ×7.5. (8.35) pygidial fragment, dorsal view, ROM 54049, BH 2 3 m, ×7.5. (8.36) partial pygidium, dorsalview, ROM 54050. (8.37) right librigena, external view, ROM 54051, ABR 1 13.5 m, ×7.5.



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Adrain 763

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Fig. 9. Borealarges n. sp., Douro Fm., Goodsir Creek, localityGSC 3, eastern Cornwallis Island, central Canadian Arctic, ×5.(9.1) pygidium, ventral view, ROM 54052. (9.2) left librigena,internal view, ROM 54053.



Validity and composition of the Silurian trilobite genera ...€¦ · Island, Cape Phillips...

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