J. Pa/eon/ .• 70(1). 1996. pp. 100-110Copyright © 1996. The Paleontological Society0022-3360/96/0070-0100$03.00

THE OTARIONINE TRILOBITE CYPHASPIS, WITH NEWSPECIES FROM THE SILURIAN OF NORTHWESTERN CANADA

JONATHAN M. ADRAIN AND BRIAN D. E. CHATTERTONDepartment of Palaeontology, The Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom, and

Department of Geology, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada

AIlsTRAcr- The genus Cyphaspis Burmeister, 1843, is first known from the northern Laurentian Sheinwoodian. By the late Homerian,the genus had appeared in England and Baltica, and from the Ludlow through the Lower and Middle Devonian it had an essentiallycosmopolitan distribution. The Mississippian Dixiphopyge Brezinski, 1988, may represent a relict distribution of Cyphaspis. and ifso should be considered a junior subjective synonym. Cyphaspis is considered the sister taxon of Otarion Zenker, 1833. The oldest,Sheinwoodian, species of either genus are very similar, but the clades evolved to the point of gross morphological disparity in theDevonian.New species from the Wenlock and probably Ludlow of northwestern Canada are Cyphaspis lowei. C. munii, C. buchbergeri, and

C. mactavishi. New ontogenetic material of the Zlichovian C. dabrowni (Chatterton, 1971) further demonstrates the pervasivenessof the basic juvenile morphology of the tribe Otarionini.

INTRODUCTION

THISPAPERis fourth in a series describing the aulacopleuridtrilobites of the upper Whittaker Formation and DelormeGroup of the central Mackenzie Mountains, Northwest Terri-tories, Canada. Previous works have dealt with the genera Otar-ion (Adrain and Chatterton, 1994), Harpidella and Maurotarion(Adrain and Chatterton, 1995a), and Aulacopleura and Song-kania (Adrain and Chatterton, 1995b). The aulacopleurids re-covered from these units are silicified and rank among the bestpreserved species yet found. Representatives of most of themajor clades are present, and several horizons have yieldedexcellent juvenile growth stages. As such, the ongoing descrip-tions have provided a great deal of new information relevantto studies of aula cop leurid ontogeny, phylogeny, and evolution.In concert with descriptive paleontology, an attempt has beenmade to revise the family on a world-wide basis, and to organizeits constituents into robustly defined monophyletic groups. Twosubfamilial groupings have been recognized, in part by referenceto comparative ontogenies. The less diverse Aulacopleurinaehas been discussed by Adrain and Chatterton (1995b), whilegeneric groupings within the Otarionini have been the subjectof Adrain and Chatterton (1994, 1995a). The latter theme iscontinued in the present work, through treatment of Cyphaspis,one of the major otarionine genera.Locality information follows Chatterton and Perry (1983,

1984), Over and Chatterton (1987), and Chatterton et al. (1990).The graptolite zonation referred to is that established for theCape Phillips Basin of the central Canadian Arctic (Lenz, 1990;Lenz and Melchin, 1990, 1991). These zones are cited basedupon correlation of the Mackenzie Mountains trilobite faunaswith those of the Cape Phillips Basin, description and rede-scription of which has been begun by Adrain (1994) and Adrainand Edgecombe (1995). Figured specimens are in the paleon-tological collections of the Department of Geology, Universityof Alberta, with prefix UA.

SYSTEMATICPALEONTOLOGYFamily AULACOPLEURIDAEAngelin, 1854

Subfamily OTARIONINAERichter and Richter, 1926Tribe ÜTARIONINIRichter and Richter, 1926

Genus CYPHASPISBurmeister, 1843Type species. -Phacops ceratophthalmus Goldfuss, 1843, Ei-

felian, Gees, near Gerolstein, Germany.Other species. - Information is given in the following order:

species name and author(s); original generic assignment; rockunit, age, and geographical occurrence.advenum Prantl and Pi'ibyl, 1950; Otarion (Otarion); Dvorce-ProkopLimestone, Pragian, Czech Republic.

balanops Erben, 1953; Otarion (Otarion); AhrdorfFormation, Eifelian,Germany.

barrandei Hawle and Corda, 1847; Cyphaspis; Dvorce-Prokop Lime-stone, Pragian, Czech Republic.

buchbergeri new species; Cyphaspis; Delorme Group, Wenlock (upperHomerian, Pristiograptus ludensis Zone, central Mackenzie Moun-tains, Northwest Territories, Canada.

collini Morzadec, 1983; Otarion (Otarion); Bolast Formation, Dalejan,Bretagne, France.

cornigera Hawle and Corda, 1847; Conoparia; Koneprusy Limestone,Pragian, Czech Republic.

dabrowni Chatterton, 1971; Otarion (Otarion); Taemas Formation, Zli-chovian, New South Wales, Australia.

elachopos Thomas, 1978; Cyphaspis (s.!.); holotype (Thomas, 1978, p!.7, fig. II) is from the Sheinwoodian-Iower Homerian CoalbrookdaleFormation; additional material from the upper Homerian Much Wen-lock Limestone Formation, Wenlock, Dudley and near Dudley, WestMidlands, England.

gaultieri Rouault, 1851; Cyphaspis; Marettes Formation, Dalejan, Ga-hard, Ille-et-Vilaine, France; see Morzadec (1981, 1983).

gruanum Alberti, 1969; Otarion (Otarion); "princeps" Limestone, Pra-gian, northwest Morocco.

horani Etheridge and Mitchell, 1893; Cyphaspis; Black Bog Shale, Yar-wood Siltstone Member, Ludlow, near Yass, New South Wales, Aus-tralia; see Chatterton (1971) and Chatterton and Campbell (1980).

hydrocephala Roemer, 1843; Calymene; Zlichovian, Harz Mountains,Austria.

intermedium Prand and Pi'ibyl, 1950; Otarion. as subspecies of barran-dei Hawle and Corda, 1847; Koneprusy Limestone, Pragian, CzechRepublic; considered synonym of cornigera Hawle and Corda, 1847,by Pi'ibyl and Vanek (1981, p. 175) and Ellermann (1992, p. 27).

lowei new species; Cyphaspis; Delorme Group, Wenlock (lower Hom-erian, Cyrtograptus lundgreni-Monograptus testis Zone), central Mac-kenzie Mountains, Northwest Territories, Canada.

mactavishi new species; Cyphaspis; Delorme Group, probably Ludlow,central Mackenzie Mountains, Northwest Territories, Canada.

munii new species; Cyphaspis; Delorme Group, Wenlock (mid-Shein-woodian, Monograptus instrenuus-Cyrtograptus kolobus Zone), cen-tral Mackenzie Mountains, Northwest Territories, Canada.

oceanum Morzadec, 1983; Otarion (Otarion); Kerdreolet Formation,Dalejan, Bretagne, France.

polonicum Kielan, 1954; Otarion (Otarion); Givetian, St. Croix Moun-tains, Poland.

praecedens Kielan, 1954; Otarion (Otarion), as subspecies of polonicumKielan, 1954; Eifelian, St. Croix Mountains, Poland.

100

ADRAIN AND CHATTERTON-SILURIAN TRILOBITES

sidiarounium Alberti, 1969; Otarion (Otarionella?); Sidi Ahroun Lime-stone, Pragian, central Morocco.

Diagnosis. -Otarionines with glabella inflated, overhangingpreglabellar field when occipital ring is held in vertical plane;preglabellar field short; interocular fixigenae narrow; LI small;librigenal field relatively broad and short (exsagittally); genalspine long and robust; Il thoracic segments, with long axialspine on sixth; pygidium narrow and small even for subfamily,with transverse rows of tubercles on axial rings and posteriorpleural bands; primitively three or four axial rings; pygidialdoublure broad for family.Discussion.-Adrain and Chatterton (1994) interpreted Cy-

phaspis and Otarion as sister taxa, and provided a differentialdiagnosis. Briefly, Cyphaspis is distinguished from Otarion inits shorter, more inflated glabella; smaller LI; shorter pregla-bellar field; broader, shorter (exsagittally) librigena with usuallymuch longer genal spine; possession of 11 as opposed to 12 ormore thoracic segments, with much longer axial spine on sixth;and relatively smaller, narrower pygidium, with more pro-nounced tubercle rows and broader doublure. More derivedspecies of Cyphaspis, including the type (see Thomas and Ow-ens, 1978, plate 7, figures 4, 8), display an inflated librigenaltrunk, which interrupts the contact between the posterior andlateral border furrows at the genal angle. This morphology isseen elsewhere in some species of Harpidella M'Coy, 1849 (H.spinafrons Williams in Cooper and Williams, 1935, and relatedspecies; see Adrain and Chatterton, 1995a), but never in Otar-ion.Species of Otarion (O. huddyi Adrain and Chatterton, 1994)

and of Cyphaspis (c. munii n. sp.) occurring at section Ava-lanche Lake Four, 126 m above base, are of mid-Shein wood ianage, and are apparently the oldest known members of theirrespective genera. They also appear to be the most primitiveexamples of each group, and comparison, particularly of cran-idial features, shows close similarity. Were it not for the sub-sequent separate history of each clade, showing considerablediversification until at least the Middle Devonian, the Wenlockmembers of either group might be classified together in a singlegenus. Nevertheless, both O. huddyi and C. munii possess thesynapomorphies of their respective clades, and given the mor-phological disparity between the groups achieved in the De-vonian, there is every reason to treat the sister taxa as separategenera, rather than subgenera or species-groups.Adrain and Chatterton (1994) described well-preserved on-

togenetic material of their new Otarion huddyi, and considereddevelopmental morphology, particularly of the cephalic spinearray, to be of critical importance in adducing phylogeneticrelationships within the subfamily. The tribe Otarionini wasdiagnosed on the basis of its derived j uvenile spine morphology.Its presence in Cyphaspis is demonstrated herein. Comparisonof the juvenile cranidia of Cyphaspis lowei n. sp. (Figures lAO,1.47,2.1-204) with those of O. huddyi (Adrain and Chatterton,1994, figures 5.25, 5.29, 7.1-7.3) reveals essential correspon-dence in all features of the spine array (spines labelled followingAdrain and Chatterton (1994, p. 305-306, figure I». Diagnosticof the tribe, C. lowei has G2 and G3 crowded near the front ofthe glabella, Fx2 and Fx3 suppressed, palpebral spines reducedto a single Pl, and a double row of anterior border spines. Thismorphology is seen in every species of Otarion and Cyphaspisfor which any ontogenetic information is available. As outlinedby Adrain and Chatterton (1994, page 310, figure 4), the spinearray is hypertrophied and retained in the holaspid of membersof Namuropyge.While the respective juvenile cranidia and pygidia of species

referred to Otarion and Cyphaspis are very similar, they can

101

nevertheless be differentiated. As far as is known, early-degreemeraspid sclerites of Otarion have an essentially smooth sculp-ture on areas between spines (Adrain and Chatterton, 1994,figures 7,9). Those known for Cyphaspis (the Wenlock C. loweiand the Zlichovian C. dabrowni; see Figure 2) have a distinctgranular sculpture on the dorsal areas of both cranidia and tran-sitory pygidia.Adrain and Chatterton (1994) emphasized the role of heter-

ochrony in the evolution of the Otarionini. There is some ev-idence that Cyphaspis may itself have had a paedomorphic or-igin: 1. The holaspid segment count of 11 is the fewest knownfor an otarionine. The sister group of Cyphaspis, Otarion, hasa primitive segment count of 12. 2. The oldest known speciesof Cyphaspis, C. munii n. sp., retains a short median occipitalspine in mature holaspids. It is now well established that thisfeature is very long in the earliest ontogeny of members ofOtarionini (see Adrain and Chatterton, 1994, figures 5, 7, forOtarion huddyi; see Adrain and Chatterton, 1994, figure 9 forO. brauni Perry and Chatterton, 1979; see below for C. lowein. sp.; see Chatterton, 1971 and below for C. dabrowni. Thespine becomes progressively shorter through ontogeny, and invirtually all members of the clade, is reduced to a small nodein mature holaspides. Retention in the oldest known species ofCyphaspis of a short spine is consistent with the idea that thespecies reflects development from an arrested degree Il mer-aspid of an ancestor with 12 segments. 3. Species ofCyphaspishave mature pygidia that are commonly (and primitively) highlytuberculate. Smaller Otarion pygidia are similarly tuberculate(cf. O. huddy, Adrain and Chatterton, 1994, figures 6.25, 7.8;O. brauni, Adrain and Chatterton, 1994, figure 8.30-8.32), butthe tubercles become progressively effaced in larger specimens.Hence, the Cyphaspis condition is consistent with derivationfrom a juvenile Otarion morphology.New discoveries of Telychian and earliest Sheinwoodian di-

versity will be required for a full understanding of the origin ofOtarionini and the identification of the tribe's thus far unknownsister taxon. These observations, however, allow at least theplausible suggestion that Cyphaspis evolved through arresteddevelopment ofa very late-degree meraspid of an older species.The initial, Sheinwoodian, distribution of Cyphaspis seems

to be limited to northern Laurentia, where the genus is verycommon in both the Mackenzie Mountains and the Cape Phil-lips Basin ofthe Canadian Arctic. The genus appears elsewherefor the first time in the Homerian, in the form of C. elachoposin the Coal brookdale Formation and Much Wenlock LimestoneFormation of England, together with undescribed material fromGotland, Sweden (L. Ramsköld, personal commun.). From theLudlow onward until at least the Givetian, Cyphaspis is widelydistributed, although it is absent the Malvinokaffric Realm. Anexception is the Devonian of North America, from which untilrecently the genus was unknown. A very primitive species hasrecently been discovered in the Lochkovian Haragan Formationof Oklahoma (G. J. Kloc, personal commun.).Brezinski (1988) erected the monotypic Dixiphopyge for Bra-

chymetopus armatus Vogdes, 1891, from the MississippianChouteau Limestone of Missouri, comparing the taxon to Cy-phaspis and Namuropyge Richter and Richter, 1939. Adrainand Chatterton (1994) argued that Namuropyge was a paedo-morphic member of Otarionini, with a possible origin in Otar-ion. They included Dixiphopyge with question in Otarionini.The pygidium of Dixiphopyge resembles that of Namuropygein its many segments and pleural spines, and indicates a similarpotential origin from an arrested transitory pygidium of an ear-lier species. As noted by Brezinski (1988), the inflated glabelladoes resemble that of Cyphaspis.A cranidium illustrated by Phbyl and Vanek (1981, plate 3,

102 JOURNAL OF PALEONTOLOGY, V. 70, NO.1, 1996

figure 7) as Otarion (Cyphaspis) hydrocephalum cornigerum(HawIe and Corda, 1847), from the Pragian of the Czech Re-public, shows the juvenile glabellar and occipital spines of aspecies of Cyphaspis retained as robust structures in a matureholaspid. This, as outlined by Adrain and Chatterton (1994), isthe process by which the spinose adult morphology of Namu-ropyge was achieved. Itdoes little, however, to explain the originof Dixiphopyge. Dixiphopyge lacks either prominent glabellaror median occipital spines. While its hypertrophied palpebralspines are consistent with the Otarionini morphology, its longpaired occipital spines are unknown elsewhere in Aulacopleu-roidea and, as noted by Adrain and Chatterton (1994; also Bre-zinski, 1988), the very large LI of Dixiphopyge do not agreewith those of most species of Cyphaspis (although the cranidiumfigured by Piibyl and Vanèk does have an usually large LI).Nevertheless, Brezinski's (1988) assignment of the taxon to Au-lacopleuridae remains the most plausible hypothesis, basedmainly on the structure of the pygidium and its similarity tothat of Namuropyge. If the inflated glabella is ultimately shownthrough new discoveries to reflect origin in Cyphaspis, Dixi-phopyge should be considered a subjective junior synonym, asit would create pointless paraphyly based on autapomorphies.In the present state of knowledge, it seems best to continue toassign Dixiphopyge with question to Otarionini.

CYPHASPIS WWEI new speciesFigures 1,2.1-2.8

Diagnosis. - Cyphaspis with glabella moderately inflated andwith dense, even sculpture of small tubercles; anterior bordertubercles suppressed in holaspid; occipital node prominent inholaspid, but not extended into spine; librigenal field with sculp-ture of dense, fine tubercles, thinning out along lateral borderfurrow; genal spine long, but relatively narrow for genus, withvery faint dorsal tubercle row in holaspid; pygidium with threeaxial rings, incipient fourth sometimes indistinguishable fromterminal piece; each pygidial segment with prominent transverserow of 10-14 tubercles.Description. -Cranidial anterior border slightly longer (sag-

ittally, exsagittally) than occipital ring, with prominent, evendorsal convexity, lacking sculpture in mature holaspides; an-terior border of similar length sagittally and exsagittally; anteriorborder furrow evenly arcuate to very slight anteriorly directed"V" shape, deep; preglabellar field of similar length (sag.) toanterior border, with prominent dorsal convexity, bearing sculp-ture of fine caecal pits largely obscured by densely scatteredsmall tubercles; glabella large, inflated, with dense, even tuber-culation, slightly larger than those on preglabellar field; preg-labellar furrow strongly arcuate, describing semicircle in dorsalview; axial furrows bowed out around LI, then parallel for short

distance to smooth grade into preglabellar furrow; LI small,with densely scattered tubercles similar in size to those of preg-labellar field; SI deep; S2 and anterior furrows obscure; inter-ocular fixigena very narrow, dorsally convex, separated frompalpebral lobe by shallow but distinct palpebral furrow, withtuberculate sculpture similar to preglabellar field; palpebral lobesnarrow, short (exsag.), with prominent PI retained in holaspidand very distinct laterally-placed pit; SO and posterior borderfurrow very deep; occipital ring with prominent median nodeand 4-8 moderately large tubercles more or less transverselyaligned; posterior border narrow (transversely), lacking dorsalsculpture.Librigenal field with sculpture of very fine, dense caecal pits

and fine tubercles; tubercles slightly larger on anterior and ad-axial areas of field, becoming smaller and less dense towardlateral border furrow and genal angle; genal trunk obscure onexternal surface, visible only on internal surface; bilobate eyesocle narrow (tr.) and somewhat subdued, anterior lobe moreprominent; eye of moderate size, not "stalked"; posterior borderfurrow deep, set off from margin by small sutural ridge; lateralborder furrow shallower than posterior border furrow; posteriorborder and lateral border of similar width, both lacking dorsalsculpture in holaspid; genal spine long, curved, with very faintfurrow running along dorsal aspect; row of evenly spaced veryfine tubercles running along dorsal aspect of genal spine adaxialto faint furrow; doublure broadest anteriorly, narrowing neargenal angle, with fine, subparallel terrace lines.Rostral plate unknown.Hypostome with arcuate anterior margin, slight ventral "lip"

sagittally; middle body grading smoothly into margin anteriorly,length (sag.) about 150 percent of maximum width across shoul-der; lateral border furrows deep in front of shoulder, shallowingslightly around shoulder and sometimes broadening into shal-low area posteriorly; middle furrow running strongly posteriorlyfrom point anterior to shoulder, sagittal midpoint about 80percent distance posteriorly on middle body; middle body smoothand unsculptured; anterior wings flared laterally and subtrian-gular, with tiny pit near extreme lateral extent; shoulder ex-tended laterally to about half width of anterior wing; lateralborder with one or two subparallel terrace lines sometimes vis-ible; posterior border transversely straight; two small, poster-omedially directed spines set at posterolateral corners of hy-postome.Thoracic segments narrow, with fulcrum set nearer to axial

furrow than lateral margin; fulcral articulatory boss only weaklydeveloped; pleural furrow deep, shallowing abruptly near tipand near contact with axial furrow; anterior and posterior pleu-ral bands of similar length (exsag.), length remaining essentiallyeven along pleural width; pleural tip with small articulating facet

FIOURE1-Cyphaspis lowei new species, from section Avalanche Lake Five, 58-60 m above base, Delorme Group, Wenlock (Homerian, correlatedwith the Cyrtograptus lundgreni-Monograptus testis Zone of the Cape Phillips Basin, central Canadian Arctic), central Mackenzie Mountains,Northwest Territories, Canada. Magnifications are x 10, except where otherwise noted. l, 6. cranidium, UA 10384, dorsal and left lateral views;2. 7, 16, holotype, cranidium, UA 10385, dorsa!, left lateral, and anterior views; 3. 8, cranidium, UA 10386, dorsal and left lateral views; 4,9, cranidium, UA 10387, dorsal and left lateral views; 5. JO. cranidium, UA 10388, dorsal and left lateral views; 11, 13, 17, cranidium, UA10389, dorsal, left lateral, and anterior views; 12, 21, right librigena, UA 10390, dorsa! and external views; 14, 22, thoracic segment, UA10391, left lateral and dorsal views; 15, left librigena, UA 10392, external view; 18, right librigena, UA 10393, external view; 19. right librigena,UA 10394, external view; 20, right librigena, UA 10395, external view; 23, thoracic segment, UA 10396, dorsal view; 24, left librigena, UA10397, internal view; 25, left librigena, UA 10398, ventrolateral view; 26, hypostome, UA 10399, ventral view; 27. hypostome, UA 10400,ventral view, xIS; 28,31. hypostome, UA 10401, dorsal and ventral views, xIS; 29, right librigena, UA 10402, internal view; 30, left librigena,UA 10403, external view; 32, thoracic segment, UA 10404, ventral view, xIS; 33, thoracic segment, UA 10405, dorsa! view, xIS; 34, thoracicsegment, UA 10406, dorsal view, xIS; 35, right librigena, UA 10407, external view; 36. pygidium, UA 10408, ventral view, xIS; 37,39,46,48, pygidium, UA 10409, ventral, dorsa!, posterior, and left lateral views, xIS; 38.45, pygidium, UA 10410, dorsal and posterior views; 40.41,44, cranidium, UA 10411, dorsa!, anterior, and left lateral views, x20; 42. pygidium, UA 10412, dorsal view; 43, pygidium, UA 10413,dorsa! view; 47, 49, cranidium, UA 10414, dorsal and left lateral views, x20.

ADRAIN AND CHATTERTON-SILURIAN TRIWBITES 103

104 JOURNAL OF PALEONTOLOGY, V 70, NO.1, 1996

FlOURE2-1-8, Cyphaspis lowei new species, from section Avalanche Lake Five, 5~0 m above base, Delorme Group, Wenlock (Homerian,correlated with the Cyrtograptus lundgreni-Monograptus testis Zone of the Cape Phil1ips Basin, central Canadian Arctic), central MackenzieMountains, Northwest Territories, Canada. All illustrations are scanning electron micrographs. Magnifications are x 40, except where notedotherwise. I, cranidium, UA 10415, dorsal view; 2. cranidium, UA 10416, dorsal view, x 55; 3, cranidium, UA 10417, dorsal view; 4. cranidium,UA 10418, dorsal view; 5, pygidium, UA 10419, dorsal view; 6. transitory pygidium, UA 10420, dorsal view; 7. transitory pygidium, UA10421, dorsal view, x55; 8, transitory pygidium, UA 10422, dorsal view. 9-18. Cyphaspis dabrowni (Chatterton, 1971), from the TaemasFormation, Zlichovian, Locality A of Chatterton (1971), New South Wales, Australia. All illustrations are scanning electron micrographs.Magnifications are x40, except where noted otherwise. 9, cranidium, UA 10423, dorsal view; 10, cranidium, UA 10424, dorsal view; Il,cranidium, UA 10425, dorsal view, x 30; 12, 15, hypostome, UA 10426, dorsal and right lateral views; 13. right librigena, UA 10427, externalview, x 20; 14, right librigena, UA 10428, external view, x 30; 16. transitory pygidium, UA 10429, dorsal view, x45; 17, transitory pygidium,UA 10430, dorsal view, x 70; 18, right librigena, UA 10431, external view, x 37.

on anterior band, lateral to and behind which are developed 5-6 short spines; axial furrow shallow; ring furrow deep; articu-lating half ring only slightly shorter (sag.) than axial ring; axialring lacking dorsal sculpture; thoracic axial spine very long,extending posteriorly past pygidium of articulated exoskeleton.Pygidium with length (sag., excluding articulating half ring)

40-45 percent of width; axial furrows shallow but meeting pos-teriorly to fully define axis; three axial rings defined, faint fourthoften merged with terminal piece; only first ring furrow well

defined, with small pseudoarticulating half ring; axial rings withtwo to four prominent transversely aligned tubercles; first threepleural segments defined, becoming increasingly faint posteri-orly, fourth sometimes weakly defined; first intrapleural furrowwell expressed; first interpleural furrow less so, and successivefurrows progressively shallower; posterior pleural bands withfour or five transversely aligned tubercles of similar size to thoseof respective axial rings; all furrows terminating at very narrowbut distinct border; doublure broadest anteriorly, extending sag-

ADRAIN AND CHATTERTON-SILURIAN TRILOBITES

ittally almost to rear of axis, with several subparallel terracelines aligned with posterior margin; pygidium with considerabletransverse flexure, describing shallow inverted "V" shape inposterior view.Discussion.-Comparisons with other new species are given

below. In addition to these taxa, the lower Homerian Cyphaspislowei is also similar to the English Wenlock C. elachopos. andto the Australian Ludlow C. horani. Most of the C. elachoposspecimens (Thomas, 1978, plate 7, figures 5, 8-13) are to somedegree flattened. The species has a maximum possible strati-graphic range from mid-Sheinwoodian to lower Ludlow. Thishas to some extent been maximized to account for poorly lo-calized museum collections (Thomas et aI., 1984), and is unlikeanything observed in well-controlled northern Laurentian col-lections. Nevertheless, on the basis of the published sample,there is no reason to suspect more than one taxon is involved.Cyphaspis lowei appears to be distinguished from C. elachoposin the possession of a sagittally shorter glabella, smaller LI,more slender genal spine, and seemingly more tuberculate py-gidium. In addition, the thoracic axial rings of C. elachoposoften have fairly prominent transversely aligned tubercles (Tho-mas, 1978, plate 7, figures 5, Il, 12), while those of C. loweiare smooth (Figure 1.22, 1.23, 1.33, 1.34). Some of these dif-ferences might be due to the poorer preservation of the Englishmaterial. On balance, however, the species, while similar, seemdistinct.Cyphaspis horani (see Chatterton, 1971, plate 24, figures 1-

6; Chatterton and Campbell, 1980, plate Il, figures 13, 14) isknown mainly from ventral morphology, but the lectotype isan external mold of an articulated dorsal exoskeleton. Again,comparison with C. lowei is hampered by different styles andquality of preservation. Cyphaspis horani, however, appears tobe distinguished in the possession of a longer, less tuberculatelibrigenal field, more slender genal spine, and relatively widerpygidium.Etymology. -After Kevin Lowe.Material. -Holotype cranidium UA 10385 (Figure 1.2, 1.7,

1.16); paratypes UA 10384, 10386-10422. All from sectionAvalanche Lake Five, 58-60 m above base, Delorme Group,Wenlock (lower Homerian, correlated with Cyrtograptus lund-greni-Monograptus testis Zone of Cape Phillips Basin, centralCanadian Arctic), central Mackenzie Mountains, NorthwestTerritories, Canada.

CYPHASPIS DABROWNI (Chatterton, 1971)Figure 2.9-2.18

Otarion (Otarion) dabrowni CHATIERTON, 1971, p. 67, pI. 17, figs. 1-37, pI. 18, figs. 13-32; CHATIERTON, JOHNSON, AND CAMPBELL, 1979,p.81O.

"Otarion" dabrowni Chatterton. THOMAS, 1978, p. 31.Otarion (Cyphaspis) dabrowni Chatterton. PRIBYL AND VANÉK, 1981,p.175.

Cyphaspis dabrowni (Chatterton). CHATIERTON AND WRIGHT, 1986, p.284.

Diagnosis.-Emended from Chatterton (1971, p. 67). Preg-labellar field very short; glabella strongly inflated, with narrowsmooth band around anterior base, directly above preglabellarfurrow; LI very small; librigenal field small in area; eye tall;genal trunk swollen and inflated; faint furrow and tubercle rowon dorsal aspect oflong genal spine; pygidium with typical threesegments bearing transverse tubercle rows, often partially ef-faced posteriorly.Discussion. -Chatterton (1971) has discussed this species, but

so much new information about the group is now available thatan updated assessment is possible. We illustrate additional newmaterial to emphasize the stability and pervasiveness of the

105

basic Otarionini meraspid anatomy (see Adrain and Chatterton,1994, figure 1.3).Material.-Topotype specimens UA 10423-10431, from the

Taemas Formation, Zlichovian, locality A of Chatterton (1971),New South Wales, Australia.

CYPHASPIS MUND new speciesFigure 3

Diagnosis. - LI large (for genus); glabella only moderatelyinflated and elongate; occipital node retained as very short spinein holaspid; librigenal field relatively narrow; lateral border broad,broadening anteriorly, wider than posterior border; genal spinestout; pygidium with three axial rings, indistinct fourth; trans-verse tubercle rows on axial rings and on both posterior andanterior pleural bands.Description. - This species is so similar to Cyphaspis lowei

that description is best accomplished through differential di-agnosis, listing all perceived contrasts.Interocular fixigenae slightly broader; glabella slightly longer

and less inflated, with slightly coarser tuberculate sculpture; LIlarger; occipital node retained as short spine versus more sub-dued tubercle; librigenal field narrower, with slightly sparser andcoarser tuberculate sculpture; lateral border broader; genal spinestouter and less curved; transverse tubercle rows present onanterior pleural bands of pygidium, versus at most one or twoabaxially set tubercles.Discussion. - Cyphaspis munii is compared with C. buchber-

geri and C. mactavishi below.Cyphaspis munii is the oldest known member of the genus.It occurs together with Otarion huddyi Adrain and Chatterton,1994. Given the close similarity of these species (see above andAdrain and Chatterton, 1994), the basis for association of scle-rites must be outlined. I. The most straightforward means ofassociating Cyphaspis sclerites is reference to the morphologyof species that do not occur with close relatives with which theymay be confused. The species C. lowei and C. mactavishi eachoccurs as the only aulacopleurid at its respective horizon. 2.Cyphaspis munii is of rare occurrence, while Otarion huddyi isvery common. Similarly, C. buchbergeri is very rare, while O.brauni, with which it occurs, is very common. 3. While thesefactors leave little doubt about assignment of most sclerites,there is very little variation in morphology of the hypostome(cf. those of Cyphaspis lowei, Figure 1.26, 1.27, 1.31, with thoseassigned to Otarion huddyi Adrain and Chatterton, 1994, figure6.18, 6.19). Itdoes not seem possible to assign hypostomes withconfidence when species of either genus occur together. Thoseassigned to O. huddyi by Adrain and Chatterton were done soon the basis of the much more common occurrence of thatspecies, but they could conceivably belong to C. munii.Etymology. -After Craig Muni.Material. -Holotype cranidium UA 10432 (Figure 3.1, 3.6,

3.11); paratypes UA 10433-10446. All from section AvalancheLake Four, 126-128 m above base, Delorme Group, Wenlock(mid-Sheinwoodian, correlated with Monograptus instrenuus-Cyrtograptus kolobus Zone of Cape Phillips Basin, central Ca-nadian Arctic), central Mackenzie Mountains, Northwest Ter-ritories, Canada.

CYPHASPIS BUCHBERGERI new speciesFigure 4

Diagnosis. -Cranidium and glabella narrow and elongate; an-terior sections of facial suture nearly parallel, only gently an-teriorly divergent; glabellar tuberculation coarse; LI very low;SOvery long (sagittally, exsagittally), especially above LI, whereit is becomes a long, subtriangular smooth area; librigenal field

106 JOURNAL OF PALEONTOLOGY, V. 70, NO.1, 1996

FlOURE3 - Cyphaspis munii new species, from section Avalanche Lake Four, 126 m above base except 5 (AV 4 128 m), Delorme Group, Wenlock(mid-Sheinwoodian, correlated with the Monograptus instrenuus-Cyrtograptus ka/obus Zone of the Cape Phillips Basin, central Canadian Arctic),central Mackenzie Mountains, Northwest Territories, Canada. Magnifications: 1-14 are x 10,15-26 are x 15. l, 6,11, holotype, cranidium,UA 10432, dorsal, left lateral, and anterior views; 2, 7, cranidium, UA 10433, dorsal and right lateral view; 3, 8, cranidium, UA 10434, dorsaland right lateral view; 4, 9, JO, cranidium, UA 10435, dorsal, left lateral, and anterior view; 5, cranidium, UA 10436, dorsal view; 12, 14,right librigena, UA 10437, external and ventrolateral views; 13, right librigena, UA 10438, extemal view; 15, pygidium, UA 10439, dorsalview; 16, pygidium, UA 10440, dorsal view; 17, 18,21,22, cranidium and right librigena, UA 10441, dorsal (palpebral), right lateral, anterior,and occipital views; 19, pygidium, UA 10442, dorsal view; 20, pygidium, UA 10443, dorsal view; 23, pygidium, UA 10444, dorsal view; 24,26, pygidium, UA 10445, dorsal view with articulating half-ring held in vertical plane, and standard dorsal view; 25, pygidium, UA 10446,ventral view.

broad, with sparse tuberculation and prominent genal trunk; eyetall; pygidium broad with very strong transverse tubercle rowson axial rings and posterior pleural bands.Description. - Description is accomplished through differen-

tial diagnosis with C. lowei.

Anterior sections offacial sutures gently, versus strongly, an-teriorly divergent in front of eye; glabella with similar inflationbut longer relative to width; glabellar tuberculation much coars-er, but less dense; LI of similar size, but less inflated; SO muchlonger (sag., exsag.); eye taller; librigenal field broader; librigenal

ADRAIN AND CHATTERTON-SILURIAN TRILOBITES 107

tubercles larger but much more sparsely distributed; genal trunkprominent on external surface, versus obscure; genal spine lesscurved; pygidium broader, with much stronger transverse tu-berculation; 9-10 axial ring tubercles versus 2-5.Discussion. - Cyphaspis buchbergeri occurs together with

Otarion brauni Perry and Chatterton, 1979 (see Adrain andChatterton, 1994). The basis for sclerite associations was givenunder discussion of C. munii above.Adrain and Chatterton (1994, page 316) regarded the Irish

species Conoparia hollandi Siveter, 1989, as a possible juniorsubjective synonym of Otarion brauni, drawing attention to thefact that of the two librigenae assigned to the former (Siveter,1989, plate 17, figures Il, 14) only one was similar to those ofOtarion brauni. In light of the additional material of O. braunifigured by Adrain and Chatterton (1994), one of the few re-maining contrasts between the species is the morphology of thesecond librigena assigned to hollandi (Siveter, 1989, page 124,plate 17, figure 14). Adrain and Chatterton (1994) questionedwhether this sclerite was actually conspecific with the remainderof the Irish material assigned to hollandi. It may well be, andif so Otarion hollandi should likely be retained as a separatespecies (Siveter [personal commun.] points out also that thepreglabellar field of specimens of O. hollandi is more steeplyinclined than that of O. brauni). Nevertheless, comparison ofthe librigena in question with those of Cyphaspis buchbergeri,with which O. brauni occurs in northern Canada, reveals strikingsimilarity (see, in particular, Figure 4.1 7). These specimens havea smaller, more tuberculate librigenal field and more robustgenal spine than is typical of species of Otarion. It is possiblethat a rare species of Cyphaspis occurs in the Irish fauna, similarto the situation in many northwestern and Arctic Canadianfaunas, to which the librigena illustrated by Siveter (1989, plate17, figure 14) belongs. A much greater sample of the Irish ma-terial, particularly of librigenae, would be required to resolvethe problem.Cyphaspis buchbergeri is distinguished from C. munii in its

narrower glabella, less anteriorly divergent anterior sections offacial suture; smaller, less inflated LI; coarser glabellar tuber-culation; much longer SO; taller eye; broader, less tuberculatelibrigenal field with prominent, versus obscure, genal trunk;slightly narrower genal spine; and broader pygidium with moreprominent transverse tubercle row, but with some developmentof tubercles on the anterior pleural bands. The species is con-trasted with C. mactavishi below.Cyphaspis buchbergeri is similar in age (late Homerian) to

Much Wenlock Limestone material of C. elachopos Thomas.Nevertheless, the early Homerian C. lowei is much more similarto the English taxon.Etymology. -After Kelly Buchberger.Material.-Holotype cranidium UA 10449 (Figure 4.3, 4.7);

paratypes UA 10447, 10448, 10450-10456, from section DR,114.3-126.5 m above base, Delorme Group, Wenlock (upperHomerian, correlated with Pristiograptus ludensis Zone of theCape Phillips Basin, central Canadian Arctic), central Macken-zie Mountains, Northwest Territories, Canada.

CYPHASPIS MACTAVISHI new speciesFigure 5

Diagnosis. -Anterior sections of facial suture subparallel toslightly anteriorly convergent immediately in front of eye; in-terocular fixigenae very broad for genus; eye short; librigenalfield narrow, tuberculation very sparse; genal trunk visible neargenal angle, but very weakly expressed.Description. -Description is accomplished through differen-

tial diagnosis with Cyphaspis lowei.

Anterior sections of facial suture nearly anteriorly convergentimmediately in front of eye, in general subparallel and anteriorlydivergent only opposite anterior border, versus strongly ante-riorly divergent; preglabellar field slightly longer; interocularfixigena much broader; L I slightly larger; glabellar tuberculationslightly coarser and less dense; librigenal field narrower; manyfewer, coarser tubercles on librigenal field; genal trunk visibleversus obscured; tubercle row on at least proximal dorsal aspectof genal spine much more robust.Discussion. - Cyphaspis mactavishi is most similar among de-

scribed species to C. lowei. While the contrasts noted aboveleave little doubt that the species are separate and distinct, thepygidia are virtually indistinguishable, although the transversetuberculation of those assigned to C. mactavishi is somewhatmore robust. Cyphaspis mactavishi is distinguished from C.munii in the possession of subparallel, versus strongly anteriorlydivergent, anterior sections of the facial sutures; smaller LI;wider interocular fixigena; median occipital structure a smallnode versus a short spine; slightly narrower librigenal field withmuch sparser tuberculation; genal trunk visible versus obscure;slightly narrower lateral border; prominent, versus tiny, dorsaltubercles on proximal part of genal spine; pygidium with muchless well-developed tuberculation on anterior pleural bands.Cyphaspis mactavishi is similar to C. buchbergeri in its more

or less subparallel anterior sections of the facial sutures and itsrelatively sparse librigenal field tuberculation, with the genaltrunk visible. It is distinguished from C. buchbergeri in its widerinterocular fixigena; broader glabella; much shorter SO; shortereye; narrower librigenal field; possession of prominent dorsaltubercles on the proximal part of the genal spine versus theirapparent absence in large holaspid specimens (faint tuberclesare visible on the smaller cheek of Figure 4.17, but not on thoseof Figure 4.14, 4.15, 4.19); and much narrower pygidium.The age of the type stratum of C. mactavishi. section AV 7,

312 m, is poorly constrained (see discussion in Edgecombe andChatterton, 1993, p. lOl)o Horizon AV 7 70 m contains trilo-bites which correlate exactly with those of section AV 5 58-60m. These strata, by correlation with the trilobites of the CapePhillips Basin of the central Canadian Arctic, are lower Hom-erian (Cyrtograptus lundgreni-Monograptus testis Zone ofLenzand Melchin, 1990, 1991). The upper constraint is a conodontsample from AV 7, 430 m, which indicates a Ludlow-PiidoHassignment (Over and Chatterton, 1987; see Edgecombe andChatterton, 1993). Hence, AV 7, 312 m is maximally lowerHomerian, but more likely upper Homerian or Ludlow. Alltrilobite species recovered are unique to the interval AV 7,255.6-312.0 m. Definitely dated upper Homerian trilobites areknown from the Cape Phillips Basin, and correlate well withthose from sections DR 114.3-147.8 m (includingOtarion brau-ni Perry and Chatterton, 1979, and Cyphaspis buchbergeri n.sp.), and section AV 4, 165-248.5 m. In addition, lowermostLudlow (Lobograptus progenitor Zone) faunas have been recov-ered from the Arctic which correlate with section DR 182.9 m.Hence, if the assumption is made that the Arctic sequence oftrilobite faunas is more or less complete and accurate, the ageof section AV 7, 312 m, would be, by exclusion, Ludlow (andyounger than earliest Ludlow) to possibly early Piidoli. It shouldbe stressed however, that while the Arctic faunas are by far themost numerous and most highly resolved known from this in-terval from anywhere in the world (Adrain, 1994), whether ornot they are complete can never be known. In the absence offurther data, it remains conceivable that the horizon could ul-timately prove to be upper Wenlock or lowermost Ludlow.Etymology. - After Craig MacTavish.Material.-Holotype cranidium UA 10458 (Figure 5.2,5.3,

5.7); paratypes UA 10457, 10459-10475. All from section Av-

108 JOURNAL OF PALEONTOLOGY, V. 70, NO.1, 1996

FIOUllE 4-Cyphaspis buchbergeri new species, from section Delorme Range, 114.3-126.5 m above base, Delorme Group, Wenlock (upperHomerian, correlated with the Pristiograptus ludensis Zone ofthe Cape Phillips Basin, central Canadian Arctic), central Mackenzie Mountains,Northwest Territories, Canada. Magnifications are x 10 except where otherwise noted. I, 5, 9, 13, cranidium, UA 10447, dorsal, ventral, rightlateral, and anterior views (DR 114.3 m); 2,6, cranidium, UA 10448, dorsal and right lateral views (DR 114.3 m); 3,4, 7, holotype, cranidium,UA 10449, dorsal, anterior, and right lateral views (DR 114.3 m); 8, 12, cranidium, UA 10450, dorsal and right lateral views (DR 126.5 m);JO. 11. cranidium, UA 10451, dorsal and left lateral views (DR 114.3 m); 14. 16. right librigena, UA 10452, external and internal views (DR

ADRAIN AND CHATTERTON-SILURIAN TRILOBITES 109

F'IouIu! 5 - Cyphaspis mactavishi new species, from section Avalanche Lake Seven, 312 m above base, probably Ludlow, Delorme Group, centralMackenzie Mountains, northwest Territories, Canada. Magnifications are x 10 except where noted otherwise. 1. cranidium, UA 10457, dorsalview; 2. 3. 7. holotype, cranidium, UA 10458, dorsal, left lateral, and ventral views; 4. 9. cranidium, UA 10459, dorsal and right lateral views;5, JO, cranidium, UA 10460, anterior and dorsal views; 6,11, cranidium, UA 10461, dorsal and right lateral views, xIS; 8,3. cranidium, UA10462, dorsal and left lateral views, xiS; 12, hypostome, UA 10463, ventral view, xiS; 14. 15. cranidium, UA 10464, dorsal and left lateralview; 16. 19. right librigena, UA 10465, external and internal views; 17. left librigena, UA 10466, external view; 18. left librigena, UA 10467,external view; 20. left librigena, UA 10468, external view, xiS; 21, left librigena, UA 10469, external view; 22. right librigena, UA 10470,external view; 23.25, pygidium, UA 10471, dorsal and ventral views, xIS; 24, thoracic segment, UA 10472, dorsal view; 26, thoracic segment,UA 10473, dorsal view, xiS; 27, pygidium, UA 10474, dorsal view, xIS; 28, right librigena, UA 10475, external view, xiS.

+-126.5 m); 15. right librigena, UA 10453, external view (DR 114.3 m); 17. left librigena, UA 10454, external view (DR 114.3 m); 18, 19, rightlibrigena, UA 10455, ventrolateral and external views (DR 126.5 m); 20-23, pygidium, UA 10456, dorsal, ventral, posterior, and left lateralviews, x 15 (DR 126.5 m).

110 JOURNAL OF PALEONTOLOGY, V. 70, NO.1, 1996

alanche Lake Seven, 312 m above base, Delorme Group, prob-ably early Ludlow, central Mackenzie Mountains, NorthwestTerritories, Canada.

ACKNOWLEDGMENTSSpecimens used in this work were collected by B.D.E.C., as-

sisted by the late D. G. Perry and several students over theyears. Participation in fieldwork by J.M.A. in 1990 was sup-ported by a grant from the Boreal Institute for Northern Studies(now the Canadian Circumpolar Institute). Technical prepara-tion was funded by Natural Sciences and Engineering ResearchCouncil (Canada) operating grants to B.D.E.C. and to A. C.Lenz. We are grateful to E. N. K. Clarkson, G. D. Edgecombe,and R. Ludvigsen for reviewing the manuscript.

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ACCEPTED4 APRIL 1995