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SERPAGU,E., AND M. GNOU. 1977. Upper Silurian cephalopods fromsouthwestern Sardinia. Bollettino della Società Paleontologica Itali-ana, 16:153-196.

STOKES,C. 1838. On some species of Orthocerata. Proceedings of theGeological Society of London, 2:688-690.

TEICHERT,C. 1933. Der Bau der actinoceroiden Cephalopoden. Pa-laeontographica, Abteilung A, 78:111-230.

ZHURA VLEVA,F. A. 1978. Some Mongolian early and middle Paleozoiccephalopods. Paleontologicheskii Zhurnal, 4:67-76 (in Russian).

J. Pa/eonl .. 64(4),1990, pp. 6~14Copyright © 1990, The Paleontological Society0022-3360/90/0064-0600$03.00

--, AND Z. G. BALASHov. 1962. Systematic section of superorderActinoceratoidea, p. 214-223. In V. E. Ruzhentsev (ed.), Funda-mentals of Paleontology, Vol. V, Mollusca-Cephalopoda I. Izdate-I'stovo Akademii Nauk SSSR, Moskva (in Russian).

ACCEPTED16 FEBRUARY1990

The Department of Earth Sciences, University of Tokyo provided$750 in support ofthis article.

ODONTOPLEURA (TRILOBITA, SILURIAN), AND A METHOD OFCONSTRAINED CONGRUENCY ANALYSIS

JONATHAN M. ADRAIN AND BRIAN D. E. CHATTERTONDepartment of Geology, University of Alberta,

Edmonton, Alberta T6G 2E3, Canada

ABsrRAcr-Odontopleura (Odontopleura) arctica, a new species of odontopleurine trilobite, is described from the Canadian Arctic.A method of cladistic analysis is detailed. Parsimony analysis should be performed treating all characters as unordered. The universeof directed trees implied by the resulting rootless network(s) can then be examined and a preferred tree selected by a criterion ofcongruency. Namely, the most parsimonious directed tree that accommodates the most congruent arrangement of character-statesshould be taken as the preferred c1adogram. Since this is essentially a general congruency method operating within the constraintsof parsimony, it is termed "constrained congruency." The method is applied to the genus Odontopleura, resulting in the recognitionof two major species groups, the nominate subgenus and Sinespinaspis n. subgen. Odontopleura (Ivanopleura) dufrenoyi Barrandeis tentatively included in the genus, but considered too poorly known for cladistic analysis. Species assigned to Odontopleura(Odontopleura) include Odontopleura ovata Emmrich, Odontop/eura brevigena Chatterton and Perry, Odontop/eura (Odontop/eura)arctica n. sp., and Diacanthaspis serotina Apollonov. Species assigned to Sinespinaspis n. subgen. include Taemasaspis l/andoveryanaSnajdr, Odontopleura greenwoodi Chatterton and Perry, Odontop/eura maccal/ai Chatterton and Perry, and Odontop/eura nehedensisChatterton and Perry. Odontop/eura bambini Chatterton and Perry is tentatively placed in synonymy with Odontopleura nehedensis.The genus had a wide distribution throughout the Early and Middle Silurian, due to preferences for deep-water, distal shelf or shelf-slope transition zone habitats.

INTRODUCTION

THIS WORK describes a new odontopleurine trilobite, Odon-topleura (Odontopleura) arctica n. sp., from the Canadian

Arctic Archipelago. The six available specimens were collectedin 1953 by R. Thorsteinsson from the Marshall Peninsula (lat75°26'N; long 96005'W) on the northwest coast of CornwallisIsland (see Figure I). The specimens occur on a single slab ofargillaceous limestone, most often as external or internal molds,but in one case with the exoskeleton preserved. The sample isa glacial erratic. According to Thorsteinsson's field notes (T. E.Bolton, personal commun.), the lithology and matrix of thesample, together with its position in the glacial drift, suggestthat it was derived from the Cape Phillips Formation and thatits horizon was above the highest undoubted Ordovician grap-tolites and below the lowest undoubted Silurian graptolites. Verypoorly preserved monograptid fragments do, however, occur onthe sample, indicating a Silurian age. Hence, the block can rea-sonably be assigned to the lowermost Llandovery. The speci-mens are housed in the type collections of the Geological Surveyof Canada (abbreviated GSC).Previous work on Silurian trilobites from the Canadian Arctic

includes Whittington (1961), Bolton (1965), Perry and Chat-terton (1977), Chatterton and Perry (1979), and Thomas andNarbonne (1979). This paper represents the first Arctic recordof the genus Odontopleura Emmrich. This taxon also occurs in

the Cartadian Northwest Territories (Chatterton and Perry, 1983),the Baltic region (Bruton, 1967; Schrank, 1969), Great Britain(Thomas, 1981), southwest Ireland (Siveter, 1989), the CarnicAlps (Gaertner, 1930), the Polish Holy Cross Mountains (Tom-czykowa, 1957; see Bruton, 1968, p. 9), the southern Urals(Bruton, 1968, p. 9), Bohemia (Bruton, 1968; Snajdr, 1984b),and Kazakhstan (Apollonov, 1980). An attempt has been madeto clarify the phylogenetic relationships of the species includedin Odontopleura by means of unordered cladistic analysis. Theresulting phylogeny clearly supports a distinction between twomajor species groups, recognized as the nominate subgenus andSinespinaspis n. subgen.

METHODOLOGYThe aim of this study is not to summarize the general pro-

cedures of and justifications for cladistic methodology (manysuch review articles exist; an excellent review and introductionto the literature from a paleontological viewpoint is providedby Schoch, 1986). However, the method of cladistic analysisadopted herein differs radically from the outgroup-based pro-cedures familiar to most paleontologists. In addition, a partic-ular ontology of the term "character" is advocated. Both oftheseareas require explication.Characters. - When one has assembled and delimited the group

of taxa to be analyzed, the procedure begins by the development

ADRAIN AND CHATTERTON-CLADISTlC ANALYSIS OF TRILOBITES 601

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FIGURE /- Map showing location of the Marshall Peninsula (M.P.), from which the drift block containing the specimens described herein wascollected.

of taxonomic characters. A character is not a discrete entity,but rather a basis for comparison between taxa (see Ghiselin,1984; Colless, 1985a; Duarte Rodrigues, 1986, for discussion).Those aspects of taxa being compared are themselves not dis-crete objects ("parts": Colless, 1985a, p. 230), but rather de-scriptive statements about objects ("attributes": Colless, 1985a,p. 230). Therefore, with respect to a single (i.e., homologous)organismic "part" or "feature," one can group the study taxainto mutually exclusive classes according to their possession ofan attribute of this part. An example from the present studywill clarify the issue. Most odontopleurine trilobites have in-terior pygidial border spines, defined herein as those borderspines lying between the major border spines. "Interior pygidialborder spine" is the part. "Number of interior pygidial borderspines" is the basis for comparison, or character. Therefore "2"and "4" (i.e., "has 2," "has 4," Colless, 1985a, p. 230) are theattributes, or character-states. Some of the implications of thisontology are discussed by Ghiselin (1984) and Duarte Rodrigues(1986).It is emphasized here that characters are not inherent to the

organisms we study. Characters are something we create byspecifying a basis of comparison between attributes of homol-ogous parts of those organisms. They are subjective, not objec-tive, in nature. As Meacham (1984, p. 27) has put it: "Thecreation of a qualitative character [=character, in this discus-sion) is a complex operation that requires a great deal of bio-

logical interpretation and intuition. Because synthesis and in-terpretation are so predominant in character construction, thisprocess resembles an act of invention more than discovery."Compatibility and parsimony. -Once each study taxon has

been assigned to a particular character-state for each character,the task is to assess the best possible grouping of taxa, giventhat different groupings will likely be indicated by different char-acters. Many methods are currently advocated. One techniqueis character compatibility analysis, or clique methods (see Mea-cham, 1980, 1981, 1983, and references therein). These pro-cedures generally seek to identify the largest possible set of con-gruent characters (i.e., those whose character-state groupings ofthe study taxa are in agreement). The noncongruent charactersare then discarded, and relationships are resolved through ap-plication of parsimony to the remainder. As Farris (1983) haspointed out, use of such a technique involves assuming that ifa character exhibits any homoplasy (incongruency) whatever, itmust be homoplasious in all cases. As homoplasy increases inthe data set, more and more characters are excluded and com-patibility methods will explain an ever smaller subset of theoriginal observations (Farris and Kluge, 1979; Farris, 1983). Analternative, favored here, is the use of a cladistic, or method-ological, parsimony criterion according to the Wagner methodsformalized by Kluge and Farris (1969), Farris (1970), and Farriset al. (1970). Cladistic parsimony holds simply that homoplasyshould be minimized in tree construction. For a succinct dem-

602 JOURNAL OF PALEONTOLOGY, V. 64, NO.4, 1990

onstration that this methodological criterion is independent ofevolutionary assumptions, see Farris (1983). For an attempt toprovide a formal justification for the criterion and discussionofthe philosophical problems involved, see Sober (1983, 1985)and Felsenstein and Sober (1986).Outgroups. -Cladistic parsimony analysis conventionally

seeks a directed result. Direction is often derived through useof an outgroup criterion. In the most basic terms, this involvessome type of comparison between the ingroup and what is as-sumed to be a related monophyletic group, by means of whichthe primitive character-state for each character is specified. Ide-ally, one derives these ancestral character-states by reference tothe sister-group of the ingroup. Maddison et al. (1984) haveprovided a rigorous treatment of this type of analysis. Whatbears emphasis here is that much of their discussion is concernedwith cases in which relationships among the outgroups used areresolved. It has long been argued (e.g., Colless, 1967, 1969,1985b) that analysis under these circumstances involves circularreasoning. One analyzes the ingroup by recourse to an alreadyknown higher level phylogeny. This phylogeny, however, canonly have been derived by reference to some other prior knowl-edge (of a still higher level phylogeny), and so on in an infiniteregress.A second type of outgroup procedure escapes this charge of

circularity by dispensing with the insistence that relationshipsamong outgroups be known. In its most general invocation, thiscriterion holds that any group can be used as an outgroup foranalysis, with those character-states that occur in both the out-group and ingroup taken as primitive. Hence, the method willwork equally well regardless of the choice of outgroup, with theobvious restriction that as the phylogenetic distance betweenoutgroup and ingroup increases, homologues may become fewerin number, and the potential for homoplasy will increase. Ineffect, however, this type of analysis yields an assessment ofingroup relationships based upon the supposition that the cho-sen outgroup is in fact the monophyletic sister group of theingroup. The opinion is often expressed (e.g., Michaux, 1989,p. 22) that use of multiple outgroups will improve the analysis.If we (somehow) have knowledge of the pattern of relationshipbetween them, this may be true, according to the reasoningoutlined by Maddison et al. (1984). However, if we accept thatsuch knowledge cannot be acquired by analysis but must ratherbe asserted a priori, and choose instead this second, more gen-eral, outgroup criterion, multiple outgroups do not help at all.When the outgroup is changed, a new, different hypothesis ofsister-group relationship is in effect formulated. The central pa-rameter of the analysis, that determining polarity, has been al-tered. No consensus can be derived among the resulting phy-logenies. They have fundamentally different parametric basesand are not comparable. Support for each reduces to reexami-nation of the criteria by which the outgroup in question wasselected. Hence, under this more general invocation of the out-group criterion, additionaloutgroups simply compound uncer-tainty.From an operational viewpoint, the outgroup criterion is

sometimes difficult to invoke. Often, for a variety of reasons,no prospective outgroup may be apparent. Indeed, in the caseof many extinct groups, higher level relationships are completelyobscure, and the outgroup criterion cannot be applied.All of this is not to say that outgroups have no utility. In

some cases, there may be a mass of corroborative circumstantialevidence supporting a sister-group relationship, just as in somecases there may be a body of physical evidence supporting claimsby stratigraphic paleontologists of direct ancestry in their fossilsequences. As long as the assumptions involved are made ex-plicit, outgroup analysis may provide useful insights about in-

group relationships. The point we wish to stress is that outgroupanalysis involves making a large and restrictive a priori as-sumption of ancestry, and does not have universal applicability.Unordered analysis.-Meacham (1984, p. 27, figs. 1-3) has

identified three types of cladistic characters. The character-statesof unordered characters are not arranged in a transformationseries. There are two types of ordered characters. The character-states of undirected characters are arranged in a transformationseries, but the polarity of the series is not specified. The char-acter-states of directed characters are arranged in a polarizedtransformation series.Analysis using unordered characters is advocated here. Such

analysis will determine the most parsimonious arrangement oftaxa, given that any character-state may transform into anyother (of the same character), and that reversals are possible.No ordering or direction restrictions are placed upon the data.Such restrictions amount to a priori assumptions about rela-tionship. Rather, to use Meacham's (1984) phrase, the char-acters should be allowed to speak for themselves.However, in and of themselves, characters have nothing to

say about direction. Undirected analysis results in an undirectedtree, a minimum length Wagner Network. In order to generatea directed hierarchy, one must decide upon the position of aroot. To accomplish this, some methodological assumption isnecessary. One alternative is to apply the outgroup criterion.With a hypothetical ancestor in hand, one can either include itin the unordered analysis and place the root at the terminal nodeoccupied by it, or use the procedure advocated by Lundberg(1972), in which the ancestor is excluded from the analysis, butused to root the Network by determining the position at whichit achieves the most parsimonious fit. If outgroups are to beused, the second is clearly the less restrictive, most assumption-free, and most parsimonious (Farris, 1982) option. If not, whatthen are the options for ingroup analysis?Ontogeny. -Ontogenetic generality criteria may provide im-

portant and useful ways of producing ordered characters. Ob-viously, they require knowledge of development. To the extentthat detailed knowledge of ontogenetic development is generallyunavailable in paleontology, ontogenetic criteria are oflimitedapplication. Of course, to the extent that such information isavailable, for example in many trilobite groups, these criteriaare relevant and useful, and the reader is referred to Weston(1988) for a recent review.Patterson's method. - Patterson (1988) has suggested that what

he terms "general congruence" is the best method of ingroupanalysis. This is described (Patterson, 1988, p. 74) as " ... de-manding that the information within the character set dictatesthe polarity of characters." This is the central theme of thepresent paper: the best initial idea of relationship, and the mostassumption-free cladogram, is that derived solely from analysisof ingroup morphology.Patterson (1988, p. 74) noted that for n study taxa, there are

2n - (n + 2) possible "cladistically informative characters"(hereafter abbreviated CIe). A CIC is one that defines a subsetof the study taxa. Here, any character-state in which two ormore study taxa have membership corresponds to a CIe. For

n

n ~ 2 study taxa, there are fi (2k - 3) fully resolved cladogramsk-2

(Cavalli-Sforza and Edwards, 1967; Felsenstein, 1978). Patter-son's (1988) method is to examine all possible rooted clado-grams for the study taxa, and to score them for the number ofCIC that they accommodate. His favored cladogram is the high-est scoring.This method, however, may yield an unparsimonious result.

Ifa CIC does not fit the highest scoring cladogram at some point

ADRAIN AND CHATTERTON-CLADISTIC ANALYSIS OF TRILOBITES 603

as a unique and unreversed synapomorphy-i.e., if it demon-strates some homoplasy-it is entirely ignored, and thereforeassumed to be homoplasious in all occurrences. This is a formof compatibility analysis, as Patterson (1988, p. 77) readily ad-mits. Compatibility analysis, as stated above, explains less datathan cladistic parsimony analysis as homoplasy in the data setincreases.Method employed.-Patterson's (1988) goal, that the clado-

gram be derived solely from ingroup data, is endorsed. Ratherthan accommodating the most congruent arrangement of char-acter-states possible, however, it is argued that the primary con-sideration should be that the preferred cladogram is as parsi-monious as possible. Unordered analysis will result in one or anumber of maximally parsimonious Wagner Networks. Con-gruency can then be used to select a preferred cladogram fromthe family of trees implied by these networks.An important point here is that the tree chosen by congruency

scoring all possible rootings of a given network (a network withn terminal nodes has 2n - 3 possible root positions) is equiv-alent to that derived by placing the root on the longest branchofthat network (i.e., the branch across which the greatest num-ber of character transformations are required), assuming branchlengths are unambiguous for the topology being considered.Hence, if analysis yields a single most parsimonious network,the preferred cladogram is immediately obvious, as it is thatderived from a root positioned on the longest branch of thatnetwork. If there are multiple equally parsimonious networks,the competing candidates for the final cladogram are the longestbranch rooting of each. These competing cladograms can thenbe congruency scored, and the highest scoring taken as the finalcladogram. In the case of a tie, a consensus tree may be derivedaccording to a variety of available techniques (see Kluge, 1989,for a summary).Patterson (1988) used congruency to determine final tree to-

pology. Here, tree topology is constrained by the criterion ofparsimony. The preferred c1adogram is that which accommo-dates the maximally congruent arrangement of character-states,given that its topology requires also the fewest possible numberof character transformations. We therefore propose to refer tothis method as "constrained congruency."Unordered analysis is inherently more likely to produce mul-

tiple equally parsimonious networks than ordered or directedtechniques, since it imposes no restrictions upon the types ofcharacter transformations possible. Constrained congruency isa methodological criterion for deriving a limited number ofdirected trees from a larger number of undirected networks, bymaximizing the number of unambiguous synapomorphies unit-ing taxa.Finally, we note that although we prefer herein to treat all

characters as unordered, and to select final cladograms by thecriterion of constrained congruency, we do not deny that as-sumptions about ancestral states may often contribute impor-tant elements to a phylogenetic analysis. In our opinion, how-ever, such assumptions should be made only when there is astrong and explicit reason to do so. Blanket hypotheses of prim-itiveness of the sort required by directed outgroup analysis areundesirable.The constrained congruency method can be outlined as fol-

lows.Step I. Create a character matrix, assigning membership in

character-states as described above.Step 2. Run the data as an unordered analysis to obtain a

rootless Wagner Network (or a number of equally parsimoniousWagner Networks) for the study taxa.Step 3. Ifa single network is obtained, choose the tree obtained

by rooting the network on its longest branch. Ifmultiple net-

TABLE1-Characters used in congruency analysis of Odontopleura.Notethat the states 0, I, and 2 carry no connotations of polarity.

CranidiumI. 3L glabellar lobe: 0, absent; I, defined ventrally only; 2, definedboth ventrally and dorsally.

2. longitudinal furrow at posterior of IL glabellar lobe: 0, very shallow,IL lobe confluent with median glabellar lobe; I, deep, separatingIL from median glabellar lobe.

3. axial furrow at anterior of IL glabellar lobe: 0, very shallow, ILlobe confluent with fixed cheek; I, deep, separating IL lobe fromfixed cheek.

4. occipital lobe: 0, absent, sometimes with ventral trace of furrow;I, weakly defined; 2, strongly defined.

5. occipital furrow: 0, deep; I, shallow and broad; 2, indistinct.6. transverse distance of eye from IL glabellar lobe: 0, subequal towidth of IL lobe; I, greater than width of IL lobe.

7. length of OR spines/sagittallength of cranidium: 0, Op absent; I,less than 0.55; 2, greater than 0.80.

8. position of O.P spines: 0, O.P absent; I, distinctly posterior to me-dian occipital spine; 2, approximately lateral to median occipitalspine.

9. anterior facial suture: 0, short, subparallel to convergent opposite2L glabellar lobe; I, long, convergent opposite 2L glabellar lobe; 2,long, distinctly divergent opposite 2L glabellar lobe.

10. length of posterolateral most cranidial marginal spine: 0, absent; I,short; 2, long, extending opposite middle of 2nd thoracic segment.

II. sagittal length from anterior margin to median occipital spine baselsagittal length of cranidium: 0, 0.97-1.0; 1,0.89-0.95; 2, 0.86-0.87.

Free Cheek12. length of genal spine (measured as straight line from tip to base)1

length of remainder of free cheek (measured as straight line frombase of genal spine to anterior end of facial suture): 0, 0.61-0.63;I, greater than 0.88.

13. number of border spines on lateral aspect of genal spine: 0, I; I, 2.14. course of posterior facial suture: 0, reentrant (doublural) part not

aligned with posterodorsal part; I, posteroventral and posterodorsalparts aligned.

15. cephalic border spines at anterior of free cheek: 0, reduced to smalldenticles posterior to contact with anterior facial suture; I, persistas well defined spines to contact with anterior facial suture.

Thorax16. length and shape of anterior pleural spine on 9th thoracic segment:

0, long and tapering; I, very short, barb-like.Pygidium17. number of pairs of exterior pygidial border spines (dominant num-

ber in boldface): 0, 3-4; I, 4-5.18. number of interior pygidial border spines: 0, 2-3; I, 4.19. length of major border spineslexsagittallength of pygidium mea-

sured directly anterior to them: 0, less than 2.2; I, 2.4-2.5; 2, greaterthan 2.8.

20. sagittal length pygidiumlmaximum width pygidium: 0, 0.30-0.36;1,0.23-0.27.

21. 2nd ring furrow: 0, absent; I, present.22. shape ofpygidial outline: 0, subsemicircular; I, subtriangular.

works are encountered, examine the longest branch rootings ofeach, and score for the number of unique synapomorphies ac-commodated. This is accomplished by examining each node,and scoring for the number of character-states that include allof the taxa encompassed by that node, and exclude all of thetaxa not encompassed by that node (see Patterson, 1988).Step 4. Choose the highest scoring cladogram. If multiple

cladograms have an equally high score, the final cladogram canbe derived by a variety of available consensus techniques (seeKluge, 1989).

ANALYSIS OF ODONTOPLEURA

Data. - The characters and character-states used to code forunordered analysis of Odontopleura are shown in Table I. Thesources consulted for coding are listed in Table 2. Table 3 givesthe character matrix used in the analysis. Note that while O.

604 JOURNAL OF PALEONTOLOGY, V 64, NO. 4, 1990

TABLE 2 -Species and sources used in congruency analysis of Odonto-pleura.

Odontop/eura ovata Emmrich, 1839Bruton (1967, PI. 30, fig. I; 1968, PI. I, figs. 1-4,6,7)Schrank (1969, PI. I, figs. 1-7, PI. 2, figs. 1-5)Siveter (1989, PI. 20, figs. 1-7, 11-21, PI. 21, figs. 1,3,4,8)

Odontopleura brevigena Chatterton and Perry, 1983Chatterton and Perry (1983, PI. I, figs. 1-34)

Odontop/eura (Odontopleura) arctica n. sp.Figure 7.1-7.6

Diacanthaspis serotina Apollonov, 1980Apollonov (1980, PI. 30, figs. 1-5)

Odontopleura greenwoodi Chatterton and Perry, 1983Chatterton and Perry (1983, PI. 2, figs. 1-20, PI. 3, figs. 28-43)

Odontop/eura maccallai Chatterton and Perry, 1983Chatterton and Perry (1983, PI. 4, figs. 17-37)

Taemasaspis l/andoveryana Snajdr, 1975Snajdr (1975, PI. I, fig. 6, PI. 2, fig. 7; 1978, PI. 7, figs. 1-12, PI. 8,figs. 9-11, 13, 14, PI. 12, fig. 3)

Odontopleura bambini Chatterton and Perry, 1983Chatterton and Perry (1983, PI. 4, figs. 1-16)

Odontopleura nehedensis Chatterton and Perry, 1983Chatterton and Perry (1983, PI. 3, figs. 1-27)

(Sinespinaspis) bombini is placed in tentative synonymy withO. (S) nehedensis below, the taxa are treated separately forpurposes of analysis. Some ofthe characters and character-statesare illustrated and contrasted in Figures 2-4. The data were runon Swofford's (19 85) PAUP program, treating all multistate (i.e.,nonbinary) characters as unordered. Midpoint rooting was used,an option that roots the calculated Wagner Network at the mid-point of its longest branch, thereby determining the candidatetrees for the choice of preferred cladogram.Results. -Analysis yielded seven equally parsimonious Wag-

ner Networks, each with a consistency index of 67.4 percent.This statistic was developed by Kluge and Farris (1969) and isa measure of the range of the data (the sum of the minimumnumber of character transformations implied by the data) di-vided by the length of the Network (the number of transfor-mations required for the maximally parsimonious topology).When the seven candidate cladograms were congruency scored,two were found to be highest scoring, each accommodating 15of the CIC's. These alternatives are shown in Figure 5. Notethat they differ only in the relative positions of O. (Odonto-pleura) ovata and O. (Odontopleura) brevigena. The possiblecharacter-state assignments for the nonterminal nodes of eachof the alternative cladograms are given in Tables 4 and 5. The

consensus cladogram derived from the two maximally con-gruent rootings is shown in Figure 6, and should be taken asthe most favored hypothesis of relationship as determined bythe parameters of this study.Discussion. - The analysis reveals two major species groups,

each characterized by a suite of diagnostic features, and sepa-rated in the analysis by a branch length of 10. Each would appearto represent a natural phyletic group, and a distinction is thusmade at the subgeneric level between the nominate subgenusand Sinespinaspis n. subgen. A major question, which this anal-ysis has not attempted to resolve, is whether or not the subgenerado in fact constitute sister taxa. If the study group is monophy-letic, they do. In order to test this, it would be necessary toinclude in the analysis various species from what are assumedto be closely related genera.

SYSTEMATIC PALEONTOLOGY

Terminology. -One new term is introduced. Whittington(1956) and subsequent authors have used the term Op to referto a spine pair on the occipital ring. Whittington's example(1956, fig. l) was a Degree zero meraspid cranidium of Api-anurus barbatus Whittington. The intention, presumably, wasthat the holaspid occipital spine pair that develops from thisjuvenile pair should be called Op. However, a distinction isrequired in many odontopleurine genera, including Odonto-pleura and Diacanthaspis, between the large abaxial occipitalspines and a pair of smaller adaxially placed occipital spines.This latter pair would appear to represent the serial homologuesof the major spine pairs found on the thoracic axes, at least inOdontopleura (Odontopleura) arctica (see Figure 7.1, 7.2, 7.4).Hence, this pair likely developed from the pair present in earlyontogeny on the occipital ring, and strictly speaking should becalled Op. However, we do not wish to create confusion byaltering the traditional descriptive function of the term Op byinsisting on a strict interpretation of homology, since in somecases whether or not the prominent occipital spines are serialhomologues of the thoracic axial pairs is not immediately ob-vious. Therefore, whenever there occurs a prominent occipitalspine pair, we suggest it should be referred to as Op. Wheneverit encloses a less prominent pair as in Odontopleura (Odonto-pleura), or whenever a nonprominent pair occurs in isolationas in some species of O. (Sinespinaspis), the less prominent pairshould be referred to as Oap, designating paired axial-occipitalspines (see Figure 2).The following terms are used to distinguish between pygidial

border spines. The "major border spines" are those that runfrom the pleural ribs derived from the first axial ring, regardlessof their length. The "exterior pygidial border spines" are thosethat occur laterally to the major border spines. The "interiorpygidial border spines" are those that occur between the majorborder spines.

TABLE 3-Character matrix for congruency analysis of Odontop/eura. ? = missing data.

Character

I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22

ovata 2 0 0 2 I 0 2 I I I 2 I 0 0 0 0 I I I 0 I 0bervigena I 0 0 I I I I I I I 2 0 0 0 0 0 I I I I 0 0arctica I 0 0 I 1 I 2 I 2 2 2 I 0 0 0 0 0 I 2 I 0 0serotina I 0 I I I I 2 I 2 ? 2 1 0 0 0 ? 0 I 0 0 0 0greenwoodi 0 1 0 I 2 I 0 2 I I I 1 I I I I I I I 0 0 1maccallai 0 0 0 1 I 1 0 0 0 0 I 0 0 I I I 1 0 ? 0 0 Illandoveryana 2 I I 2 0 0 0 0 0 0 0 ? 0 ? I I 0 I 0 I 1 Ibombini 0 I I 0 2 0 0 2 0 0 0 0 0 I I I 0 0 0 0 0 Inehedensis 0 0 I 0 2 0 0 2 0 0 1 0 0 I I I 0 0 ? 0 0 I

ADRAIN AND CHATTERTON-CLADISTIC ANALYSIS OF TRILOBITES

I10

1

605

1

2FIGURE2-1, dorsal view ofcranidium ofOdontop/eura (Odontop/eura) brevigena Chatterton and Perry, x9. 2,dorsal view ofcranidium ofOdontop/eura (Sinespinaspis) greenwoodi Chatterton and Perry, x Il. Numbers refer to characters listed in Table I. The character-states illustratedabove, given as character (brevigena state/greenwoodi state), are: I (I/O), 2 (0/1), 3 (0/0), 4 (I/I), 5 (II2), 6 (I/I), 7 (I/O), 8 (112), 9 (I/I), 10(I/I), II (2/1).

Family ODONTOPLEURIDAEBurmeister, 1843Subfamily ODONTOPLEURINAEBurmeister, 1843

Genus ODONTOPLEURAEmmrich, 1839Type species.-Odontopleura ovata (Emmrich, 1839, p. 53;

from a Graptolithengestein glacial erratic of late Wenlock toearly Ludlow age, Nieder Kunzendorf, Silesia. By monotypy.Diagnosis. -Odontopleurine trilobites with large 1Land 2L

lobes; eyes small, non pedunculate, set opposite middle or rearof IL lobe, usually separated from glabella by at least width ofIL; 3L lobe rudimentary to absent; occipital lobes moderatelydeveloped to absent; large paired occipital spines may be pres-ent; numerous cephalic border spines (at least 15 on each freecheek), increasing in length posteriorly, at least posteriormostborder spine occurring on lateral aspect of genal spine; genalspine slender, curved, length measured as straight line from tipto base slightly shorter to longer than length of free cheek mea-sured as straight line from base of genal spine to anterior endof facial suture; thoracic segments with long to short tubularanterior spines and long, slender posterior spines; usually threedominant spine pairs on thoracic pleurae and a single dominantpair on rachis; second ring furrow of pygidium usually absent;2-4 (rarely more) subequal interior pygidial border spines; 3-5

1

(rarely 2) pairs of exterior pygidial border spines; major pygidialborder spines long and slender.Discussion. - Whittington (1956) compared Odontopleura to

Leonaspis, and later (1959, p. 0504) provided a diagnosis forOdontopleura. Chatterton and Perry (1983) emended this di-agnosis to accommodate the Llandovery species they assignedto the genus. Their diagnosis is itself emended above to reflectthe concept of Odontopleura adopted in this paper.Prantl and Pi'ibyl (1949), in a major revision of odontopleurid

trilobites, recognized only two species of Odontopleura, O. ovataEmmrich, 1839, from the Bohemian and Baltic Wenlock andLudlow, and O. dufrenoyi Barrande, 1846, from the BohemianWenlock. Snajdr (1979) rehabilitated O. prevosti Barrande, 1846,in a short note that referred to a single pathological specimen.Odontopleura prevosti had previously been considered a syn-onym of o. ovata by Prantl and Pi'ibyl (1949) and Bruton (1968).Chatterton and Perry (1983) described a new Wenlock speciesfrom the Canadian Northwest Territories, O. brevigena, togetherwith four Llandovery species that they considered best fit in anexpanded concept of Odontopleura. These workers also pro-posed that Taemasaspis llandoveryana Snajdr, 1975, from thelate Llandovery of Bohemia, be assigned to Odontopleura. Snajdr

15 12

14 TI

2FIGURE3-1, external view of free cheek of Odontop/eura (Odontop/eura) brevigena Chatterton and Perry, x9. 2, external view of free cheek ofO. (Sinespinaspis) macca//ai Chatterton and Perry, x 13. Character-states, given as in Figure 2, are: 12 (0/0), 13 (0/0), 14 (0/1), 15 (0/1). Inset,schematic cross sections taken just forward from the genal spine base, to illustrate character 14, demonstrating the nonaligned (3.1) and aligned(3.2) states of the opposing aspects of the posterior facial suture.

606 JOURNAL OF PALEONTOLOGY, V. 64, NO.4, 1990

1 2FIGURE4-1, dorsal viewof posterior thoracic segmentof Odontop/eura(Odontop/eura) brevigena. x 2. 2, dorsal view of posterior thoracicsegment of O. (Sinespinaspis) nehedensis, x2. States of character 16,given as in Figure 2, are (0/1).

(l984a) removed O. dufrenoyi from the genus and grouped itwith the Llandoverian Miraspis rarissima Snajdr, 1975, in thenew genus Ivanopleura. Snajdr (I984b) undertook a revision ofthe Bohemian representatives of Odontopleura, and where Bru-ton (1968) had recognized two species, O. ovata and O. dufre-noyi, Snajdr (1984b) now proposed or rehabilitated no fewerthan 13 species and subspecies names, but did not recognize.with certainty the occurrence of O. ovata. The specimen thatSnajdr (1979) had originally used to rehabilitate O. prevosti henow referred to a new species, O. sa/ma, while at the same timeproposing four subspecies for O. prevosti. Piibyl et al. (1986)considered the material assigned by Snajdr (1975, 1978) to Tae-masaspis llandoveryana to belong to both Primaspis (Meadow-townella) Piibyl and Vanek, 1965, and Odontopleura. Siveter(1989) placed most of the taxa introduced or rehabilitated bySnajdr (1984b) in synonymy with Odontopleura ovata, and con-sidered Ivanopleura to be a subgenus of Odontopleura.Almost all of the Bohemian material is compacted, resulting

in the loss of some surface detail and making taxonomy prob-lematic. Snajdr's (I984b) proposals are difficult to accept. We

believe, in agreement with Siveter (1989), that most of the namesproposed or rehabilitated by Snajdr (I984b) should be consid-ered synonyms of O. ovata. Almost all are based upon littlemore than subjective assessments of spinosity, often betweenspecimens from the same or equivalent horizons. We furtherquestion the validity of the lower Ludlow O. palava Snajdr,1984b. Siveter (1989, p. 142) accepted this species because of"the general lack of glabellar granules except for the larger pairedgranules .... " However, Snajdr (I984b) erected this taxon onthe basis of five incomplete cranidia, and of the two figured,this lack of glabellar ornament is only distinct on the holotype(Snajdr 1984b, PI. I, fig. 8). The major paired spines dominate,but other spines and tubercles are clearly present, and the spec-imen shows some evidence of abrasion. The other figured spec-imen seems to have plenty of accessory granules on its glabella.With nothing known of the rest of the trilobite, these late rep-resentatives of the genus are not demonstrably distinct from O.ovata, and should probably be referred to that taxon. In anycase, the very brief descriptions and paucity of illustrations oftaxa given by Snajdr (1984a, I984b) make his proposals difficultto incorporate into detailed comparative studies.

Subgenus IVANOPLEURASnajdr, 1984Type species. - Odontop/eura dufrenoyi Barrande, 1846, from

the Liten Formation (upper Wenlock, Monograptus flexilis toM. testis zones), Svaty Jan pod Skalou, Lodenice, and Sedlec,Czechoslovakia.

ODONTOPLEURA(IvANOPLEURA)DUFRENOYIBarrande, 1846

Odontop/eura Dufrenoyi BARRANDE,1846, p. 56.Odontop/eura dufrenoyi Barrande. BRUTON,1968,p. 9, PI. I, figs.5, 10(with synonymy).

Miraspis rarrissima Snajdr. SNAJDR,1975, p. 315, PI. 2, fig.4; SNAJDR,1978, p. 32, PI. 10, figs. 4-8, PI. 12, fig. 10; PRIBYL, VANEK.,ANDHÖRBINGER,1986, p. 267~ _

Leonaspis pokornyi Snajdr. SNAJDR,1975, p. 315, PI. 2, fig.8; SNAJDR,1978, p. 35, PI. 9, Figs. 15-18.

1vanop/eura dufrenoyi (Barrande). SNAJDR,1984a, p. 50, PI. I, Figs. 1-4 (with synonymy).

1vanop/eura rarissima (Snajdr). SNAJDR,1984a, p. 50, PI. I, figs. 5, 6,PI. 2, figs. 1,2.

FIGURE5-1,2, two preferred trees of the 105 possible c1adogramsfor the seven most parsimonious networks. Numbers on branches indicatebranch lengths. Numbers beside each node indicate number of CIC (see text) accommodated at that node. Large numbers beside c1adogramsindicate total number ofCIC's accommodated. Consistency index for each c1adogramis 67.4 percent. Note that c1adogramsdifferonly in theirrelative placement of Odontop/eura (Odontop/eura) brevigena and O. (O.) ovata.

ADRAIN AND CHATTERTON-CLADISTIC ANALYSIS OF TRILOBITES 607

FIGURE 6-1, numbering of internal nodes of ciadograms in Figure 5.1, 5.2, for listing of possible character-state assignments, given in Tables 4and 5. 2, consensus c1adogram derived from c1adograms of Figure 5.1, 5.2.

Discussion. -Snajdr (1984a) erected Ivanopleura to accom-modate Odontopleura dufrenoyi Barrande and Miraspis raris-sima Snajdr. Siveter (1989, p. 137) expressed the opinion thatin overall morphology these species so resembled Odontopleurathat Ivanopleura was best considered a subgenus ofthat genus.We are of the opinion that similarities between the taxa havelong been overestimated. With no new information to add, how-ever, we follow Siveter (1989) and place Ivanopleura withinOdontopleura (but see section on paleoecology and paleogeog-raphy below). As is evident from the above synonymy, thereappear to be no objective differences between O. (/.) dufrenoyiand the marginally older (latest Llandovery versus earliest Wen-lock) Miraspis rarissima Snajdr. Snajdr (I984a) separated thespecies only by relative spinosities of the cephalon and dimen-sions of the pygidium. Miraspis rarissima is regarded here as asubjective junior synonym of O. (/.) dufrenoyi.Despite the lengthy taxonomic history of this species, it re-

mains unsatisfactorily known. The specimens referred to it aregenerally incomplete cranidia and pygidia or severely abradedarticulated individuals. That at least most of the cranidia belong

together and represent a single distinct species seems certain.The following characters serve to distinguish 0. (I.) dufrenoyifrom other species included in Odontopleura. The fixed cheeksare very narrow, and the eye is positioned less than the widthofthe IL glabellar lobe from the glabella. The cephalic ornamentconsists of large, sparsely distributed tubercles, with the pairedglabellar spines identifiable and occasionally prominent, where-as in mature holaspids of other Odontopleura species, the pairedglabellar spines are indistinguishable from accessory glabellarspines and tubercles. There are strongly divergent Op spines.The 0ap spines occur lateral to the median occipital spine, onthe axes of the Op spines. This contrasts with the condition inO. (Odontopleura), where the Oap spines are invariably placedposteriorly to the median occipital spine, and between the Opspines.

Subgenus ODONTOPLEURA Emmrich, 1839Type species. -As for genus.Species included. -Odontopleura ovata Emmrich, 1839, from

the upper Llandovery to lower Ludlow of Europe; 0. brevigena

TABLE4-Possible character-state assignments for nonterminal nodes of c1adogram of Figure 5.1. Nodes are numbered from left to right, asshown in Figure 6.1. When more than one character-state is possible, the choices are shown vertically.

Characters

Node I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22I 2 I I 0 2 0 I I 2 0 I 0 I 0 0 0 0 0 0 0

2 I I2

2 I I 2 I I 0 I 0 I I 2 0 I I I 0 I 0 0 0 0 0I

3 0 I 2 I I 0 I 0 I 1 2 0 I I I 0 I 0 0 0 0 0I2

4 0 I 0 I I 0 I 0 0 I I 0 I 1 I 0 I 02 I I

25 0 I 0 I I 0 0 0 0 0 I 0 0 1 0 0 0 0

2 I 2 I I6 0 0 0 0 0 0 0 I 0 0 I 0 0 0 0 0 0 0

I I I 2 I2 2

7 0 0 0 2 0 0 0 I 2 0 0 0 0 0 0 0 0 0I

608 JOURNAL OF PALEONTOLOGY, V. 64, NO.4, 1990

TABLE5-Possible character-state assignments for the nonterminal nodes of the c1adogramof Figure 5.2. Format as in Table 4.

CharactersNode I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22

I 2 I I 0 2 0 I I 2 0 I 0 I 0 0 0 0 0 0 02 I

22 I I 2 I I 0 I 0 I I 2 0 I I I 0 I 0 0 0 0 03 I I 0 I I 0 I 0 I I 2 0 0 I I 0 I 0 0 0 0 0

I I2

4 0 I 0 I I 0 I 0 0 I I 0 0 I I 0 I 02 I I I

25 0 I 0 I I 0 0 0 0 0 I 0 0 I 0 0 0 0

2 I 2 I I6 0 0 0 0 0 0 0 I 0 0 I 0 0 0 0 0 0 0

I I I 2 I7 0 0 0 2 0 0 0 I 2 0 0 0 0 0 0 0 0 0

I

Chatterton and Perry, 1983, from the Wenlock of the MackenzieMountains, Northwest Territories, Canada; O. (O.) arctica n.sp., from the lowermost Llandovery of the Canadian ArcticArchipelago; Diacanthaspis serotina Apollonov, 1980, from thelowermost Llandovery of Kazakhstan.Diagnosis. -Species of Odontopleura with Op developed lat-

erally to Oap;Oappositioned distinctly posterior to median oc-cipital spine; 3S glabellar furrow visible at least ventrally; me-dian occipital spine placed distinctly forward from posteriorborder of cranidium, separated from posterior border by dis-tance greater than one width of median occipital spine; pos-teroventral (doublural) part of posterior facial suture not directlyopposite posterodorsal part; sutural ridge along posterior facialsuture on free cheek faint to absent; cephalic border spines onfree cheek reduced to small denticles posterior to contact withanterior facial suture; anterior pleural spines elongate and ta-pering, especially on posterior thoracic segments; pygidium dis-tinctly rounded and subsemicircular in ventral outline.Discussion. - Members ofthis subgenus can be readily distin-

guished from those of O. (Sinespinaspis) n. subgen. by theirpossession of Op spines, anteriorly positioned median occipitalspine, nonaligned posterior facial suture, denticulate as com-pared with fully developed anterior free cheek border spines,faint to absent as opposed to strongly developed sutural ridgealong posterior facial suture on free cheek, long as opposed toshort and barb-like anterior pleural spines, and subsemicircularas opposed to subtriangular pygidium (see Figures 2-4).Diacanthaspis laokuangshanensis Lu and Chang, 1974, from

uppermost Ashgill strata of Sichuan Province, China, may wellbelong to this subgenus. If so, it would represent the earliestknown Odontopleura, and the only known Ordovician species.A thorough reinvestigation and additional material would berequired to arrive at any firm taxonomic conclusions, however,and no attempt has been made to include the species in thepresent analysis.

ODONTOPLEURA (ODONTOPLEURA) OVATAEmmrich, 1839

Odontopleura ovata EMMRICH, 1839, p. 53, PI. I, fig.3.Odontopleura (Odontopleura) ovata Emmrich. SIVETER,1989, p. 138,PI. 20, figs. 1-7, 11-21, PI. 21, figs. 1,3,4,8 (with full synonymy).

Occurrence. - Upper Llandovery to lower Ludlow of Bohemia(Bruton, 1968; Snajdr, 1984b); Wenlock to Ludlow ofthe BalticRegion (Bruton, 1967; Schrank, 1969; Alberti, 1970), Poland(Tomczykowa, 1957), Great Britain (Thomas, 1981); possiblythe Silurian of the Carnic Alps (Gaertner, 1930); possibly theupper Wenlock ofthe Southern Urals (Bruton, 1968, p. 9); mid-upper Wenlock to lowermost Ludlow of the Annascaul Inlier,County Kerry, Ireland (Siveter, 1989); non Wenlock to lowerLudlow of the Mackenzie Mountains, Northwest Territories,Canada (Chatterton and Perry, 1983, p. 18; Siveter, 1989, p.142).Discussion. - The taxonomic history of this species was dis-

cussed under the genus Odontopleura. Siveter (1989) has pro-vided a comprehensive review.Odontopleura (O.) ovata can be distinguished from the other

three species included in the subgenus by the presence of dorsallyexpressed 3L glabellar lobes, relatively strongly developed oc-cipitallobes, eyes placed a transverse distance from the IL lobeabout subequal to the width of the IL lobe as opposed to adistance greater than the width, and the presence of a weaklyimpressed second ring furrow on the pygidium (see Siveter,1989, PI. 20, figs. 12, 16, PI. 21, fig. 4).Chatterton and Perry (1983, p. 18) reported the possible oc-

currence of this species from upper Wenlock to lower Ludlowstrata of the Delorme Range of the Mackenzie Mountains. Theavailable material is still insufficient to allow proper specificassignment. However, it does not represent a Laurentian oc-currence of O. (O.) ovata, as it clearly lacks the distinctive gla-bellar morphology (well-defined 3L and occipital lobes) of that

-+FIGURE7-1-6, Odontopleura (Odontop/eura) arctica n. sp. 1.dorsal view,latexcast ofholotype, GSC95875, externalmold ofcomplete individual,x3. 2. 4, dorsal and dorsolateral views, two separate latex casts of paratype GSC 95876, external mold of complete individual, both x4; 3.dorsal view, paratype GSC 95877, internal mold of complete individual, x2.5; 5, ventral view, latex cast of paratype GSC 95878, internal andexternal mold of molt ensemble, x 5; 6, dorsal view, latex cast of counterpart externalmold of paratype GSC 95879, pygidiumwith exoskeletonpreserved, x 5.

ADRAIN AND CHATTERTON-CLADISTIC ANALYSIS OF TRIWBITES

1

3

5

609

2

4

6

610 JOURNAL OF PALEONTOLOGY, V. 64, NO.4, 1990

species. The material may represent a distinct new species, orpossibly a variant of O. (O.) brevigena, with longer Op spines.Proper description will await the accumulation of adequate ma-terial.

ODONTOPLEURA (ODONTOPLEURA) BREVIGENAChatterton and Perry, 1983

Odontop/eura brevigena CHATTERTON AND PERRy, 1983, p. 18, PI. 1,figs. 1-34.

?Odontop/eura perpeta SNAJDR,1984b, p. 103, PI. 2, figs. I, 2.Odontopleura (Odontop/eura) brevigena Chatterton and Perry. SIVETER,1989, p. 142.

Occurrence.-Wenlock of the Mackenzie Mountains, North-west Territories, Canada.Discussion. - It should be noted that Chatterton and Perry's

(1983, PI. l, figs. 6-9) holotype has a teratological pygidium,with five interior pygidial border spines. Further specimens col-lected from the type locality have yielded two more teratologicalpygidia, each with six fully developed interior pygidial borderspines. Such examples are rare, however, as these specimenscompare with dozens of normal pygidia collected from the samelocality.Odontopleura (O.) brevigena differs from the other species

assigned to the subgenus in the presence of a hypostome witha distinctly crennate posterior margin (see Chatterton and Perry,1983, PI. I, figs. 16, 25), relatively short Op spines, and havinggenal spines distinctly shorter than the remainder of the freecheek.As noted by Siveter (1989, p. 142), O. perpeta Snajdr, 1984b,

seems very similar to O. (O.) brevigena, and may be a juniorsynonym. The Bohemian material, however, is as yet too poorlyknown to permit a proper comparison.

ODONTOPLEURA (ODONTOPLEURA) SEROTINA(Apollonov, 1980)

Diacanthaspis serotina APoLWNov, 1980, p. III, PI. 31, figs.1-5.

Occurrence. - Lowermost Llandovery of Kazakhstan.Discussion. - Although not especially well known, the form

of the cranidium and free cheek leaves no doubt that this speciesbelongs in the subgenus. It appears to be closely related to thecontemporaneous Odontopleura (Odontopleura) arctica n. sp.,united in particular by the distinctive anterior facial sutures,which are initially divergent and do not begin to converge untilopposite the middle of the 2L glabellar lobe. The pygidium, ifcorrectly associated, is unusual for Odontopleura, as the majorborder spines do not appear to be exceedingly long and the dorsalsurface is much less spinose than normal.Odontopleura (Odontopleura) serotina can be distinguished

from all other species assigned to the subgenus particularly byits deep axial furrows, which serve to separate the anterolateralportion of the IL glabellar lobes from the fixed cheeks, and bythe presence of much shorter major pygidial border spines.Odontopleura (O.) serotina and O. (O.) arctica n. sp. differ col-lectively from the other two species assigned to the subgenusby the presence of initially divergent anterior facial sutures andthe presence of three, as opposed to four, exterior pygidial borderspines. Odontopleura (O.) serotina differs further from O. (O.)arctica n. sp. in having a much narrower, slightly longer, andmuch less spinose pygidium.It is acknowledged that some of these differences could be

due to the quality and mode of preservation. That O. (O.) se-rotina represents a distinct species, phylogenetically close to O.(O.) arctica, does not seem at issue. More and better illustratedmaterial would be required, however, for a truly satisfactorydifferential diagnosis.

ODONTOPLEURA (ODONTOPLEURA) ARCTICA n. sp.Figure 7.1-7.6

Material. -Holotype GSC 95875, an external mold ofa com-plete individual. Paratypes GSC 95876, an external mold of acomplete individual; GSC 95877, an internal mold of a com-plete individual; GSC 95878, an associated cranidium, two freecheeks, and thoracic segment; GSC 95879, a pygidium withoriginal shell material preserved; GSC 95880, an isolated tho-racic segment (not figured). All from a single block of shale, aglacial erratic collected from the Marshall Peninsula, northwestcoast of Cornwallis Island, Canadian Arctic, and assigned to thelowermost Llandovery, Cape Phillips Formation.Diagnosis. -A species of Odontopleura (Odontopleura) with

3L glabellar lobes defined ventrally only; axial furrows veryshallow at anterior of IL glabellar lobes; occipital lobes weaklydefined; eyes placed a transverse distance from IL glabellar lobegreater than width of IL lobe; Op spines long, reaching as faras 6th thoracic segment; anterior facial sutures long and diver-gent opposite 2L glabellar lobe; posterolateralmost cranidialmarginal spine long, extending to midlength of 2nd thoracicsegment; genal spine subequal in length to slightly longer thanremainder of free cheek; pygidium with three pairs of exteriorborder spines; major pygidial border spines at least three timesas long as exsagittal length of pygidium measured directly an-terior to them; pygidium approximately four times as wide assagittal length; second ring furrow of pygidium wholly absent.Discussion.-A comparison with Odontopleura (Odontopleu-

ra) serotina may be found under the discussion ofthat species.Odontopleura (Odontopleura) arctica differs from O. (O.) bre-

vigena in having longer Op spines; anterior facial sutures thatare divergent, as opposed to convergent opposite the 2L glabellarlobes; longer posterolateral most cranidial marginal spines; long-er genal spines; three as opposed to four exterior pygidial borderspines; and longer major pygidial border spines.Odontopleura (Odontopleura) arctica differs from O. (0.) ova-

ta in lacking dorsally expressed 3L glabellar lobes; having weakas opposed to strongly defined occipital lobes; eyes placed agreater transverse distance from the IL glabellar lobes; anteriorfacial sutures divergent as opposed to convergent opposite 2Lglabellar lobes; longer posterolateral most cranidial marginalspines; three as opposed to four pairs of exterior pygidial borderspines; longer major pygidial border spines; pygidium aboutfour, as opposed to three, times as wide as sagittally long; andlacking any impression of the 2nd ring furrow of the pygidium.GSC 95878 (Figure 7.5) appears to represent a molt ensemble.

The configuration of the associated elements indicate that thisspecies behaved during ecdysis in a manner similar to that ofO. (O.) brevigena (Chatterton and Perry, 1983, p. 19, PI. I, figs.1-4), the only other species of Odontopleura for which evidencefor such behavior has been presented. Molting in both of thesespecies involved a separation and rotation of the free cheeksand displacement of the hypostome. According to Chattertonand Perry (1983, p. 19), the trilobite then crawled out frombeneath the remaining articulated elements and over the sep-arated hypostome and free cheeks. This analysis is supportedhere, as the cranidium (Figure 7.5) has clearly remained in closearticulation with the Ist thoracic segment.

Subgenus SINESPINASPISn. subgen.Type species. - Odontopleura greenwoodi Chatterton and Per-

ry, 1983.Etymology. - From the Latin preposition sine, without, the

Latin noun spina, spine, and the Greek noun aspis, a shield.Gender is feminine.Species included. -Odontopleura greenwoodi Chatterton and

Perry, 1983;Odontopleura maccallai Chatterton and Perry, 1983;

ADRAIN AND CHATTERTON-CLADISTIC ANALYSIS OF TRILOBITES 611

Odontopleura nehedensis Chatterton and Perry, 1983; ?Odon-topleura bombini Chatterton and Perry, 1983; all from the Llan-dovery of the Mackenzie Mountains, Northwest Territories,Canada; Taemasaspis llandoveryana Snajdr, 1975, from theLlandovery of Bohemia.Diagnosis. -Odontopleurine trilobites with 3L glabellar lobes

usually completely absent; occipital lobes usually weak or ab-sent; occipital furrow usually shallow and indistinct; occipitalring with Oap spines only, or entirely lacking paired occipitalspines; Op never developed; anterior facial suture generally short,subparallel to convergent opposite 2L glabellar lobe; spine usu-ally absent from posterolateralmost aspect of cranidial margin;median occipital spine either at posterior cranidial margin orwithin one median spine width from margin; genal spine usuallyshorter than remainder offree cheek; posteroventral (doublural)part of posterior facial suture aligned with posterodorsal part;strong sutural ridge along posterior facial suture on free cheek;cephalic border spines at anterior of free cheek persist as fullydeveloped spines to contact with anterior facial suture; anteriorpleural spines very short and barb-like; number of interior py-gidial border spines may be reduced in number to two; pygidiumsubtriangular in ventral outline, usually with an anterior inflec-tion of the median ventral doublure.Discussion. - This subgenus was contrasted with Odontopleu-

ra (Odontopleura) under the discussion of that subgenus.

ODONTOPLEURA (SINESPINASPIS) GREENWOODIChatterton and Perry, 1983

Odontopleura greenwoodi CHATTERTONAND PERRY, 1983, p. 19, PI. 2,figs. 1-20, PI. 3, figs. 28-43.

Occurrence. - Middle Llandovery (Pterospathodus celloni zone)of the Mackenzie Mountains, Northwest Territories, Canada.Discussion. -An autapomorphy of Odontopleura (Sinespi-

naspis) greenwoodi among all species of Odontopleura is thepresence of two, as opposed to one, free cheek border spinesoccurring on the lateral aspect of the genal spine.Because Odontopleura (Sinespinaspis) greenwoodi is both the

best known and stratigraphically longest ranging species as-signed to the subgenus, it was chosen as the type species. It has,however, many morphological features that would tend to allyit with those species included in 0. (Odontopleura), includinglong and convergent anterior facial sutures, small spines presenton the posterolateral cranidial margins, and long genal spines.It does, however, have in common with the other species as-signed to O. (Sinespinaspis) a suite of uniquely shared charac-ters, just as 0. (Odontopleura) is defined by a similar suite (asshown by the cladograms of Figure 5).An argument could be put forward for the presence of Op

spines in Odontopleura (Sinespinaspis) greenwoodi. The occip-ital ring (Chatterton and Perry, 1983, PI. 2, figs. 1, 7, PI. 3, figs.29, 30, 32) typically has two pairs of occipital spines. The me-dian pair corresponds to the dominant pairs on the thoracic axesand represents Ow The lateral pair could therefore be construedas Op and be taken as homologues of the large Op spines of O.(Odontopleura). The Op spines of that subgenus, however, haveno obvious serial homologues on the thoracic axes. The lateralspine pair of O. (s.) greenwoodi has very clear serial homologues(contrast Chatterton and Perry, 1983, PI. 2, figs. I, 3). Hence,while topologically similar structures, the evidence suggests thatthe lateral spine pair of O. (s.) greenwoodi and the Op spines ofmembers of O. (Odontopleura) are non-homologous.

ODONTOPLEURA (SINESPINASPIS) MACCALLAIChatterton and Perry, 1983

Odontopleura maccallai CHATTERTONAND PERRY, 1983, p. 21, PI. 4,figs. 17-37.

Occurrence. - Llandovery (Pterospathodus celloni zone) of theMackenzie Mountains, Northwest Territories, Canada.Discussion. -Odontopleura (Sinespinaspis) maccallai can be

distinguished from O. (s.) greenwoodi by the presence ofshal-lower longitudinal furrows at the posterior of the IL glabellarlobes, a slightly deeper and better defined occipital furrow, theabsence of Oap spines, short and subparallel anterior facial su-tures, lack of posterolateral cranidial marginal spines, a muchshorter genal spine, and a variable (2-4) number of interiorpygidial border spines, as opposed to a constant four.Odontopleura (Sinespinaspis) maccallai differs from O. (s.)

nehedensis in the following features: axial furrows at anterior ofIL glabellar lobes shallow as opposed to deep; occipital lobesweakly defined as opposed to wholly absent; occipital furrowshallow but evident as opposed to indistinct; eyes placed trans-versely farther from the IL glabellar lobes; Oap spines absent;and four as opposed to three pairs of exterior pygidial borderspines.

ODONTOPLEURA (SINESPINASPIS) LLANDOVERY ANA(Snajdr, 1975)

Taemasaspis llandoveryana SNAJDR, 1975, p. 314, PI. I, fig. 6, PI. 2,fig. 7; SNAJDR, 1978, p. 28, PI. 7, figs. 1-12, PI. 8, figs. 9-14, PI. 12,fig. 3; RAMsKÖW, 1984, p. 249; PRIBYL, VANEK, AND HÖRBINGER,1986, p. 267.

Odontopleura l/andoveryana (Snajdr). CHATTERTONAND PERRY, 1983,p. 18.

Taemasaspis l/andoveryiana Snajdr. SIVETER, 1989, p. 137.

Occurrence. - Upper Llandovery, Hyskov area, near Beroun,Czechoslovakia.Discussion. - The association of the sclerites figured by Snajdr

(1975, 1978) as Taemasaspis llandoveryana has been questionedby Piibyl et al. (1986), who considered most of the material tobelong to Primaspis (Meadowtownella), with some of the l2ygidia(they did not specify which) referred to Miraspis rarissima Snajdr,1975, a species they included in Odontopleura. Following Chat-terton and Perry (1983) and Siveter (1989), the figured cranidiaseem more similar to the Mackenzie Mountains Llandoveryspecies here grouped in Odontopleura (Sinespinaspis) than toPrimaspis (Meadowtownella). That most of the pygidia figuredby Snajdr (1978) belong with the cranidia seems reasonable,since his Plate 7, figure 7 illustrates the dorsal surface of arelatively well-preserved articulated exoskeleton, confirming theassociation. Snajdr's (1978) Plate 8, figure 12 would appear tobe the only questionable assignment, and was not used in thecladistic analysis herein (see Table 2).The relationships of this species are somewhat problematic.

By parsimony, there are two equal length networks differing intheir placement of Odontopleura (Sinespinaspis) llandoveryana(one of which was discarded by congruency). This is partly aproblem of the material available and the standards of preser-vation and illustration of that material. Of more consequence,however, is the simple fact that, with regard to the subgenus,0. (s.) llandoveryana is highly autapomorphic. It has no fewerthan five character-states (in characters 1,4,5,20, and 21) notshared with any other member of the subgenus. Following fromthis, O. (s.) llandoveryana may be distinguished from all otherspecies included in Sinespinaspis by the following features: 3Lglabellar lobes expressed dorsally; occipital lobes strongly de-fined; occipital furrow deep; pygidium about four, as opposedto three, times as wide as long; and strongly impressed 2nd ringfurrow of pygidium present.An undescribed odontopleurine species from the Llandovery

of the Forbes district, New South Wales, closely resemblesOdontopleura (Sinespinaspis) llandoveryana (L. Sherwin, per-sonal commun.). This material consists of well-preserved ex-

612 JOURNAL OF PALEONTOLOGY, V. 64, NO.4, 1990

ternal molds of articulated individuals, and its description shouldprovide a sound basis for comparison and evaluation of theBohemian material.

ODONTOPLEURA (SINESPINASPIS) NEHEDENSISChatterton and Perry, 1983

Odontop/eura nehedensis CHATTERTON AND PERRY, 1983, p. 20, PI. 3,figs. 1-27.

?Odontop/eura bombini CHATTERTON AND PERRY, 1983, p. 22, PI. 4,figs. 1-16.

Occurrence.-Middle to upper Llandovery (Pterospathoduscelloni to P. amorphognathoides zones) of the Mackenzie Moun-tains, Northwest Territories, Canada.Discussion. -Chatterton and Perry (1983) recognized Odon-

topleura (Sinespinaspis) nehedensis and O. (s.) bombini as sep-arate species. They speculated (p. 13) that the slightly older O.(s.) nehedensis might be a direct ancestor of 0. (s.) bombini,the latter occurring 37 m higher in the same section (each occursby itself in other sections, but only in section AV I are theyfound in stratigraphic succession). They did not provide a dif-ferential diagnosis for the species. From a purely morphologicalstandpoint, the species differ only in the relative depth of thelongitudinal furrows at the posterior of the IL glabellar lobes,the position of the median occipital spine, and the number ofinterior pygidial border spines. Of these, the first could be afunction of preservation and of comparison of differently sizedspecimens, as all available O. (s.) bombini material is very small(Chatterton and Perry, 1983, p. 23). The second seems genuine,with the median spine set very slightly forward from the pos-terior cranidial margin in O. (S.) nehedensis but directly at themargin in O. (s.) bombini. As for the condition of the pygidialborder spines, the number of interior spines ranges from 2 to 4in 0. (s.) nehedensis, but is restricted to two in O. (s.) bombini.The entire sample of pygidia of 0. (s.) bombini is quite small,however, and this character exhibits some variability even inspecies for which the number is all but constant (see 0. (0.)brevigena above). In all other aspects of morphology, O. (s.)nehedensis and O. (S.) bombini are identical, and given thediscussion above, distinction between them is of very limitedbiostratigraphical utility. The possibility must therefore be ac-knowledged that the two taxonomic species represent tempo-rally separated populations orthe same phyletic lineage. There-fore, pending further information, they are placed in questionablesynonymy.Odontopleura (Sinespinaspis) nehedensis was contrasted with

0. (s.) maccallai under the discussion of that species. It maybe distinguished from O. (s.) llandoveryana by the absence ofthe latter species' many autapomorphies. Odontopleura (s.) ne-hedensis differs from O. (s.) greenwoodi in the following features:axial furrows at anterior of IL glabellar lobes deep as opposedto shallow; occipital lobes entirely absent; eyes placed trans-versely nearer to the IL glabellar lobes; anterior facial suturesshorter; no spines at posterolateral part of cranidial margin;genal spines shorter than remainder of free cheeks; one as op-posed to two border spines occurring on lateral aspect of genalspines; three as opposed to four pairs of exterior pygidial borderspines; and usually less than four as opposed to four (or more)interior pygidial border spines.

PALEOECOLOGY AND PALEOGEOGRAPHY

Studies of Silurian trilobite paleoecology are few, but includeThomas (1980), Mikulic (1980), Mikulic and Watkins (1981),Männil (1982), and Chlupac (1987). Both subgenera of Odon-topleura were widely distributed. Hence, no particular paleo-biogeographic pattern can be recognized among the 10 known

species. This broad distribution seems likely to have been di-rectly related to the trilobites' choice of habitat. All of the speciesincluded in Odontopleura had, on present evidence, a relativelynarrow ecological valence, preferring the deeper waters of theouter shelf or of the shelf-slope transition zone. An exceptionis Odontopleura (Ivanopleura) dufrenoyi. This Bohemian speciesoccurs in shallow-water deposits, included by Chlupac (1987)in his Bumastus-Sphaerexochus-Cheirurus assemblage, whichhe assigned to Boucot's (1975) Benthic Assemblage 3 or 2. Thus,the doubt expressed above about the systematic position of thisspecies is borne out by an ecological division between it and allother species included in Odontopleura.Odontopleura (Sinespinaspis) llandoveryana is included by

Chlupac (1987) in his Stenopareia-Aulacopleura assemblage,assigned to Boucot's (1975) Benthic Assemblage 4. Odonto-pleura (Odontopleura) ovata is included by Chlupac (as O. pre-vosti) in his Aulacopleura konincki assemblage, assigned to Bou-cot's (1975) Benthic Assemblage 4 or 5. The Irish O. (O.) ovatamaterial was regarded by Siveter (1989, p. 156) as occurring ina distal shelf environment. All of the Mackenzie Mountainsspecies are known from relatively deep water, distal shelf-slopeenvironments (Chatterton and Perry, 1983). The drift blockupon which the known specimens of O. (O.) arctica n. sp. occuris composed of dark, fine-grained, argillaceous, micritic lime-stone. The only other fossils present are the above-mentionedgraptolite fragments and a single pedicle valve of a smoothatrypid, or possibly athyridid, brachiopod. The lithology of thesample, the presence of graptolites, and the undisturbed natureof the articulated trilobites suggest a low-energy, probably low-oxygen, deep-water environment. As deeper water forms, there-fore, members of Odontopleura were not subject to the ende-mism of more onshore species, having wider opportunities fordispersal and being less affected by eustatic sea-level fluctua-tions. This accounts for their almost global distribution throughEarly and Middle Silurian times.

ACKNOWLEDGMENTS

C. Patterson, who refereed the manuscript, is particularlythanked for insight into the equivalency between congruencyand longest branch rooting. A. T. Thomas, the other referee,also provided useful suggestions for the improvement of themanuscript. We thank T. E. Bolton for arranging loan of thespecimens. G. D. Edgecombe is thanked for discussion of themethodological section of the manuscript. L.Ramsköld broughtDiacanthaspis serotina to our attention and provided infor-mation on his work in progress on odontopleurid classification.L. Sherwin provided information about an undescribed speciesof Odontopleura (Sinespinaspis) from New South Wales. Prep-aration of this study was supported by a Natural Sciences andEngineering Research Council operating grant to B.D.E.C.

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ACCEPTED24 JANUARY1990

THE UPPER DEVONIAN (FRASNIAN) CONODONT SEQUENCE INTHE LIME CREEK FORMATION OF NORTH-CENTRAL IOWA ANDCOMPARISON WITH LIME CREEK AMMONOID, BRACHIOPOD,

FORAMINIFER, AND GASTROPOD SEQUENCESJED DAY

Department of Geography-Geology, 1IlinoisState University, Normal 61761

ABsrRAcr- The Upper Devonian (Frasnian) conodont fauna of the Lime Creek Formation of north-central Iowa is dominated byspeciesof Polygnathus. Patterns of speciescomposition and abundance are consistent with the Polygnathus biofaciesdescribed fromthe Frasnian of the Northwest Territories of western Canada. Consequently, the standard Frasnian conodont zones, defined onsequences developed in the Palmatolepis biofacies, are not applicable to the Lime Creek sequence. The Lime Creek conodontsequencecorrelateswith Zones 4, 5 and Faunal Interval 7 of the Frasnian conodont sequencein the Alberta Rockiesand with similarsequences in the southwestern United States. The Pb elements of Palmatolepis semichatovae Ovnatanova and Ancyrognathus?deformis (Anderson) are described and illustrated for the first time.In the Lime Creek Formation of north-central Iowa, brachiopods of the lowermost part of the Nervostrophia thomasi Zone of

Day (1989a) occur in Zone 4, brachiopods of most of the N. thomasi, Douvi//ina arcuata, and Cyrtospirijer whitneyi Zones spanconodont Zone 5, and the E/ita inconsueta and Iowatrypa owenensis Zones occur in Faunal Interval 7. Speciesof the ammonoidManticoceras and of the gastropodsFloyda, Turbonopsis, and Westerna are restricted to Faunal Interval 7. Speciesofthe calcareousforaminifer Nanice//a first occur in Zone 5, and are joined by speciesofMultiseptida high in Zone 5.

INTRODUCTION

THIS STUDY outlines the Frasnian conodont sequence as it isdeveloped in three sections of the Upper Devonian Lime

Creek Formation in north-central Iowa (Figures 1-3). Detailedknowledge of the conodont sequence allows for calibration ofLime Creek brachiopod zones, as well as biostratigraphicallyuseful calcareous foraminifers, ammonoids, and selected gas-tropods in the upper Frasnian of the Iowa Basin in the U.S.Midcontinent.Strata of the Lime Creek Formation in north-central Iowa

record open- and restricted-marine deposition in cratonic-shelfand shelf-margin settings (Figure 4). The Lime Creek conodontfauna differs significantly from faunas of the Palmatolepis bio-facies developed in offshore equivalents in eastern Iowa (Sweet-land Creek Shale) and the Selmier Shale in the Illinois Basin(Figure 4). Composition and patterns of species abundance ofLime Creek conodont faunas discussed here and by Metzger(1989) are similar to those described from the Frasnian Poly-gnathus biofacies by Klapper and Lane (1985).Owing to the dominance of species of Polygnathus and general

absence of Palmatolepis, Ancyrognathus, and Ancyrodella, directcorrelations of the Lime Creek sequence with the standard con-odont sequence developed in the Frasnian Palmatolepis biofa-cies (Ziegler, 1958, 1962) is not possible. However, the LimeCreek and related conodont sequences in the Frasnian of NewMexico and Arizona are correlated directly with Zones 4, 5, andFaunal Interval 7 of the Alberta Rockies zonation of Klapperand Lane (1989) in which the divisions above Zone 4 are definedby elements of the Polygnathus biofacies.

PREVIOUS INVESTIGATIONS

The first study of the Lime Creek conodont fauna was byAnderson (1964, 1966). Nearly all specimens identified as Pal-matolepis gigas by Anderson (1966) are now placed in P. semi-chatovae (see synonymy of P. semichatovae in Klapper and Lane,1985, and this study), which necessitates revision of Anderson's(1966) assignment of the Lime Creek to the Lower Palmatolepisgigas Zone (cited in Klapper et aI., 1971, p. 302). Other im-portant species illustrated by Anderson (1966) include Palma-tolepis foliacea and Polygnathus deformis (here questionablyassigned to Ancyrognathus, following the usage of Metzger, 1989).Day (1987) established ranges of species of the gastropod

genera Floyda and Turbonopsis relative to conodonts in theLime Creek Formation. Day (1989a) discussed the distributionof conodont faunas with respect to the brachiopod zonation inthe Lime Creek in northern Iowa (Figure 2).Metzger (1989) described Polygnathus-dominated conodont

faunas and calcareous foraminifers from shallow-water faciesof the subsurface Lime Creek Formation in north-central Iowaand southeastern Nebraska, and proposed correlations similarto those presented in this study. However, because the LimeCreek conodont faunas reported by Metzger lack species of Pal-matolepis, they cannot be correlated directly with the AlbertaRockies Frasnian zonation of Klapper and Lane (1989).

UTHOSTRATIGRAPHY AND DEPOSmONAL ANDPALEOGEOGRAPHIC SE'ITING

Witzke (1987) delimited major facies tracts and discussed thedepositional setting of the Lime Creek Formation and its equiv-