Paleontological Society

Systematics and Paleobiology Author(s): Niles Eldredge and Michael J. Novacek Source: Paleobiology, Vol. 11, No. 1 (Winter, 1985), pp. 65-74 Published by: Paleontological Society Stable URL: http://www.jstor.org/stable/2400424 Accessed: 04-01-2016 19:37 UTC

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This content downloaded from 132.248.28.28 on Mon, 04 Jan 2016 19:37:58 UTC All use subject to JSTOR Terms and Conditions Paleobiology,11(l), 1985, pp. 65-74

Systematicsand paleobiology

Niles Eldredgeand MichaelJ. Novacek

Abstract.-Systematics,ostensibly the "old" paleontology,actually plays a centraland crucial role in modernpaleobiology. We argue that a revisedontology has recentlydarified the natureof species and has expresslyadded monophyleticgroups to the rosterof spatiotemporallybounded entities-"individuals -that are now seen as participantsin the evolutionaryprocess. Systematics is the studyof species and monophyletictaxa, and fossilsalone providethe data on the temporalboundedness of such taxa. Cladistics(phylogenetic systematics) is explicitlygeared to the recognitionof monophyletictaxa. We reviewaspects of the core problemof characteranalysis in systematics,particularly addressing the still contendedissue of the seeminglycompetitive claims of three methodologies:out-group comparison, comparativeontogeny, and the "paleontologicalmethod." We findthat these methodsoverlap in their basic assumptionsto a significantextent, yet each retainsa characteristicand distinctiveflavor. They are not all "the same," nor are theyalways "complementary"'-and no one methodis superiorto the others in all circumstances. Far frombeing the Victoriansymbol of a moribundscience, systematics lies at thevery heart of modern paleobiologicalresearch, providing the centraldata forpaleobiology's truly unique contribution,both real and potential,to evolutionarybiology in general.

Niles Eldredgeand Michaelj. Novacek. Departmentsof Invertebrates and VertebratePaleontology, American Museumof Natural History,Central Park Westat 79thSt., New York,New York10024.

Accepted: November5, 1984

Searchingfor the connectionbetween system- evolved or that eutherianmammals are mono- atics and paleobiologyis like asking why the phyletic. PaleontologicalSociety supports not one but two And so we ask, What is the data base of journals:Journal of Paleontology,heavily given paleobiology?Perusal of the firstdecade of Pa- over to the descriptionof taxa (predominantly leobiologyreveals the heavyimpact of ecological species),and Paleobiology,seemingly devoted to and functionalmorphological theory, relying re- just about everythingbut systematics.Paleobiol- spectivelyon analyzedoccurrences of various sorts ogyembodies the ideas that are half of any sci- of ecologicalunits and on the physicalanalysis ence's lifeblood.Here one findsout why fossils of organismalphenotypes as the data base. But are interestingat all, and what relevancethey therehave also been manydiscussions of "evo- may have to an understandingof life'spast and lution," particularlydiversity studies, and these perhapseven some of theforces that have shaped usually involve numbers of subunits within thathistory. In contrast,systematics often seems units--suchas familieswithin orders. Clearly a dull, atheoretical,and forevercommitted mind- large proportionof studiespublished in Paleo- lesslyto dustingoff, correcting, and adding to biologydepend directly on systematicsas a source the accomplishmentsof our forerunners. of data. Yet mostof us also realizethat the otherhalf This latterstate of affairsstrikes us as highly of any science'sessential fluids is information, appropriate.In themost direct discussion of sys- statementsabout the real world that are pur- tematics-how it is done and what its relevance portedto be true. Certainlytheory informs our trulymight be for paleobiology-that has yet data, even to the point of influencingheavily appeared in these pages, Cracraft(1981) em- what we thinkwe observeabout nature.Yet it phasized the need fordades (be they"real" or is the informationthat keeps the theoryhonest. "imagined") to be monophyletic:for monophy- That is how we reallymake progressin the his- letictaxa are literallybranches on thetree of life. tory of knowledge: ideas consistentlyverified More thanmetaphor is at workhere: life, we all eventuallyleave the realmof theoryand become agree,has had a history.There has been "descent "fact." There is no seriousdoubt that life has withmodification," and it is the generalaim of ? 1985 The PaleontologicalSociety. All rightsreserved. 0094-8373/85/1 101-0006/$1.00

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systematicsto identifyall the integralrami on about Ghiselin's (1974a, b) "radical individu- that tree.' Thus is life's historyreconstructed, alism," we see immediatelythat contemporary and that, it seems clear, is the basic natureof biologicaltheory has not,in general,seen species the data base whichpaleontology (and system- and monophyletictaxa of rank higher than aticsin general)can giveto evolutionarybiology. species as "individuals,"that is, as spatiotem- Cracraft's(1981) paper should be consultedfor porallybounded entities. If one doeslook at such more detail on why monophylyis important- entitiesin thisway, the ontologyof evolutionary and why it is that systematicsis relevantfor biology,the list of "things"we thinkparticipate paleobiology. in someway in theevolutionary process, is some- We wish, here, to go a bit further.Specifi- what expandedfrom the conventionalgenes, or- cally, we are concernedwith what systematics ganisms,populations, and species (the latterin (includingsystematic paleontology) can contrib- a generallyahistorical sense) to include species ute to paleobiology-and herewe mean partic- and highertaxa as actual historicalunits. And ularlythe genealogicaland economicaspects of thisimplies that the data of systematicsare di- evolution.(See Eldredgeand Salthe119841, Vrba rectlyrelevant-really for the first time-to test- and Eldredgei19841, and Eldredge 119851for ing notionsof evolutionaryprocess. And paleon- discussionsof these twin aspects of the evolu- tologyis our primesource of informationon the tionaryprocess in explicitlyhierarchical terms.) temporalboundedness of individual taxa. We It seemsto us thatsystematics points the way to emerge,in short,holding the cards when it comes a deeper understandingof what paleobiology to decidingwhat the grosserpatterns of the his- holds as unique in its data base. To the query, toryof lifehave been,even though such patterns What is unique about thefossil record? the usual may not requirehigher-level processes for their responseis, of course,time. From the vantage explanation.Paleobiology is thusfreed to devise point of systematics,though, time is only part testabletheory, and to consultits own data base of the answer.Much moreto the point,we ap- to testits theory.And, of course,to some extent pear to be at the brink of adopting a revised thisis aleady going on. We need no longeras- ontologyof the biologicalrealm. Indeed, Hull cribeall aspectsof the anatomicalmodification (1980) has even claimed that no progressin betweenthe Warrawoona prokaryotes and Blan- evolutionarybiology is in prospectuntil we do can bisonsto the vagariesof shiftingallelic fre- revise our basic conceptionson the nature of quencies. biological entities,going beyond the obvious "commonsense"ontology and beginningto see Systematics:Seeing the Forest for the Trees that there are additional biological entitiesat The Modern Synthesis,according to some of play in theevolutionary game. Bettertheory and its more recentchroniclers, gave us a deep ap- laboratoryinstrumentation have now convinced preciationof variation.No two organisms,real- us of the existenceof codons,pseudogenes, and ly,are exactlyalike, and as Lewontin(e.g., 1974) transposons-and we even think we know has been pointingout foryears, an appreciation somethingof theirnature and how theyshape of variationwas one of the majorfacets of Dar- the courseof evolution.An enhancedontology win's revolution.Its reemphasisin the synthesis could also embracethe rethinkingof ecological had an immediateimpact on systematics;it was units, and here paleontologybecomes directly J. S. Huxleywho named boththe "modernsyn- relevant(Eldredge and Salthe 1984; Eldredge thesis" and the "new systematics"within the 1985; Salthe 1985). But our subjectis system- briefspan of two years.The reason forthe as- atics,and that leaves taxa. In short,if we think sociationbetween the two is obvious enough: interorganismicvariation within populations and I We are awarethat some dadists(see, e.g., Platnick1979) speciesis the raw stuffon whichselection works. maintainthat theirs is a searchsimply for "natural groups," Evolutionin the Darwiniantradition, of course, withno attendantnotion of evolutioninvolved. That "nat- is mostly concernedwith adaptation through uralgroups" and "monophyletictaxa" amountto the same thingis axiomaticin the particularcanon of systematicswe natural selection.As Mayr (1942, pp. 6-7) adopt here. wrote:

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The old systematicsis characterizedby the born; one must consult SystematicZoology to centralposition of the species. No work, or findmost of the discussion.Whatever their in- verylittle, is done on infraspecificcategories volvement in those battles over systematics [subspecies].A purelymorphological species methodology,paleobiologists seem increasingly definitionis employed. Many species are to have adoptedsome versionof Hennig's "phy- knownonly from single or at best a veryfew logeneticsystematics" as a routineitem in their specimens;the individual is thereforethe basic analyticarsenal. And forgood reason:Simpson taxonomicunit. There is greatinterest in pure- (1975, p. 14) and Mayr (1974, p. 98), prom- ly technicalquestions of nomenclatureand inentspokesmen for "evolutionary systematics," "types." The major problemsare those of a long ago concededthat the emphasison shared catalogueror bibliographer,rather than those derivedfeatures as theway to recognizebranches of a biologist. of the phylogenetictree is not only sound, but The new systematicsmay be characterized a usefulcontribution, as it makes explicitwhat as follows:The importanceof the species as has always been sensed but not fullygrasped such is reduced,since most of the actual work before. A common assertion that Hennig's is done with subdivisionsof the species,such methods are a rigorousversion of "good old as subspeciesand populations.The population systematics"is not far-fetched(see, e.g., Nelson or ratheran adequate sample of it, the "se- and Platnick 1981). Some nineteenth-century ries" of the museumworker, has become the dassificationshave withstoodover a hundred basic taxonomicunit. The purelymorpholog- yearsof scrutinybecause theirsubdivisions are ical speciesdefinition has been replacedby a well definedby distinctiveshared-derived fea- biological one, which takes ecological,geo- tures-for example,De Blainville's(1816) rec- graphical,genetic, and otherfactors into con- ognitionof eutherianmammals based on repro- sideration.The choosingof the correctname ductivetraits. Recent compilations of paperswith forthe analyzedtaxonomic unit no longeroc- a strongsystematics content, written primarily cupies the centralposition of all systematic by paleontologists(see, e.g., Ciochon and Chi- work and is oftenless subject to argument arelli 1980; Eldredgeand Stanley1984) reveal betweenfellow workers. The materialavail- that dadisticsis now the predominantmethod able forgeneric revisions frequently amounts of choice. to manyhundreds or even thousandsof spec- This is relevantsimply because cladisticsem- imens,a numbersufficient to permita detailed bodies a featureof life that Darwin (1859) studyof the extentof individualvariation. pointedout so long ago: homologiesare nested. From the point when a featurefirst appears in The result:much of systematics(induding, phylogenetichistory, it will be passed along in certainly,paleontological systematics), from the some guise (i.e., in the same or transformedver- 1940s throughthe present day, has been a thor- sion) to descendanttaxa. Anotherway of putting oughgoingfocus on species-and, as Mayrhim- it: all specifiableattributes have a finitedistri- selfurged, on patternsof variation within species. bution in the biota. The 9 + 2 patternof in- Less emphasizedhave been patternsof relation- ternalanatomy of cilia and flagellaseems ubiq- ship among species-and, especially,among uitous, at least within Eukaryota. Mammary dustersof species:genera, families, and so forth. glands are restrictedto Mammalia. Fingerprint Only, in fact,since Hennig's (1966) book ap- patternsare supposedly unique to individual peared in Englishtranslation has therebeen a Homosapiens organisms. The moral:systematics detectableswing back to more rigorousconsid- proceedsby mapping the distributionsof such erationof phylogeneticrelationships among taxa attributes.In so doing, "natural groups" of all sizes (meaning,roughly, "rank"). monophyletictaxa, branchesof the treeof life- Much of the furorover "evolutionary system- are delineated,defined, and recognized. atics," "phenetics,"and "dadistics" seems to With thisstrategy, we discardthe long-wind- have passed paleontologyby. The debate,in any ed argumentsabout thevalue of "adaptive" ver- case, was largelyover beforePaleobiology was sus "nonadaptive" characters;the distinction

This content downloaded from 132.248.28.28 on Mon, 04 Jan 2016 19:37:58 UTC All use subject to JSTOR Terms and Conditions 68 NILES ELDREDGE & MICHAEL J. NOVACEK seemsto have restedmostly on the antiquityof activityof using characterdistributions to des- the adaptationand the currentperceived utility ignatedumps of organisms,to give thema name of the attribute.Though it is difficultnow to so we can talk about them(itself a matterof no construepentameral symmetry (in all but the small importance).But it is stillwidely believed mostprimitive of echinoderms[Haugh and Bell thathigher taxa are figmentsof mankind'sim- 19801) as an "adaptation,"hemoglobin is about preciseand arbitraryclassificatory propensities. as old and stillseems "adaptive." Yet each tells Hull's (1980) "commonsenseontology" sees us somethingabout phylogeneticrelationships. onlyorganisms, and possibly,in some contexts, All charactershave a distribution,hence all char- speciesactually existing in nature.Many system- actersare usefulin systematics;but not all char- atistsand othersorts of biologistsstill seem to actersare distributedequally widely. Correct ap- doubt thateven speciesexist. According to this prehensionof characterdistribution is still not outlook, highertaxa patentlydo not "exist," an easy task, but gone now is the need forex- and so are not "real"'-and thus need not be plicit "weighting"schemes based on some pu- takenoverly seriously. What is important,in this tative"adaptive" value assignedto one character point of view, is only the characters-a view, or another. once again, that primarilyreflects an ideology Cladisticsis no panacea. It is hard to do a about what evolutionis and how it operates.At good piece of systematicsresearch using dadis- best taxa are merelyarbitrarily defined segments tics-indeed, harderthan ever before.The sys- of a phyleticcontinuum; at worst,they are a tem is logicallymuch more rigorous,requiring hodge-podge not even necessarilyrelated by everyavailable itemof evidence.But, in theory, commondescent. In sucha worldview, the char- we now have an explicitmethodology that al- actersgive the taxon, and apart frompure no- lows us to evaluate hypothesesof monophyly. menclature,we need not take those taxa too And thisturns out to be what paleontologycan seriously. give of lastingvalue to comparativeevolutionary But considerthe standardform that paleo- biologyin general. biologicaldiscourse has takenin manypapers in The centraltheme-that all featureshave a thisjournal (e.g., Sepkoski 1978, 1979, 1981). finitedistribution-opens up thegame a bit over Consider,too, Raup's work along similarlines, the rathernarrow construct afforded us by the and noteparticularly his analogybetween species New Systematics.Organisms vary within pop- and "partides" say, gas moleculestrapped in ulations,to be sure:but populationsvary within a canister.This corpus of work implicitlyand species,species within genera, and so forth.We explicitlytakes taxa (regardlessof magnitudeof must not overlookthe fact that this hierarchi- rank) and sees themas spatiotemporallybound- cally structuredpattern of variation,this parti- ed individuals.Indeed, the investigation of "tax- tioningof attributes,is based on our evaluation onness" (Raup and Marshall 1980) and the in- of organismalattributes. From the vantage point terestinghistory of such investigation(e.g., of systematics,when we speak of interspecificSimpson 1944) assumes the realityof taxa of variancewithin a genus, we are not discussing variousranks. If it is truethat over 90% of the supposed emergentproperties of species.What speciesthat have everlived are now extinct,it is we mean, instead,is "organismalattributes that also true that most familiesare also extinct. do not varywithin species, but do varybetween Familiescome and familiesgo. The Phacopidae species." (Trilobita)arose in the Lower Silurianand de- This is preciselywhere a revisedontology of partedthis earth in the Upper Devonian, as far biologicalentities becomes important. In a the- as anyoneknows. And while thereis some ar- ory that sees the transformationof organismal gumentover whether some earlytaxa belongin attributesas both the centralpattern and the the familyor not (Morgatia, for example, has verymechanism (via selection,for the most part) conflictingsynapomorphies), there really is no of evolution,what mattersmost is the introduc- sane doubt that the familyas a whole existed. tion and subsequent transformationof evolu- We tell who's who by those characters,those tionarynovelties. Under thatparadigm, system- synapomorphies(bifurcate 3p furrow,in this aticsper se becomesa trivialpursuit, the ancillary case), but morethan thesespecifiable character-

This content downloaded from 132.248.28.28 on Mon, 04 Jan 2016 19:37:58 UTC All use subject to JSTOR Terms and Conditions SYSTEMATICS AND PALEOBIOLOGY 69 isticsof individualorganisms exists. The entire here paleontologylays daim to a unique role. lineageexists-the charactersmerely give us the Given the associationbetween fossils and time, means to recognizethe lineage. thereseems to be an obvious potentialfor dis- And sometimeswe stumble in using those criminatingmore derivedfrom more primitive characters.We make mistakes:we indude species characters. in some taxa wherethey don't belong,and leave This traditionaluse of the fossilrecord in dis- out othersthat do. We wrangleover ranking- criminatingthe derivedfrom the primitive-the all thesesources of errorand disagreementcre- so-called paleontologicalapproach-has been atingthe misapprehensionthat just because our sharplycriticized by some dadists (e.g., Nelson techniquesof recognitionare less than perfect, 1978). Ironically,the most prevalent criticism of thereforethe units-the taxa-that we are striv- dadisticsconcerns the same problemof character ing to characterizesomehow do not exist. De- discrimination.Harper (in Harper and Platnick nyingthat species, and the clustersof speciesall 1978) dubbed thisproblem the "Achillesheel" descendedfrom a singlecommon ancestral species of dadistics,because dadisticsrequires the rec- (i.e., "monophyletictaxa"), exist,seeing them ognitionof specializedtraits based on indirect, insteadas dasses or dasslike entities,is vital to largely"speculative criteria." This criticismhas the "researchprogram" of the modernsynthesis a popularrejoinder (Nelson and Platnick1981). and is the single greateststumbling block to Time-honored,predictive dassifications-even futureprogress in evolutionarybiology (see El- those dating back centuries-have always re- dredge[19851 fordiscussion). Recognizing, con- flecteddistributions of specialized,defining char- versely,that the branchesof the treeof lifehave acters.Moreover, this recognition is allowed by beginnings,histories, and ends, that they are the hierarchicalorder of diversity.The discovery thereforenonarbitrary and real, allows us to of homologyis the discoveryof a more gener- searchfor them, even thoughwe know we are alized (more indusive) conditionthat rootsone bound to make mistakesin theiridentification. or morespecialized conditions. This argumentis And it permitstheorists, such as Sepkoski and the basis of outgroupcomparison (see Eldredge Raup, to use the data of the historyof life, and Cracraft1980; Nelson and Platnick1981; visualized as though these entitieshave had a Wiley 1981). real existence,in a straightforwardand sensible Why,then, has thiscommon goal of character way to testtheir hypotheses. Taxa are the data discriminationsparked an apparentconflict be- of paleobiologicalinvestigations of evolution. tweendadistics and at leastmore traditional pa- leontologicalviews? For one thing,cladistics is The CharacterCipher: More on Paleontology clearlyantagonistic to thenotion (e.g., Gingerich and Systematics and Schoeninger1977) thatthe fossil record alone If characterizationof taxa-of spatiotempo- providesevidence for the separationof primitive rallybounded entities-so profoundlyinfluences fromderived traits. But less extremepositions ourperception of biologicaldiversity, then a par- are also vulnerable.Even paleontologistswho ticularmethodology in systematicswill be judged view theirapproach as neitherwholly indepen- in part by its power to resolvecharacter distri- dentof norsuperior to comparativebiology have butions.In thiscontext, the avenuesof paleon- been criticizedfor putting too much faithin the tology,outgroup analysis,and ontogenyhave directcorrelation between ancientness and prim- been frequentlycounterposed. Our vast storeof itiveness(Schaeffer et al. 1972; Nelson 1978). data on biologicaldiversity contains within it a Many paleontologistsseem inclinedto disre- message, a cipher,that consistsof patternsof gardthis criticism (e.g., Simpson1975). Doesn't specialized, group-definingcharacters. The a good recordshow a decent,albeit imperfect, breakingof this code- the discoveryof these correlationbetween antiquity and primitiveness? patternsof specializedtraits-is a challenging Isn't there a general pattern of evolutionary and, in cladistics,crucial enterprise for the dis- trends-despiteodd occurrenceshere and there- coveryof relationships.Obviously, the argument in thelong historiesof majorclades? Don't four- thatrelationships are best discoveredin thisway toed horsesappear earlier than three-toed horses? is not new (e.g., Gregory1910, p. 105). And It is thisinstinctive feeling about the basic reli-

This content downloaded from 132.248.28.28 on Mon, 04 Jan 2016 19:37:58 UTC All use subject to JSTOR Terms and Conditions 70 NILES ELDREDGE & MICHAEL J. NOVACEK abilityof the fossilrecord that seemingly clashes lineages,even phyla. The corollaryis that the witha dadisticperspective. fossilrecord documents such transitionswithout But theclash is moreapparent than real. Fos- referenceto the lineagesthat show them. Not silsprovide unique historicalinformation; under so. A trendmay seem moreprofound if it occurs certainassumptions, this informationindudes in parallelacross many different lineages. How- evidencefor character change. One may rejecta ever,a trendmust be (and need only be) doc- particularset of fossildata fora varietyof rea- umentedin at least one monophyleticgroup to sons, but not simplybecause it failsto conform have anyreality. Otherwise, how could we daim withpatterns revealed through other techniques. thatfossils provide direct evidence of evolution- Rejectionis moreappropriately based on the ex- aryhistory? Once again we returnto the preem- aminationof the validityof assumptionsfor the inenceof monophyleticunits. If charactertrends use of the paleontologicalapproach in a partic- are to have evolutionarysignificance, fossils that ular case. We can explainthis point by review- bear the charactersmust also bear some rela- ing, verybriefly, these basic assumptions. tionshipto each other. First,and most obviously,it is assumed that Third, the paleontologicalapproach assumes the fossilrecord in a particularcase is reasonably thatcharacters comprising a trendare takenfrom good. We won't belabor this point here. Nor equivalentontogenetic stages. It is hardlyworth- will we dwell yet again on the paleontologist's while,for example, to proposea cline based on uncertaintyprinciple-the problemof knowing a juvenilecondition in an earlyfossil, a subadult when the recordis good enough. Clearly,such conditionin a laterfossil, and an adult condition qualityis oftenaccepted without justification or in a still laterfossil. All threeconditions could is verysubjectively determined. The complete- be representedin the completeontogeny of each ness of the recordis a probabilisticargument, of thethree fossil organisms. This problem,while and one subjectto independentanalysis. In this certainlyfamiliar to paleontologists,is easilyob- regard,recent studies of depositionaland pres- scured. Paleomammalogists,for example, are ervationalcontinuity (Dingus and Sadler 1982; quick to claim that the diphyodontpattern of Schindel1982) are veryconstructive. toothreplacement allows a relativelyunambig- Second,the paleontological approach assumes uous recognitionof the adult stagein mammals. that fossilscarrying the traitsof a particular Yet standardtheories of toothhomology are now transformationare closelyrelated-that is, they suspect,partly because it is extremelydifficult to are membersof a monophyletictaxon that can distinguishjuvenile fromadult dental patterns be discriminatedreadily from a matrixof more in many Mesozoic mammals (McKenna 1975; distantlyrelated fossils. Obviously, the level of Bown and Kraus 1979). discriminationdepends on the referencesystem These assumptionsare straightforwardand of comparison.Analysis of characterchange in theirdisclosure hardly new. They become more thefossil record has been mosteffectively applied interestingwhen we examine the assumptions at the genericlevel or below (for example,the underlyingoutgroup comparison,the modus importantstudy of Chesapectenby Miyazakiand operandicommonly applied in cladistics-and Mickevich[1982)). This does not prohibitthe herewe see strikingparallels. documentationof trendsin a highertaxon, as The applicationof outgroupcomparison as- long as thatgroup is separablefrom its nearest sumes: (1) that variationof the relevantchar- relatives.If we daim, for example, to record actershas been adequatelysampled; (2) thatthe characterchange in the familyEquidae, we do ingroupand the ingroup+outgroupare mono- not want othersto doubt our recognitionof the phyleticand the outgroup-ingroupresolution familyand its members.We do not want some is justifiedby adequate charactersampling; and of our putativehorses to be, in reality,rhinos or (3) thatthe characterscompared are takenfrom tapirs. essentiallyequivalent ontogeneticstages. One This point may seem discrepantwith our may have good reasonsfor having more confi- knowlegeof large-scaletrends-the evolutionof, dence in a particularoutgroup comparison than forexample, calcified skeletons, or thetransitions in a particularcase studyof fossils.The impor- in feedingadaptations-that sweep acrossmajor tant point is that assumptionsfor eitherap-

This content downloaded from 132.248.28.28 on Mon, 04 Jan 2016 19:37:58 UTC All use subject to JSTOR Terms and Conditions SYSTEMATICS AND PALEOBIOLOGY 71 proach are broadlyequivalent. There is, more- formationfrom one conditionto anotheris di- over,no generalprinciple that allows us, in the rectlyobserved in the lifecycle of an individual case of discrepancies,to accept one technique organism,assuming the organismcan be raised uniformlyand discardthe other. There are high- under conditionsthat allow directobservation. ly corroboratedphylogenies based on characters Even when such experimentalprocedure is pro- organizedthrough outgroup comparison(see, hibitive,the assumption that different specimens e.g., severalchapters in the Ciochon and Chi- representindividuals of, say, a single species, arelli[19801 compendiumon New World pri- seems farless problematicthan the assumption mates). There are also rathercontinuous rock of monophylyat usually higherlevels in out- sequenceswith plenty of relatedfossils that dis- groupcomparison and paleontology.In fact,the play compellingpatterns of characterchange assumptionof groupmembership for a sequence (Miyazaki and Mickevich 1982). Fossil se- of fossilsor a sample of Recent adult taxa is quences and outgroup comparisonsmay even useful in drawingan analogy with ontogeny. yield congruentpatterns. But no matterhow This assumptionenables us to arrangea spec- fondlywe regardthis objective,fossil data can- trumof conditionsin a particularorder, just as not be judged simplyby theirdegree of corrob- we mightobserve them in the ontogenyof an orationof a patternbased on outgroup com- individualorganism. In ontogenythe basic ref- parison.The reliabilityof the fossilevidence can erencesystem-the individual-is known;in the be assessedindependently by, for example, stud- paleontologicalapproach or in outgroupcom- ies of stratigraphiccompleteness (Dingus and parison,the basic referencesystem-the mono- Sadler 1982; Schindel1982). phyleticgroup-is assumed or hypothesized. Ontogeny,a thirdmeans of characterdiscrim- Does the studyof ontogeny,then, transcend ination,has had a long and profoundinfluence othermeans of characteranalysis? If ontogenetic in systematics.Currently, we seem more im- transformationsare trulyisomorphic with those pressedthan ever with the role of ontogenetic of phylogeny,as Haeckel claimed-if ontogeny patternsin thestudy of charactertransformation. literally does recapitulatephylogeny-the an- Some cladists(e.g., Patterson1982) have even swerwould be decidedlyyes. But many biolo- stressedthat outgroupcomparison is merelya gists have pointed to heterochronouspatterns, surrogate,a less elegantsubstitute, for the direct deletions,truncations, and the like as significant evidenceof homologyprovided by comparative exceptionsto a Haeckelian law that always ontogeny.2 equates ontogenywith phylogeny (Alberch et al. The use of ontogenyin characteranalysis en- 1979). Recentlysome systematistshave adopted tailsassumptions that differ somewhat from those von Baer's laws in the applicationof studiesof that underpinthe paleontologicalapproach or characterdistribution and taxic relationships outgroupcomparison. Unlike the situationwith (Nelson 1978; Patterson1982). They stressthe fossils,the quality of the data in ontogenetic patternof ontogeniesthat diverge from the gen- studies seems more constrainedby materials, eral to the more particularas an independent techniques,and investigativeenergies than by means of identifyingmore inclusive and less in- any inherentimperfections of the data. More clusive sets of characters.Thus certainontoge- important,the studyof ontogenydoes not re- neticevents, such as terminalreplacement, can quire the assumptionthat the variousobserved simplybe viewed as part of the generalpattern conditions(i.e., characters)exist in membersof of divergencein the ontogeniesof diverseorgan- a singleentity. That informationis given at the isms (Fink, 1982, p. 261). Further,it is sug- basic levelof observation:in otherwords, trans- gested that truncationsor otherheterochronous eventsfor a particularontogeny are identifiable as anomalieswithin well-corroborated phyloge- 2 It should be stressedthat Patterson's(1982) definition of homologypertains to characterizationof monophyletic nies based on outgroupanalysis of othersup- taxa. Thus, Pattersonwrites (1982, p. 21): "Polarityof ho- portivecharacters (Fink 1982). Thus, well-cor- mologies(discriminating mono- and paraphyleticgroups) is roboratedphylogenies place significantconstraints resolvedby von Baer's law of ontogeny.Ingroup and outgroup comparisonsmerely order polarity to matchthat de- on patternsrevealed through the directstudy of terminedby ontogeny." ontogeny,a relationshipthat clearly parallels that

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suggestedbetween outgroup comparison and the betweenontogeny and outgroupcomparison. paleontologicalapproach. Indeed,it is theanalogy between transformation This last argumentcollides with an earlieras- in ontogenyand transformationin the fossil rec- sertion:outgroup comparison is hardlya weaker ord thatinvites one to claimthat paleontology substitutefor comparativeontogeny (Patterson offersa "verticaldimension" to the studyof 1982) if the formeris requiredfor the correct characters. understandingof ontogeneticpatterns. Like oth- We have emphasizedthe similaritiesin as- ers,we see no easy resolutionof thisissue. Per- sumptionsand difficultiesshared among these haps thisis because thereare two fundamentally threedifferent approaches to thestudy of char- differentlinks between ontogeny and phylogeny. acterevidence for phylogeny. Obviously all three In a hierarchicalcontext, ontogeny adds to the approachesare potentially useful. Because of its richnessof the characterevidence for taxa. Thus perspectiveand thenature of itsdata, each ap- comparativeontogeny, for the veryreason that proachretains some autonomy,some unique it is comparative,implies some a prioripattern qualities.Yet we do notintend here to strikea of the hierarchicalgroupings of the organisms blowfor the concept of threefold parallelism, at being compared.One does not harborgreat ex- leastas thatconcept is definedand criticizedby pectationsof ontogeneticcomparisons between Nelsonand Platnick(1981). The paleontologi- moles and monkeyflowers. In this hierarchical cal approach,comparative anatomy (outgroup context,then, both ontogeny and outgroupcom- comparison),and comparativeontogeny are not parisonemerge in practiceas differentaspects of strictlyparallel; they are sometimeslinked by a the same generalmethodology-a mappingex- commonassumption of a particularhierarchy, ercisethat sets as its goal the descriptionof the one thatmay be moreevident through one ap- distributionsof specializedtraits. proachthan another. In addition,a theoryof But what of the directcapacity of ontogeny characterpattern or recognitiondoes not explic- to revealtransformation? In this context, we find itlyrequire the inputof all threetechniques, that ontogenyoffers directly observable evidence althoughthe influenceof one techniqueover of charactermodification in developmentaltime. another-asin the case of ontogenyand out- And such modificationscan be recordedin an groupcomparison-may be difficultto detect. empiricallyrecognizable (i.e., neitherassumed The translationof thecharacter cipher is, after nor hypothesized)entity-an individualorgan- all, less perfunctorythan a parsimonysolution ism. True, there is no guaranteeof a perfect ofa givencharacter matrix. Hence, we can only match between a single ontogenetictransfor- speculateon the combinationof intuitionand mationand the courseof changeof the relevant analysisthat produced the character evidence for characterin phylogenetichistory. Furthermore, some of ourbest classifications. departuresfrom this perfect match (namely het- erochrony)might be detectedagainst a branch- Postscript ing frameworkof a phylogenywell supported Paleontologyis not the only source of insight by independentcharacters (Fink 1982). But on thehistory of life (as onestill commonly reads mightnot this "referencephylogeny" be sup- ingeneral evolutionary texts), nor is itsdata base ported in part by characterswhose homologies so imperfectthat it is bestignored in favorof a are revealedthrough ontogenetic transformation? detailed analysis among Recent organisms and Certainlythis is the case formany of our stan- taxa (as some paleontologistsand systematists dard,higher-level classifications. It was embryol- haverecently asserted). It is commonlyconceded ogy, not paleontologyor comparativeanatomy that,at thevery least, fossils add to ourknowl- of adult organisms,that unambiguouslyestab- edge of totalbiotic diversity; they give us, as lishedthe homologyof malleus and incus with well,minimum ages for the appearance of evo- articularand quadrate of moregeneralized am- lutionarynovelties, hence clades. But theygive niotetetrapods (aka "reptiles").Thus, depend- us more,including, on occasion,a glimpseof ing on a transformationalor hierarchicalcontext, whatmost probably was the actualcourse of thesphere of influencein characteranalysis shifts charactertransformation within a lineagethrough

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