Anthropoid Origins 节肢动物器官

AnthropoidOriginsRichardF.Kay,CallumRoss,BlytheA.WilliamsRecentfossildiscoverieshavegreatlyincreasedourknowledgeofthemorphologyanddiversityofearlyAnthropoidea,thesubordertowhichhumansbelong.PhylogeneticanalysisofRecentandfossiltaxasupportsthehypothesesthatahaplorhine-strepsir-rhinedichotomyexistedatleastatthetimeoftheearliestrecordoffossilprimates(earliestEocene)andthateosimiids(middleEocene,China)areprimitiveanthropoids.Functionalanalysissuggeststhatstemhaplorhinesweresmall,nocturnal,arboreal,visuallyorientedinsectivore-frugivoreswithascurrying-leapinglocomotion.Achangefromnocturnalitytodiurnalitywasthefundamentaladaptiveshiftthatoccurredatthebaseofthetarsier-eosimiid-anthropoidclade.Stemanthropoidsremainedsmalldiurnalarborealistsbutadoptedlocomotorpatternswithmorearborealquadrupedalismandlessleaping.Ashifttoamoreherbivorousdietoccurredinseveralanthropoidlineages.Morethanacenturyofstudiesinembry-ology,anatomy,andgeneticshaveresolvedthephylogenyoflivingPrimates(Fig.1).Twogreatcladesoflivingprimatesexist,theStrepsirrhini(Lemuriformes)andtheHaplorhini(TarsiusandAnthropoidea).WithintheAnthropoideaaretwoclades:Catarrhini(theOldWorldmonkeys,apes,andhumans)andPlatyrrhini(theNewWorldmonkeys).Paradoxically,however,theproblemofanthropoidoriginsisstillamongthemosthotlycontestedintheliteratureofprimateevolution;noconsen-sushasyetemergedregardingtherelation-shipsofseveralgroupsofPaleogenefossilprimatestolivingstrepsirrhinesandhaplo-rhines.Thislackofconsensushasstemmedprincipallyfromanabsenceofmorpholog-icallytransitionaltaxabetweenanthropoidsandanyofthebetterknownPaleogeneprimategroups.Herewereviewthefossildiscoveriesofthepastdecade,especiallythosethatbegintoclosethemorphologicalgapbetweenanthropoidsandotherpri-mates,andapplycladisticmethodologytotheassessmentofallavailablefossilevi-denceinanefforttoproduceabetterre-solvedphylogenyofprimates.Buildingoncomparativestudiesofprimateadaptation,weproposeanoutlineofanthropoidevolu-tionfromanadaptiveperspectiveandre-viewtheadaptivesignificanceofseveralpeculiaranthropoidfeatures.TheFossilRecordToavoidconfusioninwhatfollows,clarifi-cationisneededconcerningtheusageofseveraltaxonomicnames.ThetaxaStrep-sirrhini,Haplorhini,andAnthropoidea,asweusethem,referto“closeddescentcom-munities”orstem-basedclades(1).Anthro-poideaisthecladeofallspecies,livingorextinct,thataremorecloselyrelatedtolivingplatyrrhinesandcatarrhinesthantoTarsius.Similarly,HaplorhiniisthecladeofallspeciesthataremorecloselyrelatedtoAnthropoideaplusTarsiusthantolivingstrepsirrhines.(Fig.1).FossilfindsinNorthAfricahavenowpushedbackthefossilrecordofAnthro-poideafromtheOligoceneintotheEocene(2–4)(Fig.2),butnotaxonyetdescribedfromthelateEoceneofAfricadocumentsanintermediatemorphologybetweenan-thropoidsandeithertarsiersorstrepsir-rhines.Theoldestwell-knownanthropoids(ParapithecidaeandOligopithecidae)comefromthelateEoceneofEgypt[about37millionyearsago(Ma)](4,5).Althoughsomewhatmoreprimitivemorphologicallythananylivinganthropoid,theparapithe-cidsandoligopithecidspossessedaplatyr-rhinegradeofmorphologicalorganizationthatwassubstantiallyidenticaltothatoflivingplatyrrhines(6–10).Earlyfossiltarsiersandpossiblelemuri-formsaresopoorlyknownthattheylike-wisecontributenothingtonarrowingthemorphologicalgapbetweenAnthropoideaandotherprimates.ThefossilrecordofLemuriformesremainsavirtualblankbe-foretheMiocene;justafewdoubtfulrecordsarerecordedintheAfricanPaleo-gene(7,11).RecentfindshavenowpushedbacktheearliestoccurrenceoftarsierstothelatemiddleEoceneofAsia(about45Ma),establishingamuchgreaterminimumageforthedifferentiationofthehaplorhinecrowngroupfromotherprimates(12,13).However,thismaterialisknownonlyfromdentalremains.TwoPaleogenegroupsoftenhavebeenidentifiedaspossiblesistertaxaforAnthro-poidea.TheEocene-OligoceneAdapidae,fromNorthAmerica,Asia,Europe,andAfrica,iscommonlyconsideredtobethegroupfromwhichLemuriformesarose.However,someresearchershavealsoiden-tifiedthemasanthropoidrelatives(14–16).AnotherPaleogenegroup,theOmomyidaeofNorthAmerica,Asia,Europe,andpossi-blyAfrica,isoftenconsideredtohavegivenrisetotarsiersandtoanthropoids,eitherviaseparateomomyidstocks(17)orviaacom-monstemlineage(18).Omomyidsandadapidsarenowmuchbetterrepresentedbyskullsandlimbbones,allowingafullerphy-logeneticassessmentofthepossibilitiesthanwaspossibleonlyadecadeago.Athirdviewisthattheanthropoidlineage,al-thoughsistertoomomyids,goesbackbeforetheearliestknownomomyid(19).ThediscoveryofremainsofanewfamilyofEoceneprimatesinAsia,theEosimiidae(12,13),haspromptedinterestinthepos-sibilitythateosimiidswereancientprimi-tiveanthropoids.PhylogeneticModelsofAnthropoidOriginsToevaluatealloftheconflictinghypothesesaboutanthropoidrelationships,weunder-tookacladisticanalysisoftheevidencefromdental,cranial,andpostcranialskeletons.Atotalof256dental,cranial,andpostcranialcharacterswereassessedfor50taxa(Table1),includingplatyrrhines,lemuriforms,thebestknownancientfossilcatarrhineAegyp-topithecus,Tarsius,thebetterknownadapidsandomomyids(includingthosecitedbyvar-iousauthorsascloseanthropoi