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Body Size and Diversity Exemplified by Three Trilobite Clades

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Body size and diversity exemplified by three trilobite clades TERZY TRAMMER ANdANDRZEJ KAIM Trammer, J. & Kaim, A. 1997. Body size and diversity exemplified by three trilobite clades.- Acta Palaeontologica Polonica 42, l, l-12. Cope's rule concerns only the radiation phase of a clade, overlooking the phase of the clade decline; thus it is incomplete. Changesofbody size during the entire evolutionary history of a clade are exemplified here by three trilobite groups - ftychopariina, Asaphina and Phacopida. Increasing diversity ofthe clade is associated with increase in maximum body size during the radiation phase, and decreasing diversity is generally associated with a decreasein maximum body size. Two basic patterns of the maximum body size changes are observed dwing the decline of the clade. The first one is characterized by a high correlation between diversity and the maximum body size, and indicative of species atfrition that is nonselective with respect to the body size. The second one is characterized by a weak correlation between diversity and maximum body size, and typical of selective species attrition in relation to size. Jercy Trammer, Instytut Geologii Podstawowej, Ilniwersytet Warszawski, al. Zwirki i Wigury 93, PL-02 -089 Warszaw a, P oland; Andrzej Kaim, Instytut Paleobiologii PAN, ul. Twarda 5l/53, PL-00-l14 Warszawa' Poland. Introduction The evolutionaryhistory of an extinct cladeconsists of at leasttwo phases:the phase of diversificationor radiation (when speciesnumber increase)and the phaseof its decline or reduction (when the number of speciesdrop). Cope's rule, an old (Cope 1887)but recentlymodernized (Stanley 1973) generalization, claims that most groups have evolved from small towards larger body size. This rule concernsonly the first, diversification phase of a clade's history (Stanley 1973: figs 5-7). In effect, our knowledge of body size evolution is biased and incomplete as it disregardsthe evolution of body size during the secondphase, when a clade was on the wane.The aim of the presentcontribution is to presentan analysisof changesin body sizeduring the complete evolutionary history of a clade. Body size and diversity: TRAMMER & KAIM ^45 E I -s z^^ ILI JU J 225 4. zo T u lc o 10 5 0 40 60 80 loo 12o J:"" ,.J:tt" (';T Fig' 1. Body length related to cephalonlength in Ptychopariina,Asaphina and Phacopida.Since body length and cephalonlength are strongly correlated,length of cephaloncan be used as a size-index.Data measured from Harrington et al. (1959). The problem will be exemplified by three trilobite groups:the Early Cambrian- Late Ordovician suborder Ptychopariina Richter, 1933; the Early Cambrian-earliest Silurian suborderAsaphina Salter, 1863; and by the Late Cambrianto Late Devonian .orderPhacopida Salter, 1864. Body size for individual specieswas measuredon all adult specimensof the aforementionedtaxa illustratedinthe Treatiseon Invertebrate Paleontology(Harrington et al. 1959).Such data have been proven by our analysisto be statisticallyrepresentative. Since in mostcases the illustrationsintheTreatise show only cephalons,we measuredcephalons' lengths as a proxy for body size.we found that cephalonlength is well correlatedwith the whole body length (Fig. 1) and thus may be used as a size-index.Finally, we conshuctedsize-frequency histograms for various stagesof the evolutionary history for eachtrilobite group studied. We areaware that since1959, when the trilobite volumeof Treatisewas published, a large number of new trilobite taxa has been described.we decided,however, to conductthis study on the basisof knowledgeof trilobite history recordeduntil 1959. which, incompleteas it is, demonstratestrends in trilobite evolution.The histogram relating nilobite speciesnumber to their body size (Fig, 8) is typical also for other animaltaxa (compareMay 1988:figs 2 and6; Jablonsky1996: fig.10). This validates the representativenessof the Treatisedata.It would be interestingto seeif datafrom a larger sample - such as the future edition of the Treatise - will confirm oul conclusionsbased on the limited subset. Results In the Ptychopariina, the phase of diversification continued from the Early to Late Cambrian, and the phase of reduction from the Late Cambrian to Late Ordovician (Figs 2, 3). In the Asaphina,the phaseof diversificationpersisted from the Middle cambrian to Early ordovician, and the phase of reduction from the EarJy to Late ACTA PALAEONTOLOGICAPOLOMCA (42) (I) 1oT n=2 rara 0 l----.--- -+ OiOovician Ptychopariina 10T n=B Middre n=403 O+-___.@-&-q Ordovician t8 toT n=39 Earty (/) 101& Ordovician tlJ oF6@G*@al--- - ul [L 50 @^ IL o30 t ,2o u rn dl l z 30 20 Middle Cambrian 10 0 30 20 Early '10 Cambrian 0 CEPHALON LENGTH (mm) Fig. 2. Frequency distribution of cephalon length among speciesof Ftychopariina in various intervals of their evolutionary history. During the Cambrian radiation phase, maximum body size and diversity increased,while during Ordovician reduction phasethe marimum body size and diversity decreased'Data (including stratigraphic range of the clade) from Harrington et aI. (1959). Ordovician (Figs 4, 5). We found that in both groups, maximum cephalonsize is strongly correlatedwith diversity. It increasedduring the radiation phase,and de- creasedduring the reductionphase (Figs 2-5).To the contrary,we did not find strong correlationbetween maximum cephalonsize and speciesnumber in the Phacopida (Figs6,7). Discussion Many moretrilobite specieshad smalland intermediate cephalon sizes than large sizes (Fig. 8). Such a body size pattem is largely result of cladogeneticdiffrrsion (passive trend of McShea 1994) awayfrom an originally small-sizedancestor as shown by Gould (1938)and McKinney (1990a,b). The processof diffirsion and,in addition,the highertotal originationrate of smaller-sizedspecies then large ones(Dial & Marzluff 1988;McKinney 1990b)implies that the origin of a large trilobite specieswas a rare or improbableevent. Thus the correlationbetween maximum body size and diversity may be discussedand explainedin termsof probability. 'seAIEArq ,(rer ezrse8rul pe,lerqo" slerlrrueru leql pelou (AtAil,(epe15 puu sleuruuru ',firsre.nrp ere ,frsre.trp qBFIpuu ezrsdpoq a3.re1ueel11eq uo4eleJros;o seldurexereq16 'se11uourlue q8r,qJo spoued qll^\ eu4l uI peprcuro3,(1pnsn seplder pge spodoqcuJq 'sproplneu'srr€JeJruruero; Suoure srruoJ JI1ImBIS;o ecuermcto eql leql pelou (ZOZ'd 'Eg6I'196I) rellnhtr'erolureqpng '(qOOOt ,{euu5trc11:886I plnog !9361ueppegce6 'sueeplssoqord'sesroq :1-g s8g :g26y f,eyrc1g)sluepor pue smesoc,(1ed'sueecelec 'selruoruure'spodorqcerq 'suereJrmrr€JoJ JoJ os1e ]nq selrqoll4 JoJfluo lou prlel sI eInJ slrlJ '(S-Z s8rg) requrnuselceds Surseercur qlIA sos?eJJulsellqollrl Suouruezrs ,(poq rrmrrrrxeru.{q.t sr sIg.T.'seseeJoul d11 ueq sesueJJepdueq,l luql lceJeql luo4 s/(oIIoJ ',(Iluenbesuoc q 'ut8rro slr ro; ,(msseceusuo4el3eds go d71Joqumu eq1 sr re8rel oql 'prru '(8 '3rg) 'serceds ur8uo s1r;o d,(llpqeqord erp sI Jeilerusoql eIqolLD e Jo ezrs 'uolsnJJrp ,(poq eqt re8rel eq] crleueSopulseql Jo 1ro1rreql q8norql 1IeJo lsrlJ ,(lereueg 'ur8uo '8ID .setcedsyo ,ftr-p.qeqordeql e1eruqseol (8 epp pcutdure eql esn,{eureu6 '00I ro 16'971qenbe Suol ruur 0g sreqrueuqlr,l serceds1o qSpo aql roJ drusseceu 'prreq 'I0'0 r/71suorprceds;o requrnu oqt reglo eql uO ro 000I/0I spnbe Suoltuut 99 '?uo1 selqelueserderqIA sarcads;o ur8uo go d firyqeqord eql ueql urur 0S oJe0I 'serceds 'e8ere,re ,(1uo 9961Suogm;1 uo suorlercedsd71 speeu serceds sr-q1;o ur8uo eq] 'aseqd ueql 'dsr sercedsue,rr8 e;o ur8uo eq];o ,(lqgqeqordeql g - uollelp€r arl;, 'p ta paE',nHreu?el'rs eurr;'z'alduro4 e,nc'(L68'0 = r) uoqelexorSuorts ,fts,r eql etou ,*.,|?rXflr] 'g '8tg 3io e8eluecred e su pepold euruedoqcr(14u1 dlrsrelrp prre ezrs ,(poq umrnrxuru eq1 m se8ueq3 (Byrt)f u\rr creoto:le 6e? 09t 009 099 0L9 ueuquPc _l o o o o o ^uPf q d_< 0t P< = ol, 9c; Fm 5r- :3 -'o_ XE qH +a :9. 56 -.(D a:.<- '!) 6' 9) 0) Fo - 5 f, = :r 0t oz 08 0v /.68'0= 't 09 ezrsApoq a 09 urnuxeu OL ,q,sren1pw 08 euluedoqclld 06 ol 00 lo 1ltn1T)IT dilhlh111gJ :{ystaup puo ans Kpog ACTA PALAEONTOLOGICA POLONICA (42) (1) Late Ordovician a lrJ O tu 8 (L o U) 4 IL o 2 E. 0 I.IJ d] f 4 z 2 0 t0 20 Asaphina tt=87 Middle Cambrian CEPHALON LENGTH (mm) Fig. 4. Frequency distribution of cephalon length among speciesof Asaphina in vmious intervals of their evolutionary history. During the Cambrian-Early Ordovician diversification phase,the maximum body size and diversity increased, while during the Ordovician phase of the reduction, maximum body size and diversity decreased.Data (including stratigraphic range ofthe clade) from Harrington et aI. (1959). rapidly during only in about 10 to 15 Ma of radiation.Bivalves, in contrast,needed much more time to develop large-sizedforms. This conforms with our explanationof the phenomenonsince mammals'diversification rates were much higherthan diversi- fication rates of bivalves (Stanley 1979) so that mammalsachieved high diversity much faster. The reduction phase.- To explain why maximum body size decreasesalong with decreasingdiversity during the reductionphase, two hypothesescan be suggested: a deterministicone and a stochasticnull hypothesis.The deterministichypothesis assumeselevated extinction and/or reduced origination rates of large-bodiedtrilobite speciesin comparisonwith small-sizedones, as postulated by Stanley(1979) and Vrba Body size and diversitv: TRAMMER & KAIM vo1o0 Asaphina 90 80 m diversity 70 a m€uimum bodysize 60 r = 0.840 50 40 \\ 30 20 10 \ c c (s (sc o.S >,'6 :c)nt.S 9'F 9'< e.9 =F ,:Y O .=o qB 9E
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  • An Inventory of Trilobites from National Park Service Areas

    An Inventory of Trilobites from National Park Service Areas

    Sullivan, R.M. and Lucas, S.G., eds., 2016, Fossil Record 5. New Mexico Museum of Natural History and Science Bulletin 74. 179 AN INVENTORY OF TRILOBITES FROM NATIONAL PARK SERVICE AREAS MEGAN R. NORR¹, VINCENT L. SANTUCCI1 and JUSTIN S. TWEET2 1National Park Service. 1201 Eye Street NW, Washington, D.C. 20005; -email: [email protected]; 2Tweet Paleo-Consulting. 9149 79th St. S. Cottage Grove. MN 55016; Abstract—Trilobites represent an extinct group of Paleozoic marine invertebrate fossils that have great scientific interest and public appeal. Trilobites exhibit wide taxonomic diversity and are contained within nine orders of the Class Trilobita. A wealth of scientific literature exists regarding trilobites, their morphology, biostratigraphy, indicators of paleoenvironments, behavior, and other research themes. An inventory of National Park Service areas reveals that fossilized remains of trilobites are documented from within at least 33 NPS units, including Death Valley National Park, Grand Canyon National Park, Yellowstone National Park, and Yukon-Charley Rivers National Preserve. More than 120 trilobite hototype specimens are known from National Park Service areas. INTRODUCTION Of the 262 National Park Service areas identified with paleontological resources, 33 of those units have documented trilobite fossils (Fig. 1). More than 120 holotype specimens of trilobites have been found within National Park Service (NPS) units. Once thriving during the Paleozoic Era (between ~520 and 250 million years ago) and becoming extinct at the end of the Permian Period, trilobites were prone to fossilization due to their hard exoskeletons and the sedimentary marine environments they inhabited. While parks such as Death Valley National Park and Yukon-Charley Rivers National Preserve have reported a great abundance of fossilized trilobites, many other national parks also contain a diverse trilobite fauna.
  • Olenid Trilobites: the Oldest Known Chemoautotrophic Symbionts?

    Olenid Trilobites: the Oldest Known Chemoautotrophic Symbionts?

    Olenid trilobites: The oldest known chemoautotrophic symbionts? Richard Fortey* Department of Paleontology, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom Communicated by Lynn Margulis, University of Massachusetts, Amherst, MA, April 3, 2000 (received for review March 1, 2000) Late Cambrian to early Ordovician trilobites, the family Olenidae, Given the widespread occurrence and taxonomic spread of were tolerant of oxygen-poor, sulfur-rich sea floor conditions, and chemoautotrophic symbiosis, it is likely to have been an ancient a case is made that they were chemoautotrophic symbionts. adaptation. Because direct evidence of the fossil bacteria seldom Olenids were uniquely adapted to this habitat in the Lower preserves, evidence of such habits tends to be inferred from Paleozoic, which was widespread in the Late Cambrian over Scan- taxonomic and͞or morphological data, which is not always dinavia. This life habit explains distinctive aspects of olenid mor- reliable (11). The long-ranging solemyid and lucinid bivalves (10) phology: wide thoraces and large numbers of thoracic segments, indicate that by the Silurian (ca. 420 million years), this life mode thin cuticle and, in some species, degenerate hypostome, and the already had been adopted by some groups with living descen- occasional development of brood pouches. Geochemical and field dants. Ancient vent associations have been recognized from at evidence is consistent with this interpretation. Olenids occupied least the Devonian (12). their specialized habitat for 60 million years until their extinction I show in this paper that even by the late Cambrian period (505 at the end of the Ordovician. million years ago) certain extinct arthropods, trilobites belonging to the family Olenidae, evolved features best understood as evidence olorless sulfur bacteria, a heterogeneous category of bacte- of sulfur chemoautotrophic mode of metabolism.