Actinopterygii; Permo.Carboniferous
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ORYCTOS.Vol.4: 3 - 15.Décembrc2002 HETEROCHRONY\ryITHIN AMBLYPTERIDAE (ACTINOPTERYGII;PERMO.CARBONIFEROUS) ? Kathrin DIETZE Institut ftr Palâontologie,Museum ftr Naturkunde,Humboldt-Universitât, Invalidenstr.43, 10099Berlin, Germany,kathrin.dietze @rz.hu-berlin.de Abstract : Certain morphological traits of the Amblypteridae, i.e. Amblypterus and Paramblypterus, suggestlocal heterochronic processesby paedomorphosis.Since data on the ontogenetic stagesof an ancestralparamblypterid speciesare not available, Elonichthys palatinus, a fairly basal actinopterygian species,is used as a model for the potential ancestralontogeny to polarize patterns of heterochrony in the Amblypteridae. Presumably,ornamentation and shapeof the skull, squamation,and growth of the opercular seriesof Paramblypterus and/orAmblypterus were affected by processesrelated to heterochrony. Key words: lower actinopterygians,Permo-carboniferous, heterochrony, paedomorphosis, skull, squamation,oper- cular series Hétérochroniechez les Amblypteridae (Actinopterygii, Permo-Carbonifère)? Résumé- Certainstraits morphologiquesdes Amblypteridae, i.e. Amblypteruset Paramblypterzs,suggèrent une hétérochroniecorrespondant à une paedomorphose.Les différentesétapes ontogénétiques des Paramblypteridae basauxn'étant pas connues, une espèced'actinoptérygien basal, Elonichthys palatinus, est utilisée comme modèle pour reconstruireun ancêtrepotentiel afin d'établirles formesd'hétérochronie chez les Amblypteridae. Vraisemblablement,l'ornementation et la forme du toît crânien,la squamation,et la croissancede la sérieopercu- laire de ParamblypteruseTloa d'Amblypterzs sont affectées par desprocessus conditionnés par l'hétérochronie. Mots-clés: Actinoptérygiensbasaux, Permo-Carboniftre, hétérochronie, paedomorphose, toit crânien,squamation, sérieoperculaire. INTRODUCTION and the body. One objectiveof the restorationin three dimensionswas to gain a certainunderstanding of the Studiesof the Amblypteridaeare connectedwith biology of Paramblypterus duvernoyi and its rela- researchon paleoecosystemsof lakesfrom the Lower tives. The likely diet and food uptake,and the likely Permianof CentralEurope (e.g.,Boy, 1994, L998,in locomotor capabilitiesof Paramblypterushave been press; Boy et aI. 1994; Clausing & Boy, 2000). dealt with earlier (Dietze, 2001). In the following, I Objectives are the reconstructionof environmental will point out heterochronicprocesses that probably conditions,paleocommunities, and food chains.The affectedthe morphology of the skull, ornamentation membersof the family Amblypteri dae,Paramblypte- of the skull bones,growth of the opercularseries, and rus duvernoyi,P. gelberti, P. decorus,and Amblypte- the serrationof the scales. rus latus, have been (re)describedrecently (Dietze, Heterochronyis the changein the relativetime of 1998,1999, 2000). Their morphology and intra-spe- appearanceor rate of development of a character cific variation has been examinedin detail and were during phylogeny and is consideredpart of evolutio- the basis for three-dimensionalmodels of the skull nary mechanisms(e.g., Gould, 1977;-Alberchet al., ORYCTOS,YoL.4,2002 1979; Alberch& Alberch, 1981;Hall, 1984;McNa- included in this genus areParamblypterus duvernoyi mara, 1986). During ontogeny,the developmentor (Agassiz, 1833), Paramblypterus gelberri (Goldfuss, onsetof growth of certain structuresmay be accele- 1847), and Paramblypterus rohani (Heckel, 1861). rated or slowed down in relation to the ancestral The remainingnominal speciesin the genus(P. cau- state,which is called peramorphosisand paedomor- datus, P luridus, P. obliquus, P. reussi, P comblei, phosis, respectively (Gould, 1977; Alberch et al., and P gaudryi) either representjunior synonyms,or 1979;McNamara,1986). are known too poorly to allow for a comparison Paedomorphosisrefers to the retentionof ances- (Dietze, 2000). Amblypterus,the other genus of the tral juvenile charactersin the descendantadult phase Amblypteridae,contains only one species,Amblypte- by either progenesis,neoteny, or post-displacement. rus latusAgassiz 1833. Progenesiscorresponds to precocioussexual matura- In the course of this study, 413 specimensof tion, neotenyto reducedrate of morphologicaldeye- Paramblypterus duvernoyl (Agassiz, 1833) with a lopment, and post-displacementto delayedonset of sizerange of 19 - 220 mm,106 specimensof Param- growth (Gould, 1977; Alberch et al., 1979; McNa- blypterusgelberti (Goldfuss, 1847)with a size range ma.ra,1986). Neoteny, progenesis, and post-displace- of 35.5 - 151 mm, 83 specimensof Paramblypterus ment can affect only certain structuresor major enti- decorus(Egerton, 1850) with a sizerange of 66 - 245 ties of the organism.This is referred to as local or mm, and 73 specimensof Amblypterus latus with a global changes,respectively (McKinney & McNa- sizerange of 34 - 128mm were examined,thus repre- mara, l99l). senting the most comprehensivelyexamined family Morphological changesrelated to heterochrony of basalfossil actinopterygiansto date.Intra-specific have been describedfor many recentvertebrate taxa, variation concerning the dermohyal, <<suborbital>>, such as cichlid (Mayer, 1987) and characid (Fink, rostral,parietal and extrascapularbones ofthese spe- 1989) fishes, salamanders(Gould, 1971: Alberch & cies havebeen described earlier (Dietze 1999,2000). Alberch, 1981), snakes(Irish, 1989), and rodents For a completelist of cataloguenumbers see Dietze (Hafner & Hafner, 1984).In fossil vertebratespecies, (2000). heterochronyis difficult to identify, sincemore often Specimensfrom the Saar-NaheBasin and the than not, ontogeneticstages of a possibleancestor are Commentry Basin are preserved as compressions not available. Still, featuresrelated to heterochrony flattened during fossilization either articulated or could be postulatedfor a variety of taxa, such as dip- disarticulated.Bones of articulatedspecimens usual- noans (Bemis, 1984), certain dissorophoid amphi- ly are somewhatspread out aroundthe midline of the bians (Boy, 1993, 1995; Schoch, 1995), dinosaurs body by post-mortem bursting, thus preventing (Long & McNamara,1995),and deer (Gould, 1974). bones from being distorted. Surface structure,such Certain morphological traits of the Amblypteri- as sculpturing of the skull roofing bones and scales, dae suggestlocal heterochronicprocesses by paedo- is presenton many specimens.AWild M8 microsco- morphosis. pe equippedwith a camera lucida was usedto draw the specimens.Drawings of the best preservedspe- cimens were used for three-dimensionalrestoration. MATERIALAND METHODS These drawings were transferred onto thin paper which was meltedon thin platesof bees'wax.These Material of the Amblypteridae, i. e. the genera paper and wax <<bones>>of the skull and palate were Paramblypterus Saavage, 1888 and Amblypterus then cut out and assembledin a three-dimensional Agassiz, 1833,examined here, is from Late Carboni- model. The paper was used as control as not to ferous to Early Permianlacustrine deposits from the exceedthe degreeof bending and to avoid too much Saar-NaheBasin of Germany(e.g., Boy, 1976, 1994; distortion of the wax and paper bones.Reconstruc- Dietze 1999,2000) and from the Commentry Basin tion of the postcranialpart was undertakenin similar of France(Blot, 1966;Poplin 1994).The type species fashion and, including the restoredfins, fit onto the of Paramblypterusis Paramblypterusdecorus (Eger- reconstructedskull and photographed.Trunk length ton, 1850)designated by Blot (1966).Other species was measured from the posterior margin of the DreTZE - HETEROCIIRONYWITHIN AMBLYPTERIDAE supracleithrumto the centre of the caudal fin. To Paramblypterus duvernoyi is characterizedby establishD-values (Schmidt-Kittler, 1984, 1986), the following combination of characters: distinct drawings of the scales and opercular bones were ornamentationof parietals,postparietals, extrascapu- digitised in AUTOC AD 12 and areasand circumfe- lars, posttemporals,dermosphenotics, supratempo- rencewere calculated.D-values can be usedto dis- rals and supracleithra.Parietals with variable lateral tinguish shapesby comparing them to the area of a process.One or two medialextrascapular(s). Additio- circle with the samecircumference (L) as the object nal lateral extrascapularscontact opercle. Rostral in question(Schmidt-Kittle\ 1984,1986).D is a des- tapering anteriorly. Sclerotic bones absent. Six criptive parameterand equalsthe area of the accor- <suborbital>>bones. Maxillary plate deep.One or two ding circle divided by the areaof the shape(F) : dermohyal bones. <Spiraculan>rounded. Opercular and subopercularareas and D-values different from those of P. gelberti. Eight branchiostegalrays. D- L2 valuesof scales1.4 tct 2.0. Area of serratedscales p= narrowing towards anal fin. Forty-two + two scale 4 n.F rows along lateral line. Paramblypterusgelberti is characteizedby the following combinationof characters:little ornamen- Objects with an area similar to that of a circle tation of parietals,postparietals, extrascapulars, post- yield D-values close to 1, whereasmore complex temporals, dermosphenotics,supratemporals and shapeshave higher D-values. supracleithra.Parietals with lateral process.One or Areas and circumference of subopercularand two medial extrascapular(s).Additional lateral extra- opercular bones calculatedin AUTOCAD 12 were scapularsdo not contact opercle. Rostral tapering also enteredinto a two-sampleanalysis. In order to anteriorly. Sclerotic bones absent.Five <<suborbital> compensatefor the size of the specimens,this value bones.Maxillary