Taphonomy of Isocrinid Stalks: Influence of Decay and Autotomy Tomasz K
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Nova Southeastern University NSUWorks Marine & Environmental Sciences Faculty Articles Department of Marine and Environmental Sciences 1-1-1995 Taphonomy of Isocrinid Stalks: Influence of Decay and Autotomy Tomasz K. Baumiller Harvard University Ghislaine Llewellyn Harvard University Charles G. Messing Nova Southeastern University, [email protected] William I. Ausich Ohio State University Find out more information about Nova Southeastern University and the Halmos College of Natural Sciences and Oceanography. Follow this and additional works at: https://nsuworks.nova.edu/occ_facarticles Part of the Marine Biology Commons, and the Oceanography and Atmospheric Sciences and Meteorology Commons Recommended Citation Baumiller, Tomasz K., Ghislaine Llewellyn, Charles G. Messing, and William I. Ausich. "Taphonomy of isocrinid stalks; influence of decay and autotomy." Palaios 10, no. 1 (1995): 87-95. This Article is brought to you for free and open access by the Department of Marine and Environmental Sciences at NSUWorks. It has been accepted for inclusion in Marine & Environmental Sciences Faculty Articles by an authorized administrator of NSUWorks. For more information, please contact [email protected]. RESEARCH LETTERS 87 skeletalmorphology. In recentyears, however,studies on soft-partanato- myof stalks of living crinoids (Grim- Taphonomyof Isocrinid Stalks: mer et al., 1984a, b, 1985; Grimmer and Holland, 1990; Holland et al., Influenceof Decay and Autotomy 1991) have provideda new perspec- tive to paleobiologistsstudying cri- noid stalks. For example, Donovan (1989) used the absence of muscles in stalksof livingcrinoids and hard- TOMASZ K. BAUMTTILTER a characteristicmorphology and is part morphologyof fossilsto argue Departmentof Earth and Planetary the site of autotomy. that fossilcrinoid stalks also lacked Sciences, Althoughstalk shedding by au- muscles;Baumiller and Ausich(1992) Harvard University, totomymay contributeto the ob- used the distributionof ligamentsin 20 OxfordSt., servedpatterns, decay experiments livingisocrinids to interpretthe pat- Cambridge,MA 02138, U.S.A. on isocrinidstalks, bothin situ and tern of fragmentationof Mississip- in the lab, suggestthat post-mortem pian stalks. These examples illus- GHISLAINE LLEWELLYN disarticulationalso results in non- tratehow data on livingcrinoids can Departmentof Earth and Planetary random fragmentation.Thus both help generate paleontological hy- Sciences, processes,autotomy and post-mor- potheses. Harvard University, tem decay, contributeto the ob- This studyis a furtherexample of 20 OxfordSt., served pattern of fragmentation. this approach.We used data on the Cambridge,MA 02138, U.S.A. Underlyingboth processes is the or- morphologyand behaviorof living is- ganization of soft tissues at synos- ocrinidsto test the hypothesisthat CHARLES G. MESSING toses. there is a preferredsite of disartic- Nova UniversityOceanographic ulation in theirstalks. To test this Center, hypothesiswe examinedstalks of ex- 8000 North Ocean Drive, INTRODUCTION tantisocrinids and subjecteda series Dania, FL 33004, U.S.A. of them to a set of experimental The recentuse of submersiblesfor treatments.Having establishedthat WILLIAM I. AUSICH the studyof stalked crinoids has pro- a preferredsite ofdisarticulation ex- Departmentof GeologicalSciences, duceda wealthof data on theecology, ists,we thenexamined Mesozoic and Ohio State University, morphology,and biostratinomyof Cenozoic isocrinidstalks to deter- 155 S. Oval Mall, these animals (Macurda and Meyer, mineif, in thesefossil specimens, the Columbus,OH 43210, U.S.A. 1974; Roux, 1980a, b; Conan et al., site of disarticulationwas the same 1981;Messing et al., 1988;Holland et as in livingisocrinids. al., 1991;Baumiller et al., 1991;Llew- ellynand Messing,1994). Isocrinids ISOCRINID STALK PALAIOS, 1995, V. 10, p. 87-95 have been the focus of most of the MORPHOLOGY, AUTOTOMY, ecological and biostratinomic re- AND BIOSTRATINOMY Stalks of isocrinidcrinoids are dif- search, whereas the morphologyof ferentiated into cirri-bearingcol- representativesof all 5 livingorders The soft-and hard-partstructure umnals (nodals) and columnals ofcrinoids has been studiedin detail of isocrinidstalks has been studied lacking cirri (internodals). This (Grimmer et al., 1984a, b; 1985; in detail by several investigators skeletaldifferentiation allowed us to Grimmerand Holland,1990; Holland (Macurda and Meyer, 1975; Roux, test whetherstalk fragmentationis et al., 1991). These data have given 1974, 1975, 1977; Donovan, 1984; random or whetherit occurs pref- us a better,though in comparisonto Grimmeret al., 1985). The isocrinid erentiallyat a specificarticulation. otherinvertebrate groups still rather stalk is organizedinto two distinct Our analyses indicate that the pat- rudimentary,understanding of living regions:a shortproximal growing re- ternsof fragmentationin multicol- crinoids,which is criticalfor inter- gionin whichnew columnals develop, umnal segmentsof extant isocrinids pretingfossil crinoids. Fossil crinoid and a distalregion in whichcolumnal collected by submersible,by dredg- stalks,for example, have oftenbeen arrangementand size remain con- ing,and in sedimentsamples, as well used forsystematic, taxonomic, and stant.Two typesof columnals can be as those found as fossils,are non- biostratigraphic purposes (Glu- distinguishedin thestalk: the nodals, random. The preferred plane of chowski,1981; Hagdorn,1983, 1986; which bear appendages called cirri, fragmentationcorresponds to the Moore and Jeffords,1968; Schubert and the internodals,which lack cirri. synostosis,the articulationbetween et al., 1992; Simms,1989; Stukalina, In externalappearance the isocrinid a nodal and the internodaldistal to 1988). These approaches have gen- stalk consistsof repeatingsegments it. In isocrinidsthis articulation has erally relied on interpretationsof (noditaxes),each composed of a set Copyright? 1995,SEPM (Societyfor Sedimentary Geology) 0883-1351/95/0010-0087/$3.00 This content downloaded from 137.52.76.29 on Mon, 9 Jun 2014 16:43:52 PM All use subject to JSTOR Terms and Conditions 88 BAUMILLERETAL. of internodalsbounded on its distal ie, 1984). The physicalproperties of nodal as the distalmost (terminal) end by a cirri-bearingnodal (Fig. 3A the MCT's, such as stiffnessand vis- columnal. in Baumillerand Ausich,1992). Each cosity,may be controlledby the or- segment contains approximately ganism; autotomymay involve the LABORATORY EXPERIMENTS equal numbersof columnals,except activereduction of the stiffnessand/ for the proximalregion where new or viscosityof the ligament.It is not The decay experimentsconducted internodalsare intercalated. knownwhy or howfrequently autot- by Baumillerand Ausich(1992) were The regularpattern of the nodi- omy of stalk segments occurs. If limited in scope: only four incom- taxis skeletalmorphology is also re- sheddingof distal stalk segmentsis plete stalk segmentswere used, the flectedin the organizationof isocrin- frequent,the majorityof multicol- specimenshad been frozenprior to id softtissues (Grimmer et al., 1985). umnal segments (pluricolumnals) the experiments,the complete se- In each noditaxis,long ligamentfi- found in the sediment should ter- quence of disarticulationwas ob- bers,called through-goingligaments, minatedistally at a nodal ratherthan servedover a period of only 6 days, pass throughthe stereomof the in- an internodal. withonly a singlespecimen observed ternodalsand into the nodal where Alternatively,a patternof nodal- duringan additional 15-day period theyterminate (Fig. 3B in Baumiller terminatedpluricolumnals could be and under modified experimental and Ausich, 1992). Only shortliga- producedby another mechanism: the conditions,and onlya singlespecies mentfibers, called intercolumnallig- differentialresistance of synostosial was tested. In an attemptto extend aments,penetrating no deeper than and non-synostosialarticulations to and confirmthose results,the decay tensof microns into the stereom, con- decay. Baumillerand Ausich (1992) sequencesof 12 specimensof two dif- nect the nodal to the adjacent distal arguedthat synostoses, because they ferentisocrinid species [(Endoxocri- internodal,called the infranodal. This lack thicker, through-goingliga- nus parrae (Gervais)and Chladocri- patternis then repeatedin the sub- ments and because they may bear nus decorus (Carpenter)] were ob- sequent noditaxis.Thus the stalk is special structuresfacilitating autot- servedfor up to 60 days (Fig. 1). The subdividedinto noditaxes, each held omy,would be the firstto disarticu- specimens were placed in 60-liter, togetherby long ligamentsand con- late followingdeath, thus producing aerated, sea-watertanks and main- nectedto othernoditaxes by articu- nodal-terminatingpluricolumnals. tained in the dark at either18 or 20? lations bearing only short ligament Decay experimentson fourshort stalk C. They were monitoreddaily and fibers.The lattertype of articulation fragmentsof the isocrinidCenocri- the patternsof fragmentationwere is called the synostosis.The synos- nus asterius (Linne) confirmedthis recorded.The resultslargely confirm tosisis easilydistinguished from oth- prediction:the stalk segmentsdis- the conclusionsof the previousstudy er typesof articulations (symplexies) articulatedfirst at the synostosialar- (Baumiller and Ausich, 1992): the in livingand fossilisocrinids because ticulations,while the otherarticula- synostoses fragmentedbefore the of its relativelyfeatureless skeletal tionsremained intact for several days symplexies (articulations