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Reproductive Biology of the Cerro Cuadrado (Jurassic) Fossil Conifers: Pararaucaria Patagonica

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Reproductive Biology of the Cerro Cuadrado (Jurassic) Fossil Conifers: Pararaucaria Patagonica Amer. J. Bot. 64(6): 733-744. 1977. REPRODUCTIVE BIOLOGY OF THE CERRO CUADRADO (JURASSIC) FOSSIL CONIFERS: PARARAUCARIA PATAGONICA RUTH A. STOCKEY Departmentof Botany,The Ohio StateUniversity, Columbus 43210 A B S T R A C T Seventy-twosilicified cone specimensof Pararaucariapatagonica Wieland fromthe Cerro Cuadrado (Jurassic)petrified forest in Patagoniawere studiedby use of thinsections and re- flectedlight. Traces fromthe cone axis stele to the bract and ovuliferousscale are separate at theirorigins. In cross sectionthe abaxiallyconcave ovuliferousscale trace and massivecir- cularbract trace branch half-way out intothe cone-scalecomplex. Two triangular-shapedbun- dles of fibersfollow the scale trace into the laminarpart of the ovuliferousscale. Both sur- faces of the ovuliferousscale possess hairs whichmay have assistedin cone closure. Cones typicallycontain one flattened,winged seed per ovuliferousscale. Multi-layeredseed integu- mentsare representedby an innerfleshy layer of large cells filledwith a black amorphous material,a sclerotestaconsisting of wedgesor fan-shapedgroups of sclereidsoriented at right angles to the seed surface,and a thin,often crushed fleshy layer. Seed wings consistof anastomosing,branched cells resemblingglandular hairs and containingmany intercellular spaces. Well-preservedpolycotyledonous embryos containing up to eightcotyledons are present in severalcones. Tissues of the embryoincluding the shootapex, calyptroperiblem,hypocotyl, and cotyledonsare described.On the basis of anatomicaland morphologicalfeatures, speci- mensof P. patagonicaare comparedto membersof both extantand extinctfamilies of coni- fersincluding the Araucariaceae,Taxodiaceae, Pinaceae, Cupressaceae,and Cheirolepidaceae. THE CERRO CUADRADO petrifiedforest in Pata- known fromthe petrifiedforest and at firstwas gonia (Santa Cruz, Argentina) was initiallyde- thoughtto representtwo distinctspecies, P. pata- scribed by Windhausen (1924). Among the gonica and P. elongata. In 1935 Wieland demon- silicifiedremains found there are twigswith leaf stratedthat the range of charactersin specimens scars,wood, supposed seedlings,and threegenera of Pararaucaria did not warrantthe recognition of coniferouscones that were deposited in place of two species, since the variation within the by a volcanic ash (Wieland, 1935; Menendez, cones was no more than that occurringin cones 1960). Many specimens, principallycollected of extant Pinus species. This initial description from the three volcanic peaks of the region was based on 20 cone specimens of the iField (Cerro Cuadrado, Cerro Alto, and Cerro Madre Museum collection throughthe use of polished e Hija) ultimatelybecame the propertyof Amer- surfaces (Wieland, 1935). Wieland believed the ican and European museums. Among these re- cone representeda transitionform between the mains is the silicifiedovuliferous cone Pararau- Araucariaceae and the Pinaceae based on seed caria patagonica, first described by Wieland and cone-scale features,and cone vasculariza- (1929) in a preliminarytreatment of the Field tion. He placed it in the Cheirolepidaceae,a fam- Museum of NaturalHistory (Chicago) collection. ily of Mesozoic coniferserected by Hirmer and This cone is the smallerof the two ovulate cones Horhammer (1934) and emended by Jung (1968). 1 Received for publication21 October 1976; revision Calder (1953) emended the genericdiagnosis accepted 1 February1977. of Pararaucaria to fitthe range of variationseen The authorwishes to thankthe followingpeople for in the BritishMuseum collection and employed theirgracious loan of specimensand use of laboratory thin sectioningin additionto studies of polished facilities: Dr. Eugene S. Richardson,Field Museum of NaturalHistory, Chicago; Mr. CedricShute, British Mu- faces. Structureof the xylem in the cone axis seum of Natural History,London; Dr. Hans Tralau and was compared to extantconifer families. In ad- Dr. BrittaLundblad, Naturhistoriska Riksmuseet, Stock- dition, the presence of many cotyledonsin the holm; Dr. James M. Schopf and Dr. Stig Bergstrom, embryoand the winged nature of the seed were United States Geological SurveyCoal Geology Labora- toryand OrtonMuseum, The Ohio State University;Dr. reported. Calder placed Pararaucaria in the Francis M. Hueber, United States National Museum, Taxodiaceae because of the greatdiversity within SmithsonianInstitution. Special appreciationis expressed the family (sensu Pilger, 1926) stating that it to Dr. ThomasN. Taylorfor his help and guidancedur- ing this study. Supportedin part by National Science resembledno one living genus in the combina- Foundationgrants BMS 75-14221 and BMS 74-21105. tionof characters. 733 734 AMERICAN JOURNAL OF BOTANY [Vol. 64 4Y ab' ' h ;A0 July, 1977] STOCKEY-PARARAUCARIA PATAGONICA 735 The excellentsilica permineralizationof these cheids showed a greatercontrast with this tech- cones offersa rare opportunityto studydelicate nique. Most slides, however,were leftunstained seed and embryotissues some of whichappear to and mountedin HSR (Harleco SyntheticResin). have cellularcontents. The purpose of thispaper A numberof taxa of coniferseed wings were is to provide a detailed analysis of the cones of studied for comparison with those of Pararau- Pararaucaria with particular emphasis directed caria. These included seed wings of several gen- at seeds and embryosand to comparethese cones era of the Pinaceae, Cupressaceae, Taxodiaceae, with those of several extant as well as extinct and Agathis australis (D. Don) Salisburyin the coniferfamilies. Araucariaceae. MATERIALSAND METHODS-The presentstudy STRATIGRAPHY-The age of the petrifiedforest utilizes72 cone specimensassignable to the fos- is still not accuratelydetermined; however, most sil taxon Pararaucaria patagonica on the basis of workerstoday follow the interpretationsof Fer- externalmorphology and previouslycut surfaces. uglio (1949, 1951) who believes that the Cerro Thirty-fivecones were selected for sectioning Cuadrado sedimentshave a Middle to Late Juras- based on examinationof previous cuts made by sic age (Calder, 1953; Menendez, 1960; Stockey, earlier workers. Material includes specimens 1975a). fromfour collections: The Field Museum of Na- tural History (Chicago), the British Museum DESCRIPTION-General features-Cones vary (Natural History) London, NaturhistoriskaRiks- in shape from conical to cylindrical,sometimes museet (Stockholm), and Orton Museum of ovoid, and are 5.1-2.3 cm long and 2.6-1.3 cm Geology (The Ohio State University,Columbus). in diam (Fig. 1). Numerous helically arranged The cones are completelysilicified and appar- cone-scale complexesare arrangedin a 3/8 phyllo- entlycontain littleor no organic material. Dar- taxyaround a slendercone axis. Each cone-scale row (1936) pointed out the tendencyof cones complex is composed of a large, woody ovulif- from these localities to display differentcolors erous scale which is subtended by a smaller of quartz replacing differentseed tissues. Em- woody, flattenedbract (Fig. 1, 2). Externally bryos appear to be replaced by chalcedony,and cone-scalesresemble those of certainmembers of the space once occupied by the nucellus is filled the Taxodiaceae, e.g., Sciadopitys Siebald and with a transparentquartz. Some cone specimens Zuccarini and Sequoiadendron Buchholz; how- appear to be more porous than others,especially ever, the bract and ovuliferousscale of Pararau- betweenthe ovuliferousscale and bract,between caria are not fused but free for almost theiren- sclereidsof the stoneylayer of the seed, and in tirelength (Fig. 3, 6). the cavityonce occupied by nucellus. Most cones In less weatheredspecimens (Fig. 2), the outer are composed- of dense a-quartz (Stockey, surfaceof the ovuliferousscale appears striated. 1975a). None of the specimensthus far observed No laminartip, umbo, or extensionof the ovulif- are known froma volcanic ash matrix,as is the erous scale into distinctlobes has been observed. case for some specimens of Araucaria mirabilis Some cones show evidence of scorched areas or (Calder, 1953). pittingof the ovuliferousscales and distortion TRA-Bond 2114 Water White Transparent due to crushing,suggesting evidence of burial by Epoxy Adhesive (TRA-CON, Inc., Medford, volcanic ash. In a few weatheredcones, seeds Massachusetts) was used for mounting speci- with visible internaltissues are exposed. Only mens to the glass slides. This epoxy has a refrac- four specimens of those examined show pieces tive index (1.565) close to that of quartz thus of cone peduncle,and all of these appear to have giving excellent optical properties. Few cones poorly preservedleaves surroundingthe axis of showed littlecontrast with most tissuesappearing the type described by Calder (1953). She fig- clear-buffin color. Thin sections of these were ured one BritishMuseum specimenwith spirally stained in a 5% aqueous Malachite Green solu- arranged,broad, lanceolate leaves with striated tion (Bartholomew,Matten, and Wheeler,1970) surfaces that show a sharp transitionto fertile for 11/2 minutes. Details of pittingon the tra- scales. No cuticleremains are present. Fig. 1-7. Pararaucariapatagonica. 1. Externalsurface of ovulate cone. 031218. X 2. 2. Externalsurface of less weatheredcone. Arrowindicates striation of ovuliferousscale externalsurface P13988. x 2. 3. Outermostpor- tionsof the cone-scalecomplex showing large cells with amorphouscontents. P139-- I #1. X 25. 4. Longitudinal sectionof the cone axis at a level of tracedivergence. P13978 A #1. X 7. 5. Transversesection of cone axis. P13961 #2. x 14.
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