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Hooked: Habits of the Chinese Permian gigantopterid Gigantonoclea

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Based upon anatomical evidence, Permian aged gigantopterid fossils are in general reconstructed as climbing or scrambling plants. Gigantonoclea, a genus of adpressed gigantopterid foliage from the Permian of northern China, has been reported to
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  Hooked: Habits of the Chinese Permian gigantopterid  Gigantonoclea Leyla J. Seyfullah a, ⇑ , Ian J. Glasspool b , Jason Hilton a a School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK  b Science and Education, The Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, IL 60605, USA a r t i c l e i n f o  Article history: Received 1 October 2013Received in revised form12 December 2013Accepted 17 January 2014Available online 28 January 2014 Keywords: Cathaysian flora Gigantonoclea GigantopteridGrowth architectureShanxi ProvinceShihhotse formation a b s t r a c t Based upon anatomical evidence, Permian aged gigantopterid fossils are in general reconstructed asclimbing or scrambling plants.  Gigantonoclea , a genus of adpressed gigantopterid foliage from thePermian of northern China, has been reported to co-occur with hook-like organs that were interpretedas indicating ascrambling/climbing habit. Wereinvestigatedthese hook-likestructures andre-evaluatedthe nature of the co-occurrences in context with the flora preserved in each plant-bearing fossil ‘bed’ inthe North China sedimentary succession. New findings show that the species  Gigantonoclea hallei  proba-blyclimbedusingspeciallyadaptedclustersofcompoundgrapplinghook-likeshootsborneonthestems.This structural arrangement comprising shoots of hooks is new to the scrambling/climbing concept ingigantopterids. However, a key figured specimen previously reported as showing intermediatehook-tippedleafmorphologyonasolepinnuletipisdiscountedassuchandisreinterpretedasa‘normal’pinnule partially hidden under sediment that results in an unusual appearance to this pinnule tip.Adaptations for climbing or scrambling based upon ‘hooked leaves’ observed in  Gigantonoclea lagrelii are no longer supported and are reinterpreted as incompletely expanded leaves where the vernationprocess was interrupted. These data weaken prior interpretations of   G. lagrelii  as a climber/scramblerand raise doubts about the ubiquity of hooks amongst the gigantopterids as structures enabling themto climb or scramble their way through the Permian world.   2014 Elsevier Ltd. All rights reserved. 1. Introduction Gigantopterids are an enigmatic group of plants that aregrouped by their megaphyllous leaves with distinctive reticulatevenation and their distribution in North and South America andSoutheast Asia throughthe Permian(Glasspool et al., 2004; DiMicheleet al., 2011). Although they are unlikely to be monophyletic(Glasspool et al., 2004; DiMichele et al., 2011), the gigantopteridsrepresent intriguing examples of convergent evolutionin the plantkingdom as they possess anatomical and morphological similari-ties to modern angiosperms (flowering plants, Halle, 1927; Li andTaylor, 1998, 1999), while occurring in the Late Palaeozoic over100Ma before these plants are thought to have first evolved (Bellet al., 2010). Gigantopterids are generally thought to have seedplant affinities (Glasspool et al., 2004; Taylor et al., 2006; DiMicheleet al., 2005, 2011), although their higher-order relationships re-main unknown: few reproductive organs have been describedandthosethatareknownhavebeencharacterisedwithinsufficientdetail to determine their botanical affinity (Li and Yao, 1983;Mamay, 1989; Wang, 1999; Glasspool et al., 2004; DiMicheleet al., 2011). DiMicheleetal. (2005) havesuggestedapeltaspermous (seed plant) affinity for some American gigantopterids based onassociations of the leaves and peltaspermous reproductive organs.Although various species and genera have been assigned to thegigantopterids (e.g. Appendix 1 of  Li et al. (1994)), the gigantopte-rid concept was restricted by Glasspool et al. (2004) to includeonly the genera  Gigantopteris  Schenk ex. Potonié emend Glasspoolet al. and  Gigantonoclea  Koidzumi that are characterised by thepresence of megaphylls with continuous laminae, eucamptodr-omous venation, and higher-order veins, third order or above,that anastomose to form complex meshes while lacking suturalveins (for summary of excluded genera see DiMichele et al.,2011). However, the venation of   Gigantopteris  is far more complexand angiosperm-like than that of   Gigantonoclea  and on this basisthese two genera appear to be quite distinct within this concept.Both  Gigantopteris  and  Gigantonoclea  have been reported fromChina, Southeast Asia (Halle, 1927, 1929; Asama, 1974) and Oman(Berthelin et al., 2003), with further reports of   Gigantopteris  fromTurkey (Wagner, 1962) and Mexico (Carrillo Bravo, 1965) and Gigantonoclea  from Papua New Guinea and Thailand (Li and Shen,1996). However,  Gigantopteris  does not occur in North America http://dx.doi.org/10.1016/j.jseaes.2014.01.0201367-9120/   2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Present address: Courant Research Centre Geobiology,Georg-August-Universität Göttingen, Goldschmidtstraße 3, 37077 Göttingen,Germany. Tel.: +49 (0)551 3991296. E-mail address:  leyla.seyfullah@geo.uni-goettingen.de (L.J. Seyfullah). Journal of Asian Earth Sciences 83 (2014) 80–90 Contents lists available at ScienceDirect  Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes  and the occurrence of   Gigantonoclea  reported by Mamay (1988)remains uncertain (DiMichele et al., 2011).Our current understanding of gigantopterid growth habit is pri-marily based on evidence from anatomically preserved leaves andstems from the Late Permian of southern China that preserve evi-dence of adaptations for climbing that suggest these plants werevine- or liana-like.  Aculeovinea  Li et Taylor (Li and Taylor, 1998)has spines on its stem and  Vasovinea  Li et Taylor (Li and Taylor,1999) has spines and glandular trichomes on its stem that areinterpreted as adaptations for climbing. This interpretation of growthhabitin Vasovinea  isfurthersupportedbyitsco-occurrencewith isolated compound hook structures assumed to belong to thesame plant (Li and Taylor, 1999).Several other Palaeozoic pteridosperms have been interpretedas climbing plants, vines or lianas including  Pseudomariopteris Danzé-Corsin (Krings and Kerp, 2000) and  Karinopteris  Boersma(DiMichele et al., 1984), from which cuticular preparations showprolongations of the pinnaaxes withrecurvedtips. Cuticular prep-arations show various tendril type appendages in the pterido-sperms  Dicksonites pluckenetii  (Schlotheim ex Sternberg) Sterzel(Krings et al., 2003),  Blanzyopteris praedentata  (Gothan) Krings etKerp (Krings et al., 2003) and  Lescuropteris genuina  (Grand’Eury)Remy et Remy (Krings and Kerp, 1997). Unfortunately cuticularpreservation is unknown in  Gigantopteris  and  Gigantonoclea  fromnorthern China, and therefore other evidence is required to assesstheir growth habits.Adaptations for climbing in  Gigantopteris nicotianaefolia  fromnorthern China have not been previously identified (Glasspoolet al., 2004), but foliage with apparently hooked tips has beeninterpreted as evidence of a climbing habit for  Gigantonoclea lagre-lii  (Halle,1929). Also, asinglepinnuletipassignedto Gigantonocleahallei  was interpreted by Halle (1929) as having a ‘hooked’ apex,while various hook-like structures have been associated with  G.hallei  and have been interpreted as indicative of a climbing habit(Halle, 1927, 1929). This interpretation of   Gigantonoclea  fromnorthern China (Halle, 1929) led Yao (1983) to interpret the ecol- ogy of tropical southern Chinese foliage remains attributed to Gigantonoclea  that co-occurred with similar hook-like structuresas scrambling woody plants lacking specialised organs of attach-ment. In our view, such interpretations remain tentative.Hereweevaluateevidencefortheclimbinghabitof  Gigantonoc-lea  from the Lower and Upper Shihhotse formations of northernChina, with specimens held in the Halle Collection in Sweden. Thisis one of the largest collections of compression/impression plantfossils from the Permian of Shanxi Province and includes speci-mens on which many Cathaysian species circumscriptions arebasedincluding Gigantonoclea hallei and G. lagrelii .Halle’shistoricalcollection is unique since the localities are no longer available andcomparable collections do not exist. This collection also permitsreinvestigation of the specimens Halle (1927, 1929) figured asbearing hook-like structures in association with  Gigantonoclea foliage fragments to determine their structure and affinity. 2. Geological setting  The plant fossils examined are from the Permian of ShanxiProvince, China that were collected from specific ‘beds’ withinthe sedimentary succession exposed in the Eastern and WesternHills section of the Tai-Yuan-Fu (now Taiyuan) area as docu-mented by Norin (1922) and Halle (1927). These ‘beds’ are not equivalent to geological ‘beds’ but rather comprise tens of metres of strata that are equivalent to lithostratigraphic mem-bers within a formation (see Glasspool et al., 2004). Althoughnot from individual beds, the ‘beds’ are useful for stratigraphicsub-division and enable localised correlations between Easternand Western Hills sections (see Norin, 1922; Halle, 1927). Thefossils are from the Lower and Upper Shihhotse formations(Norin, 1922; Halle, 1927; Shen, 1995; Stevens et al., 2011) thatprogress from fluvial/deltaic into fluvial, alluvial and lagoonalfacies with frequent coal seams (Liu, 1990), the flora of whichis generally interpreted as representing riparian plant communi-ties (e.g. Stevens et al., 2011).The Lower Shihhotse Formation is assigned to the upper part of the Lower Permian corresponding to the upper part of the Kungu-rianStageoftheCisuralianandthelowerpart of theRoadianStageof the Guadalupian. The Lower Shihhotse Formation grades up-wardsintotheUpperShihhotseFormationisconsideredtobemid-dle to late Permian age. The age range of the Upper ShihhotseFormation is uncertain but probably from the latest Wordian orearliest Capitanian to either the end of the Capitanian (c. 5Maduration Stevens et al., 2011), or to the middle of the Wuchiapin-gian Stage of the Lopingian (c. 10Ma duration, Stevens et al.,2011).Stratigraphiccorrelationisbasedonregionalscalelithostra-tigraphy and plant fossil biostratigraphy for which further strati-graphic resolution is unavailable (see Shen, 1995; Glasspoolet al., 2004; Hilton and Cleal, 2007; Wang, 2010; Stevens et al.,2011). 3. Materials and methods Specimens are deposited in the Department of Palaeobotany,Swedish Museum of Natural History, (NRM) Stockholm. Each slabin each ‘bed’ was checked for any plant macro fossil remains and,where feasible, all were identified. Gigantopterid foliage and/orhook-likestructures,alongwithanyadditionalevidenceforaclimb-inghabit(e.g.sinuousandrarelybranchingstems)werenoted.Thefive‘beds’  sensu  Norin(1922)andHalle(1927)thatcontaingigant- opterid foliage and also hook-like structures (Table 1) were sepa-rated and reconstructed as much as possible. As previously notedbyHiltonandLi(2003)andSeyfullahandHilton(2009),insomein- stances individual slabs fromthis collection containdifferent partsof the same fossil plant specimenand canallowthe reconstructionof larger articulated fossil plant specimens by physically matchingsurfacesofeachslabwithotherslabsandidentifyingadjacentslabsor parts and counter-parts of the same slabs where present. Re-assembly of the fossil plant parts allows the most complete speci-mens to be investigated rather just than basing observations andconclusions ontheisolatedslabsalone.Therearethreespeciesofgigantopterid sensulato presentintheHallecollection:  Gigantonoclea hallei  (Asama 1959) ‘Gu and Zhi’ 1974, Gigantonoclea lagrelii  (Halle) Koidzumi 1936 and  Cathaysiopteris whitei (Halle)Koidzumi1936.Specimensof  Cathaysiopteris wereveryfragmen-taryandrestrictedto‘beds’ 13, 14and17, andnoclimbing-relatedor-ganswerefoundinthesebeds, exceptforaportionofundeterminablestem,thus Cathaysiopteris and‘beds’13,14and17wereexcludedfromthisstudy.Foliageassignabletoeitherofthetwo Gigantonoclea speciesoccurs as fragments of different sizes across seven ‘beds’ (Table 1). In ‘bed’ 26, sevensmall fragmentsof   G. lagrelii  occur, but nootherorgansof interest were found besides liana-like stem fragments. A separatesmall fragment of ? G. lagrelii  also occurs in ‘bed’ 33, but this speciesassignmentcouldnotbeconfirmedandnoclimbing-relatedorganswerefound in this ‘bed’, and so this was also excluded from the study. Leaf morphology was carefully checked to exclude any damage caused byherbivory that might affect any interpretations since Glasspool et al.(2003) documented herbivory to be fairly common in  Gigantonoclea from this collection. For each remaining ‘bed’’, all plant remains wereidentified to ensure that the floral composition was known (Table 2).Some specimens had historically been prepared by dégagement to re-move overlying sediment (see Fairon-Demaret et al., 1999). No fossilswithcuticleorcuticularremainswererecoverable. L.J. Seyfullah et al./Journal of Asian Earth Sciences 83 (2014) 80–90  81  Specimens were digitally photographed using a Canon EOS 10Ddigital SLR camera with 50-mmmacro lens. Higher magnificationswere achieved using a Zeiss Stemvi microscope fitted with an Axi-ocam digital camera. 4. Results Gigantonoclea hallei  and  G. lagrelii  are distinguished by thelevel of venation of their foliage, and their leaf morphology(see Glasspool et al., 2004, for full details), and for neither speciesis a complete frond preserved (Fig. 1a and b). The leaf species aredistributed across the Lower and Upper Shihhotse formations. G. hallei  is found exclusive of   G. lagrelii  in ‘beds’ 21, 22 and 28,andco-occurringwithitin‘beds’18and20. G. lagrelii occursexclu-sive of   G. hallei  in ‘bed’ 26 (Table 1).There are two apparent types of hook-like structures present inthe Halle collection. The first type are here called ‘long hooks’ andare found in four ‘beds’ (20, 21, 22 and 28; Table 1, and Fig. 1c–e). These long hooks are often found isolated, broken off froma largerstructure (Fig. 1d and e), although some are preserved as part of   Table 1 Co-occurrences of organs thought to belong to gigantopterid plants in ‘beds’ from the Halle collection, NRM, Stockholm. Dash indicates absence of specimens. ‘Bed’ number Number of assignable plant fossils in ‘beds’ of the Shihhotse formation G. hallei G. lagrelii  Hook-like structure Liane-type stems33 – <1 (Fragment) – –28 6 – 4 Long hooks –22 5 – 1 Long hook –26 – 7 – 621 32 – 7 Long hooks –20 ?1 14 6 Long hooks –18 ?3 23 ‘Hooked leaves’ –  Table 2 Systematic summary of fossil plants present in each ‘bed’ from the Taiyuan succession from the Halle collection, NRM, Stockholm. Dash indicates presence. Affinity Genus Bed number18 20 21 26 22 28 33Lycophyte  Lepidodendron  –Equisetales  Annularia  – – – – –  Annularites  – – – – – –cf.  Annularites  –  Asterophyllites  – – – Calamites  – – Bowmanites  –cf.  Macrostachya  – Sphenophyllum  – – – – –?  Thallites  –Fern  Oligocarpia  –  Asterotheca  – – – – – Pecopteris  – – – – – –cf.  Pecopteris  – Ptychocarpus  – – Phyllotheca  – Protoblechnum  – – – – Tingia  – Plagiozamites  – –Fern and gymnosperm  Sphenopteris  – – – Neuropteridium  –cf.  Neuropteridium  –  Aphlebia  – –Gymnosperm  Neuropteris  – – – Odontopteris  – Emplectopteris  – Callipteris  – – –cf.  Callipteridium  – Saportaea  –cf.  Psygmophyllum  – Taeniopteris  – – – –cf.  Taeniopteris  – Cordaites  – – Chiropteris  – Nystroemia  –‘  Acanthocarpus ’ – – Carpolithus  – – –cf.  Carpolithus  –cf.  Trigonocarpus  – Cardaicarpus  – Cornucarpus  – – Rhabdocarpus  – Samaropsis  –cf.  Samaropsis  –82  L.J. Seyfullah et al./Journal of Asian Earth Sciences 83 (2014) 80–90  compound shoot systems as figured by Halle (1927, Pl. 48,Figs. 1–7, 1929, Fig. 1) and can resemble grappling hooks (Halle, 1927, Pl. 48, Figs. 1–7; here Fig. 1c) with additional specimens found during this investigation. A second type of hook-like struc-tures only occurs in one ‘bed’, ‘bed’ 18 (Table 1). These were de-scribed by Halle (1929) as ‘hooked leaves’ with supposedlycutinized extensions continuing from the midvein of the pinnulesand resulting in an elongated and sometimes recurved tip(Fig. 1f). While atypical, this morphology has been interpreted byGlasspool et al. (2004: Fig. 7.1) as belonging to  G. lagrelii . 4.1. Observations on ‘hooked leaves’ and atypical examples of G.lagrelii ‘Hooked leaves’ are only observed in ‘bed’ 18 and one figuredspecimen (part and counterpart S128465a, b; Fig. 1f; Halle, 1929, Pl. 2, Figs. 3–6) is key to their interpretation. Another specimen(S128457) can also be positively attributed to this morphology,more tentatively along with S128463 and S128464. It is notewor-thy that although  G. lagrelii  foliage occurs in other ‘beds’ this atyp-ical morphology is not recorded elsewhere, though long hooks(‘bed’ 20) and liana-like stems (‘bed’ 26) are (Table 1).Specimen S128465 preserves several more or less typical, vari-ably complete, small, leaflets assignable to  G. lagrelii  and a sectionof indeterminate stem (Figs. 1f and 2a–f). All of the leaflets are incomplete and many appear asymmetrical, with the pinnules onone side of the leaflet having pronounced elongate tips (Fig. 2a).Some of these leaflets comprise very narrow pinnules that taperalong their length to become spine-like; at their base higher ordervenation is discernible within the lamina, though this transitionsrelativelyabruptlyintoadarkelongateapex(Fig.2b).Someleafletsare fuller and more closely resemble typical examples of   G. lagrelii ,except that terminally they abruptly elongate forming dark hook-likeapices(Fig.2c, arrowed).Evenwithinaleaflet,thepinnuleapi-ces of one side may vary from narrowed to rounded (Fig. 2d),though this may reflect pinnule orientation within the sediment.As well as the lateral pinnules, the terminal pinnule of some leaf-lets may also appear spine-like, but here too traces of higher ordervenation are discernible in them (e.g. Fig. 2e and f, arrows). In themajority of the leaflets where the apices of the pinnules, whetherlateral or terminal, are elongate, lamina is clearly present (Fig. 2aand b, d and e) precluding these structures (‘hooked leaves’) beingtrue hooks.In specimen S128457, an apparently isolated leaflet (Fig. 2g),asymmetry across the midrib is discernible, the elongate pinnulespreserving narrow traces of lamina, particularly toward the base.Based on this morphology this specimen is tentatively comparedwith the ‘hooked leaf’ forms of   G. lagrelii  described above, even Fig. 1.  Foliage and climbing organs from the Halle collection. Scale bars=10mm except  a  =20mm,  d  and  e  =2mm. (a) A large fragment of   Gigantonoclea hallei  bearing aresemblance to angiosperm foliage. S128414a, ‘bed’ 21. (b)  Gigantonoclea lagrelii  leaf fragment with venation .  S128461, ‘bed’ 18. (c) Remains of a shoot system with hookedappendages. S128447, ‘bed’ 21. (d)Isolatedhookwithsharpapex.S139046, ‘bed’ 20. (e)Apairofisolatedhooksshowingelongateform.S139055, ‘bed’ 20. (f)Massofhookedleaves associated with a stem fragment S128465a, ‘bed’ 18. L.J. Seyfullah et al./Journal of Asian Earth Sciences 83 (2014) 80–90  83  though there is no discernible venation pattern. Similarly, the leaf-let asymmetry of S128463 (Fig. 2h), thickened pinnule apices(Fig. 2i) and evident lamina (Fig. 2 j), although without venation (Fig. 2 j), suggest this affinity.No venation is visible in specimen S128464 (Fig. 3), however,thispoorlypreservedexampleisalsotentativelyassignedto G. lag-relii  baseduponthe general pinnule outlineand varyingdegrees of asymmetryintheirshape. Inplaces,theacroscopicpinnules(thosepointedtowardstheapex)appeartotaperintoelongatetips(Fig.3,white arrow), but in others this may be taphonomic artefact. Thebasioscopicpinnules(thosefacingthebase)arenotwell-preservedacross the specimen, but where distinct appear to have morerounded apices (Fig. 3, black arrow). 4.2. Observations on hooks and G. hallei The key specimencitedbyHalle (1929; his ‘ Gigantopteris nicoti-anaefolia ’; S128441a) as a ‘hook-bearingsegment’ of foliage is nowlargely obscured by age-darkened and cracked Canada balsam(Fig. 4a). This specimen was reported as the link between theleaves and the long hook type for  G. hallei , where Halle (1929, p.240) states ‘it is very badly preserved and indistinct, but evidently Fig. 2.  Hookedleaves associatedwith G. lagrelii . Scalebar=5mm. Allspecimensfrom‘bed’ 18. (a)Leafletwithelongatetips topinnules(S128465a). (b) Leafletwithelongatepinnules with clear lamina reaching to the apices (S128465a). (c) Incomplete leaflets with expanded lamina and small apical extension to the pinnules, hook-like apicalextension arrowed, although it is not clear whether there are traces of lamina up to the apex of this tip (S128465a). (d) Longest leaflet with variation in pinnule tips(S128465a).(e)Leafletfragmentwithadark, apparentlythickenedveinwiththinlaminatraceseithersideofthevein(arrowed,S128465a).(f)Variousfragmentsoverlying, asecond fragment with a dark, possibly thickened apex with lamina (arrowed, S128465b). (g) Isolated asymmetrical leaflet with dark veins and narrow lamina, tentativelyassigned to this leaf type, S128457. (h) A further leaflet here tentatively assigned to this leaf type, along with two recognizable fragments of   G. lagrelii , S128463. (i)Enlargement of the apex of h showing the asymmetry of the leaflet and the thickened tip to the pinnules. (j) Enlargement of the base of h showing almost completelyexpanded pinnule, but venation is not discernable.84  L.J. Seyfullah et al./Journal of Asian Earth Sciences 83 (2014) 80–90
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