The first discovery of in situ Verrucosisporites applanatus spores from the Middle Triassic flora from Bromsgrove (Worcestershire, UK)

    The first discovery of in situ Verrucosisporites applanatus spores from the Middle Triassic flora from Bromsgrove (Worcestershire, UK) Leyla J. Seyfullah, Evelyn Kustatscher, Wilson A. Taylor PII: DOI: Reference:

S0034-6667(13)00077-8 doi: 10.1016/j.revpalbo.2013.04.004 PALBO 3456

To appear in:

Review of Palaeobotany and Palynology

Received date: Revised date: Accepted date:

28 November 2012 17 April 2013 24 April 2013

Please cite this article as: Seyfullah, Leyla J., Kustatscher, Evelyn, Taylor, Wilson A., The first discovery of in situ Verrucosisporites applanatus spores from the Middle Triassic flora from Bromsgrove (Worcestershire, UK), Review of Palaeobotany and Palynology (2013), doi: 10.1016/j.revpalbo.2013.04.004

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The first discovery of in situ Verrucosisporites applanatus spores from the Middle

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Triassic flora from Bromsgrove (Worcestershire, UK).

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Leyla J. Seyfullaha,1*, Evelyn Kustatscherb and Wilson A. Taylorc

Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston,

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Birmingham, B15 2TT. UK.

(Present address and contact for corresponding author)

Courant Research Centre Geobiology, Georg-August-Universität Göttingen,

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Goldschmidtstraße 3, 37077 Göttingen, Germany. E-mail address: [email protected]

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Museum of Nature South Tyrol, Bindergasse 1, 39100 Bozen/Bolzano, Italy.

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goettingen.de; tel: +49-551-3991296; Fax: +49-551-397918

Department of Biology, University of Wisconsin-Eau Claire, Eau Claire, WI 54701. USA.

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ABSTRACT

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Triassic plant remains are uncommon globally, with few Early-Middle Triassic floras well

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documented. Thus, the Middle Triassic (Anisian) of Bromsgrove, Worcestershire, UK

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provides new insights into the terrestrial biota at this time and is extremely valuable since it provides the majority of fossil plants from the UK terrestrial Triassic sequence. This small but diverse flora comprises typical gymnospermous (Willsiostrobus, Pelourdea) and sphenopterid

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(Schizoneura, Neocalamites) elements of an Anisian-age flora. Reinvestigation of megafossil

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remains led to the discovery of a previously unknown and undescribed plant fossil with in situ spores, Bromsgrovia willsii gen. et sp. nov. The in situ spores were extracted and examined by light, scanning electron and transmission electron microscopy. The Bromsgrove Anisian

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flora is summarised and illustrated along with the first occurrence of in situ Verrucosisporites applanatus spores, a marker for the Middle Triassic. The parent plant of Verrucosisporites

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applanatus is suggested to be a horsetail with an unusual morphology.

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Keywords: Anisian; fossil plant; horsetail; in situ spore; Middle Triassic; UK.

1. Introduction In Europe, the plant megafossil record from the Permian to the early Middle Triassic is poorly known (Kerp, 2000); the Early Triassic sediments are rare in the rock record due to extensive sedimentation hiatus (Bourquin et al., 2011) and many of the terrestrial deposits from this time are unfossiliferous red beds. However, Grauvogel-Stamm and Ash (2005) summarized palynological and megafossil evidence following the end-Permian mass extinction event, and reported that European Triassic floras are marked by an initial survival

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period dominated by the lycopsid Pleuromeia (Münster) Corda, as shown by the Early

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Triassic (Olenekian) Pleuromeia flora of Germany (Fuchs et al., 1991), with a relatively long

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recovery period up to the earliest Middle Triassic. This recovery period is marked by the

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resurgence of conifers in the Early Anisian, as shown by the ‘Grès á Voltzia’ Formation, northeastern France; and then the resurgence of pteridosperms and cycadophytes in the Late

and Roghi, 2006; Kustatscher et al. 2007).

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Anisian as illustrated by the Dont Formation of the Dolomites, northeastern Italy (Kustatscher

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In the UK, there is a paucity of fossils from the Triassic sediments (Benton et al., 2002), with some basins devoid of any kind of fossils (Benton et al., 2002). The Lower Triassic (Induan-Olenekian) has only rare fossil animals, invertebrate trace fossils and

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vertebrate footprints (King and Benton, 1996; Powell et al., 2000). Only the Middle Triassic

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(Anisian) has ‘significant’ numbers of fossils in the UK (Benton et al., 2002). These fossils

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include tetrapods and their trace fossils, fishes, crustaceans, brachiopods and single specimens of a scorpion and a mussel. The plant remains (both micro- and macrofloral) are found only in

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a few beds in a few localities in the UK. In Cheshire the Tarporley Siltstone Formation has very rare plant megafossils. In the Midlands plant megafossils are reported from the Bromsgrove Sandstone Formation and fewer from the Arden Sandstone Formation (Warrington and Ivimey-Cook, 1992; Barclay et al., 1997); whereas the Tarporley Siltstone Formation contains only plant microfossils (Warrington et al., 1980). This work focuses on a special reproductive organ found in the British Midlands flora of the Bromsgrove Sandstone Formation (Anisian) of Bromsgrove (Worcestershire, UK) from the L.J. Wills collection. This unique fructification yielded verrucate in situ spores which enables a comparison between the botanical affinity of the macroremains (horsetail) and the

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so far supposed affinity of the spores in the dispersed form (ferns); the study of the spores is

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based both on morphology and ultrastructure of the spore wall.

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2. Materials and methods

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2.1 Collections repositories

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The Wills Collection is the major collection of the British Midlands Triassic material. This collection includes both geological and paleontological material and is housed in three locations: the Lapworth Museum, University of Birmingham, with the majority of the figured

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plant material and slides held at the Sedgwick Museum, University of Cambridge.

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Unfortunately all the original slides are lost along with those of more recent authors’ on this

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collection. Additional relevant materials from the Lapworth Museum (borehole samples) and Black Country Museum (local sediment examples from known localities) were also reviewed.

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Some thirty specimens are also stored at the Natural History Museum of London (labels indicate: Coll by L. G. Wills esq. M.A.).

2.2 Origin of the collections

The majority of the Wills collection is Anisian in age and comes from four former quarries that are no longer productive. Three of the quarries have been filled in and built over, while the land with the fourth is privately owned, with no access granted. These former quarries are located in the Hill Top area of Bromsgrove in Worcestershire which is 21 km southwest of Birmingham, or 150 km northwest of London (Ordanance Survey Reference SO 949 698, Fig.

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1). The collection covers two occurrences of plant fossils (as well as other fossil materials) found in the Triassic succession of the Midlands (Fig. 2). Here we focus on the plants of

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Anisian age. These fossil plants are listed as originating from either the ‘Lower Keuper

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Sandstone’ or the ‘Waterstones’ or the ‘Buildingstones’ (Wills, 1910; 1970). These are all now included in the Finstall Member.

2.3 Fossil preparation and imaging

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APPROXIMATE POSITION OF FIG. 1

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All specimens illustrated here are of previously unpublished material held at the Lapworth Museum, Birmingham. The material described and figured by Wills (1910) refers to

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specimens from the Sedgwick Museum, Cambridge. Materials held in the Natural History Museum, London were also reviewed, but are not illustrated here. Specimens examined using

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light microscopy were photographed with a Canon EOS-10D digital camera attached to a Zeiss Stereo Stemmi 2000-C microscope. Small portions of the sporangiophore were macerated with Schulze’s solution. The resulting spores were either mounted on glass slides using glycerine jelly for light microscope observation and photographed using a Canon EOS10D digital camera attached to Zeiss Axio A1, or mounted on a carbon-covered scanning electron microscope stub using a wet hair, sputtered with platinum/palladium (2 x 120 s at 20 mA, 10 nm coat thickness) using an Automatic Sputter Coater (Canemco Inc., Quebec, Canada) and examined under a field emission SEM (Carl Zeiss LEO 1530). TEM analysis involved embedding individual spores or spore masses in Spurr low viscosity embedding medium (reformulated as per Ellis, 2006), in shallow aluminium weighing dishes. Specimens

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were then cut from the dishes with the proper orientation for at least one trilete arm to appear

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in perfect cross section. Specimens were viewed with a JEOL-2010 TEM fitted with a side

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mounted AMT (Woburn, MA, USA) digital camera. Images were processed (cropped,

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rotated, tone balanced, backgrounds blacked out) in Adobe Photoshop v. 8 (LM and SEM) or Photoshop CS5 Extended (TEM) and plates constructed in Corel-Draw v. 12, or Photoshop CS5 Extended. Cuticle preparations of other compression materials of the same collections

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failed to yield any recoverable cuticle.

2.4 Terminology

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We have adopted standard terminology for spore walls that considers the layer in which the

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germinal aperture is located to be the exospore (Lugardon, 1978).

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APPROXIMATE POSITION OF FIG. 2

3. Geological setting

3.1 British onshore Triassic succession

The British Triassic comprises a number of separate basins which have different sedimentary and subsidence histories, making the Triassic succession across the UK difficult to establish (McKie and Williams, 2009). The base of the Triassic has not yet been identified anywhere in the British Isles, even though several Permo-Triassic boundary-spanning successions occur, but these are nearly all unfossiliferous (Benton et al., 2002; Hounslow and Ruffell, 2006). The

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upper boundary is defined by the base of the Jurassic System (Warrington et al., 1980; Benton

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et al., 2002; Hounslow and Ruffell, 2006), this being in the basal portion of the predominantly

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Jurassic Lias Group (Warrington et al., 2008; Wignall and Bond, 2008). This fossil paucity

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means the stages of the Triassic Period (as summarised by Lucas, 2010) cannot be identified, so the British terrestrial Triassic is divided into three lithostratigraphic units, the Sherwood Sandstone Group, the Mercia Mudstone Group and the Penarth Group. These correspond

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approximately to the Induan and Olenekian (Sherwood Sandstone Group), Anisian through to

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the Rhaetian (Mercia Mudstone Group), and the latest Rhaetian (Penarth Group; Fig. 2), although regional variations are substantial due to diachronous deposition of these units (Hounslow and Ruffell, 2006).

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During the Triassic, the British Isles lay beyond the western termination of the Tethys Ocean and drifted northwards from a paleolatitude of about 16°N to 34°N (Hounslow and

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Ruffell, 2006). This drift is not thought to have had a deep impact on the climate which was dominated by a strong monsoonal circulation (Parrish, 1993; Hounslow and Ruffell, 2006).

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The UK Triassic succession is interpreted as a transition from a continental fluvial environment to marine conditions (Benton et al., 2002; Hounslow and Ruffell, 2006; Howard et al., 2008) where the fluvial sandstones became marine influenced (Sherwood Sandstone Group), which was followed by local development of lacustrine and marine playa systems (Mercia Mudstone Group), often with substantial amounts of halite deposition during the Anisian and Carnian. Marine conditions became widely established in the Late Triassic (Rhaetian, Penarth Group to Lias Group).

3.2 British Midlands Triassic succession

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The lithostratigraphy of the British Midlands follows that of the UK as a whole (Sherwood

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Sandstone Group, Mercia Mudstone Group , Penarth Group), but there are some very distinct

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localized variations with the inferred ages of units when compared with the generalized UK

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Triassic lithostratigraphy (see Old et al., 1991; Warrington and Ivimey-Cook,1992; Barclay et al., 1997; Fig. 2.) The diachronously deposited Sherwood Sandstone Group spans the PermoTriassic boundary to the Anisian (Middle Triassic; Hounslow and Ruffell, 2006). The

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Sherwood Sandstone Group is locally divided by the Hardegsen disconformity, separating the

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unfossiliferous Early Triassic (Induan-Olenekian) from the fossiliferous early Middle Triassic (Anisian, Benton et al., 2002; Hounslow and Ruffell, 2006). The Sherwood Sandstone Group interdigitates with the Mercia Mudstone Group, and the base of the Mercia Mudstone Group

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is also diachronous (Howard et al., 2008). The rarely fossiliferous Mercia Mudstone Group is Middle (Anisian) to Late Triassic (late Norian or Rhaetian) age based on palynological

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evidence (Hounslow et al., 2004) and is overlain by the Late Triassic (Rhaetian) Penarth Group which contains fairly abundant marine fossils (Hounslow and Ruffell, 2006).

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In the Worcester basin (Fig. 2) the Sherwood Sandstone Group comprises three formations: the basal Kidderminster Formation which is underlain by an unconformity, the overlying Wildmoor Formation which terminates in an unconformity, and the overlying Bromsgrove Sandstone Formation. The Bromsgrove Sandstone Formation comprises two members: the basal Burcot Member and the Finstall Member (Barclay et al., 1997; Hounslow and Ruffell, 2008). The majority of known animal and plant macrofossils are from the Anisian Finstall Member of the Sherwood Sandstone Group (Fig. 2).

4. Results

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4.1 The Middle Triassic British Midland flora

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The Anisian-aged flora from the Finstall Member of the Bromsgrove Sandstone Formation

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has been partially listed by Wills (1910) and some identifications have since been revised.

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APPROXIMATE POSITION OF PLATE I

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Most plant remains are preserved as impressions, some compressions, and there are many indeterminable pith casts present (Plate I, 1-3) showing varying degrees of threedimensionality and levels of preservation, and evidence of fluvial sorting (Plate I, 2). Most

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pith casts or internal molds, where determinable, have an equisetalean affinity (Plate I, 3); although some are also gymnospermous, and all these occur in the sandier sections. In the

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mudstone lenses more diverse fragmentary plant remains are seen (Plate I, 4-5). Wills collected and published (1910) roots, pith casts and leaves (Plate I, 5) of Schizoneura

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paradoxa Schimper et Mougeot, 1844 (Wills, 1910; text-figs 21-24; pl. 12, pl. 14 figs 1, 3; pl. 15, figs 1-2, pl. 16; pl. 17 figs 1, 3, 7; pl. 19 figs 1, 3, 7; pl. 21). Male coniferous cones (Plate I, 6) originally assigned to Voltzia heterophylla (?) Brongniart, 1828 (Wills, 1910, pl. 20) have since been reinvestigated and attributed to Willsiostrobus willsii (Grauvogel-Stamm and Schaarschmidt, 1978, 1979). Leaves of the gymnospermous Pelourdea vogesiacus (Schimper et Mougeot) Seward, 1917 (Plate I, 7), described by Arber previously (1907) as Zamites grandis (Wills, 1910; text-fig. 26; pl. 14, fig. 2) are also present, with some remarkably long and intact leaves. Rare examples of Neocalamites sp. are also present (Plate I, 8). Other taxa figured by Wills (1910) include a portion of “Equisetites arenaceus (?)” (Wills, 1910; pl. 19, fig. 4) too badly preserved to be attributed at species level, and the enigmatic sole specimen of

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Strobilites sp. (text-fig. 27, spores fig. 4 of pl. XXI). Unpublished material in the Sedgwick

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Museum includes a specimen labelled “Chiropteris digitata? Kurr”; however the preservation

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is not good enough for a classification at genus level.

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The palynological record of this formation shows a more diverse flora with lycopsids, sphenopsids, (Calamospora nathostii (Halle) Klaus), ferns (e.g., Cyclogranisporites Potonié et Kremp, Osmundacidites Couper), diverse gymnosperms (Lueckisporites triassicus Clarke,

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Alisporites toralis (Leschik) Clarke) (Wills, 1910; Chaloner, 1962; Clarke, 1965; Warrington,

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1970, Pattison et al., 1973). Three species of the dispersed spore genus Verrucosisporites are recorded: V. thuringiacus Mädler, V. morulae Klaus and V. applanatus (Mädler) Adloff et

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Doubinger (Clarke, 1965; Warrington, 1970).

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5. Systematics

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APPROXIMATE POSITION OF FIG. 3

5.1 Diagnosis

Genus: Bromsgrovia n. gen.

Diagnosis: Thin stem with elongate acicular leaves and at least two strobili maturing asynchronously, with terminal strobilus maturing first. Strobili slightly rounded, composed of densely inserted sporangiophores. Sporangiophores polygonal to isodiametric. In situ spores circular to sub-triangular, slightly granulate to almost smooth exine to verrucate, with conspicuous trilete mark, similar to the Verrucosisporite-type of dispersed spores.

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Derivation of name: From the Bromsgrove area in the Midlands, where the paleobotanical

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materials were collected by L. J. Wills.

Type species: Bromsgrovia willsii n. sp., here designated.

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Remarks: A sole specimen lacking a counterpart but easily distinguishable from other

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Species: Bromsgrovia willsii n. sp.

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sphenopsid cones based on the size and shape of the strobili, and the thin stems and leaves.

Diagnosis: Herbaceous plant with narrow stem and elongate acicular leaves and at least two

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strobili maturing asynchronously. Terminal (mature) strobilus and lateral shoot-borne less mature. Strobili roundish, composed of densely inserted sporangiophores. Sporangiophores polygonal to isodiametric. In situ spores circular to sub-triangular, approx. 120 µm, verrucate,

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with conspicuous trilete mark ½ - ⅓ spore diameter, similar to the Verrucosisporites applanatus type of dispersed spores. Immature spores with slightly granulate to almost smooth exine.

Derivation of name: to honor the collector L. J. Wills for his contribution to the Triassic paleobotany of the British Midlands.

Holotype: number BU5248A-D (including slides) (Plate II, Fig. 1), here designated. The figures of Plates II-VI illustrate details of the holotype, including of the spores macerated

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from the sporangia that are referable to Verrucosisporites applanatus (Mädler) Adloff et

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Doubinger.

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Repository: Lapworth Museum, University of Birmingham, UK

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Geographical occurrence: Bromsgrove, Worcestershire, UK

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Stratigraphic occurrence: Anisian, Middle Triassic.

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APPROXIMATE POSITION OF Plate II

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5.2 Description of Bromsgrovia willsii n. gen. and sp.

The incompletely preserved holotype is 70 mm long and is an adpression with little organic

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material remaining. The fructification comprises a single, narrow stem bearing terminally a large, nearly circular strobilus (28 mm wide, 24 mm long) with polygonal to isodiametric sporangiophores, along with a second smaller strobilus and up to five attached leaves (Fig. 3, Plate II, 1). There is no known counterpart to this specimen.

Stem The stem bearing the reproductive and foliar structures has a maximum length of 47 mm, is 4 mm wide at the base (Plate II, 1–3), and decreases to 2 mm width just below the attached main strobilus (Plate II, 1). The stem appears slightly flexuous and longitudinally striated (Plate II, 4–5). The majority of the stem is just the remains of an impression, although toward

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the base there are remains of coaly material (Plate II, 2, black arrow). At least one node (Plate

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II, 3) can be distinguished with attachment of leaves in the lower part of the stem (Plate II, 2,

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basal 2 white arrows) with up to 68 mm long leaves attached. The leaves arise at acute angles.

Foliar structures

Five elongate acicular leaf-like structures appear to be attached to the stem (Plate II, 1). The

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two clearly attached foliar structures are at the base of the specimen (Plate II, 3). The first is

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68 mm long, and 0.75 mm wide at its widest part. It departs the stem at 4.5 mm from the base of the stem at a very acute angle that almost immediately flattens into a less acute angle. The remainder of this structure then bends upwards and runs almost parallel to the stem and gently

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tapers (Plate II, 1). The second leaf, 37 mm long, departs the stem slightly higher (6.5 mm from the base of the stem) and shows an inflated point of attachment. This second leaf departs

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at an acute angle from the stem and shows little deviation in its length, but there is a break in the impression of 8 mm, after which the remains of the foliar organ can be seen to continue

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(Plate II, 1). A third fragmentary foliar structure arises from the stem at 17 mm from the stem base. The fragment has a very acute angle of departure and is only 3.8 mm long (Plate II, 2, third white arrow from base). At 31.8 mm from the stem base, a possible fourth leaf fragment (6.4 mm long) is seen to depart the stem at a moderately acute angle (Plate II, 2, uppermost white arrow). This fourth foliar structure appears to subtend the smaller fertile structure but due to the position of the organs and the preservation of the stem, evidence of attachment of both the reproductive stem and the foliar organ cannot be shown conclusively (Plate II, 2–6). A fifth foliar structure occurs towards the top of the stem and departs the stem 5.5 mm below the main sporangiophore at nearly 40 degrees (Plate II, 5, arrowed). There are no indications of venation observed.

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APPROXIMATE POSITION OF PLATE III

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APPROXIMATE POSITION OF PLATE IV

Terminal, mature strobilus

The terminal strobilus has an incomplete, more or less spherical outline. Part of the strobilus

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has been preserved only as an impression, although about half of it also has some dark

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compression material remaining on one side (Plate II, 1; Plate III, 1). Where the organic material has been lost, the rock surface is not smooth, but retains the impression of the heads of the sporangiophores which are polygonal-isodiametric in shape (Plate III, 1). The

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sporangial masses appear dark brown-black with reddish spores visible (Plate III, 2) and are a relatively thick (2–2.5 mm) layer with sediment encircling the sporangial clusters (Plate III,

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1). Spores have a circular amb with a conspicuous trilete mark (Plate IV, 1), and measure up to 130 µm in diameter, with a fairly thick wall (Plate IV, 1-2) and are verrucose (Plate IV, 2;

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Plate V, 1–3). The verrucae (2-6 µm at the base; 1–2 µm high) are slightly larger and more defined away from the contact surface and have variable basal shapes (Plate IV, 2; Plate V, 1– 3). The in situ more mature spores correspond closely to the dispersed spore species Verrucosisporites applanatus (Mädler) Adloff et Doubinger.

Immature strobilus This is a faintly visible irregular to ovate shaped structure that is partially obscured by the larger primary fertile structure overlapping this smaller structure (Plate II, 1, 6). This smaller outline of the original body has a maximum size of 10.25 mm long and 7.5 mm wide and it is borne on a small lateral stem that appears to depart the main stem in the axil of the fourth leaf

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(Plate II, 1, 4–6). There are some remaining clusters of dark spherical-oval compression

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material measuring 0.65–1.2 mm in diameter (Plate IV, 3 4), which are immature sporangial

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clusters (Plate IV, 3) containing thin-walled, barely ornamented, slightly granulose trilete

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spores (Plate IV, 4) measuring an average of 90 µm in diameter.

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APPROXIMATE POSITION OF PLATE V

APPROXIMATE POSITION OF PLATE VI

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TEM observations of spores from the terminal strobilus The mature spores have exospores that are approx. 5 µm thick throughout, except slightly

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thicker (up to 8 µm) near the proximal suture (Plate VI, 1, 2). The exospore is also mostly homogeneous except for zones of sponginess, in patches just under the outer surface (oz), and

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near the inner extent of the wall (iz). The outer zone sponginess is more pronounced in some sections than others (cf. Plate VI, 1 vs. 2), and could represent damage caused by the treatment in Schulze’s solution.The inner zone is thicker on either side of the proximal suture and thins considerably in the distal wall (Plate VI, 1, bottom of image). Both the inner and the outer zones of patchiness delimit a thin surface layer. The inner thin surface layer (lining the spore lumen) extends up into the sutural groove and nearly comes into contact with the outer surface layer at top of the groove (Plate VI, 2, asterisk). TEM sections do not reveal any equatorial zone of thickening. This is consistent with the non-preferential way the spores compress.

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The solid surface layer delimited by the outer zone of sponginess is not interpreted as

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a perispore. Being composed of different material than the exospore, and not being resistant to

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acetolysis in extant spores, perispores are generally presumed to not withstand the effects of

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diagenesis, at least in most groups.

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6. Discussion

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6.1 Affinity of Bromsgrovia willsii gen. et sp. nov.

This fructification is unlike any Triassic plant described to date and its affinity has been

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deduced from two separate lines of information.

Spore affinity

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The in situ spores are assigned to Verrucosisporites applanatus (Mädler) Adloff et Doubinger based on their overall morphological and size similarity which are in agreement with Clarke’s

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(1965) description for this dispersed spore species (Clarke’s V. contactus; Warrington, 1970) from the Anisian sediments of the Midlands. Clarke (1965) highlights the contrast between the less strongly sculptured contact faces and the more coarsely verrucose distal spore surface. The size and shape of the verrucae are also very similar, with the same height range and irregularly-shaped verrucal bases. The larger size of the in situ spores, the well-defined contact area with finer verrucae when compared with the remainder of the spore surface, and the slightly smaller heights of the verrucae distinguishes them from V. morulae Klaus, which is recorded from both Anisian and Carnian sediments in the Midlands (Clarke, 1965; Warrington, 1970) and the Carnian of Europe (Klaus, 1960). The smaller size of the verrucae distinguishes our in situ spores from V. thuringiacus Mädler as well as the delicate aperture in

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the latter species. The dispersed spore V. morulae is one of the markers of an Anisian age in

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both the UK and across terrestrial European sequences (Warrington, 1970; Kustatscher and

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Roghi, 2006) and is recorded from the same locality as Bromsgrovia, but V. applanatus has a

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less defined Triassic age range. The verrucal height of the in situ spores and their larger size also distinguish them from Converrucosisporites tumulosus (Leschik) Roghi (formerly V. tumulosus) which has not been recorded from the UK, but is recorded from the Carnian of the

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Alps (Roghi, 2004). The immature spores are not compared to dispersed spore genera since

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we do not believe they are likely to be found dispersed.

Dispersed spores of Verrucosisporites applanatus have been also recorded from the Early Anisian ‘Grès á Voltzia’ Formation, northeastern France (Grauvogel-Stamm, 1978),

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the Late Anisian (Pelsonian) of the Dont Formation, Kühwiesenkopf/Monte Prà Della Vacca Section, Northern Italy (Kustatscher and Roghi, 2006), the Late Carnian of Middle Siberia

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(Ilyina and Egorov, 2008) and the Anisian to Carnian of the French and Spanish Pyrennes (Fréchengues et al. 1993).

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According to Balme (1995, p. 104) Verrucosisporites-type of spores were found in situ in Sporangiostrobus rugosus Bode, 1928 from the Carboniferous of Germany, a cone attributed to the Isoetales. Most Verrucosisporites type of spores were however recorded in situ from ferns such as some Carboniferous Zygopteridales, Carboniferous-Permian Marattiales, Botryopteridales and Osmundales (Balme, 1995; Taylor et al., 2009; Raine et al., 2011). Ash (1969) described delicately sculptured spores comparable to Verrucosisporites sp. C of Bharadwaj and Singh (1964) and Verrucosisporites morulae Klaus, 1964 from the Triassic Osmundaceous fern Cynepteris lasiophora Ash, 1969. During the Middle Triassic the most logical parent plants would be the Osmundales (e.g., Kustatscher et al., 2010) as so far putative in situ Verrucosisporites spores were yielded by only this group.

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The ultrastructural features that are common to nearly all extant fern spores that have been examined include: 1) a two parted exospore; 2) a very thin inner exospore layer that

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“forms a characteristic apertural ridge with a median narrow slit, consisting of a projecting

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fold of the substructure overlaid with the outer later that is much thinner but unbroken above the apex of the fold” (Lugardon, 1990); and 3) channels or voids in the outer layer in the vicinity of the apertural fold. The spores examined for this study have all of these features.

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Lacking any sign of lamellae, the spores of this study do not resemble those of the

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lycophytes. However, despite their lack of ultrastructural resemblance to the spores of the extant sphenophyte, Equisetum, several of the few fossil representatives of the sphenophytes compare at least as favorably as extant ferns. In the words of Lugardon and Brousmiche

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Delcambre (1994) “The most striking fact emerging from this study (exospore ultrastructure in Carboniferous sphenopsids) is the remarkable ultrastructural resemblance between the wall

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of fossil sphenopsids and the exospore of filicopsid spores.” Thus, the data on spore wall ultrastructure can support either fern or sphenopsid affinity. This result is also intriguing in

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the light of the monophyletic relationship inferred by molecular data between ferns and horsetails (Pryer et al. 2001), a point noted by equisetalean spore ultrastructural work performed by Grauvogel-Stamm and Lugardon (2009).

Affinity of the fructification Despite the incomplete nature of the specimen, this fructification is assigned tentatively to the sphenophytes based on the structure of the strobili, in combination with the ultrastructural details of the spores. The macromorphology of the plant remains poses an interesting arrangement of features, with the strobili strongly resembling a sphenophyte, where sporangia are clustered together, usually on a sporangiophore (Kelber and Van Konijnenburg-van

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Cittert, 1998), and these sporangiophores are aggregated in to strobili at the tips of stems or

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laterally to the main stem (Kelber and Van Konijnenburg-van Cittert, 1998). However, the

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stem and leaves of Bromsgrovia are not typical for a sphenophyte. In a typical sphenophyte,

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there is an articulate stem and a circle of elongated leaves at the clear nodes. Our specimen instead has apparently single leaves, or at least does not show a complete circle of leaves, some with slightly sheathing bases. This arrangement of characters is unknown in any

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sphenophyte. Sporangiophores bearing clusters of sporangia are characteristic of

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sphenophytes, however they could not be identified from the material and were not recovered in maceration, but these structures are delicate and appear not to have been preserved here. Also the elaters, well known from extant sphenophytes, were not detected in the mass of in

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situ spores but their delicate texture is difficult to preserve as fossils (Kurrmann and Taylor, 1984). We cannot see in which other group to place this unique specimen, since it in no way

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resembles ferns or lycophytes, based on the leaf and stem morphology. The roundish strobili partially resemble Equisetites arenaceus (Jaeger) Schenk, 1864

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from the Ladinian of the Germanic Basin, although in that case the strobili are not arranged at the end of the stem but on lateral shoots in groups of three, with different maturations and far smaller (50-60 µm) spores (for more details see Kelber and Van Konijnenburg-van Cittert, 1998). Our specimen terminates with one more mature strobilus and has an additional one which is borne on a lateral branch , which also differentiates it from E. mougeotii (Brongniart, 1828) Wills, 1910 that had fertile structures described from the Anisian Dont Formation, Italy (Kustastcher et al. 2007). E. mougeotii has larger obovate strobili borne on small apical branches with 5-6 whorls of sporangiophores and small (30-45 µm) in situ trilete spores (Kustastcher et al. 2007)

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The Triassic sphenophyte common in European collections is Schizoneura paradoxa

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Schimper et Mougeot, 1844, which has leaves arranged in two groups, and its strobili

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Echinostachys Brongniart (Grauvogel-Stamm, 1978), are elongate, with sporangiophores

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having elongate outgrowths of the umbo, and the in situ spores are of the Calamospora-type. Our specimen has instead roundish strobili, no apparent ornamentation to the sporangiophores and quite distinctive verucose spores. Cones of Equicalastrobus Grauvogel-Stamm et Ash

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1999 are also discounted, since they too have leaf-like umbo projections (Grauvogel-Stamm

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and Ash, 1999).

Cones of Equisetostachys verticillata from the Anisian of France (Grauvogel-Stamm, 1978) have larger hexagonal sporangiophores, unlike our specimen, - and yield Calamospora

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type of in situ spores; the in situ spores of E. nathorstii Halle 1908 and E. suecicus Halle 1908 from the Rhaeto-Liassic of Sweden are smaller (35-50 µm ) globose or smooth and

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trilete spore types (Halle, 1908). Based on the differences of the morphology of the in situ spores, other cone species are discounted as they have smooth and alete spores of the

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Calamospora type: Equisetites muensteri Sternberg 1833 from the Upper Triassic of Greenland (Harris, 1931), E. lyelli (Mantell 1833) Allen 1941 from the Lower Cretaceous of England (Watson and Batten, 1990), E. pusillus Villar de Seoane 2005, from the Aptian of Argentina (Villar de Seoane 2005) and E. columnare Brongniart 1928 from the Middle Jurassic of Yorkshire (Harris,1978) bearing alete but scabrate spores and E. laterale Phillips 1829 from the Lower Jurassic of Australia (Gould, 1968). Equisetum boureaui Vozenin-Serra et Laroche 1976 from the Upper Triassic of Cambodia and E. thermale Channing, Zamuner, Edwards et Guido, 2011, from cones associated with foliage from the Jurassic of Patagonia, both have much smaller smooth spores (Vozenin-Serra and Laroche, 1976; Channing et al. 2011). Smoother and smaller spores could represent immature forms, particularly as they are

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found in situ, and it is possible that they may later have developed ornamentation.

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Interestingly, a combination of alete and trilete small spores have been found in Equisetites

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arenaceus (Kelber and Van Konijnenburg-van Cittert, 1998). The spores recovered here lack

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elaters, and often these are not recovered in Equisetalean fossil remains, but they have been found in other species, notably Spaciinodum collinsonii (Osborn et Taylor) Schwendemann et al. 2010 from the Middle Triassic of Antarctica (Schwendemann et al. 2010).

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Neocalamites merianii (Brongniart) Halle, 1908 has whorls of leaves and a thickening of the

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stem at the nodal level. So far no fertile structures have been found attached for this genus, although a couple have been associated with the vegetative remains, each without yielding spores. Escapa and Cunéo (2006) describe a fertile structure from the Permian of Patagonia,

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and Dobruskina (1995) from Triassic of Madygen, Middle Asia, and based on this morphology, Carnian reproductive structures such as those from Lunz am See (Austria Pott et

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al. 2008) and Svalbard (Pott in press) have been assigned to this plant, each being clearly elongate structures, unlike the rounded fructification described here. Neocalamites horridus

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Zan, et al. 2012 from the Upper Triassic of China has strobili attached which are similar to those of N. merianii, but vary in details of the sporangiophores (Zan et al. 2012). However, since Neocalamites is a distinctly different morphogenus than we report here, this genus cannot be used for our specimen. Thus, it has become necessary to create a new genus and species for the specimen from Bromgrove.

6.2 Other Triassic plants with unclear affinities

Bromsgrovia described here shows a macromorphology indicating an equisetalean affinity, but the spores indicate a possible affinity with ferns, although the work by Grauvogel-Stamm

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and Lugardon (2009) showed the large variability of the horsetail spore wall ultrastructure

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through time and that horsetail spores may share ultrastructural similarities with the primitive

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ophioglossalean ferns. This adds some strength to our interpretation of Bromsgrovia as an

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unusual horsetail fructification. Bromsgrovia is not the only Anisian plant to show an unusual combination of characters. One other unusual reproductive organ, Lugardonia paradoxa Kustatscher, Hemsley et Van Konijnenberg-van Cittert from the Anisian of Kühwiesenkopf,

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the Dolomites, Italy appears from its macromorphology to have gymnospermous affinities,

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but the spore ultrastructure suggest a pteridophyte affinity. The systematic affinity of Lugardonia remains unclear although a tentative fern affinity is suggested (Kustatscher et al.,

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7. Concluding remarks

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these plants will become clearer.

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2009). As more plants are recovered from Triassic sediments, it is hoped that the affinity of

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There are no Early Triassic floras known in the UK. The Induan–Olenekian sediments are nearly barren (King and Benton, 1996; Powell et al., 2000) and even in the terrestrial Permian-Triassic boundary-spanning sequences, the Permian-Triassic boundary cannot be identified (Hounslow and Ruffell, 2006). The fossil paucity at this time is not uncommon, and to date only one fossiliferous Permian-Triassic section has been detailed, in North China (Wang, 1996). This section shows a Pleuromeia-dominated flora proliferating after the EndPermian extinction event, which is mirrored by the Early Triassic (Olenekian) Pleuromeia flora of the Eifel region of Germany described by Fuchs et al. (1991) and that of the Bowen Basin, Queensland, Australia (Cantrill and Webb, 1998), along with the lycopsid-dominated Early Triassic section of Siberia (Dobruskina, 1985).

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Grauvogel-Stamm and Ash (2005) suggested a relatively long recovery period during the early Middle Triassic, which is marked by the resurgence of conifers in the Early Anisian,

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as shown by the ‘Grès à Voltzia’ Formation, northeastern France; and then the resurgence of

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pteridosperms and cycadophytes in the Late Anisian as illustrated by the Dont Formation of the Dolomites, northeastern Italy (Broglio Loriga et al., 2002; Kustatscher and Roghi, 2006; Kustatscher et al. 2007). The relatively small and impoverished British Midlands flora seems

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to fit slightly more closely with the more conifer dominated ‘Grès à Voltzia’ Formation than

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the more mixed and slightly younger flora of the Dont Formation, but the small collection size should be borne in mind. Perhaps unsurprisingly, the Bromsgrove Sandstone Formation flora is quite different in apparent composition from the pteridosperm and sphenopsid dominated

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flora of the Ermaying Formation, North China (Wang, 1996). Overall, reviewing the Middle Triassic floras, there appear to be some differences in composition, which may indicate

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provincialism developing in the Early Middle Triassic floras in different basins, which would be expected, but the small sample sizes and allochthonous nature of some floras must be

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remembered.The Anisian Bromsgrove flora is impoverished, highly fragmented and allochthonous flora that shows evidence of fluvial sorting. Despite these issues, the Anisian plants include the equisetalean Schizoneura and the coniferophytes Willsiostrobus and Pelourdea (formerly Yuccites), as well as a fructification with a unique combination of characters: Bromsgrovia willsii n. gen. and sp. which has two strobili attached showing different levels of maturity corresponding to their spatial positioning and resembles an equisetalean plant, but it has in situ spores referable to the dispersed spore Verrucosisporites applanatus, a spore so far attributed to the ferns. After Lugardonia, this is now the second plant interpreted with mixed affinities from the Middle Triassic of Europe, opening the discussion on some of the interpreted affinities of the dispersed spores and pollen.

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Acknowledgements

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LJS would like to particularly thank Jon Clatworthy (Lapworth Museum, University of Birmingham, UK) and Matt Riley (Sedgwick Museum, Cambridge, UK) for help and access to the Wills collection and for loans; Dorothea Hause-Reitner for SEM support; Prof.

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Dr. Lea Grauvogel-Stamm and Prof. Dr. Johanna van Konijnenburg-van Cittert for support

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and very helpful discussion. The manuscript greatly benefited from the critical remarks and comments of Christian Pott (Stockholm) and an anonymous referee. The contribution by LJS was funded by the Dorothea Schlözer Postdoctoral Programme at the Georg-August-

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Universität Göttingen. The study of the material of the Natural History Museum of London by

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EK has been possible thanks to the project “The Middle Triassic Floras of Europe – how

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different was the composition of the different areas really?” (GB-TAF-4231) funded through SYNTHESYS, which was made available by the European Community - Research

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Infrastructure Action under the FP7 "Structuring the European Research Area" Programme. This paper is publication number 90 from the Courant Research Centre Geobiology that is funded by the German Initiative of Excellence.

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Wills, L.J., 1910. On the fossiliferous Lower Keuper Rocks of Worcestershire: With

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descriptions of some of the plants and animals discovered therein. Proceedings of the

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Geologists' Association 21, 249-331.

Wills, L.J., 1970. Triassic successions in the central Midlands in its regional setting. Quarterly

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Journal of the Geological Society of London 126, 225-283.

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Zan, S., Axsmith, B.J., Escapa, I., Fraser, N.C., Liu, F. and Xing, D. 2012. A new Neocalamites (Sphenophyta) with prickles and attached cones from the Upper Triassic of

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China. Palaeoworld 21, 75–80.

Figure legends

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Fig. 1. Map of UK showing the position of the former quarries at Hill Top, Bromsgrove.

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Fig. 2. Triassic lithostratigraphy of the British Isles and the British Midlands. (Sst = Sandstone, Fm = Formation, thick dark zigzag line indicates disconformity/unconformity, leaf symbols indicate both occurrence and relative abundance of plant fossils in the succession.)

Fig. 3. Drawing of the British Midlands Triassic (Anisian) Bromsgrove Sandstone Formation fructification showing the smaller immature and the larger (apical) more mature strobili and their relationship to the strap-like foliage. Dotted lines indicate a presumed outline of the apical strobilus hidden under the remaining sediment. Scale bar = 10 mm.

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Plate I. Plant macrofossils from the British Midlands Triassic (Anisian) Bromsgrove

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Sandstone Formation. (1) BU5256. Various pith casts and impression showing differing

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preservation modes. Scale bar = 20 mm. (2) BU5257. Flow-sorted pith casts and stem

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impressions. Scale bar = 50 mm. (3) BU5258. Two typically preserved internal pith casts of Schizoneura paradoxa (arrowed). Scale bar = 50 mm. (4) BU5259. Mudstone detrital surface with numerous plant fragments. Scale bar = 20 mm. (5) BU5260. Various fragments of plant

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material, with the distinctive leaves of Schizoneura paradoxa (arrowed). Scale bar = 50 mm

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(6) BU5262. Willsiostrobus cone partially obscured by compressed wood. Scale bar = 50 mm. (7) BU5261. Yuccites leaf fragment. Scale bar = 50 mm. (8) BU5263. Neocalamites sp.

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diaphragm with leaf sheaths. Scale bar = 20 mm.

Plate II. Fructification with attached foliage from the British Midlands Triassic (Anisian)

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BU5248.Scale bar = 5mm unless otherwise indicated. (1) Overview of specimen. Scale bar = 10 mm. (2) Basal region of the sporangiophorous stem showing attachment of four foliar

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structures (white arrows) and remains of stem organic material (black arrow). (3) Detail of (2) showing remains of organic material of the stem between the two basalmost foliar organs. (4) Detail of (2) showing the probable attachment of a foliar structure (arrowed) subtending the secondary strobilus. (5) Apex of stem with fifth leaf-like structure (arrowed). (6) Detail of (5) showing the incomplete nature of both strobili and their size difference.

Plate III. Fructification with attached foliage from the British Midlands Triassic (Anisian) BU5248A. (1) The terminal strobilus, where the majority of the sporangia are no longer preserved, but the impression of their former position is observable on the left; on the right side of the image the fragments of the sporangia are still present. Scale bar = 10 mm. (2)

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Detail of an individual sporangium at the edge of the remaining sporangial mass of the

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terminal sporangium. Scale bar = 500 µm. (3) Incomplete nature of the immature strobilus.

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Scale bar = 2 mm. (4) Detail of sporangia of the l strobilus. Scale bar = 1 mm. ()

Plate IV. In situ spores and spores masses obtained from Bromsgovia gen. et sp. nov. from the British Midlands Triassic (Anisian) BU5248B-D (1) Polar view of trilete spore with a

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circular amb at the edge of a spore mass from the terminal strobilus. Scale bar = 100 µm. (2)

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Edge of spore mass showing verrucose spores with folding and the smoother contact surface when compared with the remainder of the spore surface, from the terminal strobilus. Scale bar = 100 µm. (3) Sporangial mass macerated from immature strobilus. Scale bar = 500 µm. (4)

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Spore from the immature strobilus with a weakly granulose surface and a trilete mark

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(composite of 3 stacked images). Scale bar = 50 µm.

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Plate V. Scanning electron micrographs of the in situ Verrucosisporites spore surface ornamentation, macerated from the primary strobilus. (1) Overview of verrucose spore surface morphology. Scale bar = 50 µm. (2) Densely packed verrucae on spore surface, showing irregular size and distribution. Scale bar = 10 µm. (3) Detail of verrucae, showing differing heights and basal shapes. Scale bar = 2 µm.

Plate VI. Transmission electron micrographs of the in situ Verrucosisporites spores. Images depict different positions along the same suture of one spore. (1) Image showing sutural groove in cross-section. Thinnest area at the top of the suture meets the spore surface at a

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shallow groove. Two zones of sponginess are shown. Inner zone (iz) most clearly seen at

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base of suture and much thinner in distal wall (bottom of image). Scale bar = 1 µm. (2) Dark

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layer lining spore lumen also lines sutural groove and nearly meets outer surface layer at the

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peak of the groove (asterisk). Outer spongy zone more pronounced than in 1 and may

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represent damage from treatment with Schulze’s solution. Scale bar = 1 µm.

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Highlights: Here we document a rare Triassic fossil flora from the U.K.

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The Anisian Bromsgrove flora is the most fossiliferous one known in the U.K. to date.

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We describe a new species of fossil horsetail with in situ Verrucosisporites spores.

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We show the development of the in situ spores at different maturation levels.

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Dispersed Verrucosisporites spores may have equisetalean not fern affinities.

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