Anatomically-preserved tree-trunks in late Mississippian

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Review of Palaeobotany and Palynology 160 (2010) 154–162

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Review of Palaeobotany and Palynology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / r e v p a l b o

Anatomically-preserved tree-trunks in late Mississippian (Serpukhovian, late Pendleian–Arnsbergian) braided ﬂuvial channel facies, near Searston, southwest Newfoundland, Canada Howard J. Falcon-Lang a,⁎, Jean Galtier b a b

Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK UMR Botanique et Bioinformatique, CIRAD, TA A-51/PS2, 34398 Montpellier, France

a r t i c l e

i n f o

Article history: Received 7 December 2009 Received in revised form 16 February 2010 Accepted 16 February 2010 Available online 26 February 2010 Keywords: Carboniferous Mississippian Serpukhovian Newfoundland braided ﬂuvial fossil wood Pitus pteridosperm tree-rings

a b s t r a c t Little is known of the Mississippian palaeobotany of Newfoundland, Canada. Here we improve this situation by describing anatomically-preserved tree-trunks from the Codroy Valley, southwest Newfoundland. The tree-trunks, which have incomplete lengths of up to 8.3 m, occur in braided ﬂuvial channel facies of the Searston Formation, a late Pendleian–Arnsbergian (upper Serpukhovian, 326.4–325 Ma) unit. Three morphotypes are present. The ﬁrst, Pitus primaeva Witham shows exceptionally wide rays (1–8-seriate, rarely to 16-seriate) and tracheids with multiseriate pits. The second, cf. Pitus withamii (Lindley and Hutton) Witham has rather narrower rays (1–3-seriate), and unusually shows ray cells pitted on all walls. Both morphotypes probably represent arborescent pteridosperms. The third, Protopitys scotica Walton is characterized by the occurrence of very short rays (mode: 1 cell high), and represents a putative progymnosperm. Associated megaﬂoral assemblages are dominated by Diplotmema and Adiantites, which may have comprised the foliage of the lignophytes described herein. However, in marked contrast, palynological assemblages suggest that arborescent lycopsids, sphenopsids and ferns dominated regional vegetation make-up. One resolution to this paradox is the lignophytes may have been growing on levees or well-drained uplands to the south, and washed into the basin in river channels, while pteridophytic vegetation occupied the ﬂoodplain. This inference is supported by occurrence of irregular growth interruptions in the fossil woods, suggesting trees grew under a seasonally dry tropical climate. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Anatomically-preserved plants are extremely abundant in the Mississippian rocks of northwest Europe (Scott et al., 1984; Scott and Galtier, 1996). Plants are siliciﬁed, calciﬁed or preserved as charcoal, the product of wildﬁre, and commonly, though not elusively, associated with volcanic environments (Scott, 1990). Widespread volcanism in this region was related to the northward subduction of the Rheic oceanic plate along the Galicia–Brittany–Massif Central line, which generated lithospheric stretching and magmatism in the British back-arc region, and uplift within the Variscan orogenic zone further south (Leeder, 1982, 1987, 1988). Although fossil plant localities are scattered across the orogenic belt in mainland Europe (e.g. Galtier et al., 1998a), by far the richest concentration occurs in the Midland Valley of Scotland (Scott et al., 1984), where volcanism was accompanied by rapid subsidence and the accumulation of a thick terrigenous succession. To date more than twenty sites have been described ⁎ Corresponding author. Department of Earth Sciences, Royal Holloway, Egham, Surrey TW20 0EX, UK. E-mail address: [email protected] (H.J. Falcon-Lang). 0034-6667/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.revpalbo.2010.02.009

in detail from this basin (Falcon-Lang, 2000) and many others await full analysis. Like the Midland Valley of Scotland, the Carboniferous basins of Newfoundland, Canada, developed along the reactivated Caledonian lineaments during the closure of the Rheic Ocean (Leeder, 1982, 1987, 1988). However, in contrast, remarkably few fossil plant assemblages have been described from this latter region. To date, a rich compressed megaﬂora (Bashforth, 2005) and a hundreds of permineralized cordaitalean tree-trunks (Falcon-Lang and Bashforth, 2004, 2005) have been found in a Pennsylvanian (Moscovian) outlier near Stephenville, SW Newfoundland (Latitude: 48°34′28″N, Longitude: 58°35′21″W). However, in Mississippian strata, fossil plants are limited to a compressed megaﬂora of uncertain age (Arber, 1910) collected at the mouth of Shawnawdithit River as it enters Red Indian Lake (Latitude: 48°37′09″N, Longitude: 58°06′29″W) and a compressed megaﬂora from the early Namurian Searston Formation (Bell, 1948) in the Bay St. George Basin region (Latitude: 47°49′30″N, Longitude: 59°19′50″W). The aim of this present paper is to augment our knowledge of Mississippian palaeobotany in Newfoundland by describing a newly discovered assemblage of permineralized tree-trunks from the Searston

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Fig. 1. Geological setting. A. Index map of Canada, B. Index map of Newfoundland, C. Carboniferous Bay St. George Basin (medium grey) highlighting the outcrop belt of the Searston Formation (dark grey) after Bashforth (2005), D. Detailed map of the outcrop belt of the Searston Formation showing the location of the fossil site between Kennedy Point and The Block, E. Summary stratigraphic column for the Searston Formation and its correlation with global stratigraphy (after Heckel and Clayton, 2006; Utting and Giles, 2008).

Formation. These discoveries shed new light on the diversiﬁcation of gymnosperms during a critical period in evolutionary history leading up to the Mississippian–Pennsylvanian boundary (Gerrienne et al., 1999). This time interval witnessed a signiﬁcant rise in plant diversity (Knoll, 1986; Raymond, 1996) and marked a changeover from seasonally dry vegetation dominated by gymnosperms and ferns to the establishment of widespread lycopsid ‘Coal Forests’ (DiMichele et al., 2001; Gastaldo et al., 2009). The new discoveries also add to the comparatively small number of late Mississippian localities with permineralized plants in North America (Lacey and Eggert, 1964; Taylor and Eggert, 1967; Jennings, 1979; Dunn 2004).

2. Geological setting The fossils described in this paper were discovered in coastal cliffs west of Searston, near the mouth of the Great Codroy River, southwest Newfoundland, during reconnaissance work by one of us (HFL) in the summers of 2004 and 2005 (Map Reference, Codroy 11-0/14, Scale 1:50,000; Fig. 1A–C). The rocks in this region comprise the type section of the ∼2950-m-thick Searston Formation (Knight, 1983), which is of late Pendleian–Arnsbergian age (upper Serpukhovian, 326.4–325 Ma) based on miospore assemblages (Reticulatisporites carnosus biozone; Utting and Giles, 2008). Thus, they are assigned to the latest Mississippian

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Table 1 Summary of quantitative anatomical data for the three morphotypes and comparison with previously described morphotaxa (after Gordon, 1935; J. Galtier, unpublished data). Specimen number (form taxon) This study NHM V.67418 NHM V.67420/1 NHM V.67422 Comparative material KID 674 HM GOR 1478 HM KID 210/211 HM KID 484/485 HM SCO 9319 NHM Pb 3320/2256

Morphospecies

Number of rows of tracheid pits (mean)

No. of cross-ﬁeld pits per ﬁeld (mean)

Ray height in no. of cells (mean)

Ray width in no. of cells (mean)

Tracheid diameter in microns (mean)

Ray density (number/mm2)

Pitus primaeva cf. Pitus withamii Protopitys scotica

3–6 (4.81) 1–4 (1.54) 1–3 (1.12)

2–8 (4.46) 1–8 2–4

6–65 1–56 (7.19) 1–7 (1.16)

1–16 (3.91) 1–3 (1.39) 1

39–92 (53.38) 22–58 (39.51) 27–31 (27.58)

5.3 14 61

Pitus antiqua Pitus dayi Pitus primaeva Pitus withamii Pitus withamii Protopitys scotica

3–5 3–5 3–5 3–4 – 1–3

– – – 5–8 – 1–12

3–146 (29) 2–43 (14) 2–63 (16.4) 2–78 (14) 2–53 (14) 1–3

1–8 1–6 1–8 1–3 1–4 1

64–85 (72) 30–61 (44) 61–75 (69) 68–88 (79) 50–70 (58) 20–25

3 13.8 5 10 10.2 –

subsystem (Heckel and Clayton, 2006) and immediately pre-date the major ﬂoral break that occurs at the Mississippian–Pennsylvanian boundary in Atlantic Canada (Calder, 1998). Speciﬁcally, our fossils were located in the middle part of the Searston Formation between Kennedy Point (Latitude: 47°49′31″N, Longitude: 59°19′50″W) and The Block (Latitude: 47°47′39″N, Longitude: 59°20′01″W), where they were extracted directly from sea-cliffs, 10–15 m high (Fig. 1D, E). This interval is ∼1420 m above the base of the Searston Formation as measured from its northernmost outcrop at Capelin Cove (Utting and Giles, 2008) and the locality is bounded on its south side by the second unnamed brook south of Kennedy Point (Latitude: 47°48′35.85″N, Longitude: 59°19′44.60″W) as marked on the 1:50,000 map (Codroy 11-0/14). The site is positioned at the base of the cliffs directly below the small conurbation known as Ford Farm (see stratigraphic log in foldout enclosure in Knight, 1983). Knight (1983) carried out the only detailed facies analysis of the Searston Formation conducted to date. The dominant sedimentary motif comprises single- or multi-storey channel sandstone bodies, up to 20 m thick, with stepped bases that locally show up to 10 m of erosional relief. Channel-ﬁlls commonly contain a basal lens of intraformational conglomerate (including fragments of pedogenic carbonate) overlain by medium- to coarse-grained sandstone with trough cross-beds (palaeoﬂow: west and northwest). The uppermost channel-ﬁll comprises ﬁne-grained sandstone showing ripple crosslamination, convolution lamination, and some channels in the upper ﬁll contain rooted lenses of grey-green mudstone. These major

(4.4) (3) (3.5) (1.6) (1.7)

channel bodies occur within successions dominated by red mudstone and siltstone (typically 2–40 m thick) containing scattered pedogenic carbonate nodules, mudcracks and roots, interbedded with thin beds of red sandstone and mud-chip conglomerate. Knight (1983) interpreted the Searston Formation as the product of a meandering river system, drawing heavily on the work of Allen (1963, 1964, 1970), which was much in vogue at the time. However, the predominance of stacked ﬁning-upward units of trough cross-bedding and the absence of large-scale lateral accretion surfaces more closely resemble the deposits of sandy braided systems (Cant and Walker, 1978), with mud-ﬁlled channels in the upper parts of bodies representing abandonment facies (Gibling et al., 2010). Furthermore, the occurrence of multi-storey sandstone bodies with deeply erosive bases may suggest these drainages were conﬁned within shallow valleys (Gibling, 2006). Thick successions of red mudstone with pedogenic carbonate nodular units are interpreted as the deposits of seasonally dry interﬂuves. This ﬁts with palaeoclimate inferences for this part of southwest Laurasia, based on palaeosols and tree-rings, which indicate monsoonal conditions with a distinct dry season (Wright, 1990; Falcon-Lang, 1999). 3. Material and methods Fossil tree-trunks are very common in the major channel bodies in the middle part of the Searston Formation, where they are especially associated with basal intraformational conglomerate lenses or coarsegrained trough cross-bedded units. Most of these fossils are coaliﬁed,

Plate I. Anatomy of Pitus primaeva Witham from the Searston Formation, Newfoundland; 1. 2. 3. 4. 5. 6. 7. 8.

tracheids showing multiseriate pitting, RLS, scale: 100 µm, V.67418; Close-up of tracheid pitting, RLS, scale: 40 µm, V.67418; Cross-ﬁeld pitting, RLS, scale: 75 µm, V.67418; Detail of ray parenchyma, RLS, scale: 450 µm, V.67419; Very large multiseriate rays; the example on the left may in fact represent the fusion of two rays, TLS, scale: 450 µm, V.67419; More typical multiseriate rays, TLS, scale: 600 µm, V.67418; very wide, closely spaced rays in transverse section demonstrating dominance of parenchyma, TS, scale: 1.5 mm, V.67418; Growth interruption denoted by a zone of small diameter tracheids, TS, scale: 1.25 mm, V.67418.

Plate II. Anatomy of cf. Pitus withamii (Lindley and Hutton) Witham from the Searston Formation, Newfoundland, Canada; (see on page 158) 1. 2–3. 4. 5. 6. 7.

2–3-seriate tracheid pits and rays, RLS, scale: 120 µm, V.67420; Detail of cross-ﬁeld pits, RLS, scale: 50 µm, V.67420; Tall rays, up to 2–3 cells wide, TLS but slightly oblique, scale: 450 µm, V.67420; Detail of parenchyma cells in short ray, RLS, scale: 200 µm, V.67421; Ray cells showing profuse pitting on tangential walls, TLS, scale: 80 µm, V.67420; Tracheids and rays showing profuse pitting on transverse/horizontal walls, TS, scale: 175 µm, V.67420.

Plate III. Anatomy of Protopitys scotica Walton from the Searston Formation, Newfoundland, Canada, all V.67422; (see on page 159) 1. 2. 3. 4. 5. 6.

Tracheids showing uniseriate, contiguous pits, and short rays, RLS to slightly oblique, scale: 400 µm; General TS showing 16 mm diameter axis with one prominent growth interruption near outer edge. The very small central “dark” area, interpreted as the pith is b 800 µm, scale: 3 mm; Small rays, mostly 1 cell high, TLS, scale: 150 µm; An inﬂated ray cell, TLS, scale: 150 µm; Detail of wood showing tracheids and inﬂated ray cells, TS, scale: 300 µm; A growth interruption deﬁned by a zone of narrow tracheids. Very short rays also visible, TS, scale: 400 µm.

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Plate I.

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Plate II (caption on page 156).

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Plate III (caption on page 156).

159

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or sandstone-cast, and show no anatomical preservation. However, ﬁve specimens observed near Ford Farm (Latitude: 47°48′35.85″N, Longitude: 59°19′44.60″W) showed preservation of cellular anatomy in the ﬁeld and were collected. These specimens are stored in the collections of Natural History Museum, London under the following accession numbers: V.67418 to V.67422. For each specimen, petrographic thin sections were prepared along Radial Longitudinal (RLS), Tangential Longitudinal (TLS) and Transverse (TS) surfaces, and studied using an Olympus BH-5 binocular microscope and image analyzer in the Earth Sciences Department at Royal Holloway. For most specimens more than one section was obtained for each orientation. Fossil wood characters were described quantitatively using the standard approach (FalconLang and Cantrill, 2000; Oakley and Falcon-Lang, 2009; Oakley et al., 2009), whereby 100 measurements are taken for each character, and the mean, range, and standard deviation determined. This quantitative approach is essential because wood anatomy is typically rather variable at different spatial scale (Falcon-Lang, 2005). Even so, because only small areas of each tree-trunk were sufﬁciently well preserved for anatomical analysis, it proved impossible to fully understand intra-tree variability for this material.

are spaced 2–8 tracheids apart (mean: 3.79±1.82, n=100), but preservation is insufﬁcient to determine mean length. Botanical afﬁnity: These two specimens compare very closely with the original material of Pitus primaeva Witham (Table 1). Based on secondary xylem alone, only ray width and height allow discrimination between the four known morphospecies of Pitus (Gordon, 1935; Long, 1979). However, such characters are highly dependent on ontogeny (Falcon-Lang, 2005) as demonstrated by a quantitative description of type material made by one of us (JG) and summarized in Table 1 (Falcon-Lang et al., 2010). Nonetheless, P. primaeva bears closest resemblance to our material, having rays up to 63 cells high (compared to up to 65 cells high in our material) and up to 10 cells wide (up to 8 cells in our material, or rarely up to 16 cells). In mature specimens of P. antiqua, rays are of greater height and lower density, and in Pitus withamii are substantially narrower (Table 1). For many years, the systematic position of Pitus was enigmatic (Scott, 1900); however, anatomical studies have since provided support for the hypothesis that it was an arborescent pteridosperm (Long, 1979; Galtier & Meyer-Berthaud, 2006).

4. Systematics

Supercohort: Lignophytia Kenrick and Crane 1997 Order and Family: incertae sedis Morphospecies: cf. Pitus withamii (Lindley and Hutton) Witham (Plate II; Table 1) Material: NHM V.67420, NHM V.67421

Based on qualitative and quantitative description (Table 1), three distinct morphotypes were evident in the ﬁve specimens analyzed. We describe these morphotypes in full and consider their likely botanical afﬁnity. 4.1. Morphotype 1 Supercohort: Lignophytia Kenrick and Crane 1997 Order and Family: incertae sedis Morphospecies: Pitus primaeva Witham (Plate I; Table 1) Material: NHM V.67418, NHM V.67419 Description: This morphospecies is principally described from NHM V.67418, a fragment of a tree-trunk with an incomplete length of 8.3 m and a maximum of diameter of 0.12 m (the largest trunk observed in the section). The specimen comprises the outer part of the trunk, the inner region, being recrystallized. Secondary observations were made in NHM V.67419, a fragment from a tree-trunk with an incomplete length of 1.1 m, which belongs same morphospecies. However, preservation was too patchy for quantitative analysis of this specimen. In RLS, tracheids show multiseriate, contiguous, alternate bordered pitting (Plate I, 1). Tracheid pitting is typically 4–5-seriate, rarely 3–6-seriate (mean 4.81 ± 0.31, n = 100), and comprises small hexagonal pits (12 µm diameter) with an oval and more or less horizontal aperture (8 µm), poorly deﬁned (Plate I, 2). Ray parenchyma cells are 150–290 µm long with simple, oblique end-walls (Plate I, 4). They show 2–8 oval pits per cross-ﬁeld (mean: 4.46 ± 1.76, n = 100; Plate I, 3). In TLS, tracheid walls are unpitted. Rays are exceptionally large (up to 0.6 mm wide by 2.2 mm high), being 1–8-seriate and rarely up to 16seriate (mean: 3.91 ± 1.19, n = 100), and 6–65 cells high (Plate I, 5, 6). However, some of the widest rays may have resulted from the fusion of two rays as indicated by fusiform discontinuities locally observed (Plate I, 5). Ray parenchyma cells are typically 24–35 µm wide and 24–38 µm high. Ray density is locally b5–6 rays/mm2 (mean: 5.3, n = 3), based on the number of incomplete rays in the unit area, equivalent to about 50– 55% parenchyma by tangential cross-sectional area. In TS, tracheids show radial diameter of 39–92 µm (mean: 53.38 µm± 13.5, n=100) and tangential diameters in the 51–80 µm range (Plate I, 7). Weakly developed growth interruptions are present, spaced erratically, and with 2–5 latewood cells b15 µm in radial diameter (Plate I, 8). Rays

4.2. Morphotype 2

Description: This morphotype is based on two tree-trunk specimens, NHM V.67420 and NHM V.67421, which have incomplete lengths of 1.1 and 2.0 m, respectively, and diameters of 0.15 and 0.18 m, respectively. Both specimens are very similar. As a result of patchy preservation, the quantitative data summarized below was collected from both specimens. In RLS, tracheids show multiseriate, contiguous, alternate (96%) or locally sub-opposite (4%) bordering pitting (Plate II, 1, 2). Tracheid pitting is typically 1–2 seriate, or locally 3–4 seriate especially near tracheid end-walls (mean: 1.54 ± 0.61, n = 100). Pits have circular borders (8 µm) and oval apertures (5 µm). Rays comprise parenchyma cells, which are typically 150–280 (rarely 380) µm long with simple, oblique end-walls, or may be shorter, 42–80 µm long (Plate II, 5), and show 1–8 oval pits per cross-ﬁeld (Plate II, 3). Axial parenchyma is rare. In TLS, tracheid walls are unpitted. Rays are commonly 1–2-seriate, or rarely 3-seriate (mean: 1.39 ± 0.54, n = 100) and are typically 1–35 cells high (Plate II, 4), though locally they may be up to 56 cells high (mean: 7.19 ± 9.13, n = 100). The tallest rays (up to 2.88 mm) may contain 3-seriate portions up 10 cells high. Ray parenchyma cells are 21–30 µm (rarely 48 µm) high and 15–21 µm (rarely 35 µm) wide and may show profuse pitting on tangential walls (typically 1–15 pits per cell; Plate II, 6). Ray density is 12–17/mm2 (mean: 14, n = 3), equivalent to about 30–35% parenchyma by tangential cross-sectional area. In TS, tracheids show radial diameters of 22–58 µm (mean: 39.51 µm ± 9.21, n = 100) and tangential diameters in the 20–37 µm range. Weakly developed growth interruptions are present, spaced erratically (0.3–2.4 mm), and with latewood cells b15 µm in radial diameter. Some ray cells show profusely pitted horizontal walls (Plate II, 7). Rays are spaced 1–8 tracheids apart (mean: 3.28 ± 1.14, n = 100), and are up to 1.1 mm in length. Botanical afﬁnity: These specimens are most similar to Pitus withamii (Lindley and Hutton) Witham, agreeing closely with tracheid and ray dimensions and pitting. However, that type material for that morphotaxon shows rather lower ray density and lacks the occurrence of ray cells that are profusely pitted on all walls (Table 1). We considered whether this latter feature might signal the occurrence of ray tracheids in our woods. Ray tracheids are rarely seen in early

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arborescent plants, but occur in the late Devonian progymnosperm Callixylon (Arnold 1931; Beck et al., 1982; Chitaley and Cai, 2001) and are seen in many modern conifers (IAWA Committee, 2004). Rare examples are also known in the Mississippian taxon, Calamopitys (Galtier, unpublished data). However, measurements show there is no difference in the length, height and wall thickness of pitted and unpitted cells in our material, and we conclude that only ray parenchyma cells with thickened walls are present. Due to the key differences highlighted, we refer our material to P. withamii with uncertainty. 4.3. Morphotype 3 Supercohort: Lignophytia Kenrick and Crane 1997 Plesion/Order: Protopityales Morphospecies: Protopitys scotica Walton Material: NHM V.67422 Description: This morphotype is described from specimen NHM V.67422, a 16 mm diameter woody axis lacking any preserved primary or extraxylary tissue (Plate III, 2). A central “dark” region interpreted as the pith is 600–850 µm in diameter, but this pith and the immediately surrounding tissue shows no cellular anatomy. The following description is for the secondary xylem cylinder only. In RLS, tracheids show uniseriate, or rarely 2–3-seriate (mean: 1.12 ± 0.24, n = 100), contiguous or locally spaced, alternate bordered pitting (Plate III, 1). Tracheid pits are circular (8–15 µm diameter) with circular apertures (5 µm diameter). Ray parenchyma cells are 150–180 µm long with simple, oblique end-walls. They show 2–4 oval pits per cross-ﬁeld (too few examples preserved to quantify). In TLS, tracheid walls are unpitted. Rays are exclusively uniseriate and typically only 1–7 cells high (mode: 1 cell high), this being an especially characteristic feature of the wood (Plate III, 3). Ray parenchyma cells are typically 19–25 µm high and 19–20 µm wide. Ray density is 58–66/mm2 (mean: 61, n = 3), equivalent to about 10– 15% parenchyma by tangential cross-sectional area. One unusual feature is the occurrence of a very few isolated parenchyma cells, which are very large (inﬂated), up to 221 µm high and 64 µm wide (Plate III, 4). In TS, tracheids show a rather uniform radial diameter of 27–31 µm (mean: 27.58 µm ± 1.2, n = 100) with tangential diameters in a similar range (Plate III, 5). One weakly developed growth interruptions is present (Plate III, 6). The inﬂated cells (radial diameter up to 159 µm) occur in very low density scattered through the xylem (b1/mm2). Rays are spaced 2–17 tracheids apart, and typically only 100–270 µm long. Afﬁnity: This specimen bears a close similarity to the morphogenus Protopitys. Of the two known species, our material is quite distinct from Protopitys buchiana Goeppert (1850) from Silesia and from Vosges, France, which differs in its wide, uniseriate/scalariform tracheid pits (Galtier et al., 1998a). However, it conforms closely to a second species, Protopitys scotica Walton (Table 1), sharing the following key features: the occurrence of very low uniseriate rays (mode: 1 cell high) and tracheids with typically 1–2 (rarely 3–4) rows of bordered pits (Walton, 1957; Smith, 1962). However, the distinctive inﬂated parenchyma cells seen in our material are absent in this morphospecies. Furthermore, the absence of a preserved pith and primary tissue in our specimen means that a full comparison cannot be made. Nonetheless, it worth emphasizing that occurrences of Protopitys in Silesia, France, and Scotland (Galtier and MeyerBerthaud, 2006) are mostly of very similar age to the Newfoundland specimen, with two Tournaisian exceptions (Decombeix et al., 2005) Another close match with our material is the type specimen of Endoxylon zonatum (Kidston) Scott, which likewise has very low rays and occurs in early Namurian (Pendleian) rocks at Dalry, Ayrshire, Scotland (Scott, 1924; Lacey, 1953), precisely time-equivalent to our assemblage in Newfoundland. However, E. zonatum and Protopitys

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scotica are so similar that they are probably conspeciﬁc. The afﬁnity of Protopitys is uncertain, but the occurrence of a bifacial vascular cambium, well-developed pycnoxylic wood, together with pteridophytic reproductive organs (Walton, 1957) bearing Calamospora-type miospores (Playford, 1962) may suggest assignment to the progymnosperms (Beck, 1976). 5. Megaﬂoral and palynoﬂoral records from the Searston Formation Earlier studies have recorded a sparse megaﬂoral assemblage from the Searston Formation (Bell, 1948). This material includes the lycopsid, Lepidodendron volkmannianum Sternberg, and the probable pteridosperms, Diplotmema adiantoides (Schlotheim) Gothan, and Adiantites tenuifolius (Goeppert) Schimper (Galtier et al., 1998b). The latter morphotaxon is especially common in Pendleian strata, though less so in Arnsbergian strata (Wagner, 1984). The two probable pteridosperm taxa are good candidates for the foliage of the anatomically-preserved trunks described here, but further documentation of branches with attached leaves is required to conﬁrm this. In marked contrast, palynological assemblages in the Searston Formation are dominated by the miospores of arborescent lycopsids (especially Lycospora pellucida, the miospore of Lepidodendron hickii; Willard, 1989) as well as sphenopsids and ferns, while Calamospora, the putative miospore of Protopitys, and the pre-pollen of gymnosperms is rather rare (Utting and Giles, 2008). The relatively low abundance of pteridosperm pre-pollen may reﬂect the low productivity of these plants, which probably reproduced rather infrequently as in modern cycads, or the fact that the afﬁnity of many gymnosperm palynomorphs remains highly uncertain (Dimitrova et al., 2005). Another possibility is that the apparent mismatch between megaﬂoral and palynoﬂoral record reﬂects variable taphonomy. Palynoﬂora provides a coarse-grained snapshot of the vegetation living on the braidplain. However, the anatomically-preserved treetrunks within the base of large braided channels may represent remnants of a distinct vegetation within this matrix. Most plant fragments found in river channels are either derived from riparian stands or transported downstream from hinterland regions (FalconLang and Scott, 2000). Thus we suggest that the large pteridosperm trees may have been growing on well-drained levees or uplands to the south. This is supported by the occurrence of irregular growth interruptions in nearly all the specimens suggestive of a well-drained substrate and a seasonally dry climate (Falcon-Lang, 1999). 6. Conclusions 1. We document Mississippian anatomically-preserved tree-trunks from Newfoundland for the ﬁrst time. The fossils occur in braided channel facies of the early Namurian Searston Formation and occur in the St. Georges Bay area. 2. Three morphotypes are recognized, all attributed to putative arborescent pteridosperms and progymnosperms. These include Pitus primaeva, cf. Pitus withamii and Protopitys scotica Walton. 3. Taphonomic considerations, combined with the occurrence of irregular growth interruptions in most specimens, suggest these trees may have grown on well-drained levees or in upland areas, and washed downstream. Acknowledgements Howard Falcon-Lang gratefully acknowledges a NERC Fellowship (2002-2005) held at the University of Bristol (NER/I/S/2001/00738), which funded ﬁeldwork to Newfoundland in 2004 and 2005. He thanks Arden Bashforth (Geological Museum, Copenhagen) for kindly introducing him to the St Georges Basin of Newfoundland in 2004. The present work was written during the tenure of a NERC Advanced

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Fellowship (2009-2013) held at Royal Holloway, University of London (NE/F014120/2). References Allen, J.R.L., 1963. The classiﬁcation of cross-stratiﬁed units, with notes on their origin. Sedimentology 2, 93–114. Allen, J.R.L., 1964. Studies in ﬂuviatile sedimentation: six cyclothems from the Lower Old Red Sandstone, Anglo-Welsh Basin. Sedimentology 3, 163–198. Allen, J.R.L., 1970. Studies in ﬂuviatile sedimentation: a comparison of ﬁning-upwards cyclothems with special reference to coarse-member composition and interpretation. Journal of Sedimentary Petrology 40, 298–323. Arber, E.A.N., 1910. A note on some fossil plants from Newfoundland. Proceedings of the Cambridge Philosophical Society, 15, pp. 390–392. Arnold, C.A., 1931. On Callixylon newberryi (Dawson) Elkins and Wieland. Contributions to the Museum of Paleontology, 3. University of Michigan, pp. 207–232. Bashforth, A.R., 2005. Late Carboniferous (Bolsovian) macroﬂora from the Barachois Group, Bay St. George Basin, southwestern Newfoundland, Canada. Palaeontographica Canadiana 24, 1–123. Beck, C.B., 1976. Current status of the Progymnospermopsia. Review of Palaeobotany and Palynology 21, 5–23. Beck, C.B., Coy, K., Schmidt, R., 1982. Observations on the ﬁne structure of Callixylon wood. American Journal of Botany 69, 54–76. Bell, W.A., 1948. Early Carboniferous strata of St George's Bay area, Newfoundland. Geological Survey of Canada, Bulletin 10, 1–45. Calder, J.H., 1998. The Carboniferous evolution of Nova Scotia. Lyell: The Past is the Key to the Present: In: Scott, A.C., Blundell, D.W. (Eds.), Geological Society Special Publication, 143, pp. 261–302. Cant, D.J., Walker, R.G., 1978. Fluvial processes and facies sequences in the sandy braided South Saskatchewan River, Canada. Sedimentology 25, 625–648. Chitaley, S., Cai, C., 2001. Permineralized Callixylon woods from the Late Devonian Cleveland Shale of Ohio, USA and that of Kettle Point, Ontario, Canada. Review of Palaeobotany and Palynology 114, 127–144. Decombeix, A.L., Meyer-Berthaud, B., Rowe, N.P., Galtier, J., 2005. Diversity of large woody lignophytes preceding the extinction of Archaeopteris: new data from the middle Tournaisian of Thuringia (Germany). Review of Palaeobotany and Palynology 137, 69–82. DiMichele, W.A., Pfefferkorn, H.W., Gastaldo, R.A., 2001. Response of Late Carboniferous and Early Permian plant communities to climate change. Annual Review of Earth and Planetary Sciences 29, 461–487. Dimitrova, T.K., Cleal, C.J., Thomas, B.A., 2005. Palynology of late Westphalian early Stephanian coal-bearing deposits in the eastern South Wales Coalﬁeld. Geological Magazine 142, 809–821. Dunn, M.T., 2004. The Fayetteville Flora I: Upper Mississippian (middle Chesterian/ lower Namurian A) plant assemblages of permineralized and compression remains from Arkansas, USA. Review of Palaeobotany and Palynology 132, 79–102. Falcon-Lang, H.J., 1999. The Mississippian (Asbian–Brigantian) seasonal tropical climate of northern Britain. Palaios 14, 116–126. Falcon-Lang, H.J., 2000. Fire ecology of the Carboniferous tropical zone. In: Scott, A.C., Moore, J., Brayshay, B. (Eds.), Fire and the Palaeoenvironment: Palaeogeography, Palaeoclimatology, Palaeoecology, 164, pp. 339–355. Falcon-Lang, H.J., 2005. Intra-tree variability in wood anatomy, and its implications for fossil wood systematics and palaeoclimatic studies. Palaeontology 48, 171–183. Falcon-Lang, H.J., Bashforth, A.R., 2004. Pennsylvanian uplands were forested by giant cordaitalean trees. Geology 32, 417–420. Falcon-Lang, H.J., Bashforth, A.R., 2005. Morphology, anatomy, and upland ecology of large cordaitalean trees from the Middle Pennsylvanian of Newfoundland. Review of Palaeobotany and Palynology 135, 223–243. Falcon-Lang, H.J., Cantrill, D.J., 2000. Cretaceous (Late Albian) Coniferales of Alexander Island, Antarctica. Part 1: wood taxonomy, a quantitative approach. Review of Palaeobotany and Palynology 111, 1–17. Falcon-Lang, H.J., Scott, A.C., 2000. Upland ecology of some Late Carboniferous cordaitalean trees from Nova Scotia and England. Palaeogeography, Palaeoclimatology, Palaeoecology 156, 225–242. Falcon-Lang, H.J., Henderson, E., Galtier, J., in press. Tree trunks of Pitus primaeva in Mississippian (Courceyan) rocks at Montford, near Rothesay, Isle of Bute, Scotland. Scottish Journal of Geology 46. Galtier, J., Meyer-Berthaud, B., 2006. The diversiﬁcation of early arborescent seed ferns. Journal of the Torrey Botanical Society 133, 7–19. Galtier, J., Schneider, J.-L., Grauvogel-Stamm, L., 1998a. Arborescent gymnosperms and the occurrence of Protopitys from the Lower Carboniferous of the Vosges, France. Review of Palaeobotany and Palynology 99, 203–215. Galtier, J., Meyer-Berthaud, B., Brown, R.E., 1998b. The anatomy and seed plant afﬁnities of Rhacopteris and Spathulopteris foliage from the Dinantian (Lower Carboniferous) of Scotland. Transactions of the Royal Society of Edinburgh 88, 197–208. Gastaldo, R.A., Purkynová, E., Simunek, Z., Schmitz, M.D., 2009. Ecological persistence in the Late Mississippian (Serpukhovian, Namurian A) megaﬂoral record of the Upper Silesian Basin, Czech Republic. Palaios 24, 336–350. Gerrienne, P., Fairon-Demaret, M., Galtier, J., 1999. A Namurian A (Silesian) permineralized ﬂora from the Carriere du Lion at Engihoul (Belgium). Review of Palaeobotany and Palynology 107, 1–15. Gibling, M.R., 2006. Width and thickness of ﬂuvial channel bodies and valley-ﬁlls in the geological record: a literature compilation and classiﬁcation. Journal of Sedimentary Research 76, 731–770.

Gibling, M.R., Bashforth, A.R., Falcon-Lang, H.J., Allen, J., Fielding C.R., in press. Log jams and ﬂood sediment buildup caused channel avulsion in the Pennsylvanian of Atlantic Canada. Journal of Sedimentary Research 80. Goeppert, H.R., 1850. Monographie der fossilen Coniferen. Natuurkundige Verhandelingen Hollandsche Maatschappij Wetenschappen te Haarlem 2, 286–287. Gordon, W.T., 1935. The genus Pitys, Witham, emend. Transactions of the Royal Society of Edinburgh 58, 279–308. Heckel, P.H., Clayton, G., 2006. The Carboniferous System. Use of the new ofﬁcial names for the subsystems, series, and stages. Geological Acta 4, 403–407. IAWA Committee, 2004. IAWA list of microscopic features for softwood identiﬁcation. International Association of Wood Anatomists' Journal 25, 17–70. Jennings, J.R., 1979. Distribution of fossil plant taxa in the Upper Mississippian and Lower Pennsylvanian of the Illinois Basin. In: Sutherland, P.K., Manger, W.L. (Eds.), Neuvième Congrès International de Stratigraphie et de Geologie du Carbonifère: Compte Rendu. : 2. Southern Illinois University Press, Carbondale, IL, pp. 301–312. Kenrick, P., Crane, P.R., 1997. The Origin and Early Diversiﬁcation of Land Plants: a Cladistic Study. Smithsonian Institute Press, Washington, DC. Knight, I., 1983. Geology of the Carboniferous Bay St. George subbasin, western Newfoundland. Mineral Development Division, Department of Mines and Energy, Government of Newfoundland and Labrador. Memoirs 1, 1–358. Knoll, A.H., 1986. Patterns of change in plant communities through geologic time. In: Diamond, J., Case, T.J. (Eds.), Community Ecology. Harper and Row, New York, pp. 126–141. Lacey, W.S., 1953. Scottish Lower Carboniferous plants: Eristophyton waltonii sp. nov. and Endoxylon zonatum (Kidston) Scott from Dunbartonshire. Annals of Botany 17, 579–596 N.S. Lacey, W.S., Eggert, D.A., 1964. A ﬂora from the Chester Series (Upper Mississippian) of southern Illinois. American Journal of Botany 51, 976–985. Leeder, M.R., 1982. Upper Palaeozoic basins of British Isle: Caledonides inheritance versus Hercynian plate margin processes. Journal of the Geological Society of London 139, 479–491. Leeder, M.R., 1987. Tectonic and palaeo-geographic models for the Lower Carboniferous Europe. In: Miller, J., Adams, A.E., Wright, V.P. (Eds.), European Dinantian Environments. John Wiley and Sons, Chicester, pp. 1–20. Leeder, M.R., 1988. Recent developments in Carboniferous geology: a critical review with implications for the British Isles and NW Europe. Proceedings of the Geologists' Association 99, 73–100. Long, A.G., 1979. Observations on the Lower Carboniferous genus Pitus Witham: transactions of the Royal Society of Edinburgh. Earth Sciences 70, 111–127. Oakley, D., Falcon-Lang, H.J., 2009. Morphometric analysis of Cretaceous (Cenomanian) angiosperm woods from the Czech Republic. Review of Palaeobotany and Palynology 153, 375–385. Oakley, D., Falcon-Lang, H.J., Gasson, P., 2009. Morphometric analysis of some Cretaceous angiosperm woods and modern structural and phylogenetic analogues: implications for systematics. Review of Palaeobotany and Palynology 157, 375–390. Playford, G., 1962. Lower Carboniferous microﬂoras of Spitsbergen. Palaeontology 5, 550–618. Raymond, A., 1996. Latitudinal patterns in the diversiﬁcation of Mid-Carboniferous land plants: climate and the ﬂoral break. In: Leary, L. (Ed.), Patterns in Paleobotany: Proceedings of a Czech–US Carboniferous Paleobotany Workshop, 26. Illinois State Museum Scientiﬁc Papers, pp. 1–18. Scott, D.H., 1900. Studies in Fossil Botany. Black, London. 533 pp. Scott, D.H., 1924. Fossil plants of the Calamopitys type from the Carboniferous rocks of Scotland. Transactions of the Royal Society of Edinburgh 53, 569–596. Scott, A.C., 1990. Preservation, evolution and extinction of plants in Lower Carboniferous volcanic sequences in Scotland. In: Lockley, M.G., Rice, A. (Eds.), Volcanism and Fossil Biotas. Geological Society of America Special Paper, 244. Boulder, Colorado, pp. 25–38. Scott, A.C., Galtier, J., 1996. A review of the problems in the stratigraphical, palaeoecological and palaeobiogeographical interpretation of Lower Carboniferous (Dinantian) ﬂoras from Western Europe. Review of Palaeobotany and Palynology 90, 141–183. Scott, A.C., Galtier, J., Clayton, G., 1984. The distribution of Lower Carboniferous anatomically preserved ﬂoras in Western Europe. Transactions of the Royal Society of Edinburgh: Earth Sciences 75, 311–340. Smith, D.L., 1962. Three fructiﬁcations from the Scottish Lower Carboniferous. Palaeontology 5, 225–237. Taylor, T.N., Eggert, D.A., 1967. Petriﬁed plants from the Upper Mississippian (Chester Series) of Arkansas. Transactions of the American Microscopical Society 86, 412–416. Utting, J., Giles, P.S., 2008. Palynostratigraphy and lithostratigraphy of Carboniferous Upper Codroy Group and Barachois Group, southwestern Newfoundland. Canadian Journal of Earth Sciences 45, 45–67. Wagner, R.H., 1984. Megaﬂoral zones in the Carboniferous. In: Sutherland, P.K., Manger, W.L. (Eds.), Biostratigraphy: Congres International de Stratigraphie et de Geologie du Carbonifere, 9eme, Washington and Champaign-Urbana, 1979, Compte Rendu 2, 109–134. Walton, J., 1957. On Protopitys with a description of fertile specimen Protopitys scotica from the Calciferous sandstone series of Dunbartonshire. Transactions of the Royal Society of Edinburgh 6, 333–340. Willard, D.A., 1989. Lycospora from Carboniferous Lepidostrobus compressions. American Journal of Botany 76, 1429–1440. Wright, V.P., 1990. Equatorial aridity and climatic oscillations during the Mississippian, southern Britain. Journal of the Geological Society of London 147, 359–363.

Early Mississippian lycopsid forests in a delta-plain ...