Reconstructed tree fern Alethopteris zeilleri (Carboniferous, Medullosales)

International Journal of Coal Geology 69 (2007) 68 – 89 www.elsevier.com/locate/ijcoalgeo

Reconstructed tree fern Alethopteris zeilleri (Carboniferous, Medullosales) Erwin L. Zodrow Department of Earth Sciences, University College of Cape Breton, Sydney, Nova, Scotia, Canada B1P 6L2 Received 1 January 2005; accepted 1 March 2006 Available online 24 July 2006

Abstract From a smaller open-pit area in the roof shale of the basal Cantabrian coal seam in Sydney Coalfield, Cape Breton Island, Nova Scotia, Canada, large amounts of the pteridosperm foliage Alethopteris zeilleri (Ragot) were found. This foliage is associated with abundant, naked medullosalean axes and dichotomies of varying sizes, up to 0.80-m long, cauline structures 0.90 m and 1.3 m long, detached ovules assigned to Pachytesta incrassata Brongniart, rare male-pollen organs of the type Dolerotheca Halle, rooted tree ferns in life position, and one specimen each of a juvenile medullosalean frond and root mantle. The fossils are compression/ impression-preserved, and the foliage yielded thickly cutinized cuticles with unoriented cells (57–103 by 27–57 μm) in intercostal fields. Ultimate rachises, and abaxial surfaces (excluding costal fields) show a mixture of simple and complexly-branched trichomes, and two different structural bases. These, together with fractal dimensionality of curvatures of anticlinal walls in intercostal fields, have taxonomic potential for alethopterids. The finds suggest reconstructing A. zeilleri (Ragot) as a tree, 5–7 m high, that bore both P. incrassata Brongniart and Dolerotheca-type fructifications. Its habitat was low-land coastal plains in the Pennsylvanian coal swamps of ancestral Sydney Coalfield. © 2006 Elsevier B.V. All rights reserved. Keywords: Carboniferous; Alethopterid foliage; Cuticles; Fractals; Trichomes; Fructifications

1. Introduction Alethopteris zeilleri, erected by Ragot (1955), is a foliar morphospecies from a medullosalean plant that grew widely in the Stephanian and Early Permian of tropical Laurasia. Wagner (1968) analyzed the systematics and distribution of this species which is now regarded as one of the important indices for locating the base of the Cantabrian Stage in Northern Spain (Wagner, 1984; Zodrow and Cleal, 1985; Cleal et al., 2003). Doubinger and Grauvogel-Stamm (1970), and Kerp and Barthel (1993) described naturally-macerated cuticles (see Zodrow and Mastalerz, 2001) of some A. zeilleri (Ragot) specimens E-mail address: [email protected]. 0166-5162/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2006.03.009

from its type locality (but not from the holotype which Remy et al., 1963 designated in reference to Pl. XXI, Fig. 8 of Zeiller's, 1888 memoir). Šimůnek (1989) macerated cuticles from well-preserved compressions and described stomata (pers. comm. July, 2003) of this species from the Czech Stephanian and Permian basins. This paper documents a parautochthonous assemblage of A. zeilleri (Ragot) from early Cantabrian strata in the Sydney Coalfield, Nova Scotia, Canada (Fig. 1). It includes associated male and female reproductive organs, and cauline specimens that are considered in reconstructing the plant. The specimens have also yielded well-preserved cuticles, which supplement the evidence of epidermal structures provided by the previously-described Czech specimens. The occurrence in the Sydney

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Fig. 1. Location map, Canada, northern part of Sydney Coalfield with Brogan's open-pit mining location (X), where the fossils were collected by the author, and generalized stratigraphy above the Lloyd Cove Seam in Brogan's pit.

Coalfield extends the known geographical range and palaeoenvironmental tolerance of the species, and helps confirm the cosmopolitan nature of A. zeilleri (Ragot) within palaeotropical Laurasia. 2. Materials and method 2.1. Material and preservation The plant fossils described in this paper originated from a gray, sideritic shale horizon 0.2–0.4 m above the Lloyd Cove coal seam (Fig. 1), exposed in an open-pit coal mine covering an area of about 4200 m2. The fossil flora is dominated by pinnae of A. zeilleri (Ragot), intermixed with medullosalean rachial and cauline fragments, rare compressed medullosalean-trunk vasculature, and detached ovules. The only other fossils found there are abscised pinnules of Linopteris obliqua (Bunbury) Kidston (Zodrow and McCandlish, 1978), and very rare ultimatepinna fragments of Alethopteris ambigua Lesquereux pars

nov. emend. Zodrow and Cleal 1998. A preliminary description of the site and its fossil remains was given by Zodrow (2002). Additionally, rare pollen organs, a medullosalean juvenile frond fragment, and a mining cliff section with “tree-fern” stands are newly documented. These fossils are mostly preserved as thick adpressions (Shute and Cleal, 1986) with prominent inrolled pinnule margins. Some of the pinnae are naturally macerated (Zodrow and Mastalerz, 2001) and reveal strongly cutinized laminae, midveins, and lateral veins, unusual for preserved alethopterid foliage at Sydney (see Zodrow and Cleal, 1998). Similar naturally macerated cuticles of A. ambigua Lesquereux pars nov. emend. are known, particularly from the Lloyd Cove Seam (Zodrow, 1993). 2.2. Maceration methods Ultimate pinnae of A. zeilleri (Ragot) were precisioncut from the shale matrix to prevent cross contamination by stray pinnules of other species. The pinnate compressions

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were freed from the matrix using 48% hydrofluoric acid for a few hours. The pinnae are sturdy, allowing fragments 30–50-mm long to be extracted without breakage; intact pinnule-sized cuticles were routinely recovered. Compressions were treated in Schulze's solution at room temperature in one of two ways. (1) Using the technique successfully applied to neuropteroid foliage (Cleal and Zodrow, 1989), Schulze's solution was made by dissolving 4–6 g of potassium chlorate in 150 ml of reagent-grade 68– 70% nitric acid. Maceration time ranged from 4 h to 75 h (Table 1). Clean abaxial cuticles showing clear epidermal features could only be obtained after a three-stage maceration treatment lasting 70 h (Table 1). However, intact abaxial surfaces could effortlessly be separated from the adaxial surfaces, including the midvein, at any stage of this maceration. Inrolled pinnule margins could not be separated sufficiently to observe the presence of the transition of the upper leaf surface to the lateral pinnule margin

(see Doubinger and Grauvogel-Stamm, 1970, pl. 3, Fig. 1; pl. 3, Figs. 2 and 3). Also, partly over-folded margins from ultimate-pinnae rachides prevented epidermal observation over their entire width. (2) Essentially following the method of Krings and Kerp (1997), the compressions were initially macerated for 25 h in a weaker Schulze's solution, consisting of 1–2 g of potassium chlorate dissolved in 60 ml of 40% nitric acid. Then, nitric-acid concentration was gradually increased over the following 5 days to reach a strength similar to that used by Cleal and Zodrow (1989). In both sets of macerations, detailed observations were made at each step which are summarized in Table 1. On balance, Method 2 did not improve the workability of the cuticles, nor improve the clearing of the abaxial cuticles. Adaxial cuticles, however, became clean after only after hours of maceration by either of the two methods. Over 110 glycerin-mounted slide preparations were made, including untreated compressions, macerated compressions,

Table 1 Maceration time and cuticular results, Canadian specimens of A. zeilleri (Ragot) Slide no.

Pinnule size cuticle

Maceration time (h:min)

Remarks on quality of epidermal features

3 02-267b-2 02-307/4 02-307/3 02-267b-2 02-267b-2

Near tip ultimate pinna Adaxial/abaxial (Adaxial) one (Abaxial) pinnule Abaxial midvein Adaxial

4h 22 h 24 h 24 h 28 h 28 h

02-267b-3 02-267b-1

Abaxial Complete 10-mm long pinnule (Adaxial) one (Abaxial) pinnule

30 h

Compression still black, little change Completely covered with mesophyll Ic and co cells clearly observable Ic differentiable for co fields Cells barely, but tb recognizable Midvein cells clearly visible, ic and co cells still covered with mesophyll Completely covered with mesophyll

02-267b-1/3 02-267b-1/2 1

02-253b 02-253b/3 02-253b/2

35 h 35 h 49 h

Ic, co and midvein cells visible Ic and co fields differentiable, ic obscured by mesophyll; midvein, cells and tb clearly visible Ic and co fields not visible, cells of midvein are

Stalked base of 19-mm long pinnule (Adaxial) one (Abaxial) pinnule

49 h

Ic and co fields differentiable, ic fields hidden by mesophyll, no cells visible; midvein, cells and tb clearly visible

7-mm upper part of 16-mm long pinnule (Adaxial) one (Abaxial) pinnule

75 h 75 h

Ic and oc cells clearly visible Ic cells, a few, visible; still much mesophyll present

Two-stage alkaline treatment: maceration for 24 h, then alkaline-treated, maceration for 5–27 h, then alkaline treated produced a crinkly, especially abaxial, surface and distorted cells not suited for morphometric measurement. Three-stage treatment for abaxial cuticle: 45 h in 50% Schulze's (i.e. 50% strength of nitric acid only), then 23 h in full-strength Schulze's, then alkine treated and separation of adaxial from abaxial cuticle, and both surfaces were mounted. Then, only abaxial cuticles were treated in full-strength Schulze's solution for 0 h 30 min and to 2 h. The latter treatment produced the cleanest surfaces yet, and ic and co fields are differentiable, but their cells are poorly observable; midvein cells and tb's thereon are clearly observable. Except slide 3, all others were observed under Nomarski phase-contrast mode. Abbreviations used in table: ic = intercostal, co = costal, tb = trichome base.

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trichomes, and adaxial and abaxial cuticles. The slide mounts were studied mostly using Nomarski phase-contrast techniques, and for black and white photography the reddish spectrum provided the sharpest contrast images.

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for eventual deposition with the Nova Scotia Museum, Halifax, Canada. Each hand specimen bears an accession number (e.g. 002-307). A slide mount prepared from that specimen bears the same number, followed by a slash and a number (e.g. 002-307/i, where i = 1st, 2nd…).

2.3. Calculating fractal dimension 3. Description Fractal dimensions were calculated using a standard ‘box-type’ algorithm (Dr. J. Preen, pers. comm., June, 2003). 2.4. Depository All specimens and photographic negatives are curated by the author at the University College of Cape Breton

3.1. Foliar gross morphology A preliminary description of the foliage is given by Zodrow (2002), and the following only deals with information from subsequently discovered specimens, some of which are illustrated in Figs. 2–5. These include the

Fig. 2. Alethopteris zeilleri (Ragot). Fragmentary ultimate pinnae, and crozier. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. (A) Tip portion showing constricted pinnule bases (‘neuropteroid’) in the lowermost pinnules. 002-253a. (B) Tip portion of an ultimate pinna showing longer pinnules. 002-267b-2. (C) Upper portion. 002-307. (D) Juvenile alethopterid crozier, Alethopteris zeilleri (Ragot)? Arrow points to developing pinnae. 002-301b.

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specimen in Fig. 2D which is the first Canadian record of an unfurling medullosalean alethopterid frond. It measures 20-mm across, developing pinnae are 2–3-mm long, less than 1-mm wide, and on the thick 2–3-mm wide supporting axis spines are not observed (see Cleal and Laveine, 1988). Fig. 3B shows the tip of a penultimate pinna in which pinnule individualization is rapidly taking place. The typical pinnule morphology is shown in Fig. 4. Pinnules are vaulted, show inrolled margins, and considerable variability in length from 7 to 34-mm. Width, however, is fairly constant at 7-mm wide, except near the terminals of ultimate pinnae (Fig. 3C), and penultimate pinnae (Fig. 3B), where they may be as little as 4–5-mm wide. Pinnule formation appears to conform to the pinnule-growth pattern curve documented for other alethopterid species by Zodrow and Cleal (1998). Pin-

nules are typically linguaeform and broadly attached to the rachis. Those longer than 23–25-mm are somewhat constricted at the base (‘neuropteroid’: Fig. 3D), and show lobate margins (Fig. 3E; see also specimen figured by Wagner, 1968, Pl. 64, Fig. 180a). These larger pinnules nevertheless have inrolled margins. Midveins extend for about 85 % of the pinnule length. Lateral-vein density per marginal cm, measured on selected pinnules (lengths from 7 to 25-mm) ranges from 26 to 36; it decreases towards the base of a pinnule on its basiscopic side. Within one ultimate pinna fragment (Fig. 4), the vein density was found to center around 28 to 29 veins/marginal cm. Fig. 5 shows the first record of a penultimate rachial segment of the frond of A. zeilleri (Ragot). The striate penultimate rachis is preserved for a length of 500 mm and is 6-mm wide. Proximal ultimate pinnae are inserted

Fig. 3. Alethopteris zeilleri (Ragot). Ultimate and penultimate pinnae. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. (A) Pinna with terminal pinnule. 002-267b-3. (B) Incomplete tip of a penultimate pinna showing naturally-macerated lateral veins (arrow), the venation scheme of which is repeated in the long pinnule in (E). 002-232. (C) Pinna showing short pinnules. 002-267b-1. (D) Lower portion of an ultimate pinna showing neuropteroid-like attachment of pinnules to rachis. 002-268. (E) Longest form pinnule with lobate lateral margin. 002-293.

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Fig. 5. Alethopteris zeilleri (Ragot). Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. Fragmentary penultimate rachis (pr) ca. 500mm long. Complete ultimate pinnae (ur) are identified by cross bars. Traced from photograph. 003-328.

both (Figs. 6–10). However, there is some resemblance between the epidermis of the ultimate-pinna rachis and the pinnule midvein, especially on the abaxial surface (Figs. 7

Fig. 4. Alethopteris zeilleri (Ragot). Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. Fragmentary ultimate pinna with measurements of vein density/10 mm on the acroscopic or the basiscopic pinnule margin. & Measurement is per 1/2 cm on basiscopic-pinnule margin. 002-234a.

oppositely at 35-mm intervals; ultimate pinnae are 150-mm long and the more distal ones 230-mm. Pinnules are loosely inserted, up to 25-mm long and 7-mm wide, conforming closely to pinnule morphology shown in Fig. 3D,E. The proximal pinnules show lobed margins and a constricted base; this changes gradually in distal pinnules that show deep sinuses and are broadly attached to the rachis, resembling pinnule morphology in Fig. 2B. 3.2. Epidermal features Rachises, and the adaxial surface of pinnules are strongly cutinized, the abaxial appreciably less, i.e., it is very thin. There are clear differences between the epidermal structures on the adaxial and abaxial surfaces of the pinnules, and of the rachis, and a strong differentiation between the costal and intercostal fields on

Fig. 6. Alethopteris zeilleri (Ragot). Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. Adaxial cuticle. Middle area of 21-mm long pinnule. “m” is the midvein and “c” a costal field. All anticlinal walls are thickly cutinized. Note complete absence of any trichome bases. Macerated for 45 h. Polarized light. 002-307/6.

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and 8A, respectively). Anticlinal cell walls in intercostal fields of both surfaces are slightly undulate, broadly curvy, Fig. 9. Details of the epidermal-cell dimensions and shapes are summarized in Table 2, together with Czech and French cuticles of A. zeilleri (Ragot). When pinnule margins are only slightly inrolled, longer and narrower intercostal cells with gently undulating anticlinal walls that are quasi-parallel to the pinnule margin are observed (Fig. 8B). Comparable marginal structures have been observed in foliage of other medullosalean species (e.g. Cleal and Zodrow, 1989; Cleal and Shute, 2003). The longer and narrower shape of these cells is different from the straight anticlinal walls in the elongate marginal cells illustrated by Doubinger and Grauvogel-Stamm (1970, pl. 4, Fig. 3).

The pinnules are hypostomatic. Although the stomata are highly cutinized, they are not well-preserved, and little details of their structure can be observed, other than the presence of two bean-shaped guard cells (compare with Šimůnek, 1989, Fig. 8). In early stages of maceration by either method (see 2.2. Maceration methods), the abaxial surface of the pinnules could be seen to be covered by a dense ‘mat’ of trichomes (Fig. 11A), including along the ultimate-pinna rachises, lateral veins, and on midveins, but not on the inrolled margin, nor on the adaxial surface. With increasing maceration time, the trichomes fell off and accumulated on the bottom of the petri dish. They generally oxidized on further maceration, dissolved on alkaline treatment, or some survived, leaving two distinct types of trichome bases.

Fig. 7. Alethopteris zeilleri (Ragot). Trichome bases and trichomes on an ultimate-pinna rachis. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. 002-267-3/5. (A) Two intracellular oval to round bases with thicker, cutinized necks. Macerated for 75 h. Nomarski phase contrast. (B). Type 2 “ring structure” of a trichome base showing “1 to 5, possibly 6”, subsidiary cells surrounding a very highly cutinized outer neck. Macerated for 30 h. Compare to Fig. 8A arrowed. (C) Epidermal cells of the ultimate-pinna rachis shown in (A), with in situ trichomes. Macerated for 30 h. Nomarski phase contrast. Compare with (A).

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Fig. 8. Alethopteris zeilleri (Ragot). Trichome base and cells. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. (A) Abaxial epidermis of a midvein with in situ fragmentary trichomes showing faintly (arrowed) Type 2 “ring structure” with subsidiary cells (see Fig. 7B) that are not clearly visible at the other trichome bases. Macerated for 35 h. Nomarski phase contrast. 002-267b-1/2. (B). Adaxial epidermis showing long and narrow cells at a pinnule margin. Macerated for 24 h. Nomarski phase contrast. 002-307/9.

The longest preserved trichome fragment is ca. 700 μm. It consists of 9–10 rectangular-elongate cells in a uniseriate arrangement without preserved terminal cell (Fig. 11B,C). A number of trichomes (Fig. 11D–F) show a complexly-branched structure with round, and capped terminal cells, some of which tend to be thickened (Fig. 11E, bottom, and Fig. 11F top). These could be interpreted as glandular structures (see Šimůnek, 1996, p. 19). The two types of trichome bases are structured as follows: Type 1: Simple trichome bases are centered on a single epidermal cell, or straddling two or more cellular walls. These occur along the ultimatepinna rachises (Fig. 7A and C: 23–57-μm diameter), the midvein and lateral veins of the abaxial surface (Fig. 8A: 42–57-μm diameter), the abaxial intercostal areas (Fig. 10B: 19-μm diameter), but rarely along the veins of the adaxial surface.

Type 2: Trichomes bases are surrounded by a ring of five to six ‘subsidiary’ cells (Fig. 7B). These occur on the ultimate-pinna rachises (Fig. 7B: 42-μm diameter), and on the midvein of the abaxial surface (Fig. 8A: 27–42-μm diameter). 3.3. Fractal dimensionality of anticlinal-wall curvatures Variation is noted in the shape of curvature of the anticlinal walls of the intercostal cells in both adaxial (Fig. 12) and abaxial cuticles (see also Doubinger and Grauvogel-Stamm, 1970; Šimůnek, 1989; Kerp and Barthel, 1993). In comparison, anticlinal walls in both the French and Czech specimens are sinusoidal, whereas the Canadian specimens are not, being gently undulate. An unbiased method of discriminating amongst these curvatures is by fractal geometry (Mandelbrot, 1983; Barnsley, 1988; Prussinkiewicz and Lindenmayer,

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Fig. 9. Alethopteris zeilleri (Ragot). Epidermis at a pinnule margin. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. 002-307/14. (A) Abaxial at “i” the inrolled margin is the non-descript, dark band. (B) Adaxial cuticle a few micrometers across from “i”. Black oval is a hole. Macerated for 24 h. Nomarski phase contrast.

1990), a mathematical technique already introduced into Carboniferous tree-fern simulation by Zodrow and Heggie (1992), and Heggie and Zodrow (1994). Fractal-dimensionality calculations of the curves (Fig. 12) in the Canadian, French and Czech cuticles produced values that lie within a narrow range about 1.05, and are therefore only slightly fractal, compared with Euclidean unit dimensionality for a straight line. The geometric character of the cuticular curves, therefore, fits the Von Koch curves with fractal dimension of ca. 1.098 (Harris and Stocker, 1998), which is proposed here for the first time as an additional parameter, independently calculable, for Carboniferous cuticular pteridophyll taxonomy. 3.4. Apex of medullosalean trunk Associated with the A. zeilleri (Ragot) foliage is part of a compression-preserved trunk (Fig. 13). As

preserved after fragmentation in the open-pit coal mine, it is ca. 900-mm long, but only the top 400 mm could be recovered for the collection. The most proximal preserved part of the trunk was at least 120–130-mm wide, narrowing distally to ca. 50–70mm. Margins of both the trunk and attached petioles were eroded, making it impossible for accurate width measurement. The petiolar remains are attached to the trunk at intervals of 60–80-mm. This relatively close spacing suggests that the fossil originated from near the crown of the tree (compare with a similar medullosalean trunk, where petiolate spacing is 120– 450-mm, Zodrow, 2002, Figs. 3 and 4). The most proximal petiole is 50 mm wide with a medial ridge, whereas the others are densely covered by punctae (hair, spine bases?). All of the petiolate remains are ‘naked’ without attached foliage. Although surface markings are mostly eroded, architecture and size suggest a medullosalean origin (Zodrow, 2002).

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Fig. 10. Alethopteris zeilleri (Ragot). Abaxial cuticle. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. (A) Cuticle showing intercostal cells without preserved stomata. Macerated for 30 h. Nomarski phase contrast. 002-267b-3/1. (B) Cuticle part a few micrometers distant from an ultimate pinna rachis at “u”. Intracellular? base with thickly cutinized neck (arrow). Macerated for 30 h. Nomarski phase contrast. 002-267b-3/5.

Ovules, preserved as adpressions, are common and were found associated with the foliage, axial fragments, and a cauline structure, where the ovule is found uncompressed as a cross section, infilled with sediments (Fig. 14, marked a). In lateral view, the ovules have an ovate outline with an obtuse apex, are 80–100-mm long and ca. 35-mm wide. The adpressions show either one (Fig. 15A) or two thick longitudinal ribs, depending on orientation, which suggests a trigonal longitudinal subdivision. However, one ovular specimen is preserved as a compressed cast on which the three-fold division is clearly observed. Between these major ribs are eight to ten equidistantly-spaced, thinner ribs, ca. 2-mm apart. Most of the specimens show slickensided margins which might be evidence of their impact as they hit the mud in which they were preserved. Most of the ovules occurred singly and detached. Several fragmentary specimens, however, show two or more ovules that are attached to an axis that itself is detached (Zodrow, 2002, Fig. 16a). Specimens showing aligned ovules were also collected (2005). White (1899, pp. 267–268), and Gothan and Weyland (1973, p. 317) mentioned this, but Drinnan et al. (1990) reconstructed axially stalked medullosalean ovules Stephanospermum konopeonus (small 12–15-mm long Pachytesta-type ovules) preserved in sideritic concretions from the Mazon Creek flora.

D). This is the first time that such organs have been reported from the Sydney Coalfield. From the position of the pedicel, which is clearly visible in oblique illumination (Fig. 15B), the pollen organs appear to have been orthogonally compressed relative to their long axis. The resulting split in the oval to circular shape of the fossil suggests a shape was hemispherical or pod-like. The longest diameter ranges from 17 to 20-mm, and the smallest from 15 to 16-mm. The outer margin shows delicate, pointed and paired apical structures in overlapping arrangement that are ca. 2-mm long. An accurate count of these could be ascertained from the compression. Impressed ridges and grooves, possibly representing elongate sporangia, radiate out from the upwards-facing remnant of the pedicel. The surface of one of the coalifiedcompression shows very small sub-quadrate markings arranged in parallel rows, but this is not observed in others. Because of the compression, internal structure cannot be observed, or even if the organ was originally hollow or not. The pollen organs were found clustered on a small 0.30 m × 0.35 m rock slab (compare comments by Millay and Taylor, 1979, p. 348). Collected is also one specimen compressed sideways to show a bell-shaped structure, ca. 20-mm across, and parallel-arranged ridges. A ca. 20-mm structure that resembles these organs was found near a large ovule in close proximity to a medullosalean trunk (Figs. 13 and 14 marked b).

3.6. Associated pre-pollen organs

3.7. Rooted tree-fern stumps

Adpressions of six detached male organs were found associated with the A. zeilleri (Ragot) foliage (Fig. 15B–

In a cliff section, four stumps in life position were observed rooted on the roof of the Lloyd Cove Seam

3.5. Associated ovules

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Table 2 Epidermal characters of A. zeilleri (Ragot) based on Canadian specimens (present study), Czech specimens (Šimùnek, 1989) and French specimens (Doubinger and Grauvogel-Stamm, 1970; Kerp and Barthel, 1993)

Ultimate rachial cells: Anticlinal walls Length × width Trichome bases Trichome sizes Adaxial surface: Midvein cells: Length × width Width of midvein Trichome bases Trichomes sizes Intercostal cells: Anticlinal walls Length × width Orientation Trichome bases Trichomes sizes Costal cells: Anticlinal walls Length × width Orientation Trichome bases Trichomes sizes Abaxial surface: Midvein cells: Length × width Width midvein Trichome bases Trichomes sizes Intercostal cells: Anticlinal walls Length × width Orientation Trichome bases Trichome sizes Costal cells: Anticlinal walls Length × width Orientation Trichome bases Trichome sizes Structure of stomata: Orientation Length × width No. subsidiary cells

Czech specimens

French specimens

Canadian specimens

Rectangular Straight 40–100 × 20–30 70–90 350 × 45–50 a Thickly cutinized Not recorded Not measured Not measured 70–90 Not observed Irregular, polygonal Undulate, straight 60–80 × 30–60 Unoriented 80–100 Up to 230 × 55–65a Rectangular Undulate (straight) 60–100 × 20–35 Oriented Rare, 80–100 Not recorded Weakly cutinized Tetragonal, elongate 40–100 × 20–30 Not recorded 70–90 Up to 350 × 40–50a Irregularly polygonal Wavy, sinusoidal 30–50 × 20–30 Unoriented Not recorded Not recorded Rectangular Straight Not measured Oriented Small None observed Monocyclic Irregular 24–28 × 16–20 5–6, papillate

Rectangular Straight 40–100 × 20–35 120 350 × 90a Thickly cutinized Rectangular, spindle-shaped 41–108 × 16–25 58–83 58–66 ? Irregular, polygonal Straight, undulate 22–80 × 45–88 Unoriented 120 230 × 55–65a Rectangular Straight, undulate 40–100 × 20–35 Oriented 50–58 Not recorded Weakly cutinized Variable, elongate 40–100 × 20–30 Not recorded 70 × 90 Not recorded Polygonal Undulate, sinusoidal 12–50 × 20–100 Unoriented 80 Not recorded Rectangular Straight, undulate 50 × 30 Oriented Not recorded Not recorded Monocyclic Irregular Not recorded 5–6, papillate

Irregularly rectangular Straight 61–91 × 38 23 × 57 152 × 42a Thickly cutinized Rectangular, spindle-shaped 30–156 × 11–27 150–170 None observed None observed Irregular, polygonal Undulate 59–103 × 27–57 Unoriented Rare None observed Rectangular Undulate, straight 50–144 × 15–35 Oriented Rare None observed Weakly cutinized Variable, elongate 34–133 × 12–30 700–1000 to 400–600 27 × 42 114–209 × 42–57a Irregular rectangular Broadly curved 57–95 × 34–50 Unoriented None observed 232 × 19a Rectangular? Straight Not known Oriented None observed None observed Not preserved – – –

Measurements in μm. a In situ, apical cell(s) eroded.

mined in the open pit. These are linearly 2–4-m apart, trunk diameters do not exceed 80 mm, and trunks basally flare out 450–480-mm to a height of about 450mm which is interpreted as an adventitious root system. Although both lack features for accurate taxonomic assignment, these structures are interpreted to represent

remnants of a tree-fern stand, probably alethopterid in origin. The stumps are truncated at a height of ca. 1.30 m by fine-grained, cross-laminated sandstone in which stands of Mesocalamites suckowii are preserved in life position, through truncated at about 0.80–1.10 m.

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Fig. 11. Alethopteris zeilleri (Ragot). Multiple-forked and single-file trichomes. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. Oxidized only with Schulze's for 35 h. Photographed under the red spectrum, Nomarski phase contrast. (A) Trichomes attached to a “filthy” mat (left) that is detached from an abaxial cuticle. Round structures are trapped air bubbles. 002-267b-1/3a. (B) Detached trichome, single file consisting of at least 6 cells, tip is missing. Longest cell is 117 μm and the shortest is 78 μm. 002-267b-1/7. (C) Detached trichome, single file with a budding? ramification (arrow) consisting of at least 8 cells, tip is missing. 002-267b-1/8. (D) In situ, complex trichome structure, possibly with two dichotomies. 002-253b/ 1. (E) Detached, complex-forking trichomes which are likely attached at the right to actually make it a double-forking structure. Note the wellpreserved capped tips. 002-267b-1/11. (F) Two detached trichomes: (a) shows an incompletely preserved, bifurcating structure; (b), overlain by (a), is tip-eroded. 002-267b-1/8.

Root structures (summary: Pfefferkorn et al., 2001) were not preserved. Two additional calamitean episodes followed before the surface of the Carboniferous unconformity of the Sydney Coalfield. 4. Comparisons 4.1. Compression–impression morphology Table 3 summarizes the principal gross-morphological characters of the Canadian specimens compared with specimens of A. zeilleri (Ragot), including the

holotype, and specimens from the Czech Republic. The Canadian foliage has a larger variable pinnule length but otherwise morphometric parameters are similar to those of the other specimens. The Czech samples show a larger range of vein-densities and a greater upper limit for the pinnule widths. These differences are probably due to sampling bias, although palaeoenvironmental factors cannot be ruled out. The Canadian specimens have inrolled margins, whereas the European ones do not, but this is almost certainly taphonomic-palaeoenvironmental dependent and of little taxonomic consequence.

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22): compare with Fig. 2C, or with Fig. 3C. The latter species has on average shorter (14 ± 4 mm) pinnules, but comparable pinnule width of 7 mm, and vein density of 29 ± 4/cm pinnule margin. However, distinct cuticular differences provide reliable means for separating the two species. 4.2. Epidermis Table 2 summarizes the epidermal features of A. zeilleri (Ragot) specimens from Canada, Czech Republic, and France (no such data are available for the holotype). The stomata are poorly preserved in the Canadian specimens; the epidermal topographies and measurements, however, are sufficiently similar in all three groups. The fractal dimensions calculated for the anticlinal walls of the adaxial epidermal cells are also essentially the same. These data support the gross morphological evidence that all three groups of specimens are conspecific. Fig. 12. Alethopteris zeilleri (Ragot). Adaxial intercostal cells and anticlinal curvature of selected French (Fr), Czech (Cz), and Canadian (Cad) specimens. Sources: Doubinger and Grauvogel-Stamm (1970, Pl. 1, Fig. 2), Šimůnek (1989, Fig. 7), and present specimens, respectively.

On balance, the investigated Canadian compressions conform morphologically with A. zeilleri (Ragot). The morphospecies Alethopteris grandinioides var. subzeilleri nov. var. Wagner, 1968, however, that occurs nearly exclusively in Spain, stratigraphically below A. zeilleri (Ragot), is a closely related form species. According to Wagner (1968), it is transitional from A. grandinioides Kessler to A. zeilleri (Ragot). In comparison, the grandinioides form has shorter pinnules (maximum 22 mm), pinnule margins that are more parallel-sided, vein density that averages more than 35 veins/marginal cm, a thinner midvein, and lateral veins that tend to approach the margin more at a right angle than are observed in A. zeilleri (Ragot). A. zeilleri (Ragot) compressions could also be confused with co-occurring A. ambigua Lesquereux pars nov. emend. at the horizon of the Lloyd Cove Seam in Sydney Coalfield. The latter has, however, on average shorter (13 ± 3 mm) and narrower (5 ± 1 mm) pinnules, higher vein density (36 ± 4 veins per cm margin), nearhorizontal or oblique lateral veins, but similarly broadly undulating abaxial, anticlinal cuticular walls (adaxial cells are near-isodiametric), with roughly similar intercostal cellular dimensions of 40 by 100 μm. A. zeilleri (Ragot) could also be confused with Alethopteris pseudograndinioides whose upper stratigraphical sample range coincides with the level of the Lloyd Cove Seam (Zodrow and Cleal, 1998, Text-Fig.

Fig. 13. Fragmentary, apical medullosalean trunk, impression, showing in close proximity one detached 81-mm long seed, and a 20-mm detached pollen structure (arrowed). Broken line = erosional boundary. Traced from a photograph (see Fig. 14). Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. 003-313.

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The cuticles from these three sample areas have two types of trichome base: simple ones with no specialized epidermal cells (Type 1) and complex ones surrounded by a ring of five to six subsidiary cells (Type 2), the former straddling more than one cell is also present in A. pseudograndinioides Zodrow and Cleal 1998 (Pl. 7, Fig. 5). The latter feature may have taxonomic utility, as it is not reported for any other medullosalean species. Some of the Type 1 bases (simple structure) have rather thickly cutinized necks to suspect that they could represent hydathodes, which, however, are mostly known so far from fossil marattialeans (Remy, 1975; Remy and Remy, 1977), or according to Lesnikowska and Galtier (1991) from marattialeans not older than Stephanian. 4.3. Ovules

Fig. 14. An 81-mm long uncompressed ovule, “cross-sectioned” (a) by bedding-plane splitting, probably represents Pachytesta Brongniart sp., and a pollen structure (b) that resembles ?Dolerotheca Halle sp. Both are unattached in proximity of a medullosalean stem near its crown (see Fig. 13). Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. 003-327.

The trichomes attached to the Canadian, French, and Czech cuticles are all epicuticular, without discerned internal structure, although the base is either simple or complex-structured. They are uniseriate–multicellular, and are thus similar to trichomes reported attached to the abaxial surface of permineralized A. zeilleri (Ragot) pinnules (Mickle and Rothwell, 1982). No complete in situ trichome was found, and so their overall lengths and morphologies cannot be compared. Some of the detached trichomes associated with the Canadian cuticles are multiremous, and some show tips of a type not previously reported in Alethopteris Sternberg. The nearest comparison is with the forked trichomes of A. urophylla (Brongniart) reported by Šimůnek (1996, pl. XI, 2, right), but they are nowhere near as complex in structure as the Canadian specimens are. The French cuticles have prominent papillae, mainly associated with the stomata. The absence of such papillae in the Canadian specimens is probably just due to the poor preservation of the stomata. Anyway, Kerp and Barthel (1993) attached little taxonomic significance to the presence/absence of papillae in A. zeilleri (Ragot). The French and Czech cuticles have trichomes on the adaxial surface, in contrast with the Canadian that have not.

Trigonocarpus Brongniart 1828 was originally established for elongate-oval ovules in which the sclerotesta is preserved as a lithified cast showing three or six longitudinal ribs, sometimes with a surrounding coalified sarcotesta. Today, the generic circumscription has been expanded to include coalified compressions similar to those reported in the present paper (see Hoskins and Cross, 1946). Many Trigonocarpus species probably represent various preservation stages of the ovules that are known as Pachytesta Brongniart 1874a, when anatomically preserved (e.g., Němejc, 1936; Taylor, 1965; Remy and Remy, 1977, p. 121; Gastaldo and Matten, 1978; Zodrow and McCandlish, 1980; Stewart and Rothwell, 1993; Taylor and Taylor, 1993). By virtue of their overall dimensions and trigonal ribbing, the Canadian ovules undoubtedly belong to Trigonocarpus Brongniart. Among trigonocarpalean species known from adpressions or casts, two are of comparable dimensions to the Canadian specimens. Firstly, T. grandis Lesquereux 1884 emend. Gastaldo and Matten 1978 from an unknown stratigraphical horizon in Illinois has an essentially similar shape to the Canadian ovules. It has just one secondary rib in each intercostal area separating the primary ribs, and the secondary ribs are restricted to the proximal part of the ovules. Secondly, T. leeanus Gastaldo and Matten 1978 is a little less elongate than the Canadian ovules, but has a similar arrangement of secondary ribs. The stratigraphical age of the T. leeanus holotype (from the Herrin No. 6 Coal in Illinois — lower Cantabrian) is essentially the same as that of the Canadian ovules, although there is no mention of A. zeilleri (Ragot) in the Herrin No. 6 adpression flora (Gastaldo, 1977). Among anatomically preserved ovules, two are comparable in size to the Canadian ovules: Pachytesta gigantea Brongniart 1874a and Pachytesta incrassata

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Fig. 15. Fructifications. Lloyd Cove Seam, Sydney Basin, Nova Scotia, Canada. (A) Pachytesta incrassata Brongniart, detached, with a prominent rib and in between ribs. 002-313. (B) Dolerotheca Halle sp., detached, compressed from top to bottom. At left margin parallel ridges/grooves are clearly visible. The stalk is situated off-center. 003-257. (C) Dolerotheca Halle sp., detached, compressed from top to bottom. Oblong outline showing what appears to be paired sporangia. 003-255. (D) Dolerotheca Halle sp., detached, compressed from top to bottom. Ovate-circular outline with a stalk (arrowed). 003-253.

Brongniart 1874b. Both were originally described from the late Barruelian (‘Stephanian A’) Grand'Croix flora in France, although P. gigantea is also known from the Herrin No. 6 Coal (Taylor, 1965; Smoot and Taylor, 1983/1984), and other localities. P. gigantea is nearest in size to the Canadian ovules but only has secondary ribs in the distalmost part of the ovule. P. incrassata, on the other hand, has a more comparable arrangement of secondary ribs along the entire length of the ovule. It is somewhat larger than the Canadian ovules (over 100mm long and 50–60-mm wide), but it is possible that this is due to preservation in shale causing some shrinkage, or to non-preservation of certain outer seed parts, compared to the much quicker and more complete permineralization process that preserved the Grand'Croix fossils. Another possible comparison is with Rhabdocarpus mansfieldii Lesquereux (1879–1880, pls LXXXV,

Fig. 21; pl. LXXXVII, Fig. 8), which Grand'Eury (1904) suggested might be Pachytesta Brongniart (although formal combination was not proposed). Carpolithes insignis Feistmantel 1881 is also similar in size, and Němejc (1936) transferred it to Pachytesta Brongniart, although the cross-sectional shape of these ovules remains undetermined. Bell (1943, pl. LXXIX, Fig.1) reported Rhabdocarpus sp. of comparable 80-mm length, ca. 30-mm width from the older Cumberland Basin, Nova Scotia, which, however, does not show the surface markings the specimens do from the Sydney Coalfield. The “cross-sectioned” ovule (Fig. 14 marked a) remains undetermined, but by virtue of its shape, large size, and sample horizon and association, affinity with Trigonocarpus Brongniart is suggested. A doubtful Pachytesta seed-bearing pinna is reported from Alethopteris norinii Halle (1927, pl. 29), and for an

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Fig. 16. Hypothetical arborescent Alethopteris zeilleri (Ragot) shown with attached Dolerotheca Halle sp. (arrowed), Pachytesta incrassata Brongniart ovules, juvenile fronds, and a root mantle.

alethopterid species from Halle (1933: see Stewart and Rothwell, 1993, Fig. 23.22 A). Both Grand'Eury (1904) and Němejc (1936) documented co-occurrences of P. gigantea with alethopterids, the latter author particularly with A. zeilleri (Ragot) over a larger stratigraphic range in the Carboniferous–Permian Bohemian coal basins. Buisine (1961, pl. LIV, Fig. 2–2a) also reported a Pachytesta ovule associated with Alethopteris grandini. Even in coal balls, Stewart and Rothwell (1993) noted that alethopterid foliage is associated with P. illinoense Stewart 1954. More significantly, Wagner (1968, p. 23, 160) referenced A. zeilleri (Ragot) as possible parent plant for Trigonocarpus/P. gigantea types, and Darrah (1969) pointed to the consistent association of Alethopteris Sternberg with Trigonocarpus and Pachytesta types.

On balance, the Canadian ovules fit best the concept of Brongniart's P. incrassata, noting that both P. gigantea and P. incrassata have constant major rib morphologies (Smoot and Taylor, 1983/1984, p. 174). 4.4. Pre-pollen organ A large number of Pennsylvanian compression-preserved pollen organs are known, but generally only two genera have been, and continue to be, persistently documented in association with pteridosperm Alethopteris spp. One is compressed-petrified Whittleseya Newberry 1853a, b that Halle (1933) as Whittleseyinae suggested belongs exclusively to certain alethopterid species. See, however, Jongmans (1954) who figured it with neuropterids (see also Gothan and Weyland, 1973). The genus is characterized by

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Table 3 Gross-morphological comparison of the holotype of A. zeilleri (Ragot) with Canadian, French and Czech specimens of the same species Origin of data

Pinnule length (mm)

Holotype a: Czech b: French c: Canadian:

15–25 6–8 6–24.5 4–11 15–17 5–7 6–34 4–7 Undifferentiated ultimate pinnae of penultimate pinna: 20 6 26 7

a b c d

Pinnule width (mm)

Midvein

Marginal vein density (/cm)

Lateral vein dichotomies

Subsidiary veins

Margin of larger pinnules

Non-decurrent Non-decurrent Non-decurrent Non-decurrent

30–35 28–43 – 26–36 d

1 or 2 1 or 2 – 1 or 2

Bifurcated Bifurcated – Bifurcated

Lobed – – Lobed

Slightly decurrent Slightly decurrent

29–31 33

1 or 2 1 or 2

Bifurcated Bifurcated

Lobed Lobed

Wagner (1968, p. 160). Šimůnek (1989). Doubinger and Grauvogel-Stamm (1970, pl. 1, Fig. 1). Measured as 18 per 5-mm length of margin on a 7-mm long pinnule.

being an up to 60–70-mm elongate, bell-like structure (campanulum) with external curvy-parallel, or parallel ridges that form a dentate apical margin (see reconstructions by Taylor and Taylor, 1993, p. 546). For example, Bertrand (1932, pl. XXXVII, Fig. 2) figured Whittleseya in physical association with A. ambigua Lesquereux pars nov. emend., and Buisine (1961, pl. XI, Figs. 1, 1a,b, 2) with A. serlii, and also with A. grandini (pl. LIV, Figs. 1, 1b). The second is Dolerotheca Halle 1933 typified from permineralized material with complex internal structure (Rothwell and Eggert, 1986). Compressed Dolerotheca (e.g., Gillespie and Clendening, 1967; Gillespie et al., 1975, pl. II, D; Cross et al., 1996, Figs. 23–28: 6–7), is ovate-circular in outline with an off-center stalk, and shows parallel ridges converging at the stalk. The small sub-quadrate markings mentioned (3.6. Associated prepollen organs) probably correspond to surface markings on the bottom part of compressed Dolerotheca specimen in Fig. 23.28:7 (Cross et al., 1996). In comparison with the larger number of reported co-occurrences of Whittleseya with Alethopteris spp., only a few of Dolerotheca with Alethopteris spp. are reported, although Wagner (1968, p. 23) mentioned both of these male organs in his diagnosis of Alethopteris Sternberg. An association of Dolerotheca with A. zeilleri (Ragot) is reported by Cross et al. (1996, Fig. 23–28:6,7), and another questionably with A. bohemica Franke by Obrhel (1960), although association of Trigonocarpus and Dolerotheca with probable alethopterid foliage is mentioned by Stewart and Delevoryas (1956). The present pollen specimens are taxonomically grouped with Dolerotheca Halle. Positive identification remains difficult because geochemical conditions in the Sydney Coalfield precluded plant permineralization, or coal-ball formation (Lyons et al., 1993, 1997) for direct comparison.

5. Discussion 5.1. Foliage and frond Although pinnule morphology and dimension of the compressions are variable, their cuticular morphology is conservative, and topography monotonously invariable to assume that only one [biological] species carried the pinnate foliage of A. zeilleri (Ragot) at Sydney Coalfield. In this respect, distribution of Type 1 and Type 2 trichome bases is a potentially valuable parameter for linking ultimate rachises and midveins in the isolated foliar specimens. Moreover, detailed comparisons leave little doubt, aided by an introduced novel parameter of similar fractal dimensionality, that the Canadian specimens represent A. zeilleri (Ragot). Apparent from the large foliar-sample population that has been studied is that ultimate-pinna morphology of A. zeilleri (Ragot) apparently falls into two broad architectural categories documented here for the first time. One is near-linear, narrow with basally-confluent pinnules, exemplified in Fig. 4, the other is comparatively wider, and pinnules are longer and inserted more loosely, paralleling the architecture observed in ultimate pinnae of Alethopteris serlii emend. Zodrow and Cleal 1998. The shape of the only known penultimate rachis for A. zeilleri (Ragot), Fig. 5, is straight and does not zigzag, it's monopodial (see Mägdefrau, 1956; Zodrow, 1986, Fig. 5). Its actual dimension and shape cannot be inferred, only to suggest that a larger structure is involved, probably elongate-ovate in outline. The persistently lobate-pinnule morphology is interpreted to represent the lower-frond region, where, in Laveine's (1997: summary, Fig. 2) hypothetical model quadripin-

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nate rachial structure occurs. Coal-ball evidence supports interpretation of a quadripinnate frond for Alethopteris Sternberg (Pryor, 1990). Granting the veracity of these interpretations, an actual frond of A. zeilleri (Ragot) would have been large, probably several meters in length, as already hypothesized by Laveine (1986) for Alethopteris Sternberg. 5.2. Biostratigraphic update A. zeilleri (Ragot) in the Canadian Carboniferous strata occurs only in the Sydney Coalfield, where it ranges from the Lloyd Cove Seam to the top of the Coalfield at Point Aconi (Cleal et al., 2003), i.e., in the ca. 150 m of basal Cantabrian strata. The co-occurrence of A. zeilleri (Ragot) with Odontopteris cantabrica and Sphenophyllum oblongifolium at the level of the Lloyd Cove Seam confirms the base for the Cantabrian Stage outside its stratotype in Northern Spain. This is based on the first occurrence of A. zeilleri (Ragot), in conjunction with other incoming species as palaeobotanical events, to index the Westphalian D–Cantabrian boundary (Zodrow and Cleal, 1985, p. 1470: (5); Cleal et al., 2003). Also, its presence in the Sydney Coalfield signals one of the oldest-known occurrence of the species, as in Europe A. zeilleri (Ragot) is a typical Stephanian–Autunian species (Wagner, 1968; Doubinger and Grauvogel-Stamm, 1970; Šimůnek, 1989). 5.3. Palaeoenvironments 5.3.1. Preservation A. zeilleri (Ragot) is one of the few pteridosperms known from different preservational states. This includes compression/impression, natural maceration (summary: Zodrow and Mastalerz, 2001), and possibly petrification. Additionally, the degree of coalification is variable, as shown by the lengthy maceration time needed for the Canadian specimens, in comparison with Czech and French procedures, which in itself is an indication of variable local geochemical conditions. 5.3.2. Habitat The discovery of A. zeilleri (Ragot) in Canada also adds to mapping out the differing palaeoenvironments in which the species lived. This includes the coastal plains of Sydney Basin (Gibling and Bird, 1994) and concomitantly low-land flora, the intramontaine basins of the eastern Variscan-mountain belt (Czech specimens), the more westerly basins of the Variscan chain for the French specimens (both upland floras), Spain plate-tectonically removed from

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Europe, the Appalachian-interior Basin (Blake et al., 2002), and possibly the Dunkard Basin (Gillespie et al., 1975). Perhaps low-land and up-land floras can be distinguished from each other by the more developed sinusoidal curvature of the anticlinal walls in up-land A. zeilleri (Ragot)? In agreement with conclusions reached by Doubinger and Grauvogel-Stamm (1970), Kerp and Barthel (1993), and Šimůnek (1989), abundant trichomes, coriaceous pinnules, inrolled pinnule margins, and highly cutinized cuticles in the Canadian specimens are xeric characteristics. Particularly, the thick adaxial cuticles necessitated extraordinarily-long maceration time of up to 75 h, which contrasts with 3 to 7 h for the Czech specimens (Šimůnek, 1989; pers. comm. Dr. Šimůnek, April, 2003). Other alethopterid forms (A. serlii, A. ambigua, A. lonchitica) from the Sydney Basin have comparatively thin cuticles, interpreted as mesomorphic characteristics. Xeric characteristics of cuticles cannot necessarily be interpreted in terms of climate (see Cleal, 1991). High humidity could be a factor, as well as environmentallyinduced effects by high light intensity, water or nitrogen deficiencies (Shields, 1950), conditions that were probably prevalent on the Canadian coastal plains where A. zeilleri (Ragot) lived. 5.4. Trichomes Multicellular, uniseriate trichomes from coal-ball preserved abaxial alethopterid cuticles were first reported by Leisman (1960) for Alethopteris sullivantii (Lesquereux), noting that not all alethopterids show trichomes, e.g., A. serlii (Zodrow and Cleal, 1998; see also Mickle and Rothwell, 1982: coal-ball preservation). Subsequently, simple and complex-branching trichomes were described for a number of alethopterid cuticles (11 species) mainly by Šimůnek (1988, 1989, 1996), and secondarily by Zodrow and Cleal (1998). In particular, Šimůnek (1996) differentiated between trichomes and glandular trichomes (see also Krings et al., 2003). These publications attributed functions of trichomes to insect defense, or to palaeoecological responses, such as leaf xeromorphy. It is here suggested that trichomes are potentially useful in taxonomy, as practiced already for extant fern classification (e.g., Bower, 1993; Blunden et al., 1973). Moreover, similar trichome structures have been used by Oliver and Scott (1904) for the systematics of Carboniferous Lyginopteris oldhamia (Binney) Potonié, and by Ramanujam et al. (1974) to link a detached stalk with the campanulum of Dolerotheca reedana for reconstruction purposes.

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5.5. Palaeobiology 5.5.1. Fructification attachments Stewart and Delevoryas (1956) suggested that Trigonocarpus shared a number of biological features with cycad seeds, and arguments to the point were made later by Stewart and Rothwell (1993) that the order Cycadales had its origin among Carboniferous Medullosales (see cycads and Pachytesta: Smoot and Taylor, 1983/ 1984). Cycads could, presumably, serve as a model for alethopterid reproductive-organ attachments, and that Dolerotheca and Pachytesta spp. were borne on the same type of alethopterid plant. Supportive arguments are given by Ramanujam et al. (1974) from coal-ball studies who argued that Dolerotheca-pollen organ is attached to a Myeloxylon– Alethopteris type just above a “main dichotomy”. Evidence for Trigonocarpus/Pachytesta attachment to an alethopterid structure is extremely rare (summary: Stidd, 1981). Alethopterid pinnae in which single ovules occupy, or even replace, a pinnule are reported, for example, from Halle (1927, 1933); from Arnold (1937, Fig. 1) for A. grandifolia Newberry, and for an Alethopteris sp. from Taylor and Taylor (1993, Fig. 14.107), see also Wagner (1968). The novel ovule-bearing axis reported by Zodrow (2002, Fig. 16a) could not have occupied such a position because ultimate pinnae, even 230-mm long (Fig. 5), are judged structurally incompetent for supporting loads of these large (weighty) maturing ovules. Instead, it is hypothesized that these ovuleferous axes were attached to the main rachis above the basal dichotomy, or even to the petiole itself, following Laveine's definition of alethopterid-frond structure summarized by Zodrow (2002). 5.5.2. The tree fern A. zeilleri Comprehensive fossil evidence from a stratigraphically restricted horizon on the Lloyd Cove Seam suggests reconstruction of an alethopterid-tree fern, following Rothwell's (1985) argument that “isolated organs that are found at a single locality” have implication for palaeobotanical systematics. The hypothesized A. zeilleri (Ragot) tree is not tall, 5–7-m; it had its maturing ovules in axial arrangement, and male organs attached along a main rachis were shown in Fig. 16. A summary of the evidence includes the data from Zodrow (2002), 1 to 10: 1. 1.3-m and 1.0-m long fragmentary medullosalean trunks 2. detached dichotomizing, and zig-zagging medullosalean axes

3. fragmentary vascular medullosalean part, topographically resembling Myeloxylon–Alethopteris type of medullosalean stem, see coal-ball preservation (Ramanujam et al., 1974). 4. fragmentary penultimate pinna of A. zeilleri (Ragot) 5. foliage, A. zeilleri (Ragot) 6. juvenile alethopterid frond 7. detached root mantle 8. in situ tree-fern stumps 9. associated trigonocarpalean, Pachytesta-type of large ovule, and 10. associated dolerothecan-type of pollen organ. 6. Conclusion Consensus exists that an alethopterid plant bore larger type of ovules described as Trigonocarpus/Pachytesta Brongniart, and an associated pre-pollen organ described as Dolerotheca Halle. Result of the present study supports that pteridosperm A. zeilleri (Ragot) and P. incrassata are linked. The association with Dolerotheca sp. is however more tenuous. Through this firsttime documentation, new insight is offered into this extinct species, and by inference, into the extinct medullosalean-plant group to which A. zeilleri (Ragot) belonged. This includes suggestions for (1) developing cuticular parameters based on fractal-curvature dimensionality and trichome structures, for general medullosalean taxonomy, and (2) establishing more reliable palaeoenvironmental interpretation by combining data of absence/presence of trichomes, cuticular topography, and degree of cutinization. Based on associative evidence presented, the proposal is made to regard A. zeilleri (Ragot) as natural arborescent species, of probable monoecious nature. Acknowledgements Financial support from the Natural Sciences and Engineering Research Council of Canada, and from the donors of the Petroleum Research Fund # 37539-AC8, administered by the American Chemical Society is gratefully acknowledged. I acknowledge Josef Pšenièka, West Bohemian Museum in Pilsen, Czech Republic, for discovery of the male-organ specimens (2003); James Preen, University College of Cape Breton, for studying, analyzing, calculating fractal dimensions of cuticular curvatures; and Z. Šimůnek and T.M. Zodrow for helpful comments on the MS. I am especially grateful to C.J. Cleal, National Museums and Galleries of Wales, Cardiff, UK, for helpful technical suggestions, editorial

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