Appendix B – Taxonomic remarks on plant fossils from Tynemouth Creek Formation
Many fossil species remain in open nomenclature due to the fragmentary nature of specimens. Identifications were primarily made by consulting publications that illustrate megafloral assemblages from Lower Pennsylvanian strata of New Brunswick and Nova Scotia, particularly the monograph of Bell (1944), who included specimens from the Tynemouth Creek Formation in his ‘Cumberland Flora’. Other relevant publications include those that focus on the Lancaster Formation (‘Fern Ledges and vicinity) (e.g., Dawson, 1862, 1871; Stopes, 1914), although a larger suite of literature was used. Fossil taxa for each plant group are arranged alphabetically.
Lycopsids
Lepidostrobophyllum sp. (Plate I, Fig. 1). Represented by a single incomplete sporophyll that is lanceolate, narrows abruptly to an acuminate apex, and has a prominent abaxial furrow. The specimen most resembles Lepidostrobophyllum lanceolatum (Lindley and Hutton) Bell illustrated by Bell (1944, pl. 48, figs. 1, 2). The cone fragment was probably shed from Lepidodendron sensu lato, rather than Sigillaria.
Sphenopsids
Annularia sp. cf. A. acicularis (Dawson) Matthew (Plate I, Fig. 3). Bell (1944, p. 101) characterized this fossil species as having elliptical whorls with eight to 18 parallel-sided leaves that narrow to an acuminate apex. The fragmentary nature of specimens precluded confident assignment to A. acicularis, or differentiation from Annularia aculeata Bell (Bell, 1944, p. 101), which may be synonymous.
Asterophyllites equisetiformis (Schlotheim) Brongniart. A common and easily recognized (but poorly circumscribed) Pennsylvanian fossil species characterized by whorls of linear, acutely pointed leaves that curve upwards to cup the axis. Whorls typically contain 10 or more leaves that are >10 mm long (Cleal and Thomas, 1994).
Asterophyllites grandis (Sternberg) Geinitz (Plate I, Fig. 2). In comparison with Asterophyllites equisetiformis, leaves are sickle-shaped and more strongly cup the axis (Bell, 1944, p. 104). Whorls comprise six or more leaves that are >3 mm long (Cleal and Thomas, 1994), and leaf apices generally reach the base of the succeeding whorl.
Ferns
Pecopteris pilosa (Dawson) Bell (Plate I, Fig. 6). Morphological features in a large but poorly preserved penultimate pinna fragment at GC-15 (not collectable) conform to this fossil species. Erected as Sphenopteris pilosa by Dawson (1868, p. 552), the taxon was transferred to Callipteris pilosa by Dawson (1871, p. 51), and has been described and illustrated under Pecopteris (Cyathites?) densifolia Dawson (1871, p. 56), Pecopteris miltoni Artis (Stopes, 1914, p. 41), and Pecopteris pilosa (Dawson) Bell (Bell, 1944, p. 85). Ultimate pinnae are oblong to lanceolate and end in a lobate terminal pinnule with an obtusely rounded apex. Obtuse to ovate lateral pinnules are strongly decurrent with confluent bases, imparting the rachis with a ‘wing’, midveins are decurrent, and lateral veins are curved and simple or once-divided. Stopes (1914) and Bell (1944) compared the taxon with P. miltoni Artis, which was transferred to Lobatopteris by Wagner (1958), a common Early to Middle Pennsylvanian marattialean fern.
Senftenbergia plumosa (Artis) Stur (Plate I, Fig. 4). Small and poorly preserved ultimate pinna fragments in the collection are characterized by slender, subtriangular pinnules that arise oblique to the rachis. Venation is obscured except for a prominent midvein. Specimens conform to what Bell (1944, p. 84) called Pecopteris (Senftenbergia) plumosa (Artis) Radforth forma crenata, which he considered characteristic of the ‘Cumberland flora’, and are indistinguishable from the slender forms illustrated under Pecopteris (Senftenbergia) plumosa-dentata (Artis-Brongniart) Corsin by Dalinval (1960, p. 51).
cf. Zeilleria hymenophylloides Kidston (Plate I, Fig. 13). Fragments of pinnate frond are typified by relatively small, delicate, oblique, and decurrent pinnules that are deeply incised into oblique lobes. Specimens are comparable to the type material of Z. hymenophylloides (Kidston, 1924, p. 439) and specimens referred to Sphenopteris (Zeilleria) hymenophylloides Kidston by Bell (1944, p. 72).
Pteridosperms
Alethopteris decurrens (Artis) Zeiller (Plate III, Fig. 10). This fossil species is represented by pinna fragments comprising widely spaced, very slender (2–3 mm wide), and parallel-sided (but sometimes curved) pinnules with widely forking veins. As discussed by Wagner and Álvarez-Vázquez (2008, p. 175), the species resembles forms of A. urophylla with very elongate pinnules, although A. decurrens has narrower, more broadly confluent, and more widely spaced pinnules with a lower venation density (30–40 veins per cm). Bell (1944, p. 87) illustrated several well-preserved specimens from the Cumberland Basin.
cf. Alethopteris lancifolia Wagner. A poorly preserved and incomplete pinnule, which is parallel-sided, about 10 mm wide, and has a prominent midvein and dense lateral veins (approximately 50 per cm), appears to represent the remains of an alethopterid. Despite the poor quality of preservation, the pinnule resembles A. lancifolia, a rare fossil species characterized by unusually large pinnules and a dense venation (Wagner, 1961). A specimen from the ‘Fern Ledges’ (Lancaster Formation), previously recorded as Johannophyton discrepans (Dawson) by Matthew (1909, p. 83, pl. 2, fig. 7), was reidentified by Wagner (2005) as A. lancifolia.
Alethopteris urophylla (Brongniart) Göppert (Plate III, Figs. 3, 4, 6–8). Although only represented by isolated pinnules and small ultimate pinna fragments, specimens compare closely with examples of this species that were copiously illustrated by Wagner and Álvarez-Vázquez (2008). Pinnules are obliquely oriented, characterized by a pronounced acroscopic incision (Plate III, Fig. 9) and an extended basiscopic flare (Plate III, Fig. 7), linguaeform, parallel-sided with a bluntly acuminate to obtusely rounded tip, and of variable lengths but about 4 mm wide. The prominent midvein gives rise to lateral veins that curve before running in an essentially straight line to meet the lateral margin close to 90°, usually forking once along their course and numbering about 45 veins per cm. Crucially, there are some examples of very decurrent, almost subtriangular pinnules of the type found in distal parts of ultimate pinnae of A. urophylla, a feature that Zodrow and Cleal (1998, p. 73) argued was a key characteristic to distinguish the species from Alethopteris lonchitica Sternberg. [Note that, with the exception of the illustrated holotype, Wagner and Álvarez-Vázquez (2008) argued that specimens referred to A. lonchitica by Zodrow and Cleal (1998) belong to a group of alethopterids centered around Alethopteris lonchitifolia Bertrand.] Previous records of A. urophylla in the Cumberland Basin have been included in Alethopteris discrepans Dawson (Dawson, 1868, p. 552; 1871, p. 54) and A. lonchitica (Stopes, 1914, p. 47; Bell, 1944, p. 86).
Karinopteris acuta (Brongniart) Boersma (Plate II, Fig. 9). The best preserved specimen of this lyginopteridalean pteridosperm has slender, oblique pinnules with a rather vaulted limb and an acute apex. It compares well with the slender, ‘typical’ forms figured by Danzé-Corsin (1953, p. 76) under Mariopteris acuta Brongniart. Bell (1944, p. 76) also described and illustrated numerous examples from the Cumberland Basin, although all were collected from the older Boss Point Formation or equivalent strata.
Laveineopteris sp. cf. L. hollandica (Stockmans) Cleal and Shute (Plate II, Figs. 4–6, 7, 12). Isolated pinnules and ultimate pinna fragments of this neuropteroid were found in several megafloral assemblages. The fossil species is characterized by the distinct asymmetry of its lateral pinnules on either side of an ultimate pinna: elongate, subtriangular pinnules with acutely rounded tops on one side, and linguaeform types with obtusely rounded tops on the other (Plate III, Fig. 5). The midvein is thin but extends beyond the midpoint of the pinnule, and gives rise to thin lateral veins that gently curve to meet the lateral margin at a very oblique angle in subtriangular forms (≈40 to 50°) and at a more open angle in linguaeform pinnules (≈70 to 80°). Venation density ranges from 24 to 42 (mean = 33, n = 15) veins per cm, but in most pinnules it varies from 30 to 38 veins per cm. Lateral pinnules are broadly attached near the pinna apex, which is topped by a very long and slender terminal pinnule with an acutely rounded tip (Plate II, Figs. 5, 12).
Fragments comprising small pinnules are difficult to distinguish from Neuropteris obliqua, but larger pinnules tend to be more subtriangular with more oblique lateral veins. At one locality (GC-1), typical remains are associated with a large, rounded foliar segment with relatively lax veins, a Cyclopteris pinnule form that indicates affinity with the fossil genus Laveineopteris (Cleal and Shute, 2003). The most obvious comparison is with Laveineopteris polymorpha (Dawson) Wagner (Wagner, 2008), which was erected as Neuropteris polymorpha by Dawson (1862, p. 320) based on material from the ‘Fern Ledges’ (Lancaster Formation), and which Stopes (1914, p. 58) synonymized with Neuropteris heterophylla. Laveineopteris polymorpha was also recorded in the Tynemouth Creek Formation by Bell (1944) as Neuropteris (Mixoneura) obliqua and Neuropteris tenuifolia (Schlotheim). Nonetheless, although the material at hand is morphologically indistinguishable from L. polymorpha in most aspects, the latter has a markedly lower venation density (16 to 19 veins per cm; Wagner, 2008). Assuming that Wagner (2008) documented the full spectrum of variability in L. polymorpha, and that the venation density is a reliable character, we believe that the best comparison is with the closely allied species L. hollandica (Laveine, 1967, p. 156). This presents a dilemma. Laveinopteris hollandica and L. polymorpha have identical stratigraphic distributions (Langsettian to Duckmantian), but the only reliable records of the former are from western Europe and the latter is only known from North America (Wagner, 2008). What is the probability that we overlooked a relatively common species in the study succession (despite extensive collecting), and in its stead found a morphologically similar species not yet known from North America? As alluded to by Wagner (2008, p. 151), this begs the question of whether broadening the interpretation of the intraspecific variability of L. polymorpha and L. hollandica might permit their unison. If so, L. polymorpha would be the earliest legitimate synonym.
cf. Neuralethopteris biformis (Lesquereux) Goubet et al. (Plate III, Fig. 1). This identification is based on a single pinnule that is strikingly similar to specimens described and figured by Goubet et al. (2000, p. 27). The large pinnule (38 mm long, 8 mm wide) has slightly convex lateral margins, a bluntly acuminate tip, and a cordate base. The venation is alethopteroid, with a strong midvein in a deep furrow and broadly arched lateral veins that meet the lateral margin at about 70°; the venation density is about 35 veins per cm. If correctly identified, this is the first record from outside the Appalachian Coalfield of eastern USA.
Neuralethopteris schlehanii (Stur) Cremer (Plate III, Figs. 2, 5, 8). Several small ultimate pinna fragments comprise obliquely oriented, small, elongate pinnules that are linguaeform to subtriangular and characterized by a cordate base (Plate III, Fig. 5). Pinnules from distal parts of the frond may exhibit a slightly enlarged basiscopic auricle (Plate III, Fig. 2). The depressed midvein is strong, extends to near the pinnule apex, and gives rise to coarse lateral veins that typically branch twice and follow a curving yet somewhat angular path to reach the lateral margin at close to 90°. Although remains are fragmentary, N. schlehanii is the only species of neuralethopterid that shows this combination of pinnule shape and venation (Laveine, 1967; Goubet et al., 2000). Bell (1944, p. 79) recorded several examples of the species (under Neuropteris schlehani Stur) from the succession, and following Stopes (1914, p. 64), considered Neuropteris selwyni of Dawson (1871, p. 50) to be an earlier synonym.
Neuropteris sp. cf. N. heterophylla (Brongniart) Brongniart nom. cons. (Plate II, Fig. 3). Interpretation of this fossil species is in the same sense as Laveine (1967), Cleal and Shute (1991), and Laveine and Blanc (1996). Some pinnules resemble medium-sized forms of N. obliqua, although they tend to be broader and have a flatter apex, occasionally a weakly developed basiscopic auricle, and lateral veins that are denser and non-flexuous. The most complete specimen compares well with an example figured by Laveine (1967, pl. 13, fig. 2, 2a), but assignment to N. heterophylla is tentative because all recovered remains are fragmentary and no megafloral assemblage contains the full gamut of pinnule morphologies.
Neuropteris obliqua (Brongniart) Zeiller (Plate II, Figs. 1, 2). The range of pinnule morphologies in this fossil species, perhaps the greatest of all known Early to Middle Pennsylvanian neuropterids, is well documented by Laveine (1967, p. 197). Several megafloral assemblages recorded herein contain an array of pinnule types that fall within the limits of N. obliqua. The smallest forms are slender and linguaeform to subtriangular with very oblique lateral veins, more typical pinnules are largely linguaeform with less oblique lateral veins, and the largest ‘forma impar’ pinnules from the basal part of the frond tend to be subtriangular. The thickness and density of lateral veins are equally variable, but some pinnules exhibit a subtly flexuous venation. Although the most distal pinnules in ultimate pinnae of many neuropteroids are broadly attached to the rachis, a key characteristic of N. obliqua is the fact that this ‘mixoneurid’ feature can extend downwards to more proximal parts of some pinnae. One of the most common pteridosperms in the Cumberland Basin, Bell (1944, p. 81) documented several large and well-preserved specimens under the name Neuropteris (Mixoneura) obliqua (Brongniart).
Paripteris linguaefolia (Bertrand) Josten (Plate II, Figs. 8, 13–15). A single locality (GC-9) yielded small pinna fragments and numerous isolated pinnules that are squat-linguaeform to slightly falcate with a non-cordate base, characters of the fossil genus Paripteris. The midvein is either absent or very weakly developed in the lower part of the pinnule, from where dense lateral veins appear to radiate and broadly arch to reach the lateral margin at about 70 to 90°. The venation density is about 50 to 60 veins per cm. The range of pinnule shapes and venation scheme closely corresponds to P. linguaefolia (Bertrand, 1930, p. 31; Laveine, 1967, p. 266), a fossil species more typical of Duckmantian and Bolsovian strata and hitherto unknown from Canada.
cf. Paripteris pseudogigantea (Potonié) Laveine (Plate II, Figs. 10, 11). Rare in the succession are isolated pinnules that, compared to Paripteris linguaefolia, are generally smaller, more slender, have straighter lateral margins, and a more pronounced midvein. The pinnules are too few and too fragmentary to confidently differentiate between Paripteris gigantea (Sternberg) Gothan and P. pseudogigantea (see Laveine, 1967), but we tentatively assign specimens to the latter because Bell (1944, p. 80) also recorded the fossil species in the succession.