Description

Megaspores are trilete, 360–481 (610) µm long, including acrolamella, with a spherical body that is 160–320 (260) µm (N=42) in diameter (Fig. 2.1–2.5). The body is ornamented with short to long (130 µm maximum) protuberances ranging from small mounds to spatulate appendages with foveolate to reticulate sculpture at tips (Fig. 2.1–2.6). The number of protuberances is 9–28 (20) (N=42). The acrolamella is 200–341 (277) µm long (N=42) and usually composed of six “leaves” that are twisted into a spiral above laesurae and bear distinct crenulations along their edges (Fig. 2.1–2.5). The surface is sparsely punctate (Fig. 2.7). The wall is composed of three layers (Fig. 2.8). The inner layer is ~1.8 µm thick (N=2), densely granulate to nearly homogenous; the middle layer is ~3.7 µm thick (N=2), loosely granulate, expanding and becoming an anastomosing mesh beneath and in hollow appendages and around base of acrolamella; and the outer layer is ~4.9 µm thick (N=2), gradational with underlying middle layer as granules become denser, then homogenous. The outer layer is strongly channeled, with channels appearing as punctae on surface (Fig. 2.8). Microspores found within the leaves of the acrolamella or on the surface of the megaspore are 25.2–41.5 (36.7) µm in diameter (N=15 specimens), with finely granulate (Fig. 2.9) or foveo-rugulate (Fig. 2.10) sculpture distally and acrolamella-like structure proximally.

Figure 2

Arcellites and Balmeisporites megaspores and microspores. (1–10), Arcellites disciformis Miner, Reference Miner1935, emend. Ellis and Tschudy, Reference Ellis and Tschudy1964: (1) megaspore in equatorial view illustrating bumps and underdeveloped appendages, PP55499; (2) megaspore in equatorial view, PP55500; (3) megaspore in equatorial view illustrating mixed bumps and sparse appendages, with microspores (mi) in acrolamella, PP55501; (4) megaspore in equatorial view bearing microspores (mi) in acrolamella, PP55502; (5) megaspore in equatorial view illustrating dense appendages, with microspores (mi) in acrolamella, PP55503; (6) close-up of an appendage illustrating distal perforations, PP55502; (7) close-up of megaspore surface illustrating sparse punctae, PP55502; (8) cross-section through megaspore wall illustrating inner (i), middle (m), and outer layers (o), PP55504; (9) close-up of a microspore in acrolamella illustrating finely granulate surface and twisted acrolamella, PP55505; (10) close-up of a microspore in acrolamella illustrating foveo-rugulate surface and untwisted acrolamella, PP55506; (11–16) Balmeisporites sp. cf. B .holodictyus Cookson and Dettmann, Reference Cookson and Dettmann1958: (11) megaspore in equatorial view illustrating low, incomplete reticulum, with microspore (mi) in wing-like extension, PP55507; (12) megaspore in equatorial view, OPC2054-14833; (13) megaspore in equatorial view illustrating complete reticulum, with microspore (mi) in wing-like extension, PP55508; (14) close-up of megaspore surface illustrating fine perforations within lumina, PP55508; (15) cross-section through megaspore wall illustrating inner (i), middle (m), and outer layers (o), OPC2054-14831; (16) close-up of monolete microspores, PP55508. (1–5) Scale bar=100 µm; (6, 9, 10, 14) scale bar=10 µm; (7, 8, 15) scale bar=2 µm; (11–13) scale bar=20 µm; (16) scale bar=5 µm.

Remarks

These specimens conform in all aspects to the emended diagnosis of Ellis and Tschudy (Reference Ellis and Tschudy1964), and the cross-section of the spore wall as observed with SEM is consistent with the description of A. disciformis given by Hueber (Reference Hueber1982) and Batten et al. (Reference Batten, Dutta and Collinson1996).

The consistent segregation of Arcellites hexapartitus and Arcellites disciformis has proved difficult. The degree of crenulations on the acrolamella (more pronounced in A. disciformis), the size of lumina on spatulate protuberances (irregularly reticulate in A. disciformis), presence/absence of swellings in place of protuberances (few or absent in A. disciformis), and the number of protuberances (fewer in A. disciformis) have been used to distinguish taxa (Batten et al., Reference Batten, Dutta and Collinson1996). Within the Mauldin Mountain population, Arcellites specimens show consistently strong crenulation, but otherwise show variation in development of protuberances, including presence of swellings, and of sizes of lumina on protuberances (Fig. 2.1–2.6). Both the mean number of protuberances and the range of variation observed here, and by Hueber (Reference Hueber1982; 11–26 [16]), for specimens assigned to Arcellites disciformis are lower than those observed from specimens assigned to A. hexapartitus (0–63 [26]) from North East Plaza (Lupia, Reference Lupia2004).

Approximately 62% (N=42) of all A. disciformis megaspores from Mauldin Mountain bear microspores in the folds of their acrolamellae. If found dispersed, the microspores would be assigned to the dispersed genus Crybelosporites Dettmann, Reference Dettmann1963 in agreement with previous reports of Arcellites (e.g., Cookson and Dettmann, Reference Cookson and Dettmann1958; Hueber, Reference Hueber1982; Li and Batten, Reference Li and Batten1986; Lupia, Reference Lupia2004). Unlike previous studies, two forms of the microspores are found on recovered megaspores: a finely granulate form (Fig. 2.9) and a distally foveo-rugulate form (Fig. 2.10). The finely granulate microspores match closely those figured by Hueber (Reference Hueber1982) on Aptian specimens of A. disciformis, whereas the foveo-rugulate microspores are similar to those observed on A. hexapartitus from North East Plaza (Lupia, Reference Lupia2004). Both forms were observed on some specimens, but a gradation in ornament could not be documented. Nevertheless, the finely granulate to foveo-rugulate ornament of A. disciformis microspores distinguishes them from the strongly reticulate microspores within broken specimens of Molaspora sp. cf. M. fibrosa (below) that are also assignable to Crybelosporites.

Genus Balmeisporites Cookson and Dettmann, Reference Cookson and Dettmann1958, emend. Dettmann, Reference Dettmann1995

Balmeisporites sp. cf. B. holodictyus Cookson and Dettmann, Reference Cookson and Dettmann1958

Figure 2.11–2.16

1958 Balmeisporites holodictyus Cookson and Dettmann, p. 42, pl. 2, figs. 1–6.

Description

Megaspores trilete, triangular in equatorial outline (Fig. 2.11–2.13), ~164.4–183.0 (172.0) µm tall (N=6), including trifolium, and 108.2–154.4 (138.9) µm (N=3) wide, including “wing-like extensions” sensu Dettmann (Reference Dettmann1995). The trifolium is 51.8–84.9 (67.8) µm (N=3) tall and is composed of three blades fused along its entire height. The megaspore surface is irregularly (Fig. 2.11) to strongly reticulate (Fig. 2.13), with lumina generally larger at the distal pole and near wing-like extensions. The muri vary in height from 2.5 to 8.0 (4.9) µm (N=17), with irregularly reticulate specimens having shorter muri and strongly reticulate specimens having taller muri. Complete muri vary from 0.7 to 1.4 (1.1) µm wide independent of reticulum development (Fig. 2.14). Within the lumina, the megaspore surface is perforate, especially near the bases of the muri (Fig. 2.15). The wing-like extensions are tallest at the equator and confluent with the reticulum (Fig. 2.11–2.13). The wall of the megaspore is composed of three layers (Fig. 2.15). The inner layer is 1.56–1.81 µm thick (N=2), homogenous, appearing granular at high magnification. The middle layer is 0.78–0.93 µm thick (N=2) and composed of anastomosing fibers; beneath muri and the trifolium, this layer thickens (Fig. 2.15). The outer layer is 0.31–0.52 µm thick (N=2) and forms the surface of the grain. Microspores found in the lumina of the wing-like extensions are monolete and psilate to finely granular (Fig. 2.16).

Figure 3

Molaspora sp. cf. M. fibrosa Singh, Reference Singh1983. (1) megaspore in equatorial view illustrating rugulate “knotty” surface, PP55509; (2) megaspore in equatorial view illustrating eight-fold acrolamella, PP55512; (3) megaspore in proximal polar view illustrating twisted, seven-fold acrolamella, PP55510; (4) open, untwisted acrolamella illustrating triangular lobes, PP55511; (5) close-up of megaspore surface illustrating rugulate “knotty” surface without conical projections, PP55512; (6) cross-section of megaspore wall illustrating inner (i) and middle (m) layers, and outer layer (o) without conical projections, PP55513; (7) fractured megaspore containing four reticulate microspores, PP55513. (1, 2, 7) Scale bar=100 µm; (3, 4) scale bar=20 µm; (5, 6) scale bar=10 µm.

Remarks

Attribution of all of the specimens from Mauldin Mountain and Dead Fish Point samples to Balmeisporites sp. cf. B. holodictyus is based on thickness of the megaspore wall, large size of lumina, and tall muri in the strongly reticulate specimens, which are comparable to Cookson and Dettmann’s (Reference Cookson and Dettmann1958) original diagnosis. The specimens described here differ strictly from the Balmeisporites holodictyus in possessing thinner muri compared to original material and SEM illustrations presented in Dettmann (Reference Dettmann1995). Most specimens from Mauldin Mountain and Dead Fish Point that were studied under SEM are strongly reticulate forms (Fig. 2.13).

Genus Molaspora Schemel, Reference Schemel1950, emend. Hall, Reference Hall1963

Molaspora sp. cf. M. fibrosa Singh, Reference Singh1983

Figure 3

1983 Molaspora fibrosa Singh, p. 95, pl. 26, figs. 1–7.

Description

Megaspores trilete, spheroidal (Fig. 3.1, 3.2), and 154–401 (300) µm in diameter (N=14). Acrolamellae are 73.3–144 (115) µm tall and 67.7–157 (114) µm wide (N=14), and composed of six to eight triangular lobes that are preserved pleated and twisted (Fig. 3.1–3.4) or open (Fig. 4.5). The surface of megaspores appears rugulate or “knotted” (Fig. 3.5), without prominent papillae or cones. The megaspore wall is composed of three layers (Fig. 3.6). The inner layer is 0.98–1.66 (1.26) µm thick (N=3) and homogenous. The middle layer (P1 of Batten et al., Reference Batten, Zavattieri and Collinson2011b) is densely fibrous, 5.1–5.9 (5.5) µm thick (N=3), and the outer layer (P2 of Batten et al., Reference Batten, Zavattieri and Collinson2011b) is composed of radially disposed, flattened elements that are 19.9–26.1 (22.2) µm tall. Associated microspores (Fig. 3.7) possess an acrolamella, bear rugulate-reticulate surface sculpture, and are 42.2–71.3 (54.9) µm in diameter (N=8).

Figure 4

Dijkstraisporites praetextus n. sp. (1) Megaspore in proximal polar view illustrating strong reticulum and lateral expansion of elements of the margo (lower arrowhead) and of the zona (upper arrowhead), OPC2054-14861; (2) same megaspore as in Figure 4.1 in distal polar view illustrating flanges encircling distal pole and edge of auricula (arrow), OPC2054-14861; (3) megaspore in proximal polar view, OPC2054-14859; (4) megaspore in equatorial view illustrating weak reticulum on proximal hemisphere and isolate coni/capilli on distal hemisphere, holotype, OPC2054-14857; (5) megaspore in equatorial view, PP55514; (6) megaspore in equatorial view illustrating isolated coni on proximal hemisphere and short flat elements of zona, PP55515; (7) close-up of elements formed by dissection of the zona, OPC2054-14859; (8) close-up of proximal hemisphere illustrating coni forming reticulum, OPC2054-14858; (9) close-up of distal pole illustrating nearly complete circlet of flanges, OPC2054-14860; (10) close-up of coni on proximal surface of megaspore illustrated in 4.8; (11) close-up of distal surface of holotype megaspore illustrated in 4.4; (12) cross-section of megaspore wall illustrating inner laminar zone (o1) and outer fibrous zone (o2) of outer layer, PP55516. (1–6) Scale bar=100 µm; (7) scale bar=10 µm; (8, 9) scale bar=20 µm; (10–12) scale bar=2 µm.

Remarks

The Elk Neck specimens are similar to Molaspora lobata, but lack the prominent conical/papillate projections of the outermost perine seen in most published images of M. lobata (e.g., Hall, Reference Hall1963; Kovach and Dilcher, Reference Kovach and Dilcher1988; Lupia et al., Reference Lupia, Schneider, Moeser, Pryer and Crane2000; Batten et al., Reference Batten, Zavattieri and Collinson2011b). Instead, specimens appear to possess a dominantly and consistently rugulate outer perine (Fig. 3.1–3.3, 3.5). This sculpture is congruent with the text description of the surface of Molaspora rugosa Schemel, Reference Schemel1950, but the type for Schemel’s species was placed in synonymy with M. lobata by Hall (Reference Hall1963). An attempt to locate and reexamine the type material of M. rugosa reposited at the University of Michigan was unsuccessful. Singh (Reference Singh1983, p. 95) erected the species Molaspora fibrosa for Molaspora specimens from the Cenomanian of Alberta, Canada, with a “finely fibrous perine; sculpture composed of dense fibrous matting.” These Elk Neck specimens are somewhat smaller in all dimensions than Singh’s, but otherwise agree with his circumscription. Because the absence of conical/papillate projections is unlikely to be due to abrasion—conical projections are hollow and abrasion would be expected to show as abundant holes on surface (e.g., Lupia et al., Reference Lupia, Schneider, Moeser, Pryer and Crane2000, fig. 3.20)—or simple compression, as implied by Batten et al. (Reference Batten, Zavattieri and Collinson2011b) for many of their specimens, the greater affinity is considered to fall to Molaspora fibrosa.

Multiple microspores assignable to Crybelosporites were found in two broken specimens of Molaspora sp. cf. M. fibrosa from two Mauldin Mountain samples (Fig. 3.7). If merely a chance association, they could have collected in any one of many dispersed iso-/microspores known from the dispersed palynoflora. However, both specimens show an identical, strongly rugulate-reticulate form with an acrolamella and contain four or more microspores of the same form. This form matches the known microspores of Molaspora lobata established by co-occurrence in sporocarps (Lupia et al., Reference Lupia, Schneider, Moeser, Pryer and Crane2000) and on dispersed megaspores (Batten et al., Reference Batten, Collinson and Brain2011a, Reference Batten, Zavattieri and Collinsonb).

Class Lycopsida sensu DiMichele and Bateman, Reference DiMichele and Bateman1996

Order Isoëtales sensu DiMichele and Bateman, Reference DiMichele and Bateman1996

Genus Dijkstraisporites Potonié, Reference Potonié1956, emend. Batten and Koppelhus, Reference Batten and Koppelhus1993

Remarks

The genera Dijkstraisporites and Tenellisporites (Dijkstra, Reference Dijkstra1949) Potonié, Reference Potonié1956 are very similar in form based on the revised diagnoses of Batten and Koppelhus (Reference Batten and Koppelhus1993, pp. 36–38, quoted below). In equatorial outline, the spore bodies are “circular to convexly triangular” (Dijkstraisporites) or “circular to rounded triangular” (Tenellisporites). The surface may be “smooth-scabrate but usually sculptured with granules, verrucae, or a reticulum” (Dijkstraisporites) or “granules, coni, spines, or a reticulum” (Tenellisporites). The equator of the spore bodies bear “a zona or corona which may be undulose or ribbed,” and “the outer part of the corona may comprise appendages of varying length that are often connected by threads of sporopollenin” (Dijkstraisporites), or “a corona comprising a narrow flange subtended by discrete appendages” (Tenellisporites). The equatorial appendages along the zona/corona of both genera share their morphology with their respective margos. These revised diagnoses do not explicitly capture the discussion by Batten and Koppelhus (Reference Batten and Koppelhus1993, p. 25), in which they distinguish between genera on the basis of the width of the zona/corona relative to the spore body it surrounds, namely that Dijkstraisporites has “a variably developed corona or a zona that is about as wide as, or wider than the radius of the spore.” The informal distinction based on zona/corona width:body radius was used by Batten et al. (Reference Batten, Colin and Néraudeau2010, p. 162) to attribute specimens to genus level. Batten (Reference Batten1995, p. 412) further noted that the zona/corona of Tenellisporites “has moderately to strongly developed, finger-like processes extending from it whereas that surrounding Dijkstraisporites is more irregular in form with processes often slightly expanded at the their tips, and sometimes partly fused to adjacent elements.”

Dijkstraisporites praetextus new species

Figure 4.1–4.12

Types

Holotype: OPC2054-14861 (Fig. 4.1, 4.2), Sample #1, Dead Fish Point (39°28.40’ N, 75°59.67’ W), Elk Neck Peninsula, Cecil County, Maryland, United States, Potomac Group undifferentiated, Pollen Zone II-B (middle-late Albian). Paratypes: OPC2054-14857 (Fig. 4.4, 4.11), OPC2054-14859 (Fig. 4.3, 4.7), OPC2054-14858 (Fig. 4.8, 4.10); OPC2054-14860 (Fig. 4.9), FMNH PP55514 (Fig. 4.5), PP55515 (Fig. 4.6), PP55516 (Fig. 4.12).

Diagnosis

Megaspore trilete, zonate, circular to convexly triangular in polar view; margo above laesura basally continuous, ribbed, becoming dissected at various heights into discrete processes that are expanded perpendicular to margo; zona composed of continuous flange, weakly to strongly ribbed, becoming dissected at varying widths to form discrete processes which may or may not expand towards tips; width of zona greatest where margo and zona meet; proximal hemisphere unornamented or ornamented with scattered coni, dense coni expanded and/or aligned to form reticulum, or reticulum; distal hemisphere ornamented with scattered coni and/or isolated capilli or narrow flanges and/or reticulum; distal pole bears numerous, closely spaced membranous processes, often expanded basally and fused to form continuous or nearly continuous ring.

Occurrence

Elk Neck Peninsula, Cecil County, Maryland, United States, Potomac Group undifferentiated, Zone II-B (middle-late Albian) and Zone III (early Cenomanian).

Description

Megaspore is trilete and the spore body (exclusive of zona) is 183–366 (259) µm wide (N=14) and 209–309 (284) µm tall (N=5), with a circular (Fig. 4.1) to convexly triangular (Fig. 4.3) polar amb. The margo above the laesura is variable in height, 84.8–143 (108) µm tall (N=9), ribbed, entire basally becoming dissected at varying heights into individual elements above the ribs. The elements are expanded perpendicular to margo (Fig. 4.1, bottom arrow), becoming 34.2–82.2 (52.3) µm wide (N=30) and facing the proximal pole (Fig. 4.1, 4.3, 4.4). The margo reaches the equator where it joins the zona (Fig. 4.1, 4.3–4.6). The zona is 31.7–98.9 (71.5) µm wide (N=24) interradially, and 70.2–151 (93.9) µm wide (N=12) radially. The zona is continuous at its base, becoming dissected into separate elements at varying widths (Fig. 4.1–4.3, 4.7, 4.8). The elements of the zona are slightly to greatly expanded at their tips, often perpendicular to zona, especially near apices of laesura (Fig. 4.1, top arrow). Zona is smooth, undulate, or ribbed. Auriculae are not defined. Numerous flanges are concentrated around the distal pole (Fig. 4.2, 4.4–4.6), usually forming a ring of discrete elements or a (nearly) continuous circlet (Fig. 4.9). The surface of the megaspore is unornamented, or ornamented with a weak to strong reticulum (Fig. 4.1–4.4, 4.8), variably connected flanges, and/or isolated coni; some of the coni are elongated as scattered capilli on the proximal and/or distal hemispheres (4.4–4.6, 4.10). The surface of the megaspore is perforate (Fig. 4.9, 4.10). The megaspore wall is composed of two layers (Fig. 4.12). The inner layer (not figured) is thin, homogenous, and detached from the wall or lost in broken specimens. The outer layer is 5.5–6.7 µm thick (N=2) and has two zones. The inner zone appears densely laminar in cross-section transitioning to an outer zone that appears as an open, spongy network.

Etymology

from Latin praetextus, decorated, trimmed. For the dense flanges, often in form of a ring, occupying the distal pole of the megaspore.

Remarks

Specimens assigned to this morphotype resemble both Dijkstraisporites and Tenellisporites in possessing a surface ornamentation composed of a reticulum and/or coni, and a margo and zona dissected at varying depths yielding individuated elements. Above the separation of those elements from each other, no threads connect them. The ratio of the width of the zona (at auriculae) relative to the spore body varies from 0.26–0.44 (0.36) (N=14). Thus, the zona is never as wide as or wider than the spore body, arguing for placement within Tenellisporites. However, this ratio is not part of the emended diagnoses provided by Batten and Koppelhus (Reference Batten and Koppelhus1993). Most specimens show that the margo/zona is undulate or ribbed, and the elements of the margo/zona are expanded at their tips, which are more characteristic of Dijkstraisporites (Batten, Reference Batten1995). In view of all of these features and the current generic diagnoses, the Elk Neck specimens are assigned to Dijkstraisporites.

Elongated flanges concentrated at the distal pole are otherwise known among Cretaceous megaspores only from Paxillitriletes dakotaensis Hall, Reference Hall1963. Specimens herein designated Dijkstraisporites praetextus cannot be assigned to Paxillitriletes Hall and Nicolson, Reference Hall and Nicolson1973 because of the absence of capilli adjacent to the margo (Batten and Koppelhus, Reference Batten and Koppelhus1993). Therefore, the distal polar cluster or ring distinguishes this taxon from the diagnosis of all other named species within Dijkstraisporites (or Tenellisporites).

Examination of the individual populations from Dead Fish Point and Mauldin Mountain reveals morphological differences between them. All Dead Fish Point specimens have proximal hemispheres that are ornamented with a strongly (Fig. 4.1) to weakly (Fig. 4.4) developed reticulate pattern. In contrast, most Mauldin Mountain specimens are unornamented or ornamented with only scattered coni or capilli proximally (Fig. 4.5, 4.6). However, there are specimens from Mauldin Mountain that exhibit an obvious reticulum. Likewise, all observed Dead Fish Point specimens and most Mauldin Mountain specimens possess a ring of discrete or continuous flanges distally (without or with scattered extras, Fig. 4.9), but some Mauldin Mountain specimens bear a distal cluster that does not have the appearance of a ring. Furthermore, the zona in most Dead Fish Point specimens is undulate or ribbed (Fig. 4.1–4.3), whereas it is smooth/flat in many Mauldin Mountain specimens. Thus, there is some evidence to suggest a different taxon in each assemblage. Nevertheless, there is overlap in all features, and determining whether these differences have stratigraphic importance and/or represent different taxa will require larger sample sizes and additional sample sites; for now, D. praetextus is diagnosed to include all variants.

Dijkstraisporites praetextus is extremely similar to?Paxillitriletes sp. of Batten et al. (Reference Batten, Colin and Néraudeau2010, plate VII, figs. 9–11) from the Cenomanian of France, although their specimens have a stronger reticulum on both hemispheres. Tenellisporites brasinoviensis Knobloch, Reference Knobloch1984 is also similar to members of these populations with only coni, and although no distal ring is mentioned in his description, one of the figured specimens (plate IX, fig. 4) from the Senonian of South Bohemia appears to have distal processes. Scott and Stea (Reference Scott and Stea2002) presented one image of a specimen from the Aptian–Albian of Nova Scotia identified as Paxillitriletes in distal polar view that resembles Dijkstraisporites praetextus (their fig. 6a; I note that the megaspore in their fig. 6b is Arcellites sp., which is a salvinialean fern, not Bohemisporites sp., a selaginellalean lycopsid).

Genus Flabellisporites Marcinkiewicz, Reference Marcinkiewicz1978

aff. Flabellisporites sp. of Lupia, Reference Lupia2004

Figure 5.1–5.3

2004 aff. Flabellisporites sp. Lupia, p. 653,655, fig. 4.

Description

Megaspores are trilete, azonate, auriculate, with a subtriangular outline in polar view (Fig. 5.1, 5.2), 394–436 µm in diameter (N=2). The laesura is bordered by membranous margo, continuous at base but becoming dissected into elongate, flat processes, and up to 125 µm tall including processes (Fig. 5.1, 5.2). The margo over the laesura reaches the equator contacting auriculae that are 92.5–121 (110) µm long and 44.5–95.2 (67.7) µm wide (N=3). Auriculae do not merge laterally with a zona, but instead gradually disappear (Fig. 5.3). Proximal and distal hemispheres are ornamented with a weak reticulum (Fig. 5.1–5.3). Capilli emerging from intersections of muri are tubular with slightly expanded tips (Fig. 5.3). The capilli are longer adjacent to the margo (up to 103 µm long) than interradially or on distal hemisphere (Fig. 5.1). Megaspore surface is perforate between muri.

Figure 5

Aff. Flabellisporites and Minerisporites megaspores. (1–3) Aff. Flabellisporites sp. of Lupia, Reference Lupia2004: (1) megaspore in equatorial view, PP55517; (2) megaspore in oblique proximal polar view, PP55517; (3) close-up of auricula illustrating lateral terminal without formation of a zona, PP55518; (4–6) Minerisporites sp. cf. M. “dissimilis” of Singh, Reference Singh1964: (4) cluster of three megaspores, PP55519; (5) close-up of proximal hemisphere illustrating reticulum formed from low ridges and perforate surface, PP55519, scale bar=10 µm; (6) cross-section of megaspore wall illustrating laminar layer (i) and fibrous layer (o), PP55520, scale bar=2 µm. (1–4) scale bar=100 µm.

Remarks

As noted previously (Lupia, Reference Lupia2004), the absence of a zona excludes this morphotype from common zonate Cretaceous genera, and the restriction of the longest capilli to the area adjacent to the margo preclude it from the genus Flabellisporites Marcinkiewicz, Reference Marcinkiewicz1978. Aff. Flabellisporites sp. of Lupia (Reference Lupia2004) has a wide distribution, being documented from Barremian and/or Aptian sediments in Asia (Li et al., Reference Li, Batten, Zhang and Zhang1987), Europe (Schultz and Noll, Reference Schultz and Noll1987; Nye et al., Reference Nye, Feist-Burkhardt, Horne, Ross and Whittaker2008), and North America (Sweet, Reference Sweet1979; Lupia, Reference Lupia2004), and now from the Cenomanian of North America, but is never so abundant in any sample as to support designation of a new genus.

Genus Minerisporites Potonié, Reference Potonié1956

Minerisporites sp. cf. M. “dissimilis” of Singh, Reference Singh1983

Figure 5.4–5.6

1976 Minerisporites dissimilis Tschudy, p. E6, pl. 2, figs. 1–6 (not).

1983 Minerisporites dissimilis; Singh, p. 107, pl. 35, figs. 4–6.

Description

The megaspores are trilete and zonate (Fig. 5.4), with a round outline in polar view, 479–570 (519) µm in diameter (N=6). The margo is tallest, reaching up to 66.4 µm tall, away from the proximal pole, but without forming a prominent, deep notch at pole (Fig. 5.4). The margo is thicker, 27.4–30.3 µm (N=2), near its base thinning to its apex, 4.4–13.3 (5.3) µm (N=3). The margo reaches equator meeting the zona to form slight auriculae 23.5–48.0 (37.3) µm long (N=5) and 49.9–76.8 (60.8) µm wide (N=3). The zona is 10.2–20.0 (14.6) µm wide (N=3) interradially and 5.7–13.1 (11.1) µm thick (N=4). Proximal and distal hemispheres are ornamented with an obvious, if locally weak, reticulum (Fig. 5.4) that extends onto margo and onto zona. The megaspore surface is perforate at high magnification (Fig. 5.5). The wall is composed of three layers, including a homogenous inner layer (not figured) less than 1 µm thick that is frequently missing in incomplete specimens or separated from the wall in fractured specimens (Fig. 5.6). The middle and outer layers together are ~10.5 µm thick between muri, and ~15.6 µm thick including muri. The middle layer is strongly laminated parallel to the spore surface, grading to a spongier outer layer beneath the surface.

Figure 6

Minerisporites and Paxillitriletes megaspores. (1–5) Minerisporites sp. cf. M. venustus of Lupia, Reference Lupia2004: (1) megaspore in oblique polar view illustrating isolated coni/flanges proximally and weak reticulum distally, PP55521; (2) megaspore in equatorial view illustrating weak incomplete reticulum with prominent coni developed at some junctions, PP55522; (3) megaspore in equatorial view illustrating weak reticulum without prominent junctions, PP55523; (4) close-up of distal hemisphere of megaspore illustrated in 6.1 showing ornament and perforate surface, PP55521; (5) cross-section of megaspore wall illustrating solid inner (i), laminar middle (m), and fibrous outer (o) layers, PP55524. (6–10) Aff. Paxillitriletes ales (Harris, Reference Harris1935) Batten and Koppelhus, Reference Batten and Koppelhus1993: (6) megaspore in oblique polar view illustrating distally perforate, ragged margo, capilli that increase in length toward proximal pole, and microspore (mi), PP55527; (7) megaspore in equatorial view illustrating capillus on distal side of zona (at arrow), and microspores (mi), PP55525, (8) close-up of proximal hemisphere illustrating perforate coni/flanges, PP55526; (9) close-up of distal hemisphere illustrating reticulum with elongated junctions, PP55527; (10) close-up of granulate microspore on megaspore in 6.6. (1–3, 6, 7) scale bar=100 µm; (4, 5, 8–10) scale bar=10 µm.

Remarks

The absence of a deep notch in the margo at the pole and lack of compound reticulum exclude the Elk Neck specimens from Minerisporites dissimilis Tschudy, Reference Tschudy1976 with which they otherwise are very similar, and of similar age. These megaspores most closely resemble Minerisporites “dissimilis” from the Cenomanian illustrated by Singh (Reference Singh1983, pl. 35, figs. 4–6). The Elk Neck specimens are similar in size (although with a thinner wall), with similar uniform low reticulum; likewise, both forms lack a deep polar notch and bear the continuation of the reticulum onto the margo. Singh (Reference Singh1983, p. 107) specifically attributes the absence of compound reticulum to abrasion. Specimens similar to M. “dissimilis” of Singh (Reference Singh1983) were reported as Minerisporites borealis by Gunther and Hills (Reference Gunther and Hills1972, pl. 4, fig. 19) and as Minerisporites sp. 2 by Batten et al. (Reference Batten, Colin and Néraudeau2010, pl. II, figs. 9–11, pl. III, figs. 1, 3). The absence of a deep polar notch and the presence of a low, thin margo exclude the Elk Neck specimens from Minerisporites mirabilissimus (Dijkstra, Reference Dijkstra1961) Potonié Reference Potonié1966. Likewise, the uniform low reticulum and/or relatively thick, narrow zona without strong auriculae exclude the present specimens from M. alius Batten, Reference Batten1969; M. borealis (Miner, Reference Miner1932) Potonié, Reference Potonié1956; M. marginatus (Dijkstra, Reference Dijkstra1951) Potonié, Reference Potonié1956; M. mirabilis (Miner, Reference Miner1935) Potonié, Reference Potonié1956; M. pseudorichardsonii Gunther and Hills, Reference Gunther and Hills1972; and M. venustus Singh, Reference Singh1983, which are of generally similar form or from sediments close in age.

Minerisporites sp. cf. M. venustus Lupia, Reference Lupia2004

Figure 6.1–6.5

2004 Minerisporites sp. cf. M. venustus Lupia, p. 661, fig. 7.

Description

Megaspores are trilete and zonate, with a convexly triangular amb in polar view (Fig. 6.1–6.3) and 207–255 (242) µm in diameter (N=6). The margo is membranous, 22.9–37.0 (29.3) µm tall (N=5), with a ragged edge and extends to the equator where acutely triangular auriculae 24.4–33.9 (29.3) µm long (N=5) and 34.3–49.3 µm wide (N=2) are apparent where it meets the zona (Fig. 6.1–6.3). There is no notch in the margo at its apex (Fig. 6.2). The zona is membranous and smooth to slightly ragged, 5.4–10.1 (7.8) µm wide (N=4) interradially (Fig. 6.1–6.3). The proximal surface may be ornamented with short echinae that are isolated or expanded to form short ridges or with an incomplete to complete weak reticulum with large lumina and slight projections at the intersections of the muri (Fig. 6.1–6.4). The reticulum may extend onto the base of the margo in some specimens (Fig. 6.3). The distal surface may be ornamented with elongate ridges that join to form an incomplete reticulum or with a complete weak reticulum with large lumina and slight projections at intersections of the muri (Fig. 6.1–6.3). The megaspore surface is perforate at high magnification (Fig. 6.4). The wall is composed of three layers (Fig. 6.5), including a homogenous inner layer less than 1 µm thick that is frequently separated from the wall in fractured specimens. The middle and outer layers together are ~3.4 µm thick (N=1). The middle layer is strongly laminated parallel to the spore surface, grading to a more spongy outer layer beneath the surface.

Remarks

The end-members of this morphotype have different ornaments and could be placed in separate genera—Henrisporites for the form characterized by dominantly echinate ornament (Fig. 6.1) and Minerisporites for that characterized by dominantly reticulate ornament (Fig. 6.3). However, intermediate forms combining few echinae with a more or less complete reticulum exist (Fig. 6.2). These intermediate forms with echinae on the proximal hemisphere and reticulum on the distal hemisphere bear some resemblance to Minerisporites absonus Li and Batten in Li et al., Reference Li, Batten, Zhang and Zhang1987, from which they differ because the distal reticulum is not as strong.

Minerisporites sp. aff. M. venustus is very similar both to some specimens of Henrisporites sp. aff. H. angustus of Lupia (Reference Lupia2004, fig. 5d, e) and of Minerisporites sp. cf. M. venustus of Lupia (Reference Lupia2004, fig. 7a, b) from the Aptian of the Elk Neck Peninsula. Lupia (Reference Lupia2004) noted difficulty in separating these two forms with light microscopy, but noted no intermediate forms in that sample population. Because of the sampled intermediate forms, I recognize only one taxon due to the presence of a reticulum, however weak, on most specimens. Nevertheless, given the variation in this population, I consider even an “affinity” to M. venustus unsatisfactory. These Elk Neck specimens are smaller than M. venustus as described by Singh (Reference Singh1983), and Lupia (Reference Lupia2004). Minerisporites sp. aff. M. venustus is easily distinguished from co-occurring M. “dissimilis” of Singh (Reference Singh1983) by its much weaker reticulum with narrower muri and much larger lumina, and by its ragged, membranous margo and zona.

Genus Paxillitriletes

aff. Paxillitriletes ales (Harris, Reference Harris1935) Batten and Koppelhus, Reference Batten and Koppelhus1993

Figure 6.6–6.10

1935 Minerisporites ales Harris, p. 163, pl. 25, figs. 2, 8, 9, 11.

1993 Paxillitriletes ales (Harris, Reference Harris1935) Batten and Koppelhus, p. 38.

Description

The megaspore is trilete with a round to subtriangular polar amb (Fig. 6.6, 6.7). The spore body is 224–271 (251) µm in diameter (N=4). The margo above laesura is tall, up to 83 µm, and unornamented, becoming thinner and perforate/reticulate along margin and slightly ragged (Fig. 6.6, 6.7). Margo reaches equator where it joins zona to form auriculae (Fig. 6.6) that are 68.8–86.0 (75.1) µm long (N=4) and 89.6–168 (132) µm wide (N=4). The zona is slightly ragged and thinnest interradially, 22.4–39.8 (31.8) µm (N=4), becoming gradually wider towards contact with margo. On the proximal hemisphere, some of the ornamentation are echinae, whereas others are elongated in one dimension giving a “fimbriate” appearance (Fig. 6.8). Capilli are always present adjacent to the margo and longest at the proximal pole, up to 76 µm tall and 5.7 µm wide (Fig. 6.6, 6.7). On distal hemisphere, a strong (Fig. 6.6) to weak (Fig. 6.7) reticulum is present. In specimens with a strong reticulum, the intersections of the muri may be elongated into echinae (Fig. 6.9). Capilli are also present on the distal hemisphere immediately adjacent to and on the zona (Fig. 6.7, arrow). The microspores found on the megaspore surface (Fig. 6.10) are monolete with psilate to granulate ornament, and 20.1–23.9 (21.3) µm long (N=5) and 11.8–14.1 (13.1) µm wide (N=5).

Remarks

This morphotype possesses characteristics intermediate between Minerisporites Potonié, Reference Potonié1956, emend. Batten and Koppelhus, Reference Batten and Koppelhus1993 and Paxillitriletes Hall and Nicolson, Reference Hall and Nicolson1973 emend. Batten and Koppelhus, Reference Batten and Koppelhus1993. These specimens fall within the emendation of Minerisporites in possessing an unsegmented margo, a slightly ragged zona wider radially than interradially, auriculae, and reticulate ornamentation distally, but differ in having a echinate/fimbriate sculpture without a reticulum proximally. Capilli adjacent to the margo are permitted within Minerisporites (Batten and Koppelhus, Reference Batten and Koppelhus1993, p. 37–38). Nevertheless, these specimens conform to, and are tentatively considered to have their closest affinity to, Paxillitriletes as emended by Batten and Koppelhus (Reference Batten and Koppelhus1993), primarily based on a margo subtended by hair-like processes longest at the proximal pole, and on the presence of auriculae and reticulate ornamentation distally. A ragged to poorly dissected margo is not excluded from Paxillitriletes (Batten and Koppelhus, Reference Batten and Koppelhus1993, p. 38), and is found in several species (e.g., P. ales (Harris, Reference Harris1935) Batten and Koppelhus, Reference Batten and Koppelhus1993; P. lindstroemi Huckriede, Reference Huckriede1982; P. phyllicus (Murray, Reference Murray1939) Hall and Nicolson, Reference Hall and Nicolson1973 and P. rintoulensis Tosolini in McLoughlin et al., Reference McLoughlin, Tosolini, Nagalingum and Drinnan2002).

The Elk Neck specimens resemble the Jurassic species Paxillitriletes ales in the size of the spore body, albeit at the smaller end of the range given by Harris (Reference Harris1935), in the height of the margo, length of auriculae, and length and width of capilli. Likewise, they both possess a margo that is not deeply incised and characterized by fine perforations, and fine echinae on the distal hemisphere (at least in some specimens). The zona of the Elk Neck specimens are, however, wider than in Harris’ Paxillitriletes ales. The Elk Neck specimens differs from P. ales, and all other species of Paxillitriletes, in bearing long capilli on the distal hemisphere that are restricted to a position immediately adjacent to the zona, and therefore may belong to a new taxon.

Paxillitriletes sp. aff. P. vittatus Kovach and Dilcher, Reference Kovach and Dilcher1985

Figure 7.1–7.10

1985 Paxillitriletes vittatus Kovach and Dilcher, p. 86, 88, pl. 1, figs. 1–8, pl. 2, figs. 1, 2, 4, 5.

Description

Megaspore is trilete, 314–498 (423) µm in diameter (N=4) exclusive of auriculae, with a round to subtriangular polar view (Fig. 7.1–7.4). The margo above the laesura is tall, 219–287 (252) µm (N=4), unornamented, entire basally becoming dissected into individual narrow to wide, flat to round elements (Fig. 7.1–7.3). The margo is bordered by capilli that are 208–465 (275) µm tall (N=8) and 30.3–74.1 (57.8) µm wide (N=9), and round to flattened in section (Fig. 7.1–7.5). Numerous capilli appear on each contact face, although usually seven or eight are especially prominent (Fig. 7.1, 7.2). The capilli are frequently narrower at the base expanding in diameter upward; some bifurcate, often unequally, ending bluntly or tapering (Fig. 7.5). The margo reaches equator where it joins the zona to form auriculae (Fig. 7.1–7.4, 7.6). The zona is thinnest interradially, 17.7–28.3 (21.9) µm wide (N=4), becoming wider only very close to auriculae. The auriculae are therefore sharply defined at apices of margo, 129–255 (214) µm long (N=6) and 173–208 (192) µm wide (N=9). The auriculae are lobate, with at least three lobes and frequently more (Fig. 7.6). The surface of the megaspore is ornamented on both hemispheres with a well-developed polygonal reticulum (Fig. 7.1–7.4). On both hemispheres, the intersections of the muri are elaborated as short spines. The spines become somewhat larger towards the proximal pole (Fig. 7.6), but show no trend in size on the distal hemisphere. The surfaces of the megaspore within the reticulum and of the spines and capilli are perforate (Fig. 7.7, 7.8). The megaspore wall is composed of three layers. The inner layer (not figured) is less than 1 µm thick, homogenous, and pulled away from the rest of the wall in broken specimens. The middle layer is ~3 µm thick and appears loosely laminar in cross-section, transitioning to an outer layer ~10 µm thick, which appears as a spongy network (Fig. 7.9). Microspores adherent to megaspore among capilli are monolete, 22.8–26.7 (24.3) µm long and 11.8–16.4 (14.6) µm wide (N=4), with rugulate sculpture (Fig. 7.10).

Figure 7

Paxillitriletes and Cabochonicus megaspores. (1–10) Paxillitriletes sp. cf. P. vittatus Kovach and Dilcher, Reference Kovach and Dilcher1988: (1) megaspore in oblique equatorial view illustrating large auriculae, OPC2054-14862; (2) megaspore in oblique equatorial view, PP55528; (3) same megaspore as in 7.2 in oblique proximal polar view; (4) megaspore in proximal polar view illustrating clearly lobate auriculae, PP55529; (5) close-up of proximal hemisphere illustrating robust, sometimes branching (arrow) capilli, PP55530; (6) close-up of lobate auricula, OPC2054-14862; (7) close-up of proximal hemisphere of megaspore in 7.3 illustrating conical elongation of junctions; (8) extreme close-up of surface in 7.7, illustrating perforate surface; (9) cross-section of megaspore wall illustrating inner laminar (i) and outer fibrous (o) layers, PP55530; (10) rugulate monolete microspores adherent to megaspore, OPC2054-14862; (11–13) Cabochonicus carbunculus (Dijkstra, Reference Dijkstra1951) Batten and Ferguson, Reference Batten and Ferguson1987: (11) megaspore in proximal polar view bearing few large gemmae, PP55531; (12) close-up of surface illustrating large gemmae and small Übisch(?) bodies (at arrows), PP55531; (13) close-up of proximal hemisphere illustrating surface with small perforations, PP55531, scale bar=2 µm. (1–6, 10, 11) Scale bar=100 µm; (7–9, 12) scale bar=10 µm.

Remarks

Within the genus Paxillitriletes, to which these Elk Neck specimens may be assigned due to the capilli adjacent to the dissected margo, they are similar, but not identical to, Paxillitriletes vittatus Kovach and Dilcher, Reference Kovach and Dilcher1985. The Elk Neck specimens are slightly smaller, but overlap the range of P. vittatus in diameter of spore body, length of auriculae, and length of capilli, and are slightly larger in width of auriculae and width of zona given by Kovach and Dilcher (Reference Kovach and Dilcher1985). The Elk Neck specimens are similar to P. vittatus in their lobate shape of auriculae, density, and long length of the capilli compared to all other species, and in the weak muri of the distal reticulum giving prominence to short coni where the muri intersect, and differ from P. vittatus in the more prominent proximal reticulum and branching capilli.

Paxillitriletes sp. cf. vittatus is distinct from other Paxillitriletes species found in Cretaceous deposits on the East Coast of North America. It differs from Paxillitriletes sp. of Hueber (Reference Hueber1982) and P. sp. aff. P. fairlightensis (Batten, Reference Batten1969) Hall and Nicolson, Reference Hall and Nicolson1973 in Lupia (Reference Lupia2004) in possessing sharply defined auriculae, weakly serrate zona, thick capilli, and short projections from distal muri. It differs from P. dakotaensis (Hall, Reference Hall1963) Hall and Nicolson, Reference Hall and Nicolson1973 in Tschudy (Reference Tschudy1975) in the absence of distal capilli. It differs from P. alatus (Batten, Reference Batten1969) Hall and Nicolson, Reference Hall and Nicolson1973 in Lupia (Reference Lupia2011) in possessing lobate auriculae relatively narrowly joined to zona, and thick capilli that frequently branch. One specimen from Upatoi Creek (Lupia, Reference Lupia2011, fig. 6.7) had similarly thick capilli but has broadly attached auriculae and longer distal spines.

Order Selaginellales Prantl, 1874

Genus Cabochonicus Batten and Ferguson, Reference Batten and Ferguson1987

Cabochonicus carbunculus (Dijkstra, Reference Dijkstra1949) Batten and Ferguson, Reference Batten and Ferguson1987

Figure 7.11–7.13

1949 Triletes carbunculus Dijkstra, p. 22, pl. 1, fig. 12.

1987 Cabochonicus carbunculus; Batten and Ferguson, p. 72. pl. 1, figs. 1–4, 7–9, pl. 2, figs. 1–8, pl. 3, figs. 1–7, pl. 4, figs. 1–6.

Description

Megaspore is trilete and round in polar view, 393–834 µm diameter (N=2) (Fig. 7.11). The margo is about three-fourths of the radius (Fig. 7.11). Interspersed small to large gemmae (up to 47.1 µm tall and 68.2 µm wide) cover the equator and extend over distal hemisphere; the contact area and distal pole are unornamented (Fig. 7.11, 7.12). Scars and/or undeveloped gemmae appear on the megaspore surface (Fig. 7.12, arrows). The surface appears psilate, but at high magnification is observed to be very finely perforate (Fig. 7.13). The megaspore wall is two-layered, with a very thin, homogenous inner layer, and a thick outer layer that is uniformly composed of dense fibers.

Remarks

The presence of gemmae that have a resinous appearance under reflected light unambiguously identify this taxon. Only one complete, albeit unusually small specimen with small gemmae (Fig. 7.1–7.13), one abraded specimen, and three fragments were recovered.

Genus Erlansonisporites Potonié, Reference Potonié1956

Erlansonisporites sp. cf. E. potens Lupia, Reference Lupia2011

Figure 8.1–8.7

2011 Erlansonisporites potens Lupia, p. 11, fig. 8.

Description

Megaspore is trilete, ovate in equatorial view, and circular to ovate in polar view (Fig. 8.1–8.3). The dimensions are 606–842 (749) µm (long axis, N=8) and 475–706 (607) µm (short axis, N=8) in specimens proximo-distally compressed. The specimens measure 628–753 µm tall (N=2) when equatorially compressed. The margo extends to approximately two-thirds of the radius (Fig. 8.2). In some specimens, the trilete margo is obscured to a lesser (Fig. 8.1) or greater degree (Fig. 8.3) by a dense, spongy network of threads that occupy the area between the arms. The entire surface is ornamented with a reticulum that is complete, except near margo where muri frequently terminate blindly in lumina (Fig. 8.1–8.3). The muri are 2.9–54.0 (23.6) µm tall (N=20) and 2.9–27.0 (11.6) µm wide (N=17). The muri are wider at their top then at their base, smooth, with a blunt, rounded apex (Fig. 8.4). Within the lumina, the surface bears granules or fine echinae (Fig. 8.4). The megaspore wall is composed of three layers (Fig. 8.5). The inner layer is composed of dense, aligned granules ~12 µm thick, transitioning to the middle layer composed of less dense, aligned granules ~15 µm thick; the outer zone forming the surface is composed of an open mesh ~2 µm thick. The muri are composed of dense granules without apparent alignment (Fig. 8.6).

Figure 8

Erlansonisporites megaspores. (1–7) Erlansonisporites sp. cf. E. potens Lupia, Reference Lupia2011: (1) megaspore in equatorial view illustrating margo obscured by fibrous mesh, OPC2101-14844; (2) megaspore in proximal polar view illustrating obvious margo, OPC2101-14840; (3) megaspore in proximal polar view illustrating margo obscured by fibrous mesh, OPC2101-14837; (4) close-up of reticulum on proximal hemisphere illustrating granular ornament in lumina, OPC2101-14841; (5) cross-section of megaspore wall illustrating inner fibrous layer (i), middle layer (m) of aligned granules, and outer mesh (o), OPC2101-14839; (6) close-up of broken muri illustrating granular construction, OPC2101-14838; (7) comparison at same scale of specimens of Erlansonisporites sp. cf. E. potens (OPC2101-14843) and Ricinospora sp. cf. R. pileata (Dijkstra, Reference Dijkstra1961) Singh, Reference Singh1983 (PP55533), both of which have lost their reticulum; (8–12)Erlansonisporites sp. cf. E. sparassis (Murray, Reference Murray1939) Potonié, Reference Potonié1956, specimen OPC2101-14845: (8) megaspore in equatorial view; (9) megaspore in proximal polar view; (10) close-up of ridges on proximal hemisphere illustrating granular edge; (11) close-up of surface between ridges illustrating fine mesh; (12) cross-section of megaspore wall illustrating inner fibrous layer (i) and outer layer (o) of aligned granules. (1–3, 7–9) Scale bar=100 µm; (4–6, 10, 11) scale bar=10 µm; (12) scale bar=2 µm.

Remarks

In almost every feature of ornament, surface, and wall construction, most Elk Neck specimens closely resemble the type material from the Upatoi Creek locality (Lupia, Reference Lupia2011). The Elk Neck population differs from type E. potens primarily in those specimens that have the spongiose network of sporopollenin threads that obscure the trilete form of the margo proper (Fig. 8.1, 8.3). These spongiose threads obscuring the margo (but not necessarily above it) bring those specimens close to the circumscription of the genus Ricinospora Bergad, Reference Bergad1978, emend. Li and Batten in Li et al., Reference Li, Batten, Zhang and Zhang1987. However, the other diagnostic feature of Ricinospora—an easily detachable reticulum—is not observed in most specimens. On most specimens where damage and loss of the muri is evident, a wide, pronounced scar in the former position of the muri are visible (Fig 8.6). Likewise, although not quantified, the margo and spongiose material are as likely to be damaged and/or missing from the same specimen, suggesting that the ornament is not so easily detached. A few Elk Neck specimens do show a secondarily lost reticulum indicated by narrow, faint scars, but the margo and spongiose material are missing as well (Fig. 8.7), whereas the apical ornamentation is the least detachable component of Ricinospora (Li et al., Reference Li, Batten, Zhang and Zhang1987).

Ricinospora pileata (Dijkstra, Reference Dijkstra1961) Singh, Reference Singh1983 is recorded from the Elk Neck samples (see below), but with a diameter over three times smaller (Fig. 8.7). Moreover, even ignoring size, the Elk Neck specimens with missing muri are not conspecific with R. pileata because the former have smooth and blunt muri while the latter have ragged, perforate muri. With relatively few specimens bearing fully obscured margos, and of those, few with missing muri, all of these specimens are assigned to Erlansonisporites sp. cf. E. potens.

Erlansonisporites sp. cf. E. sparassis (Murray, Reference Murray1939) Potonié, Reference Potonié1956

Figure 8.8–8.12

1939 Triletes sparassis Murray, p. 480, 482, text-figs. 3, 4.

1956 Erlansonisporites sparassis (Murray, Reference Murray1939) Potonié, p. 47.

Description

Megaspore is trilete, 599 µm tall, 682 µm wide along long axis and 442 µm (N=1) along short axis of equatorially compressed specimen (Fig. 8.8, 8.9). The margo is ~66 µm tall at proximal pole and extends one-half to two-thirds of the radius (Fig. 8.8). The surface is ornamented with ridges of varying lengths, 15.5–40.0 (27.8) µm tall and 6.7–13.0 (10.4) µm thick, that may join to form a complete lumen (Fig. 8.8, 8.9). The apices of the ridges are ornaments with granules (Fig. 8.10). The surface between the ridges is a finely perforate mesh (Fig. 10.11). The megaspore wall is composed of two layers (Fig. 8.12). The inner layer is composed of dense fibers and is 4–5 µm thick, transitioning abruptly to the outer layer that is ~15–17 µm thick and composed of less dense, aligned granules.

Remarks

The Elk Neck specimens are larger, with a thicker wall, and with a perhaps more distinct margo, but otherwise conform to the circumscription of the Erlansonisporites sparassis. Specimens of E. sparassis can be distinguished from Erlansonisporites sp. cf. E. potens by their taller margo, thicker muri, and rarely complete reticulum.

Genus Maexisporites Potonié, Reference Potonié1956

Maexisporites sp. aff. M. pusillus Lupia, Reference Lupia2011

Figure 9.1–9.3

1988 Maexisporites soldanellus Kovach and Dilcher, p. 92, pl. 1, fig. 1 (part)

2011 Maexisporites pusillus Lupia, p. 15, figs. 4–8.

Description

Megaspore is trilete, azonate, with pyramidal proximal hemisphere and rounded distal hemisphere in equatorial view, ~414 µm tall, and a convexly triangular outline in polar view, ~321 µm in diameter (Fig. 9.1, 9.2). The margo is prominent, ~52 µm tall at proximal pole and ~30 µm wide (Fig. 9.1, 9.2). The margo and surface of both hemispheres are ornamented by verrucae that are more or less isodiametric except where fused. The granules on the proximal hemisphere are wider, 2.9–17.6 (6.0) µm (N=18), and taller on average than on the distal hemisphere, 1.2–7.2 (3.2) µm wide (N=18). At higher magnification, the verrucae are seen to be composed of “piles” of submicron granules, and the surface is a mesh (Fig. 9.3).

Figure 9

Maexisporites and Ricinospora megaspores. (1–3) Maexisporites sp. cf. M. pusillus of Lupia, Reference Lupia2011, specimen OPC2101-14835: (1) megaspore in equatorial view illustrating size difference in granules/verrucae on proximal and distal hemispheres; (2) megaspore in proximal polar view; (3) close-up of surface illustrating change in ornament size across equator. (4–11) Ricinospora sp. cf. R. pileata (Dijkstra, Reference Dijkstra1961) Singh, Reference Singh1983: (4) megaspore in equatorial view illustrating faint scars of completely lost reticulum, PP55532; (5) megaspore in equatorial view illustrating partially lost reticulum, PP55533; (6) megaspore in equatorial view illustrating mostly intact reticulum, PP55534; (7) megaspore in equatorial view illustrating completely intact reticulum, PP55535; (8) close-up of fibrous mesh obscuring margo, PP55534; (9) close-up of reticulum illustrating perforate upper edge, PP55534; (10) close-up of megaspore surface mesh, PP55534; (11) cross-section of megaspore wall illustrating inner fibrous layer (i) and outer layer (o) of aligned granules, PP55536. (1, 2, 4–7) Scale bar=100 µm; (3, 8) scale bar=10 µm; (9–11) scale bar=2 µm.

Remarks

The Elk Neck specimen is larger than the similar form from the Santonian Allon locality (Lupia, Reference Lupia2011), but otherwise matches in possessing granulate verrucae that are larger on the proximal hemisphere than on the distal hemisphere.

Genus Ricinospora Bergad Reference Bergad1978

Ricinospora sp. cf. R. pileata (Dijkstra, Reference Dijkstra1961) Singh, Reference Singh1983

Figure 9.4–9.11

1961 Triletes pileatus Dijkstra, p. 13, pl. 1, figs. 16–19.

1983 Ricinospora pileata; Singh, p. 105, pl. 35, fig. 1.

Description

Megaspore is trilete; most specimens are laterally compressed, yielding an ovate to round equatorial view (Fig. 9.4–9.7). The polar axis is 177–271 (230) µm long (N=8) and the equatorial axis is 152–274 (227) µm long (N=8). The margo is short, about half or less of the radius, and elevated above body of megaspore (Fig. 9.4, 9.6). In most specimens, the margo is covered by spongiose network of fibrous threads (Fig. 9.5–9.8). The surface is covered by a reticulum composed of muri that are solid and smooth basally, becoming perforate and ragged apically (Fig. 9.9). The muri are 7.33–13.2 (10.6) µm tall (N=21) and 0.6–1.4 (1.0) µm thick (N=11). The reticulum is partially missing from most specimens (Fig. 9.5, 9.6) and only occasionally is completely lost (Fig. 9.4) or completely present (Fig. 9.7). At high magnification, the surface is finely perforate (Fig. 9.10). The megaspore wall has two layers (Fig. 9.11). The inner layer is ~2 µm thick and composed of fibers loosely parallel to the spore surface. The outer layer is ~8 µm thick and composed of aligned granules.

Remarks

The Elk Neck specimens conform to the circumscription of Ricinospora pileata given by Dijkstra (Reference Dijkstra1961) and the material illustrated by Singh (Reference Singh1983) except that they are smaller in all dimensions. Specimens of R. pileata can be distinguished from other Elk Neck specimens assignable to Erlansonisporites sp. cf. E. potens and to E. sparassis by their smaller size, and variably complete reticulum of thin, low muri with perforate upper edges.

Genus Striatriletes van der Hammen, 1955 ex Potonié, Reference Potonié1956

Striatriletes sp. cf. S. excavatus (Marcinkiewicz, Reference Marcinkiewicz1962) Sweet, Reference Sweet1979

Figure 10.1–10.5

1962 Erlansonisporites excavatus Marcinkiewicz, p. 476, pl. 11, figs. 3–6.

1979 Striatriletes excavatus; Sweet, p. 14, pl. 1, figs. 5, 6.

Description

Megaspore is trilete, circular in polar view (Fig. 10.1), ~426 µm in diameter. The margo appears sinuous, is ~32 µm tall and 19 µm wide, and extends about two-thirds of the radius of the spore (Fig. 10.1). The proximal hemisphere is ornamented with discrete verrucae and rugulate elements near the proximal pole that are up to 20 µm tall and up to 12 µm wide (Fig. 10.1, 10.2, 10.4). The rugulae are radially aligned starting approximately at the diameter of the arms of the margo and continue across the equator (Fig. 10.1, 10.2). The transition to radial alignment is marked by an incomplete ridge circling the proximal pole (Fig. 10.1, arrow). On the distal hemisphere, the ridges form a tight, regular reticulum with low muri (Fig. 10.3, 10.5). The individual elements on both hemispheres thin from base to apex, but end bluntly, without a sharp edge (Fig. 10.4, 10.5).

Figure 10

Striatriletes and Trileites megaspores. (1–5) Striatriletes sp. cf. S. excavatus (Marcinkiewicz, Reference Marcinkiewicz1962) Sweet, 1978, specimen OPC2101-14848: (1) megaspore in proximal polar view illustrating incomplete transverse ridge (arrowhead); (2) megaspore in equatorial view; (3) megaspore in oblique distal polar view; (4) close-up of proximal hemisphere illustrating rugulae (left) and sinuous margo (right); (5) close-up of distal hemisphere illustrating low reticulate ridges. (6–11) Trileites spp.: (6) megaspore in proximal polar view illustrating sunken contact facets, PP55537; (7) megaspore in proximal polar view, PP55538; (8) megaspore in proximal polar view illustrating equatorial ridge (arrowhead), PP55539; (9) close-up of distal hemisphere of megaspore in 10.7 illustrating finely perforate surface with Übisch bodies; (10) cross-section of wall of megaspore in 10.6 illustrating fibrous construction; (11) cross-section of wall of megaspore in 10.7 illustrating fibrous construction. (1, 2, 6–8) Scale bar=100 µm; (3–5, 9) scale bar=10 µm; (10, 11) scale bar=1 µm.

Remarks

The radially aligned ridges on the proximal hemisphere place this morphotype in Striatriletes, but the fact that the ridges do not extend between the arms of the margo and/or form a reticulum on the proximal hemisphere preclude assignment to Striatriletes areolatus Villar de Seoane and Archangelsky, Reference Villar de Seoane and Archangelsky2008, S. sulcatus (Dijkstra, Reference Dijkstra1961) Potonié, Reference Potonié1956, S. radialis (Gunther and Hills, Reference Gunther and Hills1972) Sweet, Reference Sweet1979, or S. minimus (Dijkstra, Reference Dijkstra1949) Batten, Reference Batten1988 from the Cretaceous. Although Striatriletes excavatus is only known from the Jurassic, the Elk Neck specimens (only two were found) closely approach the form of S. excavatus due to the robust verrucate and rugulate elements between the arms of the margo, well-delimited contact facets, and the incomplete ridge circling the proximal pole.

Striatriletes imperfectus Tosolini in McLoughlin et al., Reference McLoughlin, Tosolini, Nagalingum and Drinnan2002 is similar in possessing proximal verrucae and a delimited contact face, but its ridges and muri are poorly developed, its margo shorter, and its distal pole psilate. Striatriletes sulcatus of Tosolini et al. (Reference Tosolini, McLoughlin and Drinnan2002, fig. 8F, I), of Lupia (Reference Lupia2004, fig. 11.2, 11.3), and of Nye et al. (Reference Nye, Feist-Burkhardt, Horne, Ross and Whittaker2008); Striatriletes n. sp. of Huckriede (Reference Huckriede1982); and S. cf. sulcatus of Batten (Reference Batten1995) are also similar to Elk Neck specimens, but differ in the absence of incomplete ridge delimiting contact face. There are fewer radial ridges in the specimens of Huckriede (Reference Huckriede1982), Lupia (Reference Lupia2004), and Nye et al. (Reference Nye, Feist-Burkhardt, Horne, Ross and Whittaker2008), and the ridges thin to a fine delicate edge in Lupia’s (Reference Lupia2004) specimens.

Genus Trileites Erdtman, Reference Erdtman1947 ex Potonié, Reference Potonié1956

Trileites spp.

Figure 10.6–10.11

Description

Various trilete, psilate, circular to convexly triangular megaspores were encountered (Fig. 10.6–10.8). The diameters vary between 297 and 870 µm (N=5). The margos are low and rounded, extend about one-half to two-thirds of the radius and are set apart from the rest of the proximal hemisphere by a narrow groove all around (Fig. 10.6, 10.7). On some, the contact facets are sunken (Fig. 10.6), on some, undistinguished, and others, delimited by an equatorial ridge (Fig. 10.8, arrow). The surface appears psilate at low magnification, but at higher magnification, the surface has widely spaced to uniform perforations (Fig. 10.9). On some megaspores, scattered solid bodies, less than 5 µm wide, are seen on the distal hemisphere (Fig. 10.9). The walls are of two types, not consistently associated with presence of either equatorial ridge or scattered solid bodies. The thick walls are ~15 µm thick, and composed of narrow diameter fibers to the inside grading to larger diameter fibers on the outside (Fig. 10.10). The thin walls are ~5 µm thick and are composed of uniform fibers (Fig. 10.11).

Remarks

With no prominent ornamentation, differentiation of species assignable to Trileites relies on diameter, length of the margo, presence or absence of rims delimiting the contact facets, and wall thickness/structure (e.g., Kempf, Reference Kempf1972; Batten, Reference Batten1988). The combinations of characters seen here do not accord with any published species. A margo bounded by a groove and contact facets set off by a ridge are characters of Trileites murrayi Harris, Reference Harris1961, but the walls of Elk Neck specimens are always far thinner than 30–50 µm described originally (Harris, Reference Harris1961). Likewise, a margo extending to two-thirds of the radius without contact facets set off by a ridge are characters of Trileites persimilis Harris, Reference Harris1935, but such specimens among the Elk Neck samples are smaller than 600 µm, and have a thinner wall than the 15–20 µm described originally (Harris, Reference Harris1935). Those specimens with scattered solid bodies are reminiscent of Cabochonicus carbunculus (above), but the bodies never have a resinous appearance and never approach the size of gemmae that are normal for C. carbunculus.

Genus Verrutriletes (Dijkstra, Reference Dijkstra1951) Potonié, Reference Potonié1956

Verrutriletes diversus new species

Figures 11, 12.1–12.5

Types

Holotype: FMNH PP55540 (Fig. 11.1, 11.2, 11.18, 12.1, 12.2). Sample #7, Mauldin Mountain (39°29.24’ N, 75°59.72’ W), Elk Neck Peninsula, Cecil County, Maryland, United States, Potomac Group undifferentiated, Pollen Zone III (early Cenomanian). Paratypes: FMNH PP55541 (Fig. 11.3), PP55542 (Fig. 11.4, 11.5, 12.3), PP55543 (Fig. 11.6, 11.7), PP55544 (Fig. 11.8, 11.9), PP55545 (Fig. 11.10, 11.11), PP55546 (Fig. 11.12, 11.13), PP55547 (Fig. 11.14, 11.15), PP55548 (Fig. 11.16, 11.17), PP55549 (Fig. 12.4, 12.5).

Figure 11

Verrutriletes diversus n. sp. (1) Megaspore in proximal polar view, holotype, PP55540; (2) megaspore in distal polar view, holotype, PP55540; (3) megaspore in equatorial view, PP55541; (4) megaspore in proximal polar view, PP55542; (5) megaspore in distal polar view, PP55542; (6) megaspore in proximal polar view, PP55543; (7) megaspore in distal polar view, PP55543; (8) megaspore in proximal polar view, PP55544; (9) megaspore in distal polar view, PP55544; (10) megaspore in proximal polar view, PP55545; (11) megaspore in distal polar view, PP55545; (12) megaspore in proximal polar view, PP55546; (13) megaspore in distal polar view, PP55546; (14) megaspore in proximal polar view, PP55547; (15) megaspore in distal polar view, PP55547; (16) megaspore in proximal polar view, PP55549; (17) megaspore in distal polar view, PP55549; (18) close-up of ornamented margo, holotype, PP55540. (1–17) Scale bar=100 µm; (18) scale bar=10 µm.

Figure 12

Verrutriletes megaspores. (1–5) Verrutriletes diversus n. sp.: (1) close-up of verrucate element illustrating fibrous mesh construction, holotype, PP55540; (2) close-up of fibrous mesh forming megaspore surface, holotype, PP55540; (3) cross-section of megaspore wall illustrating thin inner homogenous (i), thin middle laminar (m) and outer unaligned granular (o) layers, noting the difference in apparent density of outer layer between torn (left) and knife-sectioned sides (right), PP55542; (4) megaspore in proximal polar view with adherent microspores (mi), PP55549; (5) close-up of megaspore in 12.4 illustrating psilate/punctate microspores, PP55549. (6–10) Verrutriletes sp. cf. V. tomtaylori Archangelsky and Villar de Seoane, Reference Archangelsky and Villar de Seoane1990, specimen OPC2101-14846: (6) megaspore in proximal polar view; (7) megaspore in distal polar view; (8) megaspore in equatorial view; (9) close-up of proximal hemisphere illustrating rugulae (left) and sinuous margo (right); (10) close-up of distal hemisphere illustrating low ridges. (1, 2) Scale bar=2 µm; (3, 5, 9, 10) scale bar=10 µm; (4, 6–8) scale bar=100 µm.

Diagnosis

Megaspore trilete, azonate, convexly triangular to circular in polar view; margo above laesura prominent, reaching equator or nearly so, always ornamented at least basally; proximal hemisphere ornamented with low to tall flat-topped verrucae (rarely baculae), often connected to form rugulae or reticula with interspersed verrucae; distal hemisphere bears same ornament as proximal hemisphere but the elements, which may not be as tall, are conspicuously less dense and show greater width or degree of connectedness.

Occurrence

Elk Neck Peninsula, Cecil County, Maryland, United States, Potomac Group undifferentiated, Zone II-B (middle-late Albian) and Zone III (early Cenomanian).

Description

Megaspore is trilete, azonate, convexly triangular to circular in polar view (Fig. 11.1, 11.2, 11.4–11.17), 238–708 (472) µm in diameter (N=22), pyramidal proximal hemisphere and rounded distal hemisphere in equatorial view when not compressed (Fig. 11.3, 11.17). The margo is prominent, 44.8–109 (74.4) µm (N=17) tall and 26.5–46.7 (37.2) µm wide (N=14), reaching equator or nearly so. The proximal hemisphere is ornamented with elements that range from low broad bumps (Fig. 11.4) to isolated verrucae (Fig. 11.6) to wide, broad verrucae or rarely baculae (Fig. 11.6, 11.10) to rugulae (Fig. 11.12) to reticula (Fig. 11.14), with interspersed verrucae. The elements are typically flat-topped (Figs. 11.18, 12.1), and verrucae are found on the margo and closer to proximal pole, whereas rugulae or reticula increase equatorially. Ornament on the distal hemisphere is similar except the elements are less densely arranged and are typically wider or more connected relative to proximal hemisphere (Fig. 11.4–11.15). The proximal ornament is sometimes taller than the distal ornament (Fig. 11.4–11.7), but always less broad/rugulate. The margo always bears ornament, sometimes only at its base (Fig. 11.4), that is similar in form but generally smaller in size than elements on the proximal hemisphere (Fig. 11.18). The verrucae are composed of anastomosing fibers (Fig. 12.1) more dense than the surrounding megaspore surface composed of a perforate mesh (Fig. 12.2). The megaspore wall is composed of three layers (Fig. 12.3). The innermost layer is homogenous, 0.37–0.78 (0.59) µm thick (N=11), while the middle layer is composed of fibers appearing aligned diagonally to spore surface, 0.91–1.69 (1.11) µm thick (N=10). The majority of the wall is formed by the outer layer that is composed of spongy fibers somewhat aligned parallel to the surface, 15.3–27 (23.2) µm thick. Microspores found on specimens (Fig. 12.4) are trilete, triangular, 31.3–36.4 (33.2) µm (N=7), with a psilate to finely pitted surface (Fig. 12.5).

Etymology

from Latin diversus, varied, diverse, several. For the wide variation in observed shape and connectedness of the elements of the ornament.

Remarks

Verrutriletes diversus is the most abundant megaspore type in all but one sample of Mauldin Mountain and Dead Fish Point. This abundance permits the characterization of the wide variance in morphology with the sampled populations. No obvious or consistent differences were observed between the two floras. The holotype (Figs. 11.1, 11.2, 11.18, 12.1, 12.2) represents the form closest to the subjective median morphology—ornament strongly developed but variable, with verrucae and short rugulae relatively dense on proximal hemisphere and wider verrucae and longer rugulae more dispersed over the distal hemisphere.

Verrutriletes diversus resembles V. composipunctatus (the type for genus) in the prominence of the margo, the presence of verrucae and rugulae, and the differentiation of the contact facets from the rest of the spore in terms of the ornament. However, the ornament on the contact facets of Verrutriletes composipunctatus is much reduced in all dimensions relative to rest of the spore, whereas in V. diversus the difference is primarily in spacing and connectedness. In addition, although size may not be reliable in separating species, the mean diameter of Verrutriletes diversus is about 170% of the mean of V. composipunctatus according to dimensions given by Batten (Reference Batten1988). In possessing (mostly) verrucae proximally and rugulae distally, Verrutriletes diversus resembles V. dubius (Dijkstra, Reference Dijkstra1949) Potonié, Reference Potonié1956, V. dasyplocoides Schultz and Noll, Reference Schultz and Noll1987, and Selaginella nehdenensis Huckriede, Reference Huckriede1982, but differs in that the density of the ornament of the latter three are not noted to vary between hemispheres, nor is the margo as prominent in S. nehdenensis. In possessing a verrucate ornament that is more dense proximally than distally, Verrutriletes diversus resembles V. maloninensis Knobloch, Reference Knobloch1984, but differs from the less prominent margo, the absence of rugulae, and the generally coarser/larger verrucae on the latter (Knobloch, Reference Knobloch1984; Batten, Reference Batten2012). Some of the specimens of V. diversus without strong ornament distally (Fig. 11.4–11.7) resemble Hughesisporites Potonié, Reference Potonié1956, but the continuity of form (specifically that there is some ornament distally and it is more elongated/rugulate) argues against recognizing a separate taxon. Hughesisporites sp. of Kovach and Dilcher (Reference Kovach and Dilcher1988) is very similar in size and ornament and may belong to this species. ?Maexisporites sp. of Li and Batten in Li et al. (Reference Li, Batten, Zhang and Zhang1987) is smaller in every dimension, but is similar in ornament.

Verrutriletes sp. cf. V. tomtaylori Archangelsky and Villar de Seoane, Reference Archangelsky and Villar de Seoane1990

Figure 12.6–12.10

1990 Verrutriletes tomtaylori Archangelsky and Villar de Seoane, p. 421, pl. 1, figs. 1–9; pl. 2, figs. 1–5; pl. 3, figs. 1–3.

Description

Megaspore is trilete, convexly triangular in polar view (Fig. 12.6, 12.7), with a diameter of 385–426 µm (N=2). The margo is sinuous, reaching the equator (Fig. 12.6), up to 39.5 µm wide and tallest, 35.5–48.1 µm (N=2), at the proximal pole (Fig. 12.8). The proximal hemisphere is ornamented with very broad, rounded verrucae to rugulae (Fig. 12.6, 12.9), ~20 µm tall and 25 µm wide, appearing somewhat disposed to radial alignment. The distal hemisphere is weakly undulate to dimpled (Fig. 12.7, 12.10). At high magnification, the surface is composed of a perforated fibrous network (Fig. 12.9, 12.10).

Remarks

The two recovered Elk Neck specimens are most similar to Verrutriletes tomtaylori in size and ornament, including vague alignment of elements (see Archangelsky and Villar de Seoane, Reference Archangelsky and Villar de Seoane1990, pl. 1, fig. 3), differing only in possessing elements that include rugulae. In giving the appearance of radial alignment of elements near the equator, these specimens approach the circumscription of Striatriletes, but elongate ridges never develop from the discontinuous elements. Verrutriletes depressus Tosolini et al., Reference Tosolini, McLoughlin and Drinnan2002 is similar, but differs in weaker ornament and in being diagnosed with sunken contact facets. In view of some specimens of Verrutriletes diversus (e.g., Fig. 11.16, 11.17), I do not regard sunken contact facets as a species character, but a preservational state, and suggest that Verrutriletes depressus should be considered a preservational state of and synonymous with V. tomtaylori unless the ultrastructure is shown to be different. Hughesisporites dettmanniae Tosolini et al., Reference Tosolini, McLoughlin and Drinnan2002 is also similar, but differs in possessing a shorter margo and a psilate, scabrate, or verrucate distal hemisphere.

Selaginellalean strobilus

Figure 13.1–13.7

Description

The fragment of the strobilus was 1.77 mm tall and 1.04 mm wide. Strobilus was compressed with two columns of 2–4 incomplete sporangia on each side (Fig. 13.1, 13.2). The fragment did not preserve either the base or apex of the strobilus. A fractured in-situ megaspore (Fig. 13.3) and in-situ microspores (Fig. 13.4) indicated that the strobilus was not unisexual. The position of the nearly complete megaspore in the same column above a microsporangium indicated that megasporangia were not exclusively basal, and that at least one column bore mixed sporangia (Fig. 13.1). A fragment of another megaspore wall in another sporangium (Fig. 13.2, arrow) indicated that at least two columns bore megasporangia. The megaspore was trilete, verrucate (Fig. 13.1), and ~350 µm in diameter. The outer megaspore wall was ~5 µm thick and composed of dense fibers (Fig. 13.5). The microspores were trilete, psilate to granulate (Fig. 13.4, 13.6, 13.7), and 25.5–30.4 (27.6) µm (N=16) in diameter.

Figure 13

Selaginellalean strobilus, specimen PP55550. (1) Side of strobilus illustrating two columns of fractured sporangia, one with a megaspore (white arrowhead) and two with microspores (black arrowheads); (2) reverse side of strobilus illustrating two columns of fractured sporangia, one with a megaspore fragment (white arrowhead) and one with microspores (black arrowhead); (3) close-up of verrucate megaspore; (4) close-up of fractured microsporangium; (5) cross-section of the wall of megaspore illustrated in 13.3; (6) psilate microspore tetrad; (7) close-up of fractured microspores illustrating trilete laesurae. (1, 2) Scale bar=250 µm; (3, 4) scale bar=100 µm; (5) scale bar=1 µm; (6, 7) scale bar=10 µm.

Remarks

This specimen was accidentally shattered while manipulating an adjacent specimen during study after only preliminary imaging was completed. With only fragments remaining and no additional specimens, it is not appropriate to erect a new taxon. The surface morphology of in-situ megaspore (Fig. 13.5) is similar to the dispersed Verrutriletes diversus, but the outer fibrous layer of the wall is thinner than the similar layer of V. diversus (Fig. 12.3). A smooth inner body is preserved inside the megaspore wall; its thick homogenous wall is likewise unlike the inner wall of V. diversus (Fig. 12.3). The in-situ microspores (Fig. 13.4, 13.6, 13.7) differ from those preserved on the dispersed V. diversus (Fig. 12.4, 12.5) in being smaller and mostly psilate, occasionally granulate, never punctate. Whether the differences in spore morphologies reflect different taxa, or just the effects of incomplete or aborted development is unknown. The strobilus was recovered from Mauldin Mountain Sample #10 (early Cenomanian).