862
Journal of Paleontology 91(5):859–870
Diagnosis.—Leaves oblong to obovate, frequently bifurcated. Margin entire to erose, occasionally sinuous, rarely deeply sinuous. Three orders of venation. Second order venation angle of attachment with primary vein 45–60°, most commonly 60°. Second order veins dissipate before margin, branching dichotomously to reach margin. In specimens exhibiting sin- uous to deeply sinuous margins, second order veins may branch to terminate in sinus or apex. Tertiary veins originate from primary vein 80–90°, occasionally slightly obtuse. Tertiary veins originate from secondary veins 40–70°. Tertiary veins may be unbranched or branch up to five times. Branching is most commonly monopodial, though dichotomous branching may also be present. Suture veins may be false, weak, or strong. False suture vein is defined as tertiary veins from adjacent secondary veins approaching one another closely but neglecting to fuse. Suture vein originates at the junction of the subjacent secondary with the primary vein and arches to run perpendicular to primary vein midway between to two adjacent secondary veins terminating at margin.
Gigantopteridium americanum (White) Koidzumi, 1934 emend. Figure 2.1–2.7
1912 Gigantopteris americana White, p. 498, pl. 43–49. 1934 Gigantopteridium americanum; Koidzumi, p. 113.
Holotype.—USNM 34070 from the Waggoner Ranch Forma- tion of North Central Texas, USA. Type specimen collected from stream bank approximately one-quarter mile south of the ford of Little Wichita River and four miles southeast of Fulda in Baylor Co., Texas.
Paratypes.—USNM 34061, 34069, 34071, 34072, 34074, 41771, 597058, 597092, 617576, and 636751. We exclude USNM 34062, 34063, 34073, which were cited among the original list of paratypes by White (1912), from our concept of species. Based on our emended diagnoses, USNM 34062 has been reassigned to G. utebaturianum n. sp. USNM 34063 and 34073 do not possess sufficient preservation of high order venation to distinguish species of Gigantopteridium.
Diagnosis.—Leaves oblong to obovate with bifurcation of fronds often present. Margin entire to erose. Three orders of venation. Second order venation angle of attachment with primary vein most frequently 60°. Second order veins branch to terminate at margin. Third order veins arise from primary vein at 80–90° and most commonly 40–60° from secondary veins. Third order venation exhibits extensive irregularly spaced monopodial and dichotomous branching into intersecondary space, fusing midway between two adjacent secondary veins to create a strong suture vein. Suture vein originates at junction between subjacent secondary vein and primary vein and termi- nates at margin.
Description.—Leaves are oblong to obovate in shape with a rounded convex apex (Fig. 2.3). Basal features were not preserved in full for any of the specimens, however, the leaves appear to narrow gradually towards the base. Leaves are likely
petiolate. Leaves are commonly bifurcate, with the forking of the primary vein usually occurring approximately one-third of the length from the base at a 45–60° angle (Fig. 2.7). The margin of the leaf ranges from entire to erose to slightly sinuous (Fig. 2.1–2.3, 2.7). Specimens have three orders of venation (Fig. 2.1, 2.2, 2.4–2.6). The width of the primary vein ranges from 1–6mm, most commonly 1.5–2.0mm. Secondary veins are opposite and regularly spaced, inserted decurrently at their point of origin at the primary vein. The angle of attachment of secondary veins with the primary ranges from 45–80°, but is most commonly 60°, becoming slightly more acute distally and more obtuse towards the base. Secondary veins taper just before the margin, in most cases branching dichotomously to reach the margin (Fig. 2.3). In specimens with more pronounced marginal sinuation, secondary veins terminate most commonly in the sinuses, rarely in the apex. Tertiary veins are subsidiary and accessory (Fig. 2.4, 2.5). Tertiary veins arise from the primary vein commonly at 80–90°, occasionally at a slightly obtuse angle. Tertiary veins arising from secondary veins originate at acute angles ranging from 40–80°, most commonly 40–60°, and exhibit extensive, irregularly spaced monopodial and dichot- omous branching. Branching of the tertiary veins can originate from the left, right, or both sides of the main vein; tertiaries frequently branch two or three times before reaching the inter- secondary suture, although tertiary veins may branch as few as one time or as many as five times (Fig. 2.5, 2.6). Tertiary veins begin to subdivide near the point of origination from the sec- ondary vein and most often branch one to two times with additional branching one-third the distance from the inter- secondary suture. Tertiary veins from any pair of adjacent secondary veins fuse to form a strong intersecondary suture vein, which originates at the junction of the subjacent secondary vein and primary vein (Fig. 2.1, 2.2, 2.5). The suture arches slightly to run parallel to the flanking secondary veins, continuing to terminate at the margin. Tertiary veins anastomose with surrounding fascicles from laterally adjacent tertiary veins to form a polygonal mesh and fuse with tertiary veins originat- ing in the opposite secondary to contribute to the intersecondary suture vein.
Remarks.—The findings from the reevaluation of the USNM materials conform to the majority of points outlined in the original diagnosis byWhite (1912) of Gigantopteris americana, which was transferred to Gigantopteridium americanum by Koidzumi (1934). However, examination of the USNM collec- tion has lead to the refinement of theG. americanum description by designating an additional species (G. utebaturianum n. sp.), segregated from what had been considered a single species of Gigantopteridium. Thus, a formal emendation of the species diagnosis made by White (1912) is required. Here we note that these characters presented in the original diagnosis: (1) sec- ondary vein termination at the margin and in the convexity of sinuate margins, and (2) strong intertertiary sutures, have been redefined because both characters are absent from nearly all G. americanum specimens as we have recircumscribed the species, although they may occur rarely. Additionally, a review of the current diagnosis of
Gigantopteridium huapingense suggests that a new combina- tion removing G. huapingense from Gigantopteridium may be
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