Koll et al.—Gigantopteridium and Cathaysiopteris taxonomy
Occurrence.—Type locality is found in Baylor County, TX, on the Fulda 7.5’ USGS quadrangle map. Exact location of the type locality is on file at the USNM and is withheld here at the request of the property owner. Stratigraphic position of type specimen is Waggoner Ranch Formation.
Description.—Leaf shape is oblong to obovate (Fig. 4.1). Several specimens exhibit bifurcation of the lamina accom- panied by forking of the primary vein approximately one-third of the length from the base (Fig. 4.1–4.3). Apex shape of the resultant portions of the leaf is rounded convex, but may trend to slightly acuminate. The base of the leaf, which is known from only a single specimen, is distinctly asymmetrical. Margin character ranges from entire to erose to sinuous, occasionally deeply sinuous (Fig. 4.1–4.3, 4.6). Secondary veins are reg- ularly spaced, pinnate and opposite in their attachment to the primary vein. Secondary attachment to the midvein is slightly decurrent. The angle of attachment ranges from 45–60°, most commonly 60°. Secondary veins terminate just before the mar- gin and, if the specimen has a lobed margin, may terminate in the apex or sinus (Fig. 4.2, 4.3, 4.6). Tertiary veins are both subsidiary and accessory (Fig. 4.2–4.5). When arising from the primary vein, tertiary veins originate at a right or slightly obtuse angle. Tertiary veins arising from major secondary veins are decurrent in attachment, opposite, and borne at an acute angle, ranging from 50–75°. Tertiary veins tend to be evenly spaced and straight. Tertiary veins commonly branch one to two times, rarely unbranched (Fig. 4.2–4.8). Branching of tertiary veins is monopodial and occurs initially near their point of origination from the secondary vein, with a possible second forking just before the intersecondary suture (Fig. 4.5, 4.8). Branches of the tertiary veins can originate from either side of the principal tertiary vein; most commonly the veinlets originate in a series of successive divisions. A weakly developed suture vein is present between adjacent secondary veins, formed by the fusion of tertiary veins from adjacent secondary veins. The suture vein originates at the junction of the subjacent secondary with the primary vein; because the suture vein is generally weakly developed, it may not strongly connect the midvein to the margin and may appear to be lacking in some specimens (Fig. 4.2, 4.3, 4.5, 4.7, 4.8).
Etymology.—Named in honor of Dr. Sergius Mamay, who worked extensively on the paleobotany of equatorial Pangea during his career with U.S. Geological Survey. Dr. Mamay credited himself as being the only left-handed, Jewish, piano playing, paleobotanist of Ukrainian descent. Greek, utebaturia (“left-handed”).
Remarks.—In his 1986 publication, Mamay stated the materials he analyzed may include two morphologically distinct leaf forms within G. yochelsonii, however the fragmentary nature of the material prevented investigation or confirmation of this possibility. Examination of the full suite of materials now available indicates that there is sufficient evidence to support the establishment of the additional species named here, G. utebaturianum n. sp. Recognition of G. utebaturianum n. sp. specimens as a distinct species, and thus separating them from
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G. americanum and G. yochelsonii, allows for the latter two species to be more clearly circumscribed. Although it shares several traits of gross leaf architecture
with both G. americanum and G. yochelsonii,G. utebaturianum n. sp. can be distinguished from them on the basis of several traits, including the angle of insertion of the tertiary veins at their point of origin from the secondary veins, the extent of tertiary branching, and structure of the intersecondary suture (compare Figs. 2, 3 with Fig. 4). Gigantopteridiumutebaturianum n. sp. is characterized by: (1) a more obtuse angle of insertion of those tertiary veins that arise from the secondary veins, 50–75° in G. utebaturianum n. sp., 30° in G. americanum, and 45° in G. yochelsonii; (2) moderate branching of one to two times in tertiary veins, as compared with two to five times in G. americanum and zero to one time in G. yochelsonii; and (3) a weak intersecondary suture, differing from the well- developed suture in G. americanum, which clearly connects to the primary vein and continues to the margin, and the lack of a suture vein in G. yochelsonii, creating a narrow open space between the tertiary veins from adjacent secondaries (i.e., what we have described as a “false” suture). Of the three North American Gigantopteridium species
recognized here, G. utebaturianum n. sp. appears to share the greatest morphological similarity with the Chinese species, Cathaysiopteris whitei. In particular, these two species have limited branching of tertiary veins, creating a distinct “herring- bone” appearance. This is a striking feature and gives them an appearance of great similarity upon initial examination. However, it does not appear that G. utebaturianum n. sp. and C. whitei represent the same species based on two important differences, as discussed below.
Structure of tertiary veins.—In G. utebaturianum n. sp. the ter- tiaries originate from the secondary veins at an angle of 50–75° then branch just beyond their point of origination from secondary vein, followed occasionally by a second branching just before termination. In contrast, the tertiary veins ofC. whitei arise from the secondary veins at more acute angles of 15–30° and extend a few millimeters parallel to the secondary vein before arching into the intersecondary space. They branch initially one-quarter to one-third of the distance between their points of origination and termination, followed rarely by a dichotomous branch just before the intersecondary suture.
The presence of a consistently strong suture in C. whitei.—A consistently strong suture originates directly from the primary vein midway between pairs of secondary veins and extends from the midvein to the margin at a 90° angle.
Remarks on C. whitei and G. huapingense.—The support for excluding C. whitei from Gigantopteridium requires further evaluation as initial morphological evidence indicates it may represent a fourth species within the Gigantopteridium- morphogroup. Defining characters encompassing the three North American Gigantopteridium species clearly distinguish the genus from other gigantopterid genera, however within the genus, traits fall within a range of more-or-less continuous variability. Currently, C. whitei is distinguished from North American Gigantopteridium based on: (1) a more obtuse angle
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