868


Journal of Paleontology 91(5):859–870


of origination of secondary veins from the primary vein, with the angle of insertion ranging from 80–90° in C. whitei and averaging ~60° in all Gigantopteridium species; (2) a more acute angle of origination of tertiary veins from secondary veins, ranging from 15–30° in C. whitei and 45–80° in Gigantopter- idium species; (3) inconsistencies in the tertiary branching structure, where C. whitei branches exclusively dichotomously whereas Gigantopteridium species branch dichotomously and monopodially; (4) accessory mesh running parallel to the midvein formed by the ultimate order of venation in C. whitei and absent in North American Gigantopteridium species; and (5) the origination of a pronounced, straight intersecondary suture in C. whitei midway between two adjacent secondary veins differing from the origination of an often zig-zagging suture zone at the junction of a secondary vein with the primary vein in Gigantopteridium (Table 1). As previously stated, G. huapingense likely should be


segregated within a distinct genus from Gigantopteridium as it is defined in this paper. Liu and Yao (2002) described G. huapingense as exhibiting accessory mesh, which is a unique trait lacking from North American Gigantopteridium, but (questionably) present in C. whitei, as described by Yang (1987) and Liu and Yao (1992). Preliminary analysis of C. whitei specimens from the collections of Halle (1927) via images provided by theNRMsuggests that accessory mesh may be absent from C. whitei. If indeed absent, this would be an additional feature supporting the removal of G. huapingense from Gigantopteridium.


Remarks on species occurrence.—The pattern of occurrence for each Gigantopteridium species throughout North Central Texas seems to support the designation of three distinct species. Of the identifiable specimens, G. americanum was the most commonly recovered species, while both G. yochelsonii and G. utebaturianum n. sp. were found to be rare. Gigantopteridium americanum appeared as the sole species present at localities as well as co-occurring with G. utebaturianum n. sp. Gigantopteridium yochelsonii occurred at localities only as the sole Gigantopteridium species present and occasionally in assemblages with Zeilleropteris wattii. Localities with only G. americanumpresent ranged in numbers of specimens fromone to more than thirty identifiable leaves. Two localities presented co-occurrence of G. americanum and G. utebaturianum n. sp. composed of ~170 and ~54 Gigantopteridium specimens, respectively, with G. americanum the most common and G. utebaturianum n. sp. being rare. One locality presented G. utebaturianum n. sp. as the sole species present, represented by a single identifiable specimen and four additional specimens identifiable to Gigantopteridium.


Conclusion


Members of North American Gigantopteridium are fairly uniform in gross leaf architecture; sharing features of broad, ribbon-like leaves that appear to be consistently petiolate, have convex apices, leaf bifurcation, and similar primary and secondary vein fabric. The ultimate order venation is crucial for distinguishing the three North American species; however, the distinctive herringbone arrangement of the higher order


Table 1. Diagnostic characters of Gigantopteridium and Cathaysiopteris species discussed in this paper: AoI = angle of insertion, * = information not available. Species


Leaf Shape G. americanum G. yochelsonii G. utebaturianum


G. huapingense (Feng) Shen


C. whitei (Halle) Koidzumi


Margin Character Oblong–obovate Erose–Entire Oblong–obovate Erose–Entire


Oblong–obovate Erose–Entire–Sinuous Oblong Oblong


Sinuous


Entire or Crenate with rounded teeth


Orders of Venation


Three Three


Three Three Three


AoI 2° to 1°


2° 60° Dissipate 50–60° Dissipate


45–60° Dissipate 55–70°


* 65–85° Dissipate


termination AoI 3° to 1° 80–90°


80–90°


90°–slightly obtuse 80–90°


40–70°; commonly 55° AoI 3° to 2° 3° branching


40–60° Up to 5x; monopodial, dichotomous; irregularly spaced


45–60°


50–75° 50–70° 20-50°;


commonly 30°


Rarely branched up to 1x; monopodial; evenly spaced


1-2x; monopodial 1-2x; monopodial


Up to 1x; monopodial


Suture Strength


Strong Absent


Weak Weak Strong


Suture Origin


Junction of subjacent 2° and 1°


Junction of subjacent 2° and 1°


Junction of subjacent 2° and 1°


Junction of subjacent 2° and 1°


Midway between two adjacent 2°


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