Locality
USGS11475
69.716° -143.408°
Demarcation Point
Plant fossils were collected from a iron-rich (sideritic) indurated layer within a gray clay on the east bank of the tributary of the Jago River. This locality is equivalent to Detterman 300P.
Description
Leaf: simple (?); symmetrical (?); shape unknown; apex unknown; base unknown; margin toothed, large (> 1 cm) triangular, apices angular acute, sinuses acute (?) angular (?), apices with a glandular tip or swelling, tooth venation consisting of a medial vein joined by a series of brochidodromous loops; palmate, perfect basal actinodromous with many pairs of pectinal veins originating from a single point; primary midvein more or less straight, moderate; a-pectinal veins of the same thickness, usually uniformly curved but sometimes slightly sinuous; a-pectinals branched admedially as well as abmedially; pectinal branches often arranged opposite or subopposite; secondaries alternate on primary midvein; both secondaries and pectinal subsidiaries forming angles of 25° or less to parent veins, often recurved but sometimes curved; tertiary veins convex, often transverse simple or forked forming acute angles with parent veins, irregular in course, often joining to form compound intersecondary veins; fourth order veins more or less straight, transverse, sometimes branched forming an orthogonal reticulum; fifth order veins transverse, more or less straight, often forming an orthogonal reticulum.
Remarks
These tantalizingly incomplete specimens represent large, apparently palmately veined, leaves with poorly organized higher order venation. The overall symmetry is bilateral rather than radial and it is not known if the leaves were peltate.
The teeth are interesting in that they possess a distinctly Platanoid character, namely the numerous brochidodromous loops subtending the medial vein. The strong higher order bracing laterals of the Chloranthoid tooth are not developed. Unfortunately the extreme tips of the teeth are missing and while it is clear that there is swollen glandular region at the apex the exact nature of this feature is not known.
The third order venation is very irregular in course and considerably weaker than the secondary venation. There is a strong tendency for the tertiaries to coalesce to form intersecondary, or rather in this case interpectinal, veins; a feature most commonly seen today in representatives of the Magnoliidae, but also present in the Hamamelididae.
These leaves were found in a fine gray silty shale to the almost total exclusion of other forms (cf. Hollick, 1936, p. 114). The only other abundant impressions that were closely associated with, and restricted to, the horizon containing these leaves were the broad strap-like forms bearing linear striations (form (RAPE)203), specimen USGS 11475.4. Examples can also be seen on specimen USGS 11475.3 and specimen USGS 11475.16. The close and restricted association of these forms leads one to speculate that they might have been part of the same plant. The strap-like impressions may represent the stems or petiole of the leaves. The leaf morphology is distinctly suggestive of an aquatic habit and the leaves do bear a resemblance to some nymphaeaceous forms. The glandular dentate margin is, however, unknown in extant Nymphaeaceae.
Hollick described a specimen which he ascribed to his genus Castaliites and which is strikingly similar to these leaves (Hollick, 1930, p. 77; Plate 41, figure 3). Of the six species he describes, Castaliites acutidentatus is the form closest to the Arctic Slope material and was found in the uppermost Cretaceous of the Alaska Peninsula. Hollick intentionally defined the genus rather broadly to include a number of apparently nymphaealean extinct plants and examination of his illustrated specimens (Hollick, 1930; Plate 41, Figs. 2-7) does reveal a considerable variation in leaf form and architecture. Too great variation, in fact, to be particularly meaningful.
There is no doubt that the leaves described here do not represent the Cretaceous and Tertiary forms of 'Nelumbo' which had a widespread distribution (for example, Hollick, 1893, p. 168, Plate 149; Hollick, 1904, p. 142, Plate 74, Figs. 1, 2; Plates 75 and 76; Plate 77, Fig. 1; Hollick, 1912, p. 160, Plate 166, Figs. 3, 4; Hollick, 1936, p. 113, Plate 61, Figs. 1-3). All the specimens of 'Nelumbo' have dichotomizing radiating pectinal veins in contrast to the bilaterally symmetrical venation, with more or less opposite secondaries, present in this material.
From the venation it appears that these specimens exhibit characters seen in modern Magnoliidae (for example the intersecondary veins and poorly organized venation) but the nature of the teeth are not strictly consistent with this assignment.
These leaves are architecturally related to the Menispermites forms of late Albian and Cenomanian time (Forms RAPE11, RAPE12, RAPE13) and the congested nature of the pectinals may be a reflection of the loss of basal lobing.