Locality
USGS11488
69.385° -148.717°
Sagavanirktok (B-3) Quad.
Sagwon section. Stratigraphically more or less equivalent to locality 11480, plant remains occurred in abundance in blocks of iron-cemented calcareous fine-grained sandstone weathering out approximately half way up the bluffs.
Description
Leaf: simple; symmetrical; ovate (?); apex missing; base lobate; margin shallowly dentate, teeth with obtuse apices and shallow rounded sinuses; venation basal imperfect marginal actinodromous; primary midvein moderate, straight; a-pectinal veins moderate, straight or slightly curved, arising at an angle of 45°; a-pectinal abmedial veins arising abmedially from the pectinals at angles of 40-55°, curved and branched abmedially; b-pectinals moderate, curved, departing midvein basal to a-pectinals, initially recurved then curved giving off branches abmedially into the lobes; abmedials curved, basal ones recurved initially, abmedially branched, departing pectinal at 50°; superior secondaries arising from the midvein at angles of 40-50°, more or less opposite, moderate, curved, the more basal ones branched repeatedly on the abmedial side, the more basal of these abmedial branches also branched abmedially and all branches terminating in the medial veins of the marginal teeth; tertiary veins transverse, percurrent, straight or convex, often forked, joining both ad- and abmedial sides of the secondary veins at an acute angle or 90°; fourth order veins forming an orthogonal reticulum.
Remarks
Unfortunately the details of the marginal venation are not preserved in this specimen and without such information comparison with other forms is difficult. The actinodromous venation with transverse tertiaries suggests a hamamelid or palmate dilleniid relationship. The secondary venation appears to be craspedodromous rather than semicraspedodromous which is typical of the palmate dilleniids and the arrangement of the tertiaries, while being concentric to the petiole in the basal half of the lamina, tends to be oblique to the midvein at a more or less constant angle in the upper half of the lamina which is more a feature of the hamamelids. The tooth shape is also more commonly found in Cretaceous hamamelids although the poor preservation of the margin means there must be some doubt as to the true nature of the teeth. This leaf is distinct from specimens USGS 11480.1, USGS 11480.3 and USGS 11488.5 in that the b-pectinals are very weak.
As far as published fossil species are concerned specimen USGS 11488.6 compares well with the Paleocene form Pterospermites auriculaecordatus Hollick (1936, p. 151-152; Plate 92, Figs. 1-5; Plate 93, Figs. 1, 2) which Bell (1949) considered to be a variable form of a specimen from the Paleocene of Western Alberta which he assigned to P. whitei. There is certainly a strong similarity with Bell's specimen (GSC No. 6275, Plate 47, Fig. 5). The generic name Pterospermites is invalid because it was erected for a seed. Ward's (1887) original description specifically mentioned rounded teeth, whereas some of Bell's specimens have angular teeth and rounded sinuses. We regard leaf forms of this type assignable to the name Corylites beringianus (Kryshtofovich) Golovneva.