Locality
Arctic Slope of Alaska locality USGS 11606, north of Maybe Creek. This locality is a bluff approximately 10 m high on the east side of an unnamed tributary of the Price River. The predominant lithologies are bentonitic clays overlying a silty sandstone capped by coal beds up to 2 m thick, which are in turn overlain by a white-gray medium-grained sandstone. Irregularly dispersed throughout the clay are nodules and sheets of ferruginous limestone (sideritic) which, although light gray when fresh, weather to a rusty brown. With the exception of some poorly preserved plant matter in the upper sandstones, and impressions of platanoid leaves in the power sandtsones, the plant material is confined to these fine-grained iron-rich nodules and is preserved as impressions totally lacking cuticle. There is little evidence of post-mortem decay but many leaves are penetrated by vertical fossil rootlets. Platanoid leaves are most common in siltier/sandier facies. The uppermost coal surface supports several in situ tree bases each of which is approximately 20 cm in diameter.
Latitude: 69.528329 °N
Longitude: -153.887128 °W
Description
Leaf: simple; symmetrical; wide elliptic; apex retuse; base missing; margin lobate, apices of lobes rounded or sometimes apparently retuse with the medial vein projecting beyond the apex to form a bristle or seta, sinuses rounded; venation pinnate, simple craspedodromous, primary vein moderate, straight; secondary veins moderate with a moderately acute (approximately 35-45°) angle of divergence from the midvein, straight usually unbranched; tertiary veins weak, angle of origin on secondaries acute on abmedial side, obtuse on admedial side, straight, usually unbranched percurrent arranged approximately at right angles to the midvein, tertiary veins in the lobes and the basal part of the lamina forming irregular loops; fourth order veins very indistinct but forming marginal loops in the lobes.
Remarks
The genera 'Quercus' Linnaeus and Quercophyllum Fontaine have frequently been reported from the Cretaceous of North America notably from the Dakota Group (Lesquereux, 1892). Knowlton (1922) also describes more leaves from the Laramie Formation which he assigns to the genus 'Quercus' with some confidence on the basis of the morphology and venation, in particular the looping of the secondaries close to the margin to form a "*** nearly continuous intramarginal line, a character observed in certain living leaves of this genus" (Knowlton, 1922, p. 127).
While I doubt the wisdom of assigning Cretaceous leaves to extant genera without clear evidence of relationship such as attached reproductive organs, the specimen USGS 11606.36 does possess characters which traditionally might place it either under the name of 'Quercus' or Quercophyllum. Morphologically it is of the Quercophyllum type but details of the venation patterns for this genus are obscure. However Upchurch (written communication, 1985) reports that examination of Potomac Group leaves assignable to Quercophyllum show low rank venation, glandular teeth with marginal accessory veins that fuse with the teeth (a chloranthoid tooth) and no obvious transversely oriented tertiary venation. The venation of specimen USGS 11606.36 has features in common with Knowlton's 'Quercus' leaves, but again there are important differences between this leaf and the definition of the extant genus, most notable of which is the higher (4th) rank of the modern Quercus.
A significant feature is the structure of the lobes and in particular the possession of a nonglandular seta or spine formed by the midvein projection beyond the lobe apex. Such a feature is characteristic of some extant members of the Fagales (Hickey and Wolfe, 1975). This, together with the pinnate venation and strongly transverse tertiaries indicates this leaf form may represent the Fagales. The antiquity of the leaf may be reflected in the poorly organized tertiary venation within the lobes.
Hollick's 'Rulac' quercifolium (1930, p. 100; Plate 29, Fig. 1a; Plate 77, Figs. 1-10; Plate 78, Fig. 7b) are similarly (through more shallowly) lobed and the behaviour of the tertiary veins within the lobes are also comparable to a degree. Hollick does not state, however, if the lobe tips were spinose and his illustrations offer insufficient detail on this point. There are however significant differences in the orientation of the tertiary veins with respect to the midvein; Hollick's tertiary veins are at an obtuse angle which decreases towards the margin.
Krassilov (1979) combined 'Rulac' quercifolium with similarly named specimens described by Krishtofovich (1960, p. 103; Plate 20, Fig. 4; Plate 21, Fig. 1) under the genus Hollickia Krassilov, a member of his 'Rosifolia'. Krassilov's illustrations only show the pinnate nature of the gross venation together with a degree of lobing approaching that of specimen USGS 11606.36. Krassilov's specimens occurred at a locality which is also reputed to have yielded Protophyllum schmidtianum, Protophyllocladus sachalinesis, Sequoia reichenbachii, and Trochodendroides sachalinensis which suggests a Coniacian age rather than the Campanian of 'Rulac' quercifolium. It would seem prudent at this time to maintain a distinction between Krassilov's specimens and those of Hollick.
These specimens should also be compared with form U275 (UIDAHO 1/14.2, Dicot 4; UIDAHO 1/14.1, Dicot 57), form U274 (UIDAHO 1/21.4, Dicot 24), and form (RO)175 (p. 457).