Grebenka, Yelisseev Locality, Site Old 35
This description of Nilssonia serotina Heer is from From Hollick (1930) (p. 43-44) "Plate 4, Figures 1-7; Plate 5, Figures 1-5a; Plate 7, Figures 6a, 6b,10a; Plate 29, Figures 3b, 5a; Plate 30, Figures 2a, 3b"
"Nilssonia serotina Heer, Miocene Flora der insel Sachalin: Flora fossilis arctica, vol. 5, No.4, p. 19, pl. 2, figs. la, 2-5, 1878" (Heer 1878)
"The figures upon which Heer's description of the species is based represent fragmentary specimens, in none of which is the summit of a frond preserved, and apparently the species has not been described or figured elsewhere than in the original place of publication. Our specimens, however, in the aggregate show every part and feature of the fronds, thus making possible the following amended and more complete description of the species:
Fronds varying in size, broadest at or near the summit, narrowed to the base, irregularly dissected or pinnatifid; segments subtriangular, rhomboidal, or ligulate, cuneate, rounded or bluntly acuminate, mostly curved slightly upward, lowest ones more or less distinct, upper ones gradually becoming approximated and ultimately merging into a truncate or broadly emarginate summit; nervation fine, simple, uniform, parallel."
From Hollick (1930) (p. 43-44)
"It is with some hesitation that I have included all these diverse forms under a single specific name; but the accompanying figures do not show all the intermediate forms contained in the collections, and as attempts to differentiate them resulted in constant shifting and changing of specimens from one group of forms to another, the decision was finally made to regard them all as belonging to one polymorphous species.
The species to which they are referred was originally described and figured by Heer from specimens obtained on the island of Sakhalin, in strata regarded as Tertiary; but Kryshtofovich (1918) as a result of investigations made in 1917, concludes that Heer's "so-called Miocene flora belongs in fact to several geological horizons not only of the Tertiary period, but also of the Cretaceous"; and in the Mgach flora, included in his Gyliakian series and regarded as of Cenomanian age, he lists Nilssonia serotina Heer.
Another closely allied species that calls for special critical study and comparison is Nilssonia comptula Heer (1878) (p. 19, pl. 4, figs. 10a, 11 - 16) described as Jurassic, from the Lena River region of Siberia. So far as I am aware the stratigraphic position of the beds in which this species occurs has not been questioned; but in view of the serious error that was made in connection with the stratigraphic relations of the Sakhalin fossil floras it may be pertinent to suggest that careful field work in the Lena River region might result in the discovery of facts that would necessitate a change or modification of opinion in regard to the exclusive Jurassic age of the flora of that region. Certain of the species, such as Podozamites lanceolatus, for example, are equally suggestive of the Cretaceous age of the flora.
In all our specimens in which the nervation is well defined it may be seen to cross or to impinge upon the midrib in the manner characteristic of Nilssonia; otherwise, if only the general form of the fronds and segments were available as diagnostic characters they
might readily be mistaken for coordinate remains of certain species of cycads, presumably of Jurassic age, such as Anomozamites schmidtii Heer (1876) (p. 100, pl. 23, figs. 2, 3; pl. 24, figs. 4 - 7) Anomozamites acutilobus Heer (1876) (p. 102, pl. 3, fig. 1a; pl. 24, figs. 1, 2, 3b; pl. 25, fig. 9) Pterophyllum helmersianum Heer (1876) (p. 104, pl. 2 - 6; pl. 29, fig. 1d) and Pterophyllum lancilobum Heer (1876) (p. 104, pl. 25, figs. 7, 8) from the province of Amur, Siberia.
It is an interesting and significant fact in connection with this species that, although it is one of the most abundant elements in the Cretaceous flora of Alaska Peninsula, it has not been found in any of the collections from the Yukon River district.
A number of the specimens present a false appearance of being pinnatifid, where the frond is merely broken or split. This condition may be seen in the upper portions of Figures 1 and 5 on Plate 4, Figure 5a on Plate 5, and throughout Figure 6b on Plate 7. In the last-named figure the frond appears to be made up of narrow segments, closely approximated; but critical examination shows this feature to be due to laceration or splitting. Apparently the fronds, in their upper parts, are normally not pinnatifid or divided, and this condition may represent a character due to age or to partial disintegration during the process of fossilization. In connection with the figures above mentioned and with Figure 10a on Plate 7comparison should be made with the fragmentary remains described and figured under the name Nilssonia stantoni Ward (1905) (p. 251, pl. 67, figs. 5, 6) from the Shasta series of California, which may represent lower parts of the same species as that to which our specimens belong. Close specific relationship is also indicated with the Jurassic species Nilssoni nipponensis Yokoyama and Nilssonia compta (Phillips) Goeppert, as identified by Fontaine (1905) (in Ward 1905) (p. 94 [N. nipponensis, pl. 17, figs. 8 - 10; N. compta, pl. 17, figs. 11 - 14]) from specimens collected in Oregon.
A large frond, representative of the species in all its normal and extranormal features, could be reconstructed from the three fragments shown in Figures 1 and 3 on Plate 5."
This photograph was made in the field. The specimen is in the collection of the Geological Institute, Russian Academy of Sciences, Moscow, Russia. For further details of the context of the collection see Spicer et al. (2002).