northern extension of Glossopteris types and their association with
European species. In 1898 an important discovery was made by
Professor Amalitzky, which carries us a step further in our search for
a connexion between the northern and
southern floras. Amalitzky found in
beds of Upper Permian age in the province
of Vologda (Russia) (Map A, V.)
species of Glossopteris and Naeggerathiopsis
typical members of the Glossopteris
flora, associated with species of the ferns
Taeniopteris, Callipteris and Sphenopteris,
a striking instance of a commingling in
the far north of the northern hemisphere
Permian species with migrants from
“Gondwana Land.” This association of
types clearly points to a penetration of
representatives of the Glossopteris flora
to the north of Europe towards the close
of the Permian period. Evidence of the
same northern extension is supplied by
floras described by Schmalhausen from
Permian rocks in the Pechora valley
(Map A, VI.), the Siberian genus Rhiptozamites
being very similar to, and probably
generically identical with, Naeggerathiopsis
of the Glossopteris flora. The
Permo-Carboniferous beds of South
Africa, India and Australia are succeeded
by other plant-bearing strata, containing
numerous species agreeing closely with
members of the Rhaetic and Jurassic
floras of the northern hemisphere. These
post-Permian floras, as represented by
the Upper Gondwana beds of India and
corresponding strata in Australia, South
Africa, and South America, differ but
slightly from the northern floras, and
point to a uniformity in the Rhaetic
and Jurassic vegetation which is in contrast to the existence of two
botanical provinces during the latter part of the Palaeozoic period.
A few plants described by Potonié from German and Portuguese
East Africa demonstrate the occurrence of Glossopteris and a few
other genera, referred to a Permo-Triassic horizon, in a region slightly
to the north of Tete in the Zambesi district (Map A, I.), where
typical European plants agreeing with Upper Carboniferous types
were discovered several years ago, and described by Zeiller in 1882
and 1901. The existence of Upper Gondwana plants, resembling
Jurassic species from the Rajmahal beds of India, has been demonstrated
in the Argentine by Dr Kurtz.
|
| (After Feistmantel.) |
|
Fig. 4.—Neuropteridium validum. From Lower Gondwana rocks, India. |
Having seen how the Glossopteris flora of the south gradually spread to the north in the Permian period, we may now take a brief survey of the succession of floras in the northern hemisphere, which have left traces in Mesozoic rocks of North America, Europe and Asia. Our knowledge of the Triassic vegetation is far from extensive; this Mesozoic Floras. is no doubt due in part to the fact that the conditions under which the Triassic rocks were deposited were not favourable to the existence of a luxuriant vegetation. Moreover, the Triassic rocks of southern Europe and other regions are typical marine sediments. The Bunter sandstones of the Vosges have afforded several species of Lower Triassic plants; these include the Equisetaceous genus Schizoneura—a member also of the Glossopteris flora—bipinnate fern fronds referred to the genus Anomopteris, another fern, described originally as Neuropteris grandifolia, which agrees very closely with a southern hemisphere type (Neuropteridium validum, fig. 4), some large Equisetaceous stems apparently identical, except in size, with modern Horsetails. With these occur several Conifers, among others Voltzia heterophylla and some twigs referred to the genus Albertia, bearing large leaves like those of Agathis australis and some of the Araucarias, also a few representatives of the Cycadales. Among plants from Lower Triassic strata there are a few which form connecting links with the older Permo-Carboniferous flora; of these we have a species, described by Blanckenhon as Sigillaria oculina, which may be correctly referred to that genus, although an inspection of a plaster-cast of the type-specimen in the Berlin Bergakademie left some doubt as to the sufficiency of the evidence for adopting the generic name Sigillaria. Another Triassic genus, Pleuromeia, is of interest as exhibiting, on the one hand, a striking resemblance to the recent genus Isoetes, from which it differs in its much larger stem, and on the other as agreeing fairly closely with the Palaeozoic genera Lepidodendron and Sigillaria. There is, however, a marked difference, as regards the floras as a whole, between the uppermost Palaeozoic flora of the northern hemisphere and such species as have been recorded from Lower Triassic beds. There is evidence of a distinct break in the succession of the northern floras which is not apparent between the Permian and Trias floras of the south. Passing over the few known species of plants from the middle Trias (Muschelkalk) to the more abundant and more widely spread Upper Triassic species as recorded from Germany, Austria, Switzerland, North America and elsewhere, we find a vegetation characterized chiefly by an abundance of Ferns and Cycads, exhibiting the same general facies as that of the succeeding Rhaetic and Lower Jurassic floras. Among Cycads may be mentioned species of Pterophyllum (e.g. P. Jaegeri), represented by large pinnate fronds not unlike those of existing species of Zamia, some Equisetaceous plants and numerous Ferns which may be referred to such families as Gleicheniaceae, Dipteridinae and Matonineae. Representatives of the Ginkgoales constitute characteristic members of the later Triassic floras, and these, with other types, carry us on without any break in continuity to the Rhaetic floras of Scania, Germany, Asia, Chile, Tonkin and Honduras (Map A, VIII.), and to the Jurassic and Wealden floras of many regions in both the north and south hemispheres. A comparative view of the plants found in various parts of the world, in beds ranging from the Upper Trias to the top of the Jurassic system, reveals a striking uniformity in the vegetation both in northern and southern latitudes during this long succession of ages. The Palaeozoic types are barely represented; the arborescent Vascular Cryptogams have been replaced by Cycads, Ginkgoales and Conifers as the dominant classes, while Ferns continue to hold their own. No undoubted Angiosperms have yet been found below the Cretaceous system. From the close of the Permian period, which marks the limit of the Upper Palaeozoic floras, to the period immediately preceding the apparently sudden appearance of Angiosperms, we have a succession of floras differing from one another in certain minor details, but linked together by the possession of many characters in common. It is impossible to consider in detail this long period in the history of plant-evolution, but we may briefly pass in review the most striking features of the vegetation as exhibited in the dominant types of the various classes of plants. Fragments of a Jurassic flora have recently been discovered by Dr Andersson, a member of Nordenskiold’s Antarctic expedition, in Louis Philippe Land in lat. 63° 15′ S. Among other well-known Jurassic genera Nathorst has identified the following: Equisetites, Cladophlebis, Todites, Thinnfeldia, Otozamites, Williamsonia pecten, Araucarites. The discovery of this Antarctic flora is a further demonstration of the world-wide distribution of a uniform Jurassic flora.
Under the head of Algae there is little of primary importance to record, but it is of interest to notice the occurrence of certain forms which throw light on the antiquity of existing families of Algae. Species referred on good evidence to the Charophyta are represented by a few casts of oögonia and stem fragments, found in Jurassic and Wealden beds, which bear a striking Algae. resemblance to existing species. There is some evidence for the occurrence of similar Chara “fruits” in middle Triassic rocks; some doubtful fossils from the much older Devonian rocks have also been quoted as possible examples of the Charophyta. The oldest known Diatoms are represented by some specimens found entangled in the spicules of a Liassic sponge, and identified by Rothpletz as species of the recent genus Pyxidicula. The calcareous Siphoneae are represented by several forms, identified as species of Diplopora, Triploporella, Neomeris and other genera, from strata ranging from the lower Trias limestones of Tirol to the Cretaceous rocks of Mexico and elsewhere. It is probable that the Jurassic Goniolina, described from French localities, and other genera which need not be mentioned, may also be reckoned among the Mesozoic Siphoneae. A genus Zonatrichites, compared with species of Cyanophyceae, has been described as a Calcareous alga from Liassic limestones of Silesia.
The geological history of Mosses and Liverworts is at present very incomplete, and founded on few and generally unsatisfactory fragments. It is hardly too much to say that no absolutely trustworthy examples of Mosses have so far been found in Mesozoic strata. Of Liverworts there are a few species, such as Palaeohepatica Rostafinskii from the Lower Jurassic Bryophyta.
