been found in the Purbecks, not one is a member of the orders
_Cheiroptera, Rodentia, Ungulata_, or _Carnivora_, which are so well
represented in the Tertiaries. No _Insectivora_ are certainly known, nor
any opossum-like Marsupials. Thus there is a vast negative difference
between the Cainozoic and the Mesozoic mammalian faunae of Europe. But
there is a still more important positive difference, inasmuch as all
these Mammalia appear to be Marsupials belonging to Australian groups,
and thus appertaining to a different distributional province from the
Eocene and Miocene marsupials, which are Austro-Columbian. So far as the
imperfect materials which exist enable a judgment to be formed, the same
law appears to have held good for all the earlier Mesozoic _Mammalia_. Of
the Stonesfield slate mammals, one, _Amphitherium_, has a definitely
Australian character; one, _Phascolotherium_, may be either Dasyurid or
Didelphine; of a third, _Stereognathus_, nothing can at present be said.
The two mammals of the Trias, also, appear to belong to Australian
groups.
Every one is aware of the many curious points of resemblance between the
marine fauna of the European Mesozoic rocks and that which now exists in
Australia. But if there was this Australian facies about both the
terrestrial and the marine faunae of Mesozoic Europe, and if there is this
unaccountable and immense break between the fauna of Mesozoic and that of
Tertiary Europe, is it not a very obvious suggestion that, in the
Mesozoic epoch, the Australian province included Europe, and that the
Arctogaeal province was contained within other limits? The Arctogaeal
province is at present enormous, while the Australian is relatively
small. Why should not these proportions have been different during the
Mesozoic epoch?
Thus I am led to think that by far the simplest and most rational mode of
accounting for the great change which took place in the living
inhabitants of the European area at the end of the Mesozoic epoch, is the
supposition that it arose from a vast alteration of the physical
geography of the globe; whereby an area long tenanted by Cainozoic forms
was brought into such relations with the European area that migration
from the one to the other became possible, and took place on a great
scale.
This supposition relieves us, at once, from the difficulty in which we
were left, some time ago, by the arguments which I used to demonstrate
the necessity of the existence of all the great types of the Eocene epoch
in some antecedent period.
It is this Mesozoic continent (which may well have lain in the
neighbourhood of what are now the shores of the North Pacific Ocean)
which I suppose to have been occupied by the Mesozoic _Monodelphia_; and
it is in this region that I conceive they must have gone through the long
series of changes by which they were specialised into the forms which we
refer to different orders. I think it very probable that what is now
South America may have received the characteristic elements of its
mammalian fauna during the Mesozoic epoch; and there can be little doubt
that the general nature of the change which took place at the end of the
Mesozoic epoch in Europe was the upheaval of the eastern and northern
regions of the Mesozoic sea-bottom into a westward extension of the
Mesozoic continent, over which the mammalian fauna, by which it was
already peopled, gradually spread. This invasion of the land was prefaced
by a previous invasion of the Cretaceous sea by modern forms of mollusca
and fish.
It is easy to imagine how an analogous change might come about in the
existing world. There is, at present, a great difference between the
fauna of the Polynesian Islands and that of the west coast of America.
The animals which are leaving their spoils in the deposits now forming in
these localities are widely different. Hence, if a gradual shifting of
the deep sea, which at present bars migration between the easternmost of
these islands and America, took place to the westward, while the American
side of the sea-bottom was gradually upheaved, the palaeontologist of the
future would find, over the Pacific area, exactly such a change as I am
supposing to have occurred in the North-Atlantic area at the close of the
Mesozoic period. An Australian fauna would be found underlying an
American fauna, and the transition from the one to the other would be as
abrupt as that between the Chalk and lower Tertiaries; and as the
drainage-area of the newly formed extension of the American continent
gave rise to rivers and lakes, the mammals mired in their mud would
differ from those of like deposits on the Australian side, just as the
Eocene mammals differ from those of the Purbecks.
How do similar reasonings apply to the other great change of life--that
which took place at the end of the Palaeozoic period?
In the Triassic epoch, the distribution of the dry land and of
terrestrial vertebrate life appears to have been, generally, similar to
that which existed in the Mesozoic epoch; so that the Triassic continents
and their faunae seem to be related to the Mesozoic lands and their faunae,
just as those of the Miocene epoch are related to those of the present
day. In fact, as I have recently endeavoured to prove to the Society,
there was an Arctogaeal continent and an Arctogaeal province of
distribution in Triassic times as there is now; and the _Sauropsida_ and
_Marsupialia_ which constituted that fauna were, I doubt not, the
progenitors of the _Sauropsida_ and _Marsupialia_ of the whole Mesozoic
epoch.
Looking at the present terrestrial fauna of Australia, it appears to me
to be very probable that it is essentially a remnant of the fauna of the
Triassic, or even of an earlier, age[7] in which case Australia must at
that time have been in continuity with the Arctogaeal continent.
[Footnote 7: Since this Address was read, Mr. Krefft has sent us news of
the discovery in Australia of a freshwater fish of strangely Palaeozoic
aspect, and apparently a Ganoid intermediate between _Dipterus_ and
_Lepidosiren_. [The now well-known _Ceratodus_. 1894.]]
But now comes the further inquiry, Where was the highly differentiated
Sauropsidan fauna of the Trias in Palaeozoic times? The supposition that
the Dinosaurian, Crocodilian, Dicynodontian, and to Plesiosaurian types
were suddenly created at the end of the Permian epoch may be dismissed,
without further consideration, as a monstrous and unwarranted assumption.
The supposition that all these types were rapidly differentiated out of
_Lacertilia_ in the time represented by the passage from the Palaeozoic to
the Mesozoic formation, appears to me to be hardly more credible, to say
nothing of the indications of the existence of Dinosaurian forms in the
Permian rocks which have already been obtained.
For my part, I entertain no sort of doubt that the Reptiles, Birds, and
Mammals of the Trias are the direct descendants of Reptiles, Birds, and
Mammals which existed in the latter part of the Palaeozoic epoch, but not
in any area of the present dry land which has yet been explored by the
geologist.
This may seem a bold assumption, but it will not appear unwarrantable to
those who reflect upon the very small extent of the earth's surface which
has hitherto exhibited the remains of the great Mammalian fauna of the
Eocene times. In this respect, the Permian land Vertebrate fauna appears
to me to be related to the Triassic much as the Eocene is to the Miocene.
Terrestrial reptiles have been found in Permian rocks only in three
localities; in some spots of France, and recently of England, and over a
more extensive area in Germany. Who can suppose that the few fossils yet
found in these regions give any sufficient representation of the Permian
fauna?
It may be said that the Carboniferous formations demonstrate the
existence of a vast extent of dry land in the present dry-land area, and
that the supposed terrestrial Palaeozoic Vertebrate Fauna ought to have
left its remains in the Coal-measures, especially as there is now reason
to believe that much of the coal was formed by the accumulation of spores
and sporangia on dry land. But if we consider the matter more closely, I
think that this apparent objection loses its force. It is clear that,
during the Carboniferous epoch, the vast area of land which is now
covered by Coal-measures must have been undergoing a gradual depression.
The dry land thus depressed must, therefore, have existed, as such,
before the Carboniferous epoch--in other words, in Devonian times--and
its terrestrial population may never have been other than such as existed
during the Devonian, or some previous epoch, although much higher forms
may have been developed elsewhere.
Again, let me say that I am making no gratuitous assumption of
inconceivable changes. It is clear that the enormous area of Polynesia
is, on the whole, an area over which depression has taken place to an
immense extent; consequently a great continent, or assemblage of
subcontinental masses of land must have existed at some former time, and
that at a recent period, geologically speaking, in the area of the
Pacific. But if that continent had contained Mammals, some of them must
have remained to tell the tale; and as it is well known that these
islands have no indigenous _Mammalia_, it is safe to assume that none
existed. Thus, midway between Australia and South America, each of which
possesses an abundant and diversified mammalian fauna, a mass of land,
which may have been as large as both put together, must have existed
without a mammalian inhabitant. Suppose that the shores of this great
land were fringed, as those of tropical Australia are now, with belts of
mangroves, which would extend landwards on the one side, and be buried
beneath littoral deposits on the other side, as depression went on; and
great beds of mangrove lignite might accumulate over the sinking land.
Let upheaval of the whole now take place, in such a manner as to bring
the emerging land into continuity with the South-American or Australian
continent, and, in course of time, it would be peopled by an extension of
the fauna of one of these two regions--just as I imagine the European
Permian dry land to have been peopled.
I see nothing whatever against the supposition that distributional
provinces of terrestrial life existed in the Devonian epoch, inasmuch as
M. Barrande has proved that they existed much earlier. I am aware of no
reason for doubting that, as regards the grades of terrestrial life
contained in them, one of these may have been related to another as New
Zealand is to Australia, or as Australia is to India, at the present day.
Analogy seems to me to be rather in favour of, than against, the
supposition that while only Ganoid fishes inhabited the fresh waters of
our Devonian land, _Amphibia_ and _Reptilia_, or even higher forms, may
have existed, though we have not yet found them. The earliest
Carboniferous _Amphibia_ now known, such as _Anthracosaurus_, are so
highly specialised that I can by no means conceive that they have been
developed out of piscine forms in the interval between the Devonian and
the Carboniferous periods, considerable as that is. And I take refuge in
one of two alternatives: either they existed in our own area during the
Devonian epoch and we have simply not yet found them; or they formed part
of the population of some other distributional province of that day, and
only entered our area by migration at the end of the Devonian epoch.
Whether _Reptilia_ and _Mammalia_ existed along with them is to me, at
present, a perfectly open question, which is just as likely to receive an
affirmative as a negative answer from future inquirers.
Let me now gather together the threads of my argumentation into the form
of a connected hypothetical view of the manner in which the distribution
of living and extinct animals has been brought about.
I conceive that distinct provinces of the distribution of terrestrial
life have existed since the earliest period at which that life is
recorded, and possibly much earlier; and I suppose, with Mr. Darwin, that
the progress of modification of terrestrial forms is more rapid in areas
of elevation than in areas of depression. I take it to be certain that
Labyrinthodont _Amphibia_ existed in the distributional province which
included the dry land depressed during the Carboniferous epoch; and I
conceive that, in some other distributional provinces of that day, which
remained in the condition of stationary or of increasing dry land, the
various types of the terrestrial _Sauropsida_ and of the _Mammalia_ were
gradually developing.
The Permian epoch marks the commencement of a new movement of upheaval in
our area, which dry land existed in North America, Europe, Asia, and
Africa, as it does now. Into this great new continental area the Mammals,
Birds, and Reptiles developed during the Palaeozoic epoch spread, and
formed the great Triassic Arctogaeal province. But, at the end of the
Triassic period, the movement of depression recommenced in our area,
though it was doubtless balanced by elevation elsewhere; modification and
development, checked in the one province, went on in that "elsewhere";
and the chief forms of Mammals, Birds and Reptiles, as we know them, were
evolved and peopled the Mesozoic continent. I conceive Australia to have
become separated from the continent as early as the end of the Triassic
epoch, or not much later. The Mesozoic continent must, I conceive, have
lain to the east, about the shores of the North Pacific and Indian
Oceans; and I am inclined to believe that it continued along the eastern
side of the Pacific area to what is now the province of Austro-Columbia,
the characteristic fauna of which is probably a remnant of the population
of the latter part of this period.
Towards the latter part of the Mesozoic period the movement of upheaval
around the shores of the Atlantic once more recommenced, and was very
probably accompanied by a depression around those of the Pacific. The
Vertebrate fauna elaborated in the Mesozoic continent moved westward and
took possession of the new lands, which gradually increased in extent up
to, and in some directions after, the Miocene epoch.
It is in favour of this hypothesis, I think, that it is consistent with
the persistence of a general uniformity in the positions of the great
masses of land and water. From the Devonian period, or earlier, to the
present day, the four great oceans, Atlantic, Pacific, Arctic, and
Antarctic, may have occupied their present positions, and only their
coasts and channels of communication have undergone an incessant
alteration. And, finally, the hypothesis I have put before you requires
no supposition that the rate of change in organic life has been either
greater or less in ancient times than it is now; nor any assumption,
either physical or biological, which has not its justification in
analogous phenomena of existing nature.
I have now only to discharge the last duty of my office, which is to
thank you, not only for the patient attention with which you have
listened to me so long to-day, but also for the uniform kindness with
which, for the past two years, you have rendered my endeavours to perform
the important, and often laborious, functions of your President a
pleasure instead of a burden.