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the question of the extinction of species at periods prior to any evidence of human existence; it does not help us in the explanation of the majority of extinctions; as of the races of aquatic invertebrata which have successively passed away.
Within the last century academicians of St. Petersburg and good naturalists have described and given figures of the bony and the perishable parts, including the alimentary canal, of a large and peculiar fucivorous Sirenian—an amphibious animal like the Manatee, which Cuvier classified with his herbivorous Cetacea, and called Stelleria, after its discoverer. This animal inhabited the Siberian shores and the mouths of the great rivers there disemboguing. It is now believed to be extinct, and this extinction seems not to have been due to any special quest and persecution by man. We may discern, in this fact, the operation of changes in physical geography which have, at length, so affected the conditions of existence of the Stelleria as to have caused its extinction. Such changes had operated, at an earlier period, to the extinction of the Siberian elephant and rhinoceros of the same regions and latitudes. A future generation of zoologists may have to record the final disappearance of the Arctic buffalo (Ovibos moschatus). Fossil remains of Ovibos and Stelleria shew that they were contemporaries of Elephas primigenius and Rhinoceros tickorrhinm.
The Great Auk (Alca impennis, L.) seems to be rapidly verging to extinction. It has not been specially hunted down, like the dodo and dinornis, but by degrees has become more scarce. Some of the geological changes affecting circumstances favourable to the well-being of the Alca impennis, have been matters of observation. A friend1, who last year visited Iceland, informs me that the last great auks, known with anything like certainty to have been there seen, were two which were taken in 1844 during a visit made to the high rock called 'Eldey,' or 'Meelsoekten,' lying off Cape Reykianes, the S. W. point of Iceland. This is one of three principal rocky islets formerly existing in that direction, of which the one, specially named from this rare bird 'Geirfugla Sker,' sank to the level of the surface of the sea during a volcanic disturbance in or about the year 1830. Such disappearance of the fit and favourable breeding-places of the Alca impennis must form an important element in its decline towards extinction. The numbers of the bones of Alca impennis on the shores of Iceland, Greenland, and Denmark, attest the abundance of the bird in 1 John Wolley, jun., Esq. F.Z.S.
former times. A consideration of such instances of modern partial or total extinctions may best throw light on, and suggest the truest notions of, the causes of ancient extinctions.
As to the successions, or coming in, of new species, one might speculate on the gradual modifiability of the individual; on the tendency of certain varieties to survive local changes, and thus progressively diverge from an older type; on the production and fertility of monstrous offspring; on the possibility, e.g. of a variety of auk being occasionally hatched with a somewhat longer winglet, and a dwarfed stature; on the probability of such a variety better adapting itself to the changing climate or other conditions than the old type—of such an origin of Alca torda, e.g.;—but to what purpose? Past experience of the chance aims of human fancy, unchecked and unguided by observed facts, shews how widely they have ever glanced away from the gold centre of truth.
The sum of the evidence which has been obtained appears to prove that the successive extinction of Amphitheria, Spcdacotheria, Triconodons, and other mesozoic forms of mammals, has been followed by the introduction of much more numerous, varied, and higher-organised forms of the class, during the tertiary periods.
There are, however, geologists who maintain that this is an assumption, based upon a partial knowledge of the facts. Mere negative evidence, they allege, can never satisfactorily establish the proposition that the mammalian class is of late introduction, nor prevent the conjecture that it may have been as richly represented in secondary as in tertiary times, could we but get evidence of the terrestrial fauna of the oolitic continent. To this objection I have to reply: in the palaeozoic strata, which, from their extent and depth, indicate, in the earth's existence as a seat of organic life, a period as prolonged as that which has followed their deposition, no trace of mammals has been observed. It may be conceded that, were mammals peculiar to dry land, such negative evidence would weigh little in producing conviction of their nonexistence during the Silurian and Devonian aeons, because the explored parts of such strata have been deposited from an ocean, and the chance of finding a terrestrial and air-breathing creature's remains in oceanic deposits is very remote. But, in the present state of the warm-blooded, air-breathing, viviparous class, no genera and species are represented by such numerous and widely dispersed individuals, as those of the order Cetacea, which, under the guise of fishes, dwell, and can only live, in the ocean.
In all cetacea the skeleton is well ossified, and the vertebra are very numerous: the smallest cetaceans would be deemed large amongst land-mammals; the largest surpass in bulk any creatures of which we have yet gained cognizance: the hugest ichthyosaur, iguanodon, megalosaur, mammoth, or megathere, is a dwarf in comparison with the modern whale of a hundred feet in length.
During the period in which we have proof that Cetacea have existed, the evidence in the shape of bones and teeth, which latter enduring characteristics in most of the species are peculiar for their great number in the same individual, must have been abundantly deposited at the bottom of the sea; and as cachalots, grampuses, dolphins, and porpoises are seen gambolling in shoals in deep oceans, far from land, their remains will form the most characteristic evidences of vertebrate life in the strata now in course of formation at the bottom of such oceans. Accordingly, it consists with the known characteristics of the cetacean class to find the marine deposits which fell from seas tenanted, as now, with vertebrates of that high grade, containing the fossil evidences of the order in vast abundance.
The red crag of our eastern counties contains petrified fragments of the skeletons and teeth of various Cetacea, in such quantities as to constitute a great part of that source of phosphate of lime for which the red crag is worked for the manufacture of artificial manure. The scanty and dubious evidence of Cetacea in newer secondary beds1 seems to indicate a similar period for their beginning as for the soft-scaled cycloid and ctenoid fishes which have superseded the ganoid orders of mesozoic times.
We cannot doubt but that had the genera Ichthyosaurus, Pliosaurti8, or Plesiosaurus, been represented by species in the same ocean that was tempested by the Balaenodons and Dioplodons of the miocene age, the bones and teeth of those marine reptiles would have testified to their existence as abundantly as they do at a previous epoch in the earth's history. But no fossil relic of an enaliosaur has been found in tertiary strata, and no living enaliosaur has been detected in the present seas: and they are consequently held by competent naturalists to be extinct.
In like manner does such negative evidence weigh with me in proof of the non-existence of marine mammals in the liassic and oolitic times. In the marine deposits of those secondary or meso
1 See 'Introduction' to Owen's History of British Fossil Mammalia, 8vo., 1846, p. xv.
zoic epochs, the evidence of vertebrates governing the ocean, and preying on inferior marine vertebrates, is as abundant as that of air-breathing vertebrates in the tertiary strata; but in the one the fossils are exclusively of the cold-blooded reptilian class, in the other, of the warm-blooded mammalian class. The Enaliosauria, Cetiosauria, and Crocodilia, played the same part and fulfilled similar offices in the seas from which the lias and oolites were precipitated, as the Delphinidce and Ealcenidce did in the tertiary, and still do in the present, seas. The unbiassed conclusion from both negative and positive evidence in this matter is, that the Cetacea succeeded and superseded the Enaliosauria. To the mind that will not accept such conclusion, the stratified oolitic rocks must cease to be monuments or trustworthy records of the condition of life on the earth at that period.
So far, however, as any general conclusion can be deduced from the large sum of evidence above referred to, and contrasted, it is against the doctrine of the Uniformitarian. Organic remains, traced from their earliest known graves, are succeeded, one series by another, to the present period, and never re-appear when once lost sight of in the ascending search. As well might we expect a living Ichthyosaur in the Pacific, as a fossil whale in the Lias : the rule governs as strongly in the retrospect as the prospect. And not only as respects the Vertebrata, but the sum of the animal species at each successive geological period has been distinct and peculiar to such period.
Not that the extinction of such forms or species was sudden or simultaneous: the evidences so interpreted have been but local: over the wider field of life at any given epoch, the change has been gradual; and, as it would- seem, obedient to some general, but as yet, ill-comprehended law. In regard to animal life, and its assigned work on this planet, there has, however, plainly been 'an ascent and progress in the main.'
Although the mammalia, in regard to the plenary development of the characteristic orders, belong to the Tertiary division of geological time, just as 'Echini are most common in the superior strata, Ammonites in those beneath, and Producti with numerous Encrini in the lowest'1 of the secondary strata, yet the beginnings of the class manifest themselves in the formations of the earlier preceding division of geological time.
No one, save a prepossessed Uniformitarian, would infer from 1 A generalisation of William Smith's.
the Lucina of the permian, and the Opis of the trias, that the Lamellibranchiate Mollusks existed in the same rich variety of development at these periods as during the tertiary and present times; and no prepossession can close the eyes to the fact that the Lamellibranchiate have superseded the Palliobranchiate bivalves.
On negative evidence Orthisina, Theca, Producta, or Spirifer are believed not to exist in the present seas: neither are the existing genera of siphonated bivalves and univalves deemed to have abounded in permian, triassic or oolitic times. To suspect that they may have then existed, but have hitherto escaped observation, because certain Lamellibranchs with an open mantle, and some holostomatous and asiphonate Gastropods, have left their remains in secondary strata, is not more reasonable, as it seems to me, than to conclude that the proportion of mammalian life may have been as great in secondary as in tertiary strata, because a few small forms of the lowest orders have made their appearance in triassic and oolitic beds.
Turning from a retrospect into past time for the prospect of time to come,—and I have received more than one inquiry into the amount of prophetic insight imparted by Palaeontology—I may crave indulgence for a few words, of more sound, perhaps, than significance. But the reflective mind cannot evade or resist the tendency to speculate on the future course and ultimate fate of vital phenomena in this planet.
There seems to have been a time when life was not; there may, therefore, be a period when it will cease to be.
Our most soaring speculations still shew a kinship to our nature: we see the element of finality in so much that we have cognizance of, that it must needs mingle with our thoughts, and bias our conclusions on many things.
The end of the world has been presented to man's mind under divers aspects:—as a general conflagration; as the same, preceded by a millennial exaltation of the world to a Paradisiacal state,— the abode of a higher and blessed race of intelligences.
If the guide-post of Palaeontology may seem to point to a course ascending to the condition of the latter speculation, it points but a very short way, and in leaving it we find ourselves in a wilderness of conjecture, where to try to advance is to find ourselves 'in wandering mazes lost.'
With much more satisfaction do I return to the legitimate deductions from the phenomena we have had under review.