Chapter XX: Part II: On the Distribution of Extinct Animals (3)

In the oldest Tertiary beds of Europe and North America, we have (even with our present imperfect record) a rich and varied mammalian fauna. As compared with our living or recent highly specialized forms, it may be said to consist of generalised types; but as compared with any primeval mammalian type, it must be pronounced highly specialised. Not only are such diversified {160}groups as Carnivora, Perrissodactyle and Artiodactyle Ungulates, Primates, Chiroptera, Rodents, and Marsupials already well marked, but in many of these there is a differentiation into numerous families and genera of diverse character. It is impossible therefore to doubt, that many peculiar forms of mammalia must have lived long anterior to the Eocene period; but there is unfortunately a great gap in the record between the Eocene and Cretaceous beds, and these latter being for the most part marine continue the gap as regards mammals over an enormous lapse of time. Yet far beyond both these chasms in the Upper Oolitic strata, remains of small mammalia have been found; again, in the Stonesfield slate, a member of the Lower Oolite, other forms appear. Then comes the marine Lias formation with another huge gap; but beyond this again in the Upper Trias, the oldest of the secondary formations, mammalian teeth have been discovered in both England and Germany, and these are, as nearly as can be ascertained, of the same age as the _Dromatherium_ already noticed, from North America. They have been named _Microlestes_, and show some resemblance to those of the West Australian _Myrmecobius_. In the Oolitic strata numerous small jawbones have been found, which have served to characterise eight genera, all of which are believed to have been Marsupials, and in some of them a resemblance can be traced to some of the smaller living Australian species. These, however, are mere indications of the number of mammalia that must have lived in the secondary period, so long thought to be exclusively "the age of reptiles;" and the fact that the few yet found are at all comparable with such specialised forms as still exist, must convince us, that we shall have to seek far beyond even the earliest of these remains, for the first appearance of the mammalian type of vertebrata.

EXTINCT BIRDS.

Compared with those of mammalia, the remains of birds are exceedingly scarce in Europe and America; and from the wandering habits of so many of this class, they are of much less value {161}as indications of past changes in physical geography. A large proportion of the remains belong to aquatic or wading types, and as these have now often a world-wide range, the occurrence of extinct forms can have little bearing on our present inquiry. There are, however, a few interesting cases of extinct land-birds belonging to groups now quite strangers to the country in which they are found; and others scarcely less interesting, in which groups now peculiar to certain areas are shown to have been preceded by allied species or genera of gigantic size.

_Palæarctic Region and N. India._--In the caves and other Post-Pliocene deposits of these countries, the remains of birds almost all belong to genera now inhabiting the same districts. Almost the only exceptions are, the great auk and the capercailzie, already mentioned as being found in the Danish mounds; the latter bird, with _Tetrao albus_, in Italian caverns; and a species of pheasant (_Phasianus_) said to have occurred in the Post-Pliocene of France, considerably west of the existing range of the genus in a wild state.

In the preceding Pliocene deposits, but few remains have been found, and all of existing genera but one, a gallinaceous bird (_Gallus bravardi_) allied to the domestic fowl and peacock.

The Miocene beds of France and Central Europe have produced many more remains of birds, but these, too, are mostly of existing European genera, though there are some notable exceptions. Along with forms undistinguishable from crows (_Corvus_), shrikes (_Lanius_), wagtails (_Motacilla_), and woodpeckers (_Picus_), are found remains allied to the Oriental edible-nest swift (_Collocalia_) and _Trogon_; a parrot resembling the African genus _Psittacus_; an extinct form _Necrornis_, perhaps allied to the plantain-eaters (_Musophaga_); _Homalophus_, doubtfully allied to woodpeckers, and _Limnatornis_ to the hoopoes. The gallinaceous birds are represented by three species of pheasants, some very close to the domesticated species; _Palæoperdix_ allied to the partridges; and _Palæortyx_, small birds allied to the American genus _Ortyx_, but with larger wings. There are also species of _Pterocles_ allied to living birds, and a small pigeon. There are numerous living genera of Accipitres; such as eagle (_Aquila_), {162}kite (_Milvus_), eagle-owl (_Bubo_), and screech-owl (_Strix_); with the African secretary-bird (_Serpentarius_), and some extinct forms, as _Palæocercus_, _Palæohierix_ and _Palæetus_.

Aquatic and wading birds were abundant, including numerous rails, bustards, herons, sandpipers, gulls, divers, and pelicans. There were also many ducks, some allied to the genus _Dendrocygna_; the Oriental genus of storks, _Leptoptilus_; _Ibidipodia_, a remarkable form allied to _Ibis_ and _Ciconia_; _Elornis_, near _Limosa_; _Pelagornis_, a large bird allied to gannets and pelicans; _Hydrornis_, allied to the ducks and petrels; _Dolichopterus_, allied to plovers. Perhaps the most interesting of these extinct birds are, however, the flamingoes, represented by forms hardly distinguishable from living species, and by one extinct genus _Palælodus_, which had very long toes, and probably walked on aquatic plants like the tropical jacanas.

The Miocene beds of North India have furnished few birds; the only one of geographical interest being an extinct species of ostrich, not very different from that now inhabiting Arabia.

On the whole, the birds of Europe at this period were very like those now living, with the addition of a few tropical forms. These latter were, however, perhaps more numerous and important than they appear to be, as they belong to inland and forest-haunting types, which would not be so frequently preserved as the marsh and lake-dwelling species. Taking this into consideration, the assemblage of Miocene birds accords well with what we know of the mammalian fauna. We have the same indications of a luxuriant vegetation and subtropical climate, and the same appearance of Oriental and especially of African types. _Trogon_ is perhaps the most interesting of all the forms yet discovered, since it furnishes us with a central point whence the living trogons of Asia, Africa, and South America might have diverged.

In the Eocene we find ourselves almost wholly among extinct forms of birds. The earliest known Passerine bird is here met with, in _Protornis_, somewhat similar to a lark, found in the Lower Eocene of Switzerland; while another Passerine form, _Palægithalus_, and one allied to the nuthatch (_Sitta_), have been {163}discovered in the Upper Eocene of Paris. Picariæ of equal antiquity are found. _Cryptornis_, from the Paris Eocene, and _Halcyornis_ from the Lower Eocene of the Isle of Sheppey, were both allied to kingfishers; while a form allied to _Centropus_ a genus of cuckoos, or, as Milne-Edwards thinks, to the Madagascar _Leptosomus_, has been found in the Upper Eocene of France. Several _Accipitres_ of somewhat doubtful affinities have been found in the same country; while _Lithornis_, from the Lower Eocene of the Isle of Sheppey, was a small vulturine bird supposed to be allied to the American group, _Cathartes_. Among the waders, some extinct forms of plovers have been found, and a genus (_Agnopterus_), allied to the flamingoes; while there are many swimming birds, such as pelicans, divers, and several extinct types of doubtful affinities. Most intersting of all is a portion of a cranium discovered in the Lower Eocene of Sheppey, and lately pronounced by Professor Owen to belong to a large Struthious bird, allied to the New Zealand _Dinornis_ and also perhaps to the ostrich. Another gigantic bird is the _Gastornis_, from the Lower Eocene of Paris, which was as large as an ostrich, but which is believed to have been a generalised type, allied to wading and swimming birds as well as to the Struthiones.

Beyond this epoch we have no remains of birds in European strata till we come to the wonderful _Archæopteryx_ from the Upper Oolite of Bavaria; a bird of a totally new type, with a bony tail, longer than the body, each vertebra of which carried a pair of diverging feathers.

_North America._--A number of bird-remains have lately been found in the rich Tertiary and Cretaceous deposits of the United States; but here, too, comparatively few are terrestrial forms. No Passerine bird has yet been found. The Picariæ are represented by _Uintornis_, an extinct form allied to woodpeckers, from the Eocene of Wyoming. Species of turkey (_Meleagris_) occur in the Post-Pliocene and as far back as the Miocene strata, showing that this interesting type is a true denizen of temperate North America. The other birds are, _Accipitres_; waders and aquatics of existing genera; and a number of extinct forms of the two latter orders--such as, _Aletornis_ an Eocene wader; {164}_Palæotringa_, allied to the sandpipers, and _Telmatobius_ to the rails, both Cretaceous; with _Graculavus_, allied to _Graculus_; _Laornis_ allied to the swans; _Hesperornis_ a gigantic diver; and _Icthyornis_ a very low form, with biconcave vertebra, such as are only found in fishes and some reptiles--also from Cretaceous deposits.

_South America._--The caverns of Brazil produced thirty-four species of birds, most of them referable to Brazilian genera, and many to still existing species. The most interesting were two species of American ostrich (_Rhea_), one larger than either of the living species; a large turkey-buzzard (_Cathartes_); a new species of the very isolated South American genus _Opisthocomus_; and a _Cariama_, or allied new genus.

_Madagascar and the Mascarene Islands._--We have here only evidence of birds that have become extinct in the historical period or very little earlier. First we have a group of birds incapable of flight, allied to pigeons, but forming a separate family, _Dididæ_; and which, so far as we yet know, inhabited Mauritius, Rodriguez, and probably Bourbon. _Aphanapteryx_, an extinct genus of rails, inhabited Mauritius; and another genus, (_Erythromachus_), Rodriguez. A large parrot, said by Prof. Milne Edwards to be allied to _Ara_ and _Microglossus_, also inhabited Mauritius; and another allied to _Eclectus_, the island of Rodriguez. None of these have been found in Madagascar; but a gigantic Struthious bird, _Æpyornis_, forming a peculiar family distinct both from the ostriches of Africa and the _Dinornis_ of New Zealand inhabited that island; and there is reason to believe that this may have lived less than 200 years ago.

_New Zealand._--A number of extinct Struthious birds, forming two families, _Dinornithidæ_ and _Palapterygidæ_, have been found in New Zealand. Some were of gigantic size. They seem allied both to the living _Apteryx_ of New Zealand and the emu of Australia. They are quite recent, and some of them have probably lived within the last few centuries. Remains of _Dinornis_ have also been found in a Post-Pliocene deposit in Queensland, N. E. Australia[5]--a very important discovery, as it {165}gives support to the theory of a great eastward extension of Australia in Tertiary times.

EXTINCT TERTIARY REPTILES.

These will not occupy us long, as no very great number are known, and most of them belong to a few principal forms of comparatively little geographical interest.

Tortoises are perhaps the most abundant of the Tertiary reptiles. They are numerous in the Eocene and Miocene formations both in Europe and North America. The genera _Emys_ and _Trionyx_ abound in both countries, as well as in the Miocene of India. Land tortoises occur in the Eocene of North America and in the Miocene of Europe and India, where the huge _Colossochelys_, twelve feet long, has been found. In the Pliocene deposits of Switzerland the living American genus _Chelydra_ has been met with. These facts, together with the occurrence of a living _species_ in the Miocene of India, show that this order of reptiles is of great antiquity, and that most of the genera once had a wider range than now.

Crocodiles, allied to the three forms now characteristic of India, Africa, and America, have been found in the Eocene of our own country, and several species of _Crocodilus_ have occurred in beds of the same age in North America.

Lizards are very ancient, many small terrestrial forms occurring in all the Tertiary deposits. A species of the genus _Chamæleo_ is recorded from the Eocene of North America, together with several extinct genera.

Snakes were well developed in the Eocene period, where remains of several have been found which must have been from twelve to twenty feet long. An extinct species of true viper has occurred in the Miocene of France, and one of the Pythonidæ in the Miocene brown coal of Germany.

Batrachia occur but sparingly in a fossil state in the Tertiary deposits. The most remarkable is the large Salamander (_Andreas_) from the Upper Miocene of Switzerland, which {166}is allied to the _Menopoma_ living in North America. Species of frog (_Rana_), and _Palæophryus_ an extinct genus of toads, have been found in the Miocene deposits of Germany and Switzerland.

Fresh water fish are almost unknown in the Tertiary deposits of Europe, although most of the families and some genera of living marine fish are represented from the Eocene downwards.

ANTIQUITY OF THE GENERA OF INSECTS.

Fossil insects are far too rarely found, to aid us in our determination of difficult questions of geographical distribution; but in discussing these questions it will be important to know, whether we are to look upon the existing generic forms of insects as of great or small antiquity, compared with the higher vertebrates; and to decide this question the materials at our command are ample.

The conditions requisite for the preservation of insects in a fossil state are no doubt very local and peculiar; the result being, that it is only at long intervals in the geological record that we meet with remains of insects in a recognisable condition. None appear to have been found in the Pliocene formation; but in the Upper Miocene of Oeninghen in Switzerland, associated with the wonderfully rich fossil flora, are found immense quantities of insects. Prof. Heer examined more than 5,000 specimens belonging to over 800 species, and many have been found in other localities in Switzerland; so that more than 1,300 species of Miocene insects have now been determined. Most of the orders are represented, but the beetles (Coleoptera) are far the most abundant. Almost all belong to existing genera, and the majority of these genera now inhabit Europe, only three or four being exclusively Indian, African, or American.

In the Lower Miocene of Croatia there is another rich deposit of insects, somewhat more tropical in character, comprising large white-ants and dragon-flies differently marked from any {167}now inhabiting Europe. A butterfly is also well preserved, with all the markings of the wings; and it seems to be a _Junonia_, a tropical genus, though it may be a _Vanessa_, which is European, but the fossil most resembles Indian species of _Junonia_.

The Eocene formations seem to have produced no insect remains; but they occur again in the Upper Cretaceous at Aix-la-Chapelle, where two butterflies have been found, _Cyllo sepulta_ and _Satyrites Reynesii_, both belonging to the Satyridæ, and the former to a genus now spread over Africa, India, and Australia.

A little earlier, in the Wealden formation of our own country, numerous insects have been found, principally dragon flies (_Libellula_, _Æshna_); aquatic Hemiptera (_Velia Hydrometra_); crickets, cockroaches, and cicadas, of familiar types.

Further back in the Upper Oolite of Bavaria--which produced the wonderful long-tailed bird, _Archæopteryx_--insects of all orders have been found, including a moth referred to the existing genus _Sphinx_.

In the Lower Oolite of Oxfordshire many fossil beetles have been found whose affinities are shown by their names:--_Buprestidium_, _Curculionidium_, _Blapsidium_, _Melolonthidium_, and _Prionidium_; a wing of a butterfly has also been found, allied to the Brassolidæ now confined to tropical America, and named _Palæontina oolitica_.

Still more remote are the insects of the Lias of Gloucestershire, yet they too can be referred to well-known family types--Carabidæ, Melolonthidæ, Telephoridæ, Elateridæ, and Curculionidæ, among beetles; Gryllidæ and Blattidæ among Orthoptera; with _Libellula_, _Agrion_, _Æshna_, _Ephemera_, and some extinct genera. When we consider that almost the only vertebrata of this period were huge Saurian reptiles like the _Icthyosaurus_, _Plesiosaurus_, and _Dinosaurus_, with the flying Pterodactyles; and that the great mass of our existing genera, and even families, of fish and reptiles had almost certainly not come into existence, we see at once that types of insect-form are, proportionately, far more ancient. At this remote epoch we find the chief family types (the _genera_ of the time of Linnæus) perfectly differentiated {168}and recognisable. It is only when we go further back still, into the Palæozoic formations, that the insect forms begin to show that generalization of type which renders it impossible to classify them in any existing groups. Yet even in the coal formation of Nova Scotia and Durham, the fossil insects are said by competent entomologists to be "allied to _Ephemera_," "near _Blatta_," "near _Phasmidæ_;" and in deposits of the same age at Saarbrück near Trèves, a well-preserved wing of a grasshopper or locust has been found, as well as a beetle referred to the Scarabeidæ. More remarkable, however, is the recent discovery in the carboniferous shales of Belgium, of the clearly-defined wing of a large moth (_Breyeria borinensis_), closely resembling some of the Saturniidæ; so that we have now all the chief orders of Insects--including those supposed to be the most highly developed and the most recent--well represented at this very remote epoch. Even the oldest insects, from the Devonian rocks of North America, can mostly be classed as Neuroptera or Myriapoda, but appear to form new families.

We may consider it, therefore, as proved, that many of the larger and more important genera of insects date back to the beginning of the Tertiary period, or perhaps beyond it; but the family types are far older, and must have been differentiated very early in the Secondary period, while some of them perhaps go back to Palæozoic times. The great comparative antiquity of the _genera_ is however the important fact for us, and we shall have occasion often to refer to it, in endeavouring to ascertain the true bearing of the facts of insect distribution, as elucidating or invalidating the conclusions arrived at from a study of the distribution of the higher animals.

ANTIQUITY OF THE GENERA OF LAND AND FRESH-WATER SHELLS.

The remains of land and fresh-water shells are not much more frequent than those of insects. Like them, too, their forms are very stable, continuing unchanged through several geological {169}periods. In the Pliocene and Miocene formations, most of the shells are very similar to living species, and some are quite identical. In the Eocene we meet with ordinary forms of the genera _Helix_, _Clausilia_, _Pupa_, _Bulimus_, _Glandina_, _Cyclostoma_, _Megalostoma_, _Planorbis_, _Paludina_ and _Limnæa_, some resembling European species, others more like tropical forms. A British Eocene species of _Helix_ is still living in Texas; and in the South of France are found species of the Brazilian sub-genera _Megaspira_ and _Anastoma_. In the secondary formation no true land shells have been found, but fresh water shells are tolerably abundant, and almost all are still of living forms. In the Wealden (Lower Cretaceous) and Purbeck (Upper Oolite) are found _Unio_, _Melania_, _Paludina_, _Planorbis_, and _Limnæa_; while the last named genus occurs even in the Lias.

The notion that land shells were really not in existence during the secondary period is, however, proved to be erroneous by the startling discovery, in the Palæozoic coal measures of Nova Scotia, of two species of Helicidæ, both of living genera--_Pupa vetusta_, and _Zonites priscus_. They have been found in the hollow trunk of a _Sigillaria_, and in great quantities in a bed full of Stigmarian rootlets. The most minute examination detects no important differences of form or of microscopic structure, between these shells and living species of the same genera! These mollusca were the contemporaries of Labyrinthodonts and strange Ganoid fishes, which formed almost the whole vertebrate fauna. This unexpected discovery renders it almost certain, that numbers of other existing genera, of which we have found no traces, lived with these two through the whole secondary period; and we are thus obliged to assume as a probability, that any particular genus has lived through a long succession of geological ages. In estimating the importance of any peculiarities or anomalies in the geographical distribution of land shells as compared with the higher vertebrates, we shall, therefore, have to keep this possible, and even probable high antiquity, constantly in mind.

We have now concluded our sketch of Tertiary Palæontology as a preparation for the intelligent study of the Geographical {170}Distribution of Land Animals; and however imperfectly the task has been performed, the reader will at all events have been convinced that some such preliminary investigation is an essential and most important part of our work. So much of palæontology is at present tentative and conjectural, that in combining the information derived from numerous writers, many errors of detail must have been made. The main conclusions have, however, been drawn from as large a basis of facts as possible; and although fresh discoveries may show that our views as to the past history of some of the less important genera or families are erroneous, they can hardly invalidate our results to any important degree, either as regards the intercommunications between separate regions in the various geological epochs, or as to the centres from which some of the more important groups have been dispersed.