Paleontology

PALEONTOLOGY. - From the Greek παλαιός "ancient," δυ "to be," and λόγος "discourse": it is the science that studies fossils, that is, the remains of animals (paleozoology) and of plants (paleophytology or paleobotany), which lived in past epochs of the earth.

Generally these remains consist of the hard parts of organisms (skeletal substance, woody substance), of their impressions, of petrified parts, while only exceptionally is the soft substance completely preserved and, very rarely, entire bodies (especially in ice, in amber, in asphalt).

I. GENERAL NOTIONS

The purpose of paleontology is the systematic study of fossils ("systematic paleontology"), whose determination can be made by comparison with living species or with already described extinct forms. Research is carried out both through the macroscopic study of specimens generally freed from extraneous parts, and by making use of instruments — chiefly the simple microscope, for specially prepared transparent "thin sections" of rocks, or for "polished sections" of plants (by reflected light); the binocular microscope, especially for isolated microfossils; and X-rays, to bring out internal peculiarities of the fossils themselves. The histological examination of certain plants has allowed an intimate knowledge of the structure of fossil organisms, even before that of living ones.

Paleontology also studies the relationships among groups of fossils, since they fall within the great divisions of the systematics of animals and plants; sometimes completing the links between living species or other groups (genera, families, etc.); and further making a notable contribution to phylogeny, morphology and the distribution of living species.

The above, however, although very important, is not the only aim that the science of fossils sets for itself; today it constitutes principally the most effective instrument for the relative dating of geological times, for understanding the biological phenomena and the climatic types of the past.

Stratigraphic study (v. STRATIGRAFIA) allows, in fact, not only to observe how fossils were deposited in the strata in which they are contained (and therefore to establish that their age is contemporaneous with that of the enclosing sediments, except as will be said further on when treating of "refossilization"), but also to establish, where the succession of strata is regular, that alongside organisms that have remained virtually unchanged throughout all geological times ("persistent forms"), there are others, fairly numerous, that have been modified in those same times; they have, that is, been transformed or evolved.

Moreover, some groups or species have disappeared at various ages in the history of the earth. Among these latter, some have carried out a very limited life cycle in time, although they sometimes had great geographic diffusion, so much so as to be, at times, all in one and the same stratum.

Comparative stratigraphic study has also brought out that some of these short-lived faunas immediately preceded or followed, at all points of the Earth, other organisms, likewise having identical characteristics of propagation in time and space. So that it has been possible to construct a scale of terms ("stratigraphic scale") consisting of associations of species or of single species of characteristic fossils, also called "index fossils".

In this way "stratigraphic paleontology" was born, based on the normal succession of strata; but, at present, it has progressed so far as to be used by itself, with confidence, for the resolution of chronological problems even in terrains so disturbed by tectonics as no longer to preserve the original order of succession.

It must, however, immediately be noted that only fossils deposited contemporaneously with the enclosing terrains have stratigraphic value, for that determined geological age; whereas if they have been reworked, or, as is usually said, "refossilized", the contemporaneity with the enclosing strata ceases, and these will thus appear to be of an older age than the true one. Reworked or allochthonous fossils are recognized because they show traces of rolling, or because they are still attached to fragments of pre-existing rock, usually of a nature different from the last enclosing rock. Thus, for example, a calcareous breccia containing rounded nummulite casts eroded from nummulites or their fragments together with mollusks of certainly more recent age will have an age that is that indicated by these latter fossils and not by the foraminifera.

Many fossils, although not having stratigraphic value, can nevertheless serve to shed light on the environmental conditions of their deposition. In this case one will speak of "facies fossils": continental: terrestrial and aquatic (fluvial and lacustrine); marine: benthic fixed and mobile, pelagic (nektonic and planktonic).

It can be concluded that paleontology and geology are intimately linked to one another and that the study of one of them, without taking account of the other, is practically devoid of results of real scientific value.

II. HISTORY

The origins of paleontology, like those of many other sciences, may be said to go back to very remote times; but only in a very recent age (the dawn of the 19th century) did it develop as an autonomous science, detaching itself from geology.

Classical antiquity possessed scant knowledge of fossils. Nevertheless, for many Greek philosopher-naturalists and later for certain medieval writers and thinkers (Albertus Magnus, G. Boccaccio, etc.), fossils undoubtedly represented the remains of organisms that had lived in epochs prior to the present one. By others, however, fossils were considered now as the product of a hypothetical "plastic" or "formative" force or, indeed, of the "lusus Naturae." In more recent times, sure opinions on the nature of fossils were held by Leonardo da Vinci, Bernard Palissy, Girolamo Fracastoro and a few others.

Among the oldest natural-history collections, to which fossil remains also belonged, are remembered those of London (17th century) and of various cities of France and Germany; the one ordered to be made in the Vatican by Sixtus V and illustrated in the Metalloleuca Vaticana of M. Mercati of 1574 (published in 1710); a collection of Aldrovandi, etc. Yet even in the centuries following the Middle Ages, especially in France and Italy, illustrious scholars attributed fossil organic remains to the Noachian deluge (the "diluvial theory"); perhaps because the fossils found in those countries, belonging predominantly to recent strata, were very similar to species currently living. In England, on the other hand, the presence of fossils very different from current species helped lead to their being regarded as extinct forms. An important milestone in the progress of paleontology was the application of the microscope by R. Hooke, in the 17th century, to the study of microfossils, to histological preparations of animals and of silicified woods, to ammonites, whose suture lines were thereby brought into evidence.

However, only in the 18th century did the first memoirs with a systematic descriptive character of fossils appear.

To Cuvier belongs the merit of having laid the scientific foundations of vertebrate paleontology, following his observations on the numerous fossil bones of animals, for the most part extinct, found in the Eocene strata of the Paris basin and through the application of comparative anatomy — founded by himself — to the science of fossils. Cuvier, however, to explain the diversity of the faunas that succeeded one another from stratum to stratum, resorted to hypotheses of telluric perturbations of an almost general character, which would have caused a great number of living beings to become extinct in one epoch, after which others arose, through successive creations or through mass immigration from other regions (theories of the revolutions of the globe and of successive creations). Cuvier therefore admitted the differences of species between strata of different ages, but was a defender of the "fixity of species." Among his followers (A. Brongniart, Agassiz, D'Archiac, etc.), A. D'Orbigny distinguished himself by exaggerating the master's theories; he admitted 27 successions of completely renewed faunas (about 18,000 species illustrated by him: Stages A, B,... etc., of D'Orbigny), placing the oldest in the Silurian. Partly taking up again the ideas of Buffon and others, Lamarck and G. S. Hilaire expounded the "transformist" idea: the former holding that the species tends to vary slowly through the transmission of characters acquired in relation to physiological causes (use and disuse of certain organs under changed conditions or habits); the latter attributing it to the environmental factor, through abrupt variations. Yet it appears that Lamarck had observed that his phyletic series were "ordered" as if according to a plan pre-established by the Creator. These two French naturalists were the true founders of "transformist or evolutionist paleontology" (v. EVOLUTION) developed subsequently by Darwin.

Given the importance of this theory, it is thought appropriate to observe that "pre-Lamarckians" were not lacking even in the Middle Ages and in the modern age: St. Augustine, for whom "not the things were created, but their causes"; and also Father Athanasius Kircher, an assertor of a "multiplication of species and not only of individual specimens." Other evolutionists were G. Bruno, Bacon, Descartes, Buffon, etc. Among the founders of invertebrate paleontology, besides D'Orbigny, Lamarck is remembered; of paleophytology, Adolphe Brongniart, and, among the founders of stratigraphic paleontology, W. Smith, the abbé Giraud-Soulavie, G. B. Brocchi, etc.

It is not possible to recall the names of the paleontologists of the end of the 19th century and those of the 20th century, given their great number.

III. PALEOZOOLOGY

In the Algonkian of North America and of the Baltic Shield, fossils are already known belonging to animals that display a high degree of evolution (echinoderms, gastropods, arthropods). Certain remains called "problematic," which appear as impressions, e.g., palaeodictyum, are referred by some to algae, by others to poriferans, jellyfish, etc. Among the protozoans, the principal fossils belong to the rhizopods: foraminiferans and radiolarians, the former provided with a calcareous shell, the latter with a siliceous one. Present-day calcareous foraminiferans, during their juvenile stage, have a chitinous shell, like their Cambrian ancestors.

Among the foraminiferans (already believed to be cephalopods even by Lamarck, and figured for the first time by Aldrovandi), which in the fossil state can reach 12-16 cm. in diameter, there are numerous characteristic forms: among the imperforate ones: orbitolina, of the Cretaceous; alveolina, very widespread in the Eocene; among the perforate ones: globotruncana, of the Cretaceous; fusulinids, of the Anthracolithic; nummulites and assilines, Paleogene; orthophragmines and lepidocyclines, Tertiary (the lepidocyclines undergo a further development in the first half of the Neocene, when they are replaced by the miogypsines); amphistegines, from the Miocene to the present. The Eocene limestones of the Maiella, of the Gargano, etc., are rich in nummulites. Today much importance is also given to microforaminiferans, especially with regard to the recent Tertiary and the Quaternary, proceeding by means of studies on a statistical basis.

The radiolarians, exclusively marine and planktonic, appeared in pre-Cambrian times (in the radiolarians of Brittany), with a skeleton in the form of a perforated sphere; but few forms are of stratigraphic importance. Nassellarians and spumellarians predominate in present-day radiolarian oozes, at depths of over 4000 meters, in the Indian and Pacific Oceans. The poriferans, also very ancient and little evolved animals, with a skeleton made up of isolated and welded pieces (spicules), live in the littoral zones, as well as at great depths, down to over 4000 meters. They are, among the metazoans, the simplest; sessile, almost all marine. The poriferans have a notable development in the Mesozoic (Triassic of St. Cassian; Turonian of Normandy, etc.). The archaeocyathids are also attributed to the poriferans, characteristic fossils of the Lower and Middle Cambrian (Australia, Sardinia, Black Mountain). The coelenterates, which correspond to the "zoophytes" of the ancient authors, comprise numerous forms important from the stratigraphic and lithogenetic point of view. The tetracorals, extinct at the end of the Paleozoic, are succeeded by the hexacorals, which appeared in the Triassic and are still living.

Other important reef-builders are the tabulates, of the Paleozoic; the stromatoporoids; the ellipsactinids, Jurassic-Cretaceous; the hydroactinids, Tertiary. Finally, the jellyfish are of lesser importance, sometimes showing beautiful impressions, such as those in the limestones of the Malm of Solenhofen; in Italy, in the Cambrian schists of Sardinia and in the Piacenzian marls of the Farnesina (Rome).

The trimerous animals, generally sessile, comprise the types of the bryozoans and the brachiopods, both still living. Among the bryozoans, colonial, only those with calcareous cells, marine (stematopods), which appeared as early as the Lower Silurian, have left fossil remains; they reached their apogee a first time in the Permian (fenestella), when the tetracorals disappeared, and a second time in the Cretaceous, when the hexacorals declined. At present the cheilostomes abound, of which there are important living colonies in the Red Sea and the Mediterranean; however, they are also very widespread in the Tertiary and early Quaternary. Among the bryozoans, some authors include the chaetetes, previously considered tabulates.

Of the brachiopods, generally both valves remain in the fossil state. The brachidium is sometimes brought into evidence, either by successive sections of the dorsal valve, or by working with X-rays. The first to appear were the inarticulates (lingula, in the Algonkian of North America); then the articulates (from the Cambrian); both groups living down to the present day. Very developed in the Silurian (over 3000 species), the brachiopods, after a slight regression in the Devonian, are renewed in the Anthracolithic (the curious richthofenia is from the Permian, with typical examples of convergence with the hippuritids of the Cretaceous); there was another renewal, in the Triassic, to then diminish in the Tertiary, as regards number of species and individuals. Of the worms, which have some stratigraphic importance in the Silurian and Devonian, few specimens are known in the fossil state, consisting above all of remains of calcareous tubes and of jaws of annelids. Perhaps tubular impressions in the sands of pre-Cambrian and early Paleozoic fossil beaches (arenicolites) can be attributed to them. The arthropods are animals with perfect bilateral symmetry, with a chitinous covering, aquatic and terrestrial. Very important is the class of the trilobites, marine fossils exclusive to the Paleozoic, whose most ancient representatives in Italy (paradoxides, olenopsis, etc.) are found in the Cambrian schists of Sardinia (Iglesiente, Sulcis), while they are very abundant in England, Bohemia, North America, etc. Among the crustaceans found in the Algonkian of Montana (Beltina Danai), mention is made of the phyllopods, with two very small valves, e.g., estheria, of the Triassic; the ostracods, e.g., cypridina, of the Devonian; while some forms are freshwater and brackish-water from the Quaternary; among the malacostracans, the brachyuran decapods of the Venetian Eocene: harpactocarcinus, ranina, etc., from the Pliocene marls of Anzio and Monte Vaticano: cancer, etc.

Fossils of uncertain systematic position are the aptychi, once believed to be opercula of ammonites, but today attributed, more generally, to crustaceans. They are flattened calcareous pieces, smooth or ornamented, frequent in the Middle and Upper Mesozoic of the Apennines (e.g., in the "aptychus schists" of the Middle Jurassic of the central Apennines).

The gigantostracans appear in the Silurian (e.g., eurypterus, in England); they have a further development in the Devonian (eurypterus, pterygotus, etc., of brackish facies). Among the arachnids there is the most ancient fossil animal with aerial respiration known so far (it is a scorpion: palaeophonus nuncius, of the Gothlandian). Among the most interesting insects: orthopterans and neuropterans, e.g., dragonflies, with a wingspan of one meter, in the Carboniferous of France and Russia. In a group akin to the arthropods, that of the pterobranchs, some paleontologists currently place the graptolites, pelagic Paleozoic animals, in floating colonies, of which the rhabdosomes of whitish color and silicatic nature (gunbelite) are found in the fossil state in the very fine blackish carbonaceous schists, especially of the Silurian and Devonian. The first to appear were the dendroids, having thecae of three dimensions (Cambrian-Carboniferous); afterwards, the graptoloids, with thecae all equal to one another. Beautiful specimens of graptoloids are found in the Gothlandian sediments of southeastern Sardinia and of the Carnic Alps. But it is only among the mollusks that the most numerous and important forms of the fossil animal kingdom are found. They are provided with a shell of a single piece, or of two pieces (rarely more than two), internal or external; while only a few forms, and perhaps their ancestors, must have been naked. Among the mollusks of the Pliocene, 50% of the species are still living. Among the anfineurans there is the genus chiton, provided with 8 calcareous plates, which lives from the Silurian to the present day.

The oldest pulmonate gastropods are found in Carboniferous sediments, and the first siphonostomes also in the Carboniferous (cerithiids). Besides the shell, variously shaped and ornamented (turreted, flattened, with helicoidal coiling, more rarely with a flat or conical spire [patella], etc.), the "radula" may also survive in the fossil state, a sort of lingual plate with teeth, as well as the operculum. In the Tertiary the gastropods take on their present characters, although the Eocene species are almost all extinct. As an appendix to the gastropods, mention is made of the pteropods, which appeared in the Upper Cretaceous, with a thin and transparent shell, and of the genera hyolithes, already noted for the Algonkian of Colorado, and conularia, Paleozoic. The scaphopods, with a shell in the form of a tube open at both ends, have lived from the Silurian to the present day. Much more important are the lamellibranchs, which appeared in the Upper Cambrian. Indeed, some genera still living today (arca, nucula, leda, avicula) go back to the early Paleozoic, while in the Devonian the first brackish-and fresh-water forms occur. With the Triassic the fauna is renewed; the reef forms reach their apogee in the Cretaceous, with the curious rudists; with the Tertiary, finally, we pass to the present forms, among which the pectinids, very widespread in the Neogene.

Among the cephalopods, many are fossils characteristic of stages and even of zones. Entire groups are extinct, for example, the ammonoids and the belemnites. Among the oldest cephalopods, mention should be made of the genus wolborthella (which is an orthoceratid) from the base of the Acadian. Of the tetrabranchiates, only the genus nautilus is alive today, while the great majority of the other nautiloids became extinct in the Upper Paleozoic, and in the Upper Miocene the aturia, which had begun in the Cretaceous. The ammonoids represent one of the most interesting "closed series" of fossils, whose extremes are found in the Lower Silurian and the Upper Cretaceous. In the Silurian the primitive goniatites appear, while in the Anthracolithic true ammonites are already known, but still in the Triassic forms of all three types coexisted (goniatitic, ceratitic, ammonitic proper) and the genus pinacoceras showed the maximum complication of the sutural line. The ammonites reach their apogee in the Jurassic, while in the Cretaceous, before their total disappearance, uncoiled forms with a ceratitic suture appeared (neoceratites). The ammonites have first-order stratigraphic importance and are very abundant in certain stratigraphic levels of the Mesozoic of the Apennines and of the central and eastern Prealps, of the Paleozoic and Mesozoic of Sicily, etc.

The order of the dibranchiates comprises: decapods, with the belemnites, exclusive to the Mesozoic (which replaced, in the Triassic, the orthoceratids among the nautiloids), and which have left, for the most part, the "rostrum", a sort of conical, semi-solid calcareous piece, like a javelin ("thunderbolts of Jupiter", of the ancient Greeks), the sepiids, still living today, etc. Among the octopods, some imprints, from the Cretaceous to the present. Of the echinoderm type, whose skeleton in the fossil state is made of calcite with easy rhombohedral cleavage, all marine, the cystoids, with synthetic characters, lived from the Cambrian to the Carboniferous; the blastoids, probably derived from the former, from the Silurian to the Permian. The remaining class of the pelmatozoans, that of the crinoids, is however much more important than the former, since it extends from the Silurian down to us, although currently represented by barely 12 genera. The crinoids are of great lithogenetic importance for the terrains of the Paleozoic, the Triassic and the Alpine Jurassic (crinoidal or "entrochus" limestones).

While the asteroids, ophiuroids and auluroids are of little importance, the echinoids, on the other hand, have in general had a very rapid evolution: in the Silurian the regular paleoechinids appeared, with archaeocidaris, and in the Lias the irregular ones (holectypids); in the Italian Paleogene terrains echinolampas is frequent, and in the Neogene, scutella and clypeaster.

The vertebrates, although less numerous than the invertebrates, are also of notable paleontological interest. The primitive jawless vertebrates, the cyclostomes, have curious affinities with exclusively Paleozoic forms. The main adaptive types of fish are the fusiform and the one compressed from top to bottom, which is realized by benthic species. The oldest fish go back to the Ordovician. Selachians, ganoids and dipnoans lived from the Devonian onward, at which time the ostracoderms or "armored fish", of brackish facies, are found in a senile phase, with morphological convergences with the gigantostracans. Elasmobranchs, ganoids and dipnoans had a notable development in the Carboniferous.

Only in the Triassic, following a renewal of the fauna, culminating in forms with a greater development of the bony part of the internal skeleton and a reduction of the dermal armor, did the teleosts appear. Of fish, besides the imprints in fine sediments (marls, clays, diatomites: M. Bolca, M. Amiata, etc.), isolated parts are more frequently found in the fossil state, especially teeth, dermal plates, bones, vertebrae, otoliths (for example, in the Miocene limestones of Sicily, Sardinia, etc.).

Amphibians are organisms adapted to terrestrial life in the adult state, with an aquatic larval stage resembling the fish from which they derive (crossopterygians). The skeleton is in general well ossified, but while the skin is naked in present forms (lissamphibians), it was provided with a solid dermal covering in a great number of fossil forms (phractamphibians), among which the stegocephalians, which had already appeared in the Upper Carboniferous, very widespread in the Permian, for example, archaegosaurus, branchiosaurus, etc. From the stegocephalians originated the Triassic labyrinthodonts (for example, mastodonsaurus), which were the most gigantic amphibians. Among the fossil forms, the Miocene salamander andrias scheuchzeri is of curiosity value, erroneously considered the skeleton of a child drowned in the Noachian deluge. Reptiles too derive from the crossopterygians or from the stegocephalian amphibians, and the oldest known forms (saureus) go back to the end of the Carboniferous of Pennsylvania. In the Permian there are reptiles mostly terrestrial, rarely aquatic (mesosaurus); among the terrestrial carnivores, the theriodonts, with characters of convergence toward the mammalian type, through heterodonty, etc., from which mammals would have derived. In the Triassic there are also tracks of unknown reptiles, called cheirothrium, because of the shape of the imprint which recalls that of a man. In this period the reptiles undergo a great differentiation in general morphology, adaptation to various kinds of food and environment (ichthyosaurs, sauropterygians, rhynchocephalians, dinosaurs, crocodilians, theromorphs, testudinates, pterosaurs, etc.), while they reach their apogee in the Jurassic with giant and strange forms, which will disappear in the Cretaceous (pterosaurs, dinosaurs, for example, tyranosaurus rex), the most gigantic, also constituting a fine example of "bipedalism", ichthyosaurs (markedly ichthyomorphous), at which time lacertids and ophidians appear. The oldest birds known so far are archaeoeris and archaeopteryx from the Upper Jurassic of Solenhofen (Bavaria); the latter as large as a big pigeon, with jaws and with conical and alveolate teeth, bony tail, therefore with reptilian characters, derived precisely from pterosaur reptiles, according to others from arboreal reptiles, with forms suited at first to parachute flight.

Other toothed birds occur in the Cretaceous of Kansas (United States of America): ichthyornis and hesperornis.

At the end of the Cretaceous the birds with reptilian characters disappear and the fauna becomes akin to the present one.

The last gigantic birds are found in the Pliocene of Santa Cruz, in South America; in the Quaternary, with the aepyornis of Madagascar and the dinornis of New Zealand, with enormous eggs with a capacity of 10 liters. Of birds, fossils of eggs and imprints of feathers are also found in the Quaternary travertines of central Italy (for example, in the Acque Albule, near Tivoli); in the peperino tuffs of the Vulcano laziale (Rome; imprints of vulture feathers). The oldest known mammals are represented, in the Upper Triassic of southern Africa and of Europe, by teeth of multituberculates, and they seem to descend from the theromorph reptiles: they had an extremely long life in the first evolutionary phase, lasting throughout the Mesozoic, with small-sized forms of lower placentals (insectivores). But it will be only at the beginning of the Tertiary that mammals will assume true importance. In this geological era they had two evolutionary phases: first, with rapid evolution followed by abrupt extinctions of archaic mammals, for example, the creodonts, carnivores, the condylarths, primitive ungulates with slender limbs suited to running and with synthetic characters (for example, the phenacodus), the amblypods, ungulates with massive limbs (Europe and America); this was followed by another phase that gave rise to the precursors of modern forms. The leporids are of North American origin. Likewise the equus, which appeared in the Eocene (eohippus, the size of a dog) and became extinct there at the end of the Tertiary; it passed into Asia, and then into Europe and Africa, where it reached its present appearance. The terrestrial mammals: proboscideans (mastodons, dinotheres), rhinoceroses, ruminants with horns, catarrhine monkeys, of Asian-African origin, invaded Europe in the Miocene. They underwent an intense evolution in the Pliocene: many genera of carnivores, equids, rhinocerotids, camelids, bovids, cervids, proboscideans, cetaceans, etc. At that time there were close relations between India and Europe, between Africa and India, while the direct relations between Europe and North America diminished. However, a migratory flow was established from Africa toward North America passing through Asia, and another between the two Americas, already interrupted since the Eocene.

As regards South America, it must be remembered that in the Pliocene there survived strange autochthonous forms of marsupials and placentals that had undergone a characteristic evolution in place since the Eocene, manifesting itself as convergences. Among marine mammals, the Neogene odontocetes are important, for example, the squalodon. Some important deposits of vertebrates are recalled: the Eocene ones of the gypsum of Montmartre (Paris), celebrated for the richness of forms and for the discoveries of Cuvier; Eocene ones of Wyoming, Utah, Colorado, New Mexico; Oligocene ones of Dakota, Nebraska, eastern Colorado; of Eocene mammals from the sands of the Orléanais, of the island of Samos, of the Pontian of Pikermi (Athens), the vertebrates of various levels of the Miocene and perhaps of the Pliocene, near Sahabi (south of Benghazi) with: fishes (elasmobranchs and teleosts), freshwater reptiles (crocodilus, trionyx) and terrestrial ones (emydids), numerous mammals (cetaceans, suids, hippopotamids, rhinocerotids, antilopids, felids, proboscideans, etc.). The fauna of Sahabi recalls that of Egypt (140 km southwest of Alexandria) and the famous deposit of Sivalik, with numerous species of carnivores, ungulates, proboscideans, primates, of the Miocene and Pliocene.

Numerous are the deposits of fossil vertebrates in Italy, among which are recalled: the famous "Pesciara" of Bolca (Vicenza), with over 150 species among Eocene elasmobranchs and teleosts of a tropical Indo-Pacific climate, the one with reptiles (crocodilus vicetinus, turtles) and mammals in the Paleogene lignites of Veneto, a similar coeval fauna near Cadibona (western Alps); of the lignite series of Gavitelli (Messina), with mammals of the Pontian; of the lignites of Montebamboli (Tuscany), with fishes, reptiles and mammals; of the Casino, near Siena, etc.; the Quaternary ones, sometimes in deposits within karstic and marine caves (for example, Puntali, S. Teodoro, in Sicily), Tyrrhenian coast (Circeo etc.); the Pleistocene deposits with mammoth and Mousterian flints in the alluvia of the Musone, near Asolo (Treviso); of the alluvia of Arena Po (Pavia), with: megaceros, alces, cervus, bison, bos, etc.; in the alluvia of the Arno; of the Tiber and the Aniene in the Roman Campagna, with: elephas antiquus, hippopotamus, rhynoceros merckii, cervus elephus, megaceros, bison priscus, bos primigenius, etc.; of Pignataro Interamna (Cassino), with elephas antiquus; of Roccasecca (Liri Valley), where there was found, among other things, a canine of hippopotamus major of notable dimensions; of Lake Venosa (Lucania); deposits in diatomites, as, for example, fishes in M. Amiata; mammals, among which elephants and bovids, in the Viterbese; deposits in the volcanic tuffs of the Roman Campagna and in the travertines of the same region, containing, among other things, eggs and imprints of bird feathers.

In western Europe the Aurignacian and Magdalenian prehistoric art has handed down many drawings and sculptures representing animals now extinct or migrated to other regions such as the mammoth, the woolly rhinoceros, reindeer, bison, bears, etc.

IV. PALEOBOTANY

The first descriptions of fossil plants in England and Germany date back to the 17th century, but the founder of paleobotany is considered to be Adolphe Brongniart, who in 1822-28 made the first classification of fossil plants. Other fundamental works are those of Blumenbach, von Schlotheim, Unger, Schimper, etc. Silicified woods had attracted the attention of St. Albert the Great as early as the 13th century.

In the oldest geological formations, also because they are generally metamorphosed, there are no certain traces of determinable plant fossils. Indirect evidence of the presence of lower plants in Precambrian sediments is however given by deposits of graphite; of coal ("shungite") on the shores of Lake Onega; iron-bearing deposits, due, like bog iron, to the action of bacteria, which were probably the first organisms to appear. In the Algonkian there are "problematic" forms in North America, in the "Belt series," perhaps cyanophycean algae (cryptozoon, newlandia, etc.); corycium aenigmaticum, in Finland.

Among the thallophytes, the surely determinable marine algae date back to the Cambrian and Silurian, contained in calcareous rocks; they are very developed in the Triassic with gyroporella and diplopora; while the lithothamnia were especially abundant in the Tertiary. Calcareous algae were able to contribute, in the same way as certain animal organisms, to forming the oolitic and pisolitic structure of many limestones, iron-bearing rocks, etc. (for example, the codiacean algae, constituting the nuclei of ooliths of the Dogger limestones of Sardinia). Among the siliceous algae, the diatoms, with a shell of amorphous silica, with ornamentations sometimes visible only under the electron microscope, have three main forms: boat-shaped or navicular; round or ellipsoidal; with a polygonal outline. Diatoms date back to the Cretaceous and, perhaps, to an older age and have formed the diatomites (of which the "fossil flour" of S. Fiora [in the Amiata] is much prized, having originated in tiny Pleistocene lakes).

The first terrestrial vascular cryptogams (plants with roots, stem and leaves) appear in the Silurian; for the Carboniferous one should remember the cycadofilicines, progenitors of the ferns and comparable to the present-day tree ferns of tropical forests (gen. sphenopteris, pecopteris, neuropteris, etc.); among the calamariaceae, calamites; among the lepidophytes, lepidodendron, sigillaria, and the root-like rhizomes called stigmaria. Horsetails and ferns are still developed in the Triassic. The latter and the conifers, also in the Jurassic. Among the phanerogamic gymnosperms one should remember: cordaites, 30-40 meters tall, and the noggeratia among the cycadeans of the Carboniferous; among the conifers: the genera voltzia and ullmannia, of the Permian. The angiosperms appear in the Jurassic (Dogger of Yorkshire and of Sardinia), when the pteridosperms were tending to disappear. They developed in the Cretaceous: salix, populus, ficus, quercus, eucalyptus, etc. In this period the monocotyledons also appear. In the Tertiary the palms are important, of which numerous trunks are found silicified (Sardinia, Cyrenaica [Sahabi], Egypt, North America, etc.).

As regards the fossil plant kingdom, the following observations can also be made: in the Anthracolithic two botanical provinces are distinguished: boreal and austral. In the latter, that is, corresponding to Gondwanaland (Australia, India, southern Africa, Borneo), the flora is formed by glossopteris and by gangamopteris; the phanerogams of the Carboniferous are all from tropical coastal environments, comparable to the present-day swamps, that is, the marshes of Virginia, of the Gulf of Mexico, etc., or to the marine areas with mangroves of the Red Sea and the Indian Ocean; the plants of the Permian have notable affinities with those of the Triassic; in the Quaternary well-defined paleobotanical provinces arise; in the Pleistocene the paleobotanical associations present fundamental characters parallel to the faunas of the same period. Among the "cold" forms, occupying the glacial areas, there is the "dryas" flora (dryas octopetala L.) of tundra or high-mountain facies, with a following of pinus montana, betula nana, salix polaris, etc.; while in the interglacial phases there are warm forms, for example, ficus carica, buxus sempervirens, vitis vinifera, etc., which spread toward the north. An evolutionary resurgence of plants occurs after the last glaciation, with forms that still live today.

The reconstruction of the climatic periods of the Quaternary is based on the study of pollens, qualitative and quantitative, contained in the strata, in the peat bogs, etc. Pollen grains have special shapes that sometimes allow the specific determination of individual plants.

Carmelo Maxia