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 plants (paleophytology or paleobotany) that lived in past ages of the earth.

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

SUMMARY:

I. General notions

II. History

III. Paleozoology

IV. Paleophytology.
I. GENERAL NOTIONS. — The purpose of paleontology is the systematic study of fossils (“systematic paleontology”), whose identification may be carried out by comparison with living species or with extinct forms already described. Research is conducted both through the macroscopic study of specimens generally freed from extraneous material, and with the aid of instruments—above all, the simple microscope, for specially prepared transparent “thin sections” of rocks, or for “polished sections” of plants (examined in reflected light); the binocular microscope, especially for isolated microfossils; and X-rays, to bring out internal features of the fossils themselves. Histological examination of certain plants has made possible an intimate knowledge of the structure of fossil organisms, even before that of living ones.

Paleontology also studies the relationships among fossil groups, since they fall within the great divisions of the systematics of animals and plants; at times completing the links among living species or other groups (genera, families, etc.); and moreover making a substantial contribution to the study of the phylogeny, morphology, and distribution of living species.

The foregoing, however, although very important, is not the sole objective pursued by the science of fossils, which today constitutes principally the most effective instrument for the relative dating

of geological periods and for understanding the biological phenomena and climatic types of the past.

Stratigraphic study (v. STRATIGRAFIA) makes it possible not only to observe how fossils were deposited in the strata in which they are contained (and hence to establish that their age is contemporaneous with that of the enclosing sediments, except for what will be said below concerning “reworking and redeposition”), 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, quite numerous, that have changed during those same periods; that is, they have been transformed or have evolved.

Moreover, certain groups or species disappeared at various ages in the history of the earth. Among the latter, some underwent a life cycle of very limited duration, although at times they had a wide geographical distribution, so much so that they are sometimes all found in the same stratum.

Comparative stratigraphic study has also shown that some of these short-lived faunas immediately preceded or followed, at every point on the Earth, other organisms that likewise possessed identical characteristics of propagation through time and space. It thus became possible to construct a scale of terms (“stratigraphic scale”) consisting of associations of species or of individual characteristic fossil species, also called “index fossils.”

In this way “stratigraphic paleontology” arose, based on the normal succession of strata; but it has now progressed to such an extent that it can be used by itself, with certainty, to solve chronological problems even in terrains so profoundly disrupted by tectonics that they no longer preserve their original order of succession.

It must be immediately pointed out, however, that only fossils deposited contemporaneously with the enclosing terrains possess stratigraphic value for that particular geological age; whereas, if they have been reworked or, as is customary to say, “re-fossilized,” their contemporaneity with the enclosing strata ceases, and the latter will consequently appear older than they really are. Reworked or allochthonous fossils can be recognized because they bear traces of rolling, or because they are still attached to fragments of pre-existing rock, usually of a nature different from that of the last enclosing rock. Thus, for example, a calcareous breccia containing rounded and eroded plasmostrachi from mummuli, or fragments thereof, together with mollusks of demonstrably more recent age, will have an age indicated by the latter fossils and not by the foraminifera.

Many fossils, although lacking stratigraphic value, may nevertheless serve to shed light on the environmental conditions of their deposition. In this case, one speaks of “facies fossils”: continental fossils—terrestrial and aquatic (fluvial and limnic); marine fossils—fixed and mobile benthic forms, and pelagic forms (nektonic and planktonic).

It may be concluded that paleontology and geology are intimately linked, and that the study of either one without taking the other into account is practically devoid of results of genuine scientific value.
II. HISTORY. — The origins of paleontology, like those of many other sciences, may be said to go back to the remotest times; but it was only in a very recent period (the dawn of the nineteenth century) that it developed as an autonomous science, separating itself from geology.

Classical antiquity possessed little knowledge of fossils. Nevertheless, for many Greek natural philosophers and later for certain medieval writers and thinkers (e.g. Alberto Magno, G. Boccaccio, etc.), fossils undoubtedly represented the remains of organisms that had lived in epochs preceding the present one. Others, however, regarded fossils either as the product of a hypothetical “plastic” or “formative process” or, indeed, as “lusus Naturae.” In more recent times, sound opinions concerning the nature of fossils were held by Leonardo da Vinci, Bernardo Palissy, Gerolamo Fracastoro, and a few others.

Among the oldest natural-history collections, which also contained fossil remains, those of London (seventeenth century) and of various cities in France and Germany are worthy of mention; so too is the collection commissioned in the Vatican by Sisto V and described in M. Mercati’s Metalloleuca Vaticana of 1574 (published in 1710); as well as a collection belonging to Aldrovandi, and others. Nevertheless, even in the centuries following the Middle Ages, especially in France and Italy, eminent scholars attributed fossil organic remains to the Noachian Flood (the “diluvial theory”); perhaps because the fossils found in those countries, belonging predominantly to recent formations, closely resembled currently living species. In England, by contrast, the presence of fossils very different from present-day species helped lead to their being regarded as extinct forms. An important stage in the progress of paleontology was the application of the microscope by R. Hooke, in the seventeenth century, to the study of microfossils, histological preparations of animals and silicified wood, and ammonites, whose suture lines were thereby brought to light.

It was only in the eighteenth century, however, that the first memoirs appeared with a systematic descriptive treatment of fossils.

Cuvier deserves the credit for laying the scientific foundations of vertebrate paleontology, following his observations of the numerous fossil bones of animals, most of them extinct, found in the Eocene formations of the Paris Basin, and for applying comparative anatomy—which he himself had founded—to the science of fossils. Cuvier, however, explained the differences between the faunas succeeding one another from stratum to stratum by hypotheses involving telluric disturbances of an almost universal character, which would have caused a large number of living beings to become extinct in one epoch, after which others would have arisen through successive creations or through mass immigration from other regions (the theories of the revolutions of the globe and of successive creations). Cuvier thus admitted differences between species in strata of different ages, but defended the “fixity of species.” Among his followers (A. Brongniart, Agassiz, D’Archiac, etc.), the one who distinguished himself by exaggerating his teacher’s theories was A. D’Orbigny, who accepted twenty-seven successions of completely renewed faunas (approximately 18,000 species illustrated by him: the A, B, ... etc. stages of D’Orbigny), placing the oldest in the Silurian. Partly reviving the ideas of Buffon and others, Lamarck and G. S. Hilaire expounded the “transformist” idea: the former maintaining that species tend to vary slowly through the transmission of acquired characteristics in relation to physiological causes (the use and disuse of particular organs under changing conditions or habits); the latter attributing this to the environmental factor, through abrupt variations. It nevertheless appears that Lamarck had observed that his phyletic series were “ordered” as though according to a plan pre-established by the Creator. These two French naturalists were the true founders of “transformist or evolutionist paleontology” (v. EVOLUZIONE), subsequently developed by Darwin.

Given the importance of this theory, it seems appropriate to observe that there were also “pre-Lamarckians” in the Middle Ages and in the modern era: s. Agostino, for whom “it was not things that were created, but rather their causes”; and also p. Atanasius Kirker, who asserted a “multiplication of species and not merely of individual beings.” Other evolutionists were G. Bruno, Bacone, Cartesio, Buffon, etc. Among the founders of invertebrate paleontology, in addition to D’Orbigny, Lamarck should be mentioned; of paleophytology, Adolphe Brongniart; and, among the founders of stratigraphic paleontology, W. Smith, the abbot Giraud-Soulavie, G. B. Brocchi, and others.

It is impossible to recall the names of the paleontologists of the late nineteenth century and of the twentieth century, given their great number.

III. PALEOZOOLOGY

In the Algonkian of North America and the Baltic Shield, fossils are already known belonging to animals that display a high degree of evolution (echinoderms, gastropods, arthropods). Some remains called “problematic,” which appear as impressions—for example, the palaeodictyum—are attributed by some to algae, by others to sponges, jellyfish, etc. Among the protozoa, the principal fossils belong

to the rhizopods: foraminifera and radiolarians, the former provided with a calcareous shell, the latter with a siliceous one. Present-day calcareous foraminifera, during the juvenile stage, have a chitinous shell, like their Cambrian ancestors.

Among the foraminifera (once believed to be cephalopods even by Lamarck, and first depicted by Aldrovandi), which in the fossil state can reach 12–16 cm in diameter, there are numerous characteristic forms: among the imperforates, orbitolina, from the Cretaceous; alveolina, very widespread in the Eocene; among the perforates, globotrancana, from the Cretaceous; fusulinids, from the Anthracolithic; nummulites and assilines, Paleogene; orthophragminae and lepidocyclines, Tertiary (the lepidocyclines underwent further development in the first half of the Neogene, when they were replaced by miogypsinids); amphistegines, from the Miocene to the present. The Eocene limestones of the Maiella, the Gargano, etc., are rich in nummulites. Today, microforaminifera are also considered important, especially with regard to the recent Tertiary and the Quaternary, with studies being conducted on a statistical basis.

Radiolarians, exclusively marine and planktonic, appeared in Precambrian times (in the radiolarites 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 more than 4000 metres, in the Indian and Pacific Oceans. Sponges, also very ancient and little-evolved animals, with a skeleton composed of isolated and fused pieces (spicules), live in littoral zones as well as at great depths, down to more than 4000 metres. They are the simplest of the metazoans; sessile and almost all marine. Sponges underwent considerable development in the Mesozoic (Triassic of S. Cassiano; Turonian of Normandy, etc.). The archaeocyathids, characteristic fossils of the Lower and Middle Cambrian (Australia, Sardinia, Montagna Nera), are also attributed to the sponges. The coelenterates, corresponding to the “zoophytes” of ancient authors, include numerous forms important from the stratigraphic and lithogenetic points of view. The hexacorals, which appeared in the Triassic and are still living, succeeded the tetracorals, which became extinct at the end of the Paleozoic.

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

The trimetamerans, generally sessile, include the types of the bryozoans and brachiopods, both of which are still living. Among the colonial bryozoans, only those with calcareous cells, marine (stelmatopods), which appeared as early as the Lower Silurian, have left fossil remains; they reached their apogee for the first time in the Permian (fenestella), when the tetracorals disappeared, and for the second time in the Cretaceous, when the hexacorals declined. At present, cheilostomes are abundant, with important colonies existing in the Red Sea and the Mediterranean; they were also very widespread in the Tertiary and the older Quaternary. Some authors include among the bryozoans the chaetetes, formerly regarded as tabulates.

In the fossil state, brachiopods generally retain both valves. The brachidium is sometimes brought to light either by making successive sections of the dorsal valve or by using X-rays. The first to appear were the inarticulates (lingula, in the Algonkian of North America); then the articulates (from the Cambrian); both groups are still living today. Very well developed in the Silurian (more than 3000 species), brachiopods, after a slight regression in the Devonian, underwent renewal in the Anthracolithic (the curious richtefenia, with typical examples of convergence with the Cretaceous hippuritids, belongs to the Permian); there was another renewal in the Triassic, followed by a decline in the Tertiary, both in the number of species and of individuals. Of the worms, which have some stratigraphic importance in the Silurian and Devonian, few fossil specimens are known, consisting chiefly of remains of calcareous tubes and annelid jaws. Tubular impressions in the sands of fossil Precambrian and early Paleozoic beaches (arenicolites) may perhaps be attributed to them. The arthropods are animals with perfect bilateral symmetry and a chitinous covering, both aquatic and terrestrial. The class of trilobites is very important: they are exclusively marine fossils of the Paleozoic, whose oldest 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 may be made of the phyllopods, with two very small valves, for example, estheria, from the Triassic; the ostracods, for example, cypridina, from the Devonian; while some forms are freshwater and brackish-water forms of the Quaternary; among the malacostracans, the brachyuran decapods of the Venetian Eocene: harpactocarcinus, ranina, etc., and of the Pliocene marls of Anzio and Monte Vaticano: cancer, etc.

The aptichi are fossils of uncertain systematic position. They were formerly believed to be opercula of ammonites, but today are more generally attributed to crustaceans. They are flattened calcareous pieces, smooth or ornamented, frequent in the Middle and Upper Mesozoic of the Apennines (for example, in the “aptichus schists” of the Middle Jurassic of the Central Apennines).

The gigantostracans appear in the Silurian (for example, eurypterus, in England); they underwent further development in the Devonian (eurypterus, pterygotus, etc., of brackish-water facies). Among the arachnids is the oldest known fossil animal with aerial respiration (it is a scorpion: palaeophonus nuncius, from the Gothlandian). Among the most interesting insects are orthopterans and neuropterans, for example, dragonflies, with a wingspan of one metre, in the Carboniferous of France and Russia. In a group related to the arthropods, that of the pterobranchs, some paleontologists currently place the graptolites: Paleozoic pelagic animals living in floating colonies, whose fossil rabdosomes are found as whitish silicaceous structures (gunbelite) in very fine blackish carbonaceous schists, especially of the Silurian and Devonian. The dendroids appeared first, with thecae of three dimensions (Cambrian–Carboniferous); later came the graptoloids, with thecae all identical to one another. Beautiful specimens of graptoloids are found in the Gothlandian sediments of southeastern Sardinia and 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 possess a shell consisting of a single piece or two pieces (rarely more than two), internal or external; 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 amphineurans there is the genus chiton, provided with eight calcareous plates, which has lived from the Silurian to the present.

The oldest pulmonate gastropods are found in Carboniferous sediments; the first siphonostomes likewise occur in the Carboniferous (cerithiids). In addition to the shell, variously shaped and ornamented (turreted, flattened, helically coiled, more rarely with a plane or conical spire [patella], etc.), the «radula», a sort of lingual plate with teeth, and the operculum may also be preserved in the fossil state. In the Tertiary, gastropods acquire their present-day characteristics, although the Eocene species are almost all extinct. Appended to the gastropods are the pteropods, which appeared in the Upper Cretaceous, with a thin and transparent shell, and the genera hyolithes, already recorded from the Algonkian of Colorado, and conularia, Paleozoic. 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, several genera that are still living today (arca, nucula, leda, avicula) date back to the Early Paleozoic, while the first brackish- and freshwater forms occur in the Devonian. With the Triassic the fauna is renewed; reef forms reach their apogee in the Cretaceous, with the curious rudists; finally, in the Tertiary, there is a transition to the present-day forms, among which the pectinids are very widespread in the Neogene.

Among the cephalopods, many are characteristic fossils of stages and even of zones. Entire groups are extinct, for example the ammonoids and the belemnites. Among the oldest cephalopods, the genus wolborthella (which is an orthoceratid), from the base of the Acadian, should be mentioned. Of the tetrabranchiates, only the genus nautilus is living today, while most of the other nautiloids became extinct in the Upper Paleozoic, and aturia, which began in the Cretaceous, became extinct in the Upper Miocene. The ammonoids represent one of the most interesting «closed series» of fossils, whose extremes are found in the Lower Silurian and the Upper Cretaceous. Primitive goniatites appear in the Silurian, while true ammonites are already known in the Anthracolithic; yet in the Triassic forms of all three types (goniatitic, ceratitic, ammonitic in the strict sense) coexisted, and the genus pinacoceras displayed the greatest complexity of the suture line. Ammonites reach their apogee in the Jurassic, while in the Cretaceous, before their total disappearance, involute forms with ceratitic sutures (neoceratites) appeared. Ammonites are of the first importance for stratigraphy and are very abundant in certain stratigraphic levels of the Mesozoic of the Apennines and the central and eastern Pre-Alps, of the Paleozoic and Mesozoic of Sicily, etc.

The order of the dibranchiates includes: decapods, with the belemnites, exclusive to the Mesozoic (which in the Triassic replaced the orthoceratids among the nautiloids), and which have for the most part left the «rostrum», a sort of semisolid, conical calcareous piece, in the form of a javelin («Jupiter’s thunderbolts», as they were called by the ancient Greeks); the sepioids, still living today; etc. Among the octopods, there are some imprints dating from the Cretaceous to the present. Of the echinoderm type, whose fossil skeleton consists of calcite with easy rhombohedral cleavage, and which are all marine, the cystoids, with generalized characteristics, lived from the Cambrian to the Carboniferous; the blastoids, probably derived from the former, from the Silurian to the Permian. The remaining class of pelmatozoans, the crinoids, is nevertheless much more important than the preceding ones, since it extends from the Silurian to the present, although today it is represented by barely 12 genera. Crinoids are of great lithogenetic importance in the Paleozoic, Triassic, and Alpine Jurassic formations (crinoid or «entrochi» limestones).

While asteroids, ophiuroids, and auloroids are of little importance, echinoids, on the other hand, have generally undergone a very rapid evolution: in the Silurian, the regular paleo echinids appeared, with archaeocidaris, and in the Lias the irregular forms (holectypids); echinolampas is frequent in Italian Paleogene formations, and in the Neogene, scutella and clypeaster.

Vertebrates, although less numerous than invertebrates, are likewise of considerable paleontological interest. The primitive vertebrates without jaws, the cyclostomes, have curious affinities with forms exclusively Paleozoic. The principal adaptive types among fishes are the fusiform type and the type compressed from top to bottom, which is realized by benthic species. The oldest fishes date back to the Ordovician. Selachians, ganoids, and dipnoans lived as early as the Devonian, when the ostracoderms, or «armored fishes», of brackish-water facies, are found in a senescent phase, with morphological convergences toward the gigantostracans. Elasmobranchs, ganoids, and dipnoans underwent considerable development in the Carboniferous.

Only in the Triassic, following a renewal of the fauna culminating in forms with a more highly developed bony portion of the internal skeleton and a reduction of the dermal armor, did the teleosts appear. In fishes, besides 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 and bony plates, vertebrae, and otoliths (e.g., 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 fishes from which they derive (crossopterygians). The skeleton is generally well ossified, but whereas the skin is naked in present-day forms (lissamphibians), it was provided with a solid dermal covering in a large number of fossil forms (stegamphibians), among which were the stegocephalians, which had already appeared in the Upper Carboniferous and were very widespread in the Permian, for example archaegosaurus, branchiosaurus, etc. The Triassic labyrinthodonts (e.g., mastodonsaurus) originated from the stegocephalians; they were the most gigantic amphibians. Among fossil forms, the Miocene salamander andrias scheuchzeri is noteworthy as a curiosity, having been erroneously regarded as the skeleton of a child drowned in the Noachian Flood. Reptiles too derive from crossopterygians or from stegocephalian amphibians, and the oldest known forms (saureus) date from the end of the Carboniferous of Pennsylvania. In the Permian there are mostly terrestrial reptiles, only rarely aquatic ones (mesosaurus); among the terrestrial carnivores were the theriodonts, with convergent characteristics toward the mammalian type, such as heterodonty, etc., from which mammals would have derived. In the Triassic there are also tracks of unknown reptiles, called cheirothrium, because the shape of the impression recalls that of a human being. During this period reptiles underwent a great differentiation in general morphology and adaptation to various kinds of food and environments (ichthyosaurs, sauropterygians, rhynchocephalians, dinosaurs, crocodilians, theromorphs, testudines, pterosaurs, etc.), while they reached their apogee in the Jurassic with gigantic and strange forms that would disappear in the Cretaceous (pterosaurs, dinosaurs, e.g., tyranosaurus rex), the most gigantic, also constituting a fine example of «bipedism»; ichthyosaurs (distinctly ichthyomorphic), at which time lacertilians and ophidians appeared. The oldest birds known thus far are archaeoeris and archaeopteryx from the Upper Jurassic of Solenhofen (Bavaria); the latter was as large as a large pigeon, with jaws and conical, socketed teeth, and a bony tail, thus displaying reptilian characteristics; it was derived precisely from pterosaur reptiles, according to some, and according to others from arboreal reptiles, with forms initially adapted to parachute-like flight.

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

At the end of the Cretaceous, birds with reptilian characteristics disappeared, and the fauna became similar to that of the present day.

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 having a capacity of 10 litres. Fossil remains of birds also include eggs and impressions of feathers in the Quaternary travertines of central Italy (e.g., at the Acque Albule, near Tivoli); and in the peperino tuffs of the Latian Volcano (Rome; impressions of vulture feathers). The oldest known mammals are represented, in the Upper Triassic of southern Africa and Europe, by the teeth of multituberculates, and apparently descended from theromorph reptiles: they had an extraordinarily long existence in the first evolutionary phase, lasting throughout the Mesozoic, with small-sized forms of lower placentals (insectivores). It was only at the beginning of the Tertiary, however, that mammals assumed real importance. In this geological era they underwent two evolutionary phases: first, a rapid evolution followed by the abrupt extinction of archaic mammals, e.g., the creodonts, carnivores; the condylarths, primitive ungulates with slender limbs suited to running and with generalized characteristics (e.g., the phenacodus); and the amblypods, ungulates with massive limbs (Europe and America); this was followed by another phase that produced the precursors of modern forms. The leporids were of North American origin. The same applies to equus, which appeared in the Eocene (eohippus, the size of a dog) and became extinct there at the end of the Tertiary; it then passed into Asia, and thence into Europe and Africa, where it attained its present appearance. The terrestrial mammals—proboscideans (mastodons, dinotheres), rhinoceroses, horned ruminants, and catarrhine monkeys, of Asian-African origin—invaded Europe in the Miocene. They underwent intense evolution in the Pliocene: many genera of carnivores, equids, rhinocerotids, camelids, bovids, cervids, proboscideans, cetaceans, etc. At that time close relations existed between India and Europe, and between Africa and India, while direct relations between Europe and North America diminished. A migratory flow from Africa to North America through Asia was nevertheless established, as was another between the two Americas, already interrupted since the Eocene.

As regards South America, it should be recalled that in the Pliocene strange indigenous forms of marsupials and placentals survived; they had undergone a characteristic in situ evolution since the Eocene, manifested in the form of convergences. Among marine mammals, the Neogene odontocetes are important, e.g., the squalodon. Several important vertebrate deposits may be mentioned: those of the Eocene gypsum of Montmartre (Paris), celebrated for the richness of their forms and for Cuvier’s discoveries; the Eocene deposits of Wyoming, Utah, Colorado, and New Mexico; the Oligocene deposits of Dakota, Nebraska, and eastern Colorado; the deposits of Eocene mammals in the sands of the Orléanais and on the Island of Samos; those of the Pontic at Pikermi (Athens); and the vertebrates of various Miocene and perhaps Pliocene levels near Sahabi (south of Benghazi), including fish (elasmobranchs and teleosts), freshwater reptiles (crocodilus, trionyx) and terrestrial reptiles (emydids), and 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 Sivalik deposit, with numerous species of carnivores, ungulates, proboscideans, and primates from the Miocene and Pliocene.

Numerous fossil-vertebrate deposits occur in Italy, among which may be mentioned: the famous “Pesciara” at Bolca (Vicenza), with more than 150 species of Eocene elasmobranchs and teleosts from a tropical Indo-Pacific climate; the deposit of reptiles (crocodilus vicetinus, turtles) and mammals in the Palaeogene lignites of the Veneto, with a similar contemporaneous fauna near Cadibona (Western Alps); the lignite series of Gavitelli (Messina), with Pontic mammals; the lignites of Montebamboli (Tuscany), with fish, reptiles, and mammals; those of Casino, near Siena, etc.; the Quaternary deposits, sometimes in deposits within karstic and marine caves (e.g., Puntali and S. Teodoro, in Sicily), and along the Tyrrhenian coast (Circeo, etc.); the Pleistocene deposits with mammoths and Mousterian flints in the alluvial deposits of the Musone, near Asolo (Treviso); those of the alluvial deposits of Arena Po (Pavia), with: megaceros, alces, cervus, bison, bos, etc.; in the alluvial deposits of the Arno, the Tiber, and the Aniene in the Roman Campagna, with: elephas antiquus, hippopotamus, rhynoceros merckii, cervus elephus, megaceros, bison priscus, bos primigenius, etc.; those of Pignataro Interamna (Cassino), with elephas antiquus; those of Roccasecca (Liri Valley), where, among other things, a canine tooth of hippopotamus major of considerable size was found; those of Lake Venosa (Lucania); deposits in diatomites, such as, for example, fish in Mt. Amiata; mammals, including elephants and bovids, in the Viterbo area; deposits in the volcanic tuffs of the Roman Campagna and in the travertines of the same region, containing, among other things, bird eggs and impressions of feathers.

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

In the oldest geological formations, also because they are generally metamorphosed, there are no certain traces of identifiable plant fossils. Indirect evidence of the presence of lower plants in Precambrian sediments is, however, provided by graphite deposits; by coal (“shungite”) on the shores of Lake Onega; and by iron deposits, attributable, like bog iron, to the action of bacteria, which were probably the first organisms to appear. In the Algonkian, “problematic” forms occur in North America, in the “Belt Series,” perhaps cyanophytic algae (cryptozoon, newlandia, etc.); corycium aenigmaticum occurs in Finland.

Among the thallophytes, definitely identifiable marine algae date back to the Cambrian and Silurian, being contained in limestone rocks; they are highly developed in the Triassic, with gyroporella and diplopora, while lithothamnia were especially abundant in the Tertiary. Calcareous algae may have contributed, 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 forming the nuclei of oolites in the Dogger limestones of Sardinia). Among the siliceous algae, diatoms, with shells of amorphous silica whose ornamentation is sometimes visible only under the electron microscope, occur in three principal forms: boat-shaped or navicular; round or ellipsoidal; and polygonal in outline. Diatoms date back to the Cretaceous and perhaps to an earlier period, and formed diatomites, of which the “fossil flour” of S. Fiora [in the Amiata], originating in tiny Pleistocene lakes, is particularly prized.

The first terrestrial vascular cryptogams (plants with roots, stems, and leaves) appear in the Silurian. For the Carboniferous, the cycadofilicineans should be recalled, progenitors of the ferns and comparable to the present-day tree ferns of tropical forests (genera sphenopteris, pecopteris, neuropteris, etc.); among the calamites, calamites; among the lycophytes, lepidodendron, sigillaria, and the root-like rhizomes called stigmaria. Equisetaceae and ferns are still well developed in the Triassic, the latter, together with conifers, also in the Jurassic. Among the gymnospermous phanerogams are remembered: cordaites, 30–40 metres tall, and noggeratia among the Carboniferous cycads; among the conifers, the genera voltzia and ullmannia of the Permian. Angiosperms appear in the Jurassic (the Dogger of Yorkshire and Sardinia), when the pteridosperms were beginning to disappear. They developed in the Cretaceous: salix, populus, ficus, quercus, eucalyptus, etc. Monocotyledons also appear during this period. In the Tertiary, palms are important; numerous trunks of them are found silicified (Sardinia, Cyrenaica [Sahabi], Egypt, North America, etc.).

With regard to the fossil plant kingdom, the following observations may also be made: in the Anthracolithic, two botanical provinces are distinguished: northern and southern. In the latter, that is, in correspondence with the land of Gondwana (Australia, India, southern Africa, Borneo), the flora is formed by glossopteris and gangamopteris. The Carboniferous phanerogams all belong to tropical coastal environments, comparable to the present-day swamps, that is, the marshes of Virginia, the Gulf of Mexico, etc., or to the marine areas with mangroves of the Red Sea and the Indian Ocean. Permian plants have considerable affinities with those of the Triassic. In the Quaternary, well-defined paleobotanical provinces arise; in the Pleistocene, paleobotanical associations display fundamental characteristics parallel to those of the faunas of the same period. Among the “cold” forms occupying glacial areas is the “dryas” flora (dryas octopetala L.), of tundra or high-mountain facies, accompanied by pinus montana, betula nana, salis polaris, etc.; whereas during the interglacial phases there are warm forms, such as ficus carica, buxus sempervirens, vitis vinifera, etc., which spread northward. A renewed evolutionary development of plants occurs after the last glaciation, with forms that still live today.

The reconstruction of the Quaternary climatic periods is based on the qualitative and quantitative study of pollen contained in strata, peat bogs, etc. Pollen grains have distinctive forms that sometimes make it possible to determine individual plants at the species level.