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Paleontological discoveries of beetles

Imprint of a fossil beetle from
collection of PIN, RAS
(Photo by D.E. Shcherbakov)

A.G. Ponomarenko

Importance and basis of studying the history

Knowledge of the history of the surrounding world is very important for its adequate understanding. History shows that nature cannot be compared to a perfect clockwork, all details of which have been carefully designed. It has turned out that many features of the recent world are the result of accidental events in the remote past. Secondly, science focuses on repeating events and we should not restrict our study to nature surrounding us at the present moment. History to a certain degree extends our knowledge telling us not only about separate episodes of development of biosphere of the Earth, but also gives us a possibility to see a sequence of essentially different biospheres analyzing structure and functioning of which we can distinguish the most fundamental features of life. As concerns our subject, Coleoptera, history increases considerably the diversity of forms available for a study replacing the reconstruction of relationships, based upon properties of recent insects, by knowledge of their ancestors. It may be assumed that in the evolution of beetles and all insects with a complete metamorphosis the evolutionary changes of larvae and adults were relatively independent, but only the history shows that the major stages of these changes do not coincide in time. The history has demonstrated that the phases of change of structure and ecological role of separate groups do not coincide, appearance of a taxon does not mean that it immediately acquires the same importance for ecosystems known for it in the contemporary period. Ecological preferences of taxa can vary essentially nearly without morphological changes. Eventually palaeoentomology has convincingly demonstrated that in the recent distribution of insects there are surprisingly few traces of their distribution in the geological past, even the recent one. I would like to take this opportunity of attracting your attention to the book of Elias (1994 - here and further see - " Bibliography on fossil beetles - supplement to catalogue" ) with detailed abstracts of all works (except those in Russian) on Pleistocene distribution of beetles. Historical biogeography, reconstruction of ancient dispersal, on the basis of the recent one, appeared to be poorly grounded and should be replaced by palaeobiogeography, tracing the changes of actual dispersal of organisms in the geological history. However, the vast material, accumulated in palaeoentomology, is still little used by entomologists.

Beetles as an palaeontological object

Collage by Pavel Korzunovich

Remnants of beetles are one of the most interesting objects of palaeonotological research. However, the study being labour-consuming, they remain poorly known and, what is even worse, few results obtained are nearly ignored by entomologists. The situation in entomology is very different from that in other divisions of zoology, where use of data on ancient animals became an integral part of phylogenetic and systematics concepts. Cladistics, however, played a negative role here, because archaic forms cannot be incorporated into its practice by virtue of its principle. At the same time in palaeoentomology and palaeontology in general beetles, one of the largest and the most diverse in ecology order of insects, should be widely used at least in perspective. It has turned out that the evolution of their diversity shows the best correlation, among all terrestrial animals, with the evolution of diversity of insects on the whole and of marine faunae (Alekseev et al., 2001, see Алексеев et al., 2001). Beetles appear to be one of the major models for comparison of the evolution of terrestrial and marine parts of the biosphere. Thus, it is impossible to resolve the question of whether the radical rearrangement of terrestrial ecosystems coincided with the crisis of marine biota near the boundary of the Cretaceous and the Palaeogene or it had occurred 35 million years earlier, when angiosperms spread, without data on the evolution of insects, beetles in particular. It is important that, because of the durability of integuments, remains of beetles are spread more widely than those of other insects, they occur more frequently in facia, favourable for deposition of plants and vertebrates and also in marine facia. Beetles like other insects spread quickly and practically simultaneously (in the geological sense), appearing in different parts of the Earth. The differences in dispersal result not from the difficulty to reach a particular location of the Earth, but because of the difficulty to enter an ecosystem already formed. Thus, the evolutionary potential of beetles is quite high, and the study of their ancient representatives is interesting from many points of view, however, it requires much effort and expertise. Unfortunately a study the palaeontology of beetles is a much more complicated task than that of Hymenoptera or Diptera. By the structure of the wing of the latter it is nearly always possible to determine to what large taxon it belongs. For the majority of discoveries of isolated elytra of beetles at the present state of knowledge it is impossible to identify the beetle by elytra. However there was a period, the Permian except its very end, when the evolution of elytra was the main evolutionary process in beetles. These beetles may be classified by the structure of elytra, which may be done by a few palaeoentomologists.

One researcher can describe and study all remains from such locality. By the end of the Permian the structure of elytra of beetles had no principal differences from that of recent ones. Thus these characters were becoming much more diverse and difficult for study in fossil remains. As a rule such identification is impossible, not only from isolated elytra, but also from relatively complete remains of beetles. For instance, the Curculionoid family of the Early Mesozoic beetles Obrienidae Zherikhin et Gratshev, 1993 was described in Rhynchophora, but a session of experts on weevils held at the end of 1999 in Canberra (Australia) decided that they should be regarded as members of the Archostemata. The reasons for such a change have not been published, and we do not know yet to what end of the system of the order of beetles this family belongs. R.A. Crowson, an eminent expert of beetles, experienced in examining fossil remains, began studying Jurassic beetles of the genus Parandrexis represented by numerous specimens well preserved, but having kept them for several years he did not describe anything. One has to examine fossil remains of beetles for years to be able to distinguish their structures. L.V. Arnoldi applied the following method for the study of fossil remains. He examined the remains imprinted on petrified rock and made a drawing of what he saw. A month and sometimes even a year later, he took the specimen and made a drawing again. This was repeated several times. After that he compared the drawings and retained only those drawings where the interpretations coincided. This however does save from errors. After forty years of study of beetle fossil remain I acquired a greater assurance in correct identification, but I still quite often make mistakes in the interpretation of details. Very diverse Mesozoic beetles cannot be studied without participation of many specialists in separate taxa. It is impossible for one expert to study all beetles of a particular locality. One of the most difficult tasks is the first placement in one or other group. Some groups, for instance, rowe beetles, click beetles or weevils are discriminated relatively easily, although the above story concerning Obrienidae shows that here, too, not everything is so simple. Cenozoic beetles can be studied only by specialists in recent groups. Eventually, a special subject of study are remains of Pleistocene beetles. In the localities a restricted set of isolated sclerites of recent species of beetles is usually represented. These can be studied by palaeoentomologists, specialized in separate regions and by qualified specialists in separate groups of beetles. A considerable advance in our understanding of ancient beetles would be development of an opinion about the nature by auctorum, i.e. by attracting a maximum possible number of specialists to the study of fossil remains. It is the hope for such a possibility made me write this text, but unfortunately in our time of cuts of science, professional science in the first turn, such hope is very weak.

In spite of the above-said palaeoenetomology has accumulated vast data on the geological history of beetles. It may be evaluated from the list of fossil beetles applied that do not include Pleistocene discoveries and beetles of obscure taxonomic status and a list of literature on fossil beetles. A consecutive presentation of geological history of beetles would be the subject of a voluminous monograph. The text proposed is short and serves attracting attention to fossil beetles rather than providing information on those. It includes mostly information that appeared after publication of " Geological History of Beetles" (Ponomarenko, 1995). However, the information is mostly available in the chapter dealing with beetles " History of Insects" (Ponomarenko, 2001); however, that book is difficult to obtain, which justified publication of the present text.

The Permian chapter of the chronicle

Beetles appear on pages of the geological record in the Permian nearly 300 mya. We cannot succeed in the study of the very origin of beetles. No transitional forms between them and other insects with a complete metamorphosis are known. Apart from that the study of early stages of the evolution of beetles is hampered because of the two groups that are not related but are very similar to beetles in the structure of elytra of insects - Protelytroptera and some cockroaches. The most ancient discoveries of beetles are indicated for the deposits of the Asselian layer of Niedermoschel locality in the vicinity of Mainz, Germany (Addresses of localities are given in the list of localities of fossil beetles"), of the most ancient layer of the Permian, in Germany (Huerschemeyer,1999). But neither drawings nor descriptions of those have been made yet, so that their true nature remains unknown. The most ancient described beetles come from deposits of the next Sakmarian layer (sometimes an even younger Artinian layer is indicated) of Boskovice graben in eastern Czechia. Discoveries of beetles there are quite numerous and diverse. They have been described in 8 genera of the family Tshecardocoleidae. Venation pattern of their cellular elytra most of all resembles venation of fore-wings of ancient megalopterans. In other structural characteristics these are quite typical beetles with moveable prothorax, most developed cryptosternic metathorax, transversal posterior coxae incorporated in the thorax, sclerotized basal sternites of abdomen and apical ones drawn inside, the ovipositor protruding outside. Their major difference from later beetles is the elytra reaching far behind the apex of the abdomen covering hind-wings, in which apex was unable to fold. The most ancient known beetles are true beetles. Their placement in a separate taxon is unjustified, because they are closer to the recent Cupedidae than to the majority of the recent beetles.

The next discoveries of beetles were made in several localities belonging to the Kungurian layer, the last layer of the Lower Permian in the Urals, the major of these being Chekarda in the Permian Region. All beetles from there belong to one and the same family Tshecardocoleidae, but veins on their elytra are to a greater degree straightened along the elytron. Beetles are rare, comprising fractions of one per cent of all discoveries.

In the numerous Artinian localities of North America, where many remains of insects have been found beetles have not been discovered, which is quite strange, because North America and Europe formed a single continent at that time. Over more that 20 million of the Early Permian history beetles had undergone nearly no changes, whereas there have been dramatic changes over several millions of years close to the end of the Permian.

One of the major processes of beetle formation was the conversion of their fore-wing into a light and durable double-layer formation, the upper surface of which was formed by dilated veins, dislodged cells to empty narrow columns - columellae. These transformations may be observed in Late Permian beetles. By the end of the Permian their elytra became indistinguishable from elytra of modern beetles.

This process occurs in two ways. In one lineage, in cupedoids veins of pre-elytron are first organized into a mechanically perfect lattice structure and then veins replace the cells converting fields of the wing into punctuated grooves. In the second lineage in schisophroids replacement occurs rapidly, immediately on the basis of little specialized venation. It is important to note that no strict dichotomy is observed, elytra with smooth surface arise in the majority of branches "evolutionary grass-plot".

Probably the smooth elytron is an adaptation to inhabiting water. Small beetles might have not smooth integument to move in water or to stand in moving water when ambient flow is laminar. For larger forms at relatively low rates turbulence arises, water resistance increases abruptly and beetle in the state of rest is torn off substratum by turbulent vortices.

At the end of the Permian beetles became on the average two times as small as before, owing to beetles for which aquatic mode of life can be assumed; beetles with supposedly terrestrial mode of life disappear from the geological record. They certainly did not disappear completely; a certain number of them survived being a link between Early Permain and Mesozoic xylophylous forms, but they became too rare, to occur in sufficient amount in deposition or survived only in regions where nearly no deposition occurred. It should be remembered that included into the geological record are almost exclusively the most common insects and, in addition to that, insects living in landscapes close to the basis of erosion, boundary between areas of erosion and sediment accumulation.Finds of beetle remains at the beginning of the Late Permian are still rare, but by the end of the Permian they become common and the portion of beetles increased by an order of magnitude and localities appear where remains of beetles are predominant.

Unlike the Early Permian, the Late Permian beetles were found on all continents of that time: in Lavrasia (North America and Europe), the largest numbers in the north-east of European Russia, on Angarida ( Siberia), in Kuznetsky and Tungus basins, in Eastern Kazakhstan, on microcontinents, later in Gondwana, in Brazil, South Africa and Australia.

These are not isolated localities, but sufficienly dense sequences of 4-6 levels differing notably in the composition of beetle remains. In Europe, on Angarida, and in Gondwana changes have the same direction and possibly the same rhythm. In Kuznetsk Basin, in the Late Permian, content of beetle remains among all other remains of beetles increased dozens of times, remains of beetles occurring in nearly any locality.

Unfortunately the majority of remains are isolated elytra. In European Russia their content during that period does not grow quickly; however evolutionary levels are located more densely. By the middle of the Late Permian xylophilous Permocupedidae disappeared everywhere almost completely. Schisophoroids with nearly or completely smooth elytra became predominant.

Possibly also elytra of the first adephages are present among them. At the very end of the Permian elytra probably belonging to polyphages spread rapidly everywhere. There is only one locality, Babii Kamen', in Kuznetsk Basin, belonging to the very end of the Permian or the beginning of the Triassic, containing relatively numerous, complete remains of beetles. The majority are polyphages, including hydrophyloids, byrrhoids, but many of them cannot be identified with certainty so far. Among adephages there are both terrestrial and aquatic forms. Aquatic larvae are absent. Schisophoroid archostemates are very few, cupedoids are absent.

The Late Permian time is interesting in one more respect when the last but one great change of the climate of the Earth took place. In the Late Carboniferous and the Early Permian the climate was similar to the recent one to the extent different stages in the unique history of the planet can resemble each other. On the giant southern supercontinent Gondwana, consisting of present Africa, India, South America, Australia and Antarctic, continent huge plain glaciers existed, some of which reached the thirtieth parallel!

However, it was not as cold in the high latitudes as it is at present. There was no glaciation on the narrow strip of the eastern extremity of Asian Angarida, stretching nearly to the pole. By the middle of the Late Permian plain glaciers, followed by sea ices, disappeared, and equable climate that spread on the Earth, had no significant seasonal or latitudinal differences. On lower latitudes climate was hot and dry, but it was not desert climate. From middle latitudes nearly to the poles the zone of more humid and temperate climate a zone of more humid and temperate climate was spread. Even on the poles negative temperature were rare if any. Such climate existed throughout the Mesozoic and a half of the Cenozoic, it was not until then that the climate gradually became more zonal and seasonal.

Any discoveries of fossil remains from the very end of the Permian are particularly interesting because at that time there occurred processes in the biosphere that led to the most large-scale extinction in the history of the Earth. The largest transformation of composition of beetles occurred much earlier than the period of mass extinction. At present the conceptions of external blast as the cause of the major evolutionary changes have become a paradigm. Asteroids falling on the Earth are regarded as the acting reason. It is seen from the above-said, that this reason did not play an essential role in the evolution of beetles. The major change in the composition of beetles was prepared for one half of the Late Permian time and then occurred very rapidly, but still before the end of the Permian. Extinction began when beetles composition had already changed, but nevertheless it had no impact on them.

Triassic chapter of the chronicle

By the end of the Permian approximately 250 million years ago the Palaeozoic era finished and from the Triassic period the next, Mesozoic era began. More than one half of all animals and plants became extinct in the sea, many large groups disappeared from the Earth. Extinction on land was not so significant, but diversity declined also. Low Triassic localities are few and their diversity is low (if Babii Kamen' is regarded as Permian). All these very similar smooth elytra in all probability belong to aquatic adephages of schisophoroids.

Xylophylous cupedids are absent. It is interesting that in these localities nearly no remains of terrestrial plants occur. Nowhere on the Earth cases of carbon formation are known. Among the terrestrial vertebrates purely aquatic labyrinthodonts are spread. Rare xylophylous beetles and representatives of polyphages appear in the Middle Triassic, but forms with elytra of schisophoroid type are predominant. It was not until the Late Triassic that the situation was restored.

Cupedids comprise up to one third of the remains, the rest are schisophoroids and polyphages. Among the latter forms close to artematopoids, click beetles appear; Byrrhidae are quite numerous. Long-rostrate Obrienidae, whether they were weevils or archostemates, could have been the first beetles related to strobiles of gymnosperms. Aquatic larvae of beetles are absent, but they appear at the very end of the Triassic simultaneously with an abrupt increase of the portion of larvae of aquatic insects among all remains. The rove beetles, that in principle are not different from the modern ones, appear from approximately the same level.

The end of the Triassic and the beginning of the Jurassic period are characterized by a recurrent decline in the diversity of both marine and terrestrial animals, including insects. It is interesting that some species including beetles are present on both sides of the boundary. Among them there is one genus that existed up to the present from deposits of the very end of the Triassic. R. Crowson described genus Omma (Cupedidae) now inhabiting in Australia. Those insects were buried in marine deposits in England and age of the finds can be determined very accurately.

Jurassic chapter of the chronicle

The Jurassic time (210-140 mya) in the history of beetles is quite interesting. There are more than 150 localities where beetles were found, but unfortunately the majority of those are situated on the territory of modern Europe and Asia. Localities on Gondwana land are few, and are very poorly known; but we can hope to obtain in the future a complete picture of the Jurassic period in the history of beetles. At present more than 600 species of Jurassic beetles belonging to 35 families have been described.

Among Jurassic insect families, extinct families constitute by the present approximately two thirds, but beetles are more "recent", extinct families constitute only a few per cent. As has been mentioned, Jurassic climate was equable, but the boundary between the hot and temperate zones was not permanent. At the very beginning it passed far from the equator, then for the most of the Jurassic that boundary was far in the south, so that the temperate zone included most of China, at the very end of the Jurassic it was replaced north to Yakutia.

These climatic shifts are well diagnosed also by distribution of beetles. A major and the best known Mesozoic group, Cupedidae, occurs only in the hottest zone. Recent representatives of that family show no such preference. From the very beginning of the Jurassic one more recent genus south American Tetraphalerus appears among cupedids. All recent cupedids exist owing to wood of angiosperms, which had not yet existed in the Jurassic time. Ecology and physiology can change essentially without any strong changes in beetle structure. It is no less surprising that in the temperate zone the click beetles almost never occur, whereas on territories situated further south they are one of the dominants. In the recent time several localities in North America and India, close to the palaeoequator have been discovered, but nearly nothing is known about beetles collected there.

There is a good chronometer for that stage, in Europe the Jurassic period is characterized relatively completely from the very beginning, from the transition from the Triassic, up to the end. It should be only taken into account that composition of beetles in Jurassic marine localities differs essentially from that in deposits of Jurassic inland lakes. Two marine sites are particularly interesting. For the end of the Early Jurassic, Lias, a number of localities in eastern, western and southern Germany, southern England and Luxembourg are known.

Their similar age is controlled by joint discoveries of ammonites. Beetles got into the deposits from different islands that existed at that time in the place of Europe. It would be interesting to study the difference of population of beetles over such vast territory, but unfortunately no regular studies of this fauna have been conducted. Ground beetles and water scavenger beetles, are predominant in these localities. Apparently these were inhabitants of coastal litter. Remains of cupedids do not occur.

Another interesting sea deposition is shallow water lagoons with abundant microscopic algae. The best known of these localities is Solnhofen in Germany where the famous archeoptheryxes were found. In calcareous sediments of algae also a large number of insects, beetles included, were deposited. The majority of beetles in the deposition are relatively large dytiscoid Coptoclavidae, in their mode of life reminiscent of whirligig beetles and collecting insects falling on water surface. Larvae of Coptoclavidae do not occur in these sediments. Large bugs Belostomatidae and Nepidae lived in lagoons together with them. Terrestrial beetles, among which xylphylous cupedids were particularly numerous, got there from land, next in occurrence frequency were ground beetles close to trachipachids. Buprestids, click beetles, water scavenger beetles and scarab beetles were less frequent.

Lake of the hot zone are somewhat similar to those lagoons. The best known of such localities is Karatau in Kazakhstan. It has been studied relatively well. From approximately one thousand of found beetles more than 200 species belonging to 23 families have been studied. There are relatively numerous adult coptoclavids, larvae do not occur also. Less numerous are water scavenger beetles and whirligig beetles; predaceous diving beetles are even less numerous. The most abundant and diverse groups are click beetles and curculionoid beetles, belonging to several families. Among these Curculionidae proper are absent. V.G. Dolin described more than one hundred of species of clich beeles (see references on fossil beetles). Cupedids, ground beetles and rove beetles are numerous. Of the large families long-horned beetles are absent, and leaf-eating beetles are represented by only extinct Protoscelinae that inhabited most probably in pachycaulous trunks of numerous Bennettitales. To judge by separate described represe ntatives of different families the majority of large groups of beetles had already existed.

Composition of beetles deposited in bottom sediments of small Jurassic lakes of Siberia, Mongolia and China is similar to the one described above and at the same time is very different from it. The most common remains here are larvae of aquatic beetles - ditiscoid Coptoclavidae and Liadytidae, water scavenger beetles. Adult Coptoclavidae occur, although not very frequently. Further northwards larvae occur more frequently; further south, the number of localities including only adults only increases. Adult coptoclavids in different localities are mostly different, but, but no larvae have been distinguished, they are structured very similarly in many Jurassic localities of different ages. It was not until the very end of the Jurassic that larvae differing in structure appeared. For Liadytidae and hydrophilids also several species by adults and one larva have been described. Among terrestrial beetles the rove beetles, pill beetles and beetles reminiscent of them in the structure of elytra are predominant. Ground beetles are rarely represented by Trachypachidae only, and the only larva found by chetome appeared to be advanced Pterostichinae (Makarov, 1995).

Cretaceous chapter of the chronicle

It is better to consider Beetles of the Early Cretaceous (140-100 mya) and Late Cretaceous (100-67 mya) separately. Early Cretaceous beetles, like other insects, are mostly typically Mesozoic and gravitate towards Jurassic ones; Late Cretaceous beetles are closer to Cenozoic ones, near the boundary of Early and Late Cretaceous nearly all extinct beetle families disappear; Late Cretaceous and Cenozoic beetles all belong to recent families; special families repeatedly described for these beetles were reduced to synonyms of the recent ones. More than 150 localities of Early Cretaceous beetles are known on nearly all continents, but mostly in Europe and Asia, the latter is the result of better knowledge of those regions.

The sites with fossils that are closest to the pole are situated in northern Siberia and Australia, site Santana in Brazil is situated almost exactly on the palaeoequator, but the majority of sites are situated in temperate latitudes, in the south of the temperate zone and in the north of hot zone. The time of formation of localities coincides with nearly the entire Early Cretaceous; only the last part of the Early Cretaceous time is characterized less, which hampers the study of transformations of beetle fauna at the time of dispersal of the most ancient angiosperms.

Diversity of aquatic beetles is not increasing. but is even declining. Jurassic families, such as Liadytidae and Parahygrobiidae no longer occur. Predaceous diving beetles, are still very rare and numbers of whirligig beetles somewhat increase. Coptoclavids are still the most widespread family. On the majority of territory they are quite diverse, but still do not occur frequently.

In eastern Asia, only one species Coptoclava longipoda Ping lived from Transbaikalia up to southern China throughout nearly the entire Early Cretaceous for approximately 30 million years, its remains occurring in huge amounts in many localities. Hundreds of adults and many thousands of larvae of this beetle have been collected. Their structure has been studied in detail up to internal apodemes, hindwings and genitalia. The beetles, their size of a large predaceous beetle, were reminiscent of whirligig beetles in their mode of life, although they were less specialized. Larvae were non-arctic predators with strong rowing middle and hind legs and seizing forelegs.

Unlike the majority of Dytiscoidea, the ancient ones included, they did not have in their jaws a channel for exaution of the prey. Their major food were probably Chaoboridae mosquitos inhabiting in great amounts in the same water-bodies. They apparently fed also on other insects. They could also attack small fish. Other aquatic beetles altogether were much less numerous than this species. Although water scavenger beetles were more diverse, particularly widely spread among them were those similar to the recent ones in the structure of adults, but very different from them in the structure of larvae.

Among terrestrial beetles the abundance of cupedids declined notably, and even more so, the abundance of other archostemates. Buprestids became the major wood consumers; they were obviously more abundant in the Cretaceous epoch than now. However, nearly all of them belonged to an extinct subfamily. Another group whose abundance had strongly increased were scarabeids; all their large taxa already existed in the Cretaceous, but there were no dung beetles, they apparently fed on decaying plant remains. Pill beetles and beetles close to artematopodids were still numerous, but the role of click beetles decreased notably, even though they remain a predominant family. Quite numerous are lower Cleroidea and Bostrichoidea beetles appear for the first time. Curculionoidea did not become more abundant, but their diversity increased; true Curculionidae appeared towards the end of the Early Cretaceous.

The last noteworthy fact in relation to Cretaceous beetles is the appearance of insect-bearing fossil resins in the Early Creataceous, which are usually incorrectly called ambers. The deposition in amber considerably extends the possibilities of studying beetles particularly small ones. Not only it is possible to study the external structure up to minute details, but also many features of the internal structure. Even DNA structure of the Early Cretaceous weevil from Lebanese "amber" was studied. Composition of beetles in benthic deposits and ambers is essentially different, so that the study of different deposits contributes greatly to our knowledge about ancient beetles. Many groups of beetles are known from ambers only.

Change of the composition related to the appearance and dispersal of angiosperms touched beetles to a much lesser extent than other insects. This could have been due to the predominance of recent families among beetles in the Mesozoic. Not a single extinct family of beetles from the Upper Cretaceous deposits is known. Particularly important changes among water beetles are known. Coptoclavids that were predominant earlier disappear completely, numbers of water scavenger beetles decrease considerably, abundance of predaceous diving beetles increases slightly, there is a significant increase in the abundance of wrihligig beetles. Aquatic leaf-eating Donaciinae appear, and they become very abundant by the very end of the Cretaceous.

Terrestrial beetles change less. Abundance of archostemates falls below one per cent, only cupedids remain, and a larva of Micromalthus was found in amber. Weevils become most abundant, they are not most abundant in only a few localities. They are followed by very abundant buprestids. Noteworthy is low abundance of ground beetles and rove beetles although there are localities, e.g. diamond pipe "Orape" in Botswana, where advanced ground beetles are predominant. In Late Cretaceous amber more than ten beetle families were found for the first time.

New (Cenozoic) history

The dramatic decline of diversity on the boundary between the Cretaceous and the Palaeogene, when many marine animals and dinosaurs became extinct, had nearly no impact on beetles. In the Russian Far East there are sufficiently rich localities on both sides of the boundary, showing no essential differences, although Labandeira (2001) described considerable extinction of beetles based upon the change of frequency of occurrence of traces of damage of leaf-eating beetles on ginger leaves.

The spectra of elytra from the Maestrichtian, the last century of the Cretaceous, and the Danian, the first century of the Palaeocene, (Palaeocene: 65-55 mya) are very similar. A similar abundance is noted for Donaciinae (similar in elytral structure with Plateumaris), weevils, whirligig beetles; cupedid Zygadenia (=Notocupes), most widely spread in the Mesozoic, has been found. The Cenozoic beetles also appear, e.g. Palaeogyrinus, typical of the Palaeogene. The Palaeocene remains poorly studied, only 19 families and 10 described species are known.

However, fauna of the Eocene(55-58 mya), following the Palaeocene, has been studied best of all, primarily because of Baltic amber. Of 101 beetle families known from the Eocene 88 were found in Baltic amber. The most widely spread families are Scirtidae, Elateridae, Anobiidae, Staphylinidae. Abundance of Scirtidae is apparently assigned to the fact that in spring they gather on male pine strobiles, and the pine tree is the most probable source of amber resin.

Anobiidae, in all probability, are associated with pine tree. The majority of data on beetles of Baltic amber are not descriptions, but only indications of discoveries, and those are extremely contradictory. The famous coleopterist E. Reitter, identifying the tremendous collection of Klebs placed nearly all beetles in European genera. Other authors described the majority of genera as exotic. Now these genera inhabit Australia, South America, south Asia, seldom Africa. About one half of the genera are described as extinct. S.M. Iablokoff-Khnzorian (1960) described six genera of Scirtidae, four of those as extinct. However, B. Klausnitser of 257 studied Scitridae did not find a single representative of extinct genera. All families of beetles described from Baltic amber are reduced to synonyms. Approximately one per cent of species are identified as recent, but partly they may be imitations. However, Tetracha carolina, an American species described from amber, was reexamined and proved to be the species, but not an imitation. Therefore, a more intensive study is needed even for Baltic amber. Eocene ambers were found in North America and Far East.

Apart from ambers other remarkable localities are also known from the Eocene. The majority of those were formed in large lakes with deep water layers poisoned by hydrogen sulfide. The Eocene was the last epoch with warm equable climate. Broad-leaved forests grew and crocodiles lived at 83ёN, nearly on the northern pole, palms grew in Kamchatka and Europe. In these localities nearly no aquatic insects occurred, and it is in these bad basins that more than a dozen of larvae described as psephenid Eubryanax have been found. Now all Psephenidae, strict rheophils, occur only in rivers and streams with high flow velocity. Remains of other aquatic insects occur more frequently in coprolites of fish than in bottom sediments. The most frequently occurring beetles here are buprestids and click beetles, but long- horned beetles are still scanty, they are fewer than stag beetles. These lakes existed in hot climate, however, insects have the appearance of inhabitants of temperate latitudes, because all stag beetles did not have enlarged mandibles.

The Eocene was followed by the Oligocene (38-25 mya) the last epoch of the Palaeogene. In the Oligocene two major processes took place that began as early as the end of the Eocene. Global cooling began, which was completed by glaciers of the Pleistocene. Cooling proceeded gradually, warmer periods alternated by cooler periods. The Oligocene was even cooler than the Miocene, which followed. Redistribution of heat on the Earth occurs through redistribution of water vapour.

Climate over the most part of the Earth became more arid. Savannahs arose in the place of former continuous forests; grasses and, in the first turn grains, dispersed widely. Grains possess many specific characteristic features, even their photosynthesis is specific. They are well adapted to habitation in a climate, which is little equable and has a pronounced seasonal pattern. At the expense of the huge mass of roots they are not only capable of procuring water, but they also quickly restore green part of plants lost as a result of draught or colds.

Therefore, they are more easily than other animals endure the eating by animals, all the more so because the eating of dry remnants of vegetation is useful for grains, otherwise the steppe turns into hummocky. At the same, owing to grain roots, soil-forming process is triggered and erosion declines abruptly. Dispersal of grains altered both terrestrial and freshwater ecosystems. On land the number of insect families consuming green mass of plants began approaching number of families of sucking insects. Numbers of butterflies and leaf-eating beetles increased, which was followed by an increase of diversity of predators and parasites.

The same process occurred also in mammals. The areas now inhabited by scanty forest animals were inhabited by herds of rhinoceros, horses and different artiodactyls. Dung beetles begin occurring much more frequently, their balls occurring permanently in the locality. Development of soil and decrease of erosion replaced also life in fresh water-bodies. Nutrients now enter them more moderately and more evenly, lakes are overgrown by macrophytes and their state is stabilized. As a result diversity of insects in them is increasing considerably. For instance, diversity of predaceous diving beetles increases by nearly an order of magnitude. Seventy-three families of Oligocene beetles are known and several hundreds of species have been described, but nearly all of them were described a long time ago, and the description is insufficient.

After the Oligocene the Miocene begins (25-5 mya) - the first epoch of the Neogene period. Even less Miocene beetles are known, only 67 families. Certainly a decline in the number of families is related only to the level of knowledge. The number of families in the Oligocene and Miocene increased relatively fast, and by the end of the Miocene it approached the recent one. Tropical rainforests appeared as early as the Oligocene and by the end of the Miocene taiga and plain tundras arose.

The majority of localities of Miocene insects belong to the temperate warm and subtropical zone, but there are near polar and tropical zones. The majority of genera and many species of insects were already the same as recent ones. Their dispersal strongly differed from the recent one. Thus, in the locality of Stavropol at that time on lowland Caucasian island no insects specific for the Caucasus were found. The only examined group of beetles is predaceous diving beetles, in their composition they are similar most of all to beetles from Northern Africa.

At the end of the Miocene the nature made an interesting experiment. The Mediterranean dried out several times leaving thick layers of salt on the former bottom. Nevertheless, the bottom was overgrown very quickly, and insects from localities on the bottom of the Mediterranean Sea differ little from those of the neighbouring areas. There are somewhat more insects characteristic of open spaces, than in localities in the vicinity of Vienna.

The last epoch of the Neogene, i.e. the Pliocene, was short only 3.5 mya and there is only one relatively completely studied Pliocene locality in Willershausen in Germany. About one half of species are recent, but European and exotic forms are also present. A beetle of the genus Сupes was found; C. madeira was found together with Calosoma sycophanta. A total of 18 families are represented. Of the 35 genera 6 are extinct. Pliocene and Pleistocene Donaciinae were thoroughly studied in Japan. Nine species were found; now 20 species occur in Japan. Only three species definitely occur in Japan, but one of them differs from Japanese subspecies. Two new species from the Pliocene and the early Pleistocene were described.

Pleistocene (recent) history of beetles was described by S.A. Kuzmina in a separate file

Imprints of fossil Curculionidae
Photo from the site

A.G. Ponomarenko
Palaeontological Institute, RAS
March 2003


Closely connected with the subject of this part isinformation on "living fossil" - Beetle Sikhotealinia zhiltsovi of the family Jurodidae.