Summary Of The Insect Fossil Record

Figure 3 summarizes the chronology, approximate diversity, and possible relationships of major groups of living and extinct insects.

Paleozoic (570-245 Mya)

The earliest remains of terrestrial animals are arthropods from the Silurian, including primitive scorpions, millipedes, and tTrigonotarbida (extinct, primitive arachnids). Two major hypotheses on the origins of the hexapods (including insects) are that they are most closely related to either the myriapods (centipedes and/or millipedes) (all comprising the Tracheata, or Atelocerata) or the Crustacea. Crustacea may actually have the oldest fossil record of all animals (formerly held by the trilobites) because some Precambrian fossils have recently been reinterpreted as crustaceans. If hexapods are closely related to crustaceans, it is most likely to be a group within Crustacea, and the earliest evidence of this stem group will probably be found in the Silurian.

THE DEVONIAN (408-362 MYA) The Devonian was a period when the continents were largely inundated and joined into the large supercontinent Pangaea. Lycopods, lycopsids, and horsetails (Equisitoidea) were common terrestrial plants; primitive groups of fishes radiated, and amphibians first appeared. The earliest record of hexapods is from the Rhynie chert of Scotland, ca. 400 mya, and is the collembolan tRhyniella praecursor (Fig. 4a), although a pair of mandibles in this chert is suggestive of dicondylic insect mandibles. The Rhynie chert also contains mites, trigonotarbids, and a primitive spider.

Approximately 10 million years younger is an undescribed archaeognathan (=Microcoryphia) from the Gaspé Peninsula in eastern Canada. Apterygotes, each with a single, long caudal filament ("Monura" = Archaeognatha), occur in the Carboniferous and Devonian (Fig. 4b). Unidentified insect remains from 378 mya are known from Gilboa, New York, along with centipedes (Chilopoda) (Fig. 2a), true spiders (Araneae), trigonotarbids, oribatid mites, and pseudoscorpions. The Gaspé and Gilboa remains are original cuticle.

THE CARBONIFEROUS (362-290 MYA) The Carboniferous period is famous for the wet, warm climates and extensive swamps of mosses, ferns, seed ferns, horsetails, and calamites. Remains of insects are scattered throughout Carboniferous coal deposits (particularly blattarian wings); two particularly important deposits are Mazon Creek, Illinois, and Commentry, France. The earliest pterygotes appear in the Carboniferous, including the Blattaria, tCaloneurodea, primitive stem-group ephemeropterans (Fig. 4f), Orthoptera, tPaleodictyop-teroidea (Figs. 4c and 4d), t"Protodonata" (Fig. 4e), and t"Pro-torthoptera"; the latter two are paraphyletic assemblages of primitive pterygotes.

Hypotheses on the evolution of insect wings include their use originally as gills or gill covers, or for mating displays, but early outgrowths of the insect pleuron most plausibly served in gliding. Feeding damage on plants is also recorded first in the Carboniferous, in the form of punctures and deep holes probably made by the long, beaked mouthparts of paleodicty-opteroid insects. Thus, insects have been evolving in close association with plants for at least 350 million years, which is longer than any other group of terrestrial animals. Arborescent plants appear in the Upper Devonian, and as Carboniferous insects increasingly dwelled in them to feed, gliding probably became so adaptive for escape and dispersal that flapping wings and powered flight evolved rather suddenly.

Putative Holometabola are recorded from the Carboniferous. One is a larva from Mazon Creek, Srokalarva berthei, many features of which are inconsistent with extant holometabolan larvae, including segmented abdominal legs, ocelli, and possible compound eyes. Legs and body segments of Srokalarva are undifferentiated, as in myriapods. Some tree fern galls (ca. 300 mya) are attributed to the Holometabola on the basis of size of frass pellets in the galls. Some Paleozoic arthropods were considerably larger than living relatives, and Carboniferous gall-making mites are also known, and so it is possible that large mites caused these ancient galls. The earliest definitive Holometabola occur in the Permian.

Blattaria (Blattoptera) This group consists of the Dictyoptera (mantises, termites, and ovipositorless roaches) plus the Paleozoic and Mesozoic "roachoids" that possessed an ovipositor. Very early, Carboniferous blattarians possessed a large, discoid pronotum and coriaceous forewings with a distinctive CuP vein. From the Carboniferous to the Cretaceous there was a gradual diminishment in the length of the ovipositor. The first true, ovipositorless roaches as well as probable oothecae appeared in the Triassic. Thus, the common view that modern roaches are exceptionally ancient is inaccurate.

fCaloneurodea and fMiomoptera Both orders are known only from the Upper Carboniferous to Permian and, with Orthoptera and Blattaria, were among the earliest known Neoptera. These insects had homonomous wings with small anal lobes. In Caloneurodea the wings had many crossveins that formed numerous square cells. Wing structure and unsegmented cerci (the latter known from only few genera) suggest relationships with the orthopteroids. The wings of Miomoptera were shorter and broader and had very reduced venation. A close relationship of Miomoptera is plausibly with the Psocoptera, but probably with the Hemiptera. With a wing length of 3 to 5 mm, these are the smallest Paleozoic pterygotes known.

Orthoptera This is an ancient Recent order extending from the Carboniferous, from which time even the distinctive synapomorphy (advanced defining feature) of saltatorial hind legs is preserved (fOedischiidae). By the Triassic, stridulatory organs on wings evolved, and some extant families had first appeared (Haglidae, Gryllidae). fElcanidae and related families (Permian to Cretaceous) are distinctive for the reduced forewing venation with numerous parallel M and Cu veins; they were probably the most diverse and abundant orthopterans in the Late Paleozoic and Early Mesozoic. Many extant families do not appear until the Cretaceous (e.g., Eumastacidae, Gryllotalpidae, Tridactylidae, Tetrigidae) or even the Cenozoic (Acrididae, Tettigoniidae, Gryllacrididae).

fPaleodictyopteroidea This group includes the orders fDiaphanopterodea, fMegasecoptera, and fPaleodictyoptera, which had very long cerci, an ovipositor, and wings with little or no anal lobe (all primitive features). It is the only definitively monophyletic group from the Paleozoic, defined by a long, rigid beak with five stylets, as well as (primitively) a well-developed pair of possible maxillary palps. Nymphs were terrestrial, with large, free wing pads bearing rudimentary venation (Fig. 4d) and mouthparts similar to those of the adults. The group is among the most primitive pterygotes, and their distinctive parapronotal lobes (often with a rudimentary venation) probably are part of the ground plan of pterygote insects. The Paleodictyoptera are probably paraphyletic with respect to the other two orders, because they possess complete wing venation with an archedictyon. Diaphanopterodea folded wings over the abdomen at rest, an ability convergent with Neoptera. Megasecoptera had substantially reduced venation, often with a graded series of crossveins (Fig. 4c). Some had striking color patterns on the wings (e.g., Spilapteridae), and some were impressively large (e.g., Homioptera, approximately 40-cm wing span).

f'Protodonata" This group is a paraphyletic assemblage of primitive pterygotes similar to true Odonata but lacking the derived features of modern, true Odonata, such as the nodus, pterostigma, and arculus. Some (i.e., Permian Meganeuridae) were the largest insects ever, with a 70-cm wing span (Fig. 4e). They existed from the Upper Carboniferous to the Permian and were clearly the dominant aerial predators for some 100 million years until flying reptiles appeared in the Triassic. Fossils with the venation of true Odonata did not appear until the Triassic.

f"Protorthoptera" (=f"Paraplecoptera") (Fig. 4g) This is another paraphyletic assemblage of primitive pterygotes, with affinities not necessarily suggested by their name. Some refer to this group as the Grylloblattida (sensu lato), but there are no derived features that indicate a relationship of these extinct insects with this relict, extant order. Some had forewings that were coriaceous (i.e., sclerotized and leathery), but usually with an archedictyon. Unlike Orthoptera, most did not have hind wings with expanded anal lobes, and none are known to have folded their forewings roof-like over the abdomen (instead, folded flat and over each other), none had saltatorial hind legs nor a tarsomere number reduced to 3. Some had raptorial forelegs; fGeraridae had large pronotal spines.

permian (290-245 mya) The Permian was a relatively short but very important period, when extensive mountain ranges were formed, such as the Appalachians; this caused the interior climates of continents to become cooler and drier. Extensive glaciation of the Southern Hemisphere also occurred. Voltziales and glossopterid plants radiated. Insect orders from the Carboniferous extended into the Permian, and many even extensively diversified. Numerous new orders appeared in the Permian: the fProtelytroptera (Fig. 4j) and primitive relatives of the Plecoptera ("Paraplecoptera") (Fig. 4h), Psocoptera (Fig. 4i), Mecoptera (Fig. 4k), Raphidioptera (Fig. 4l), Neuroptera, and Coleoptera (Fig. 4m), the last four orders being the earliest definitive records of the Holometabola. The most significant and diverse Permian insect deposit is from Elmo, Kansas (ca. 260 mya); others are from New South Wales, Australia (ca. 240 mya) and central Eurasia (ca. 250 mya).

The Permian is biologically most notable for the mass extinction that marks the brief interval between the end of this period and the beginning of the Mesozoic. It is estimated that as much as 95% of all Permian life forms became extinct by the early Triassic, although this is based largely on the marine fossil record. It is difficult to estimate the impact of the Permo-Triassic extinction on insects because many of the Paleozoic orders are paraphyletic, and it is likely that particular lineages within each survived into the Mesozoic (Fig. 3). One definitive monophyletic group, the Paleodictyopterodea, may have become extinct at the end of the Permian, but a possible survivor of this group (Thuringopteryx) occurred in the Triassic. Otherwise, major groups of insects show few effects of the most cataclysmic extinction known.

Hemiptera The earliest Permian records are the auchen-orrhynchan-like wings of fDunstaniidae, fPalaeontinidae, and fProsbolidae, which also extend into the Mesozoic. True auchenorrhynchans from the Triassic are Cercopoidea, Cicadoidea, Cicadellidae, Cixiiidae, and Membracoidea. The earliest Sternorrhyncha are fArchescytinidae, fPincombeidae, fBoreoscytidae, and fProtopsylidiidae (all from the Permian into the Mesozoic). The first diverse records of true aphids and coccoids occur in Cretaceous ambers; psylloids are older. Heteroptera are slightly younger than homopterans. Presumed Permian heteropterans are fActinoscytina (fProgonocimidae) and fParaknightia (fParaknightiidae). Venation of the former is barely different from Auchenorrhyncha; the latter had expanded parapronotal lobes, a large ovipositor, and forewings with unusual venation (perhaps an aberrant roach). The earliest true Heteroptera are various predatory aquatic bugs (Nepomorpha) from the Triassic of Virginia (Fig. 1d). By the Jurassic, phytophagous pentatomorphs and cimicomorphs appeared, and modern families were widespread in the Cretaceous.

Neuropterida This group includes the orders Raphid-ioptera and Neuroptera. Systematic position of the one Permian family of putative raphidiopteran (fSojanoraphidiidae) (Fig. 4l) has been considered doubtful, although it had a long ovipositor distinctive to this order and a series of short costal crossveins (distinctive to Neuropterida); the wing venation, however, is quite primitive. Jurassic and Cretaceous raphid-iopterans were diverse, belonging to the fAlloraphidiidae, fBaissopteridae, and fMesoraphidiidae. Raphidioptera is relict today, with three genera in two families having a disjunct distribution in the Northern Hemisphere. The only Southern Hemisphere raphidiopterans are from the Lower Cretaceous of Brazil, indicating that the group was formerly more widespread.

Definitive Neuroptera also appear in the Permian (fArcheosmylidae, fPalaemerobiidae, fPermithonidae, and fSialidopsidae). Triassic diversity is very poorly known (e.g., Psychopsidae), and by the Jurassic there appeared forms that are primitive relatives or members of the Chrysopidae, Coniopterygidae, Nymphidae, Osmylidae, and Polystoe-chotidae. An impressive Mesozoic family was the fKalligrammatidae, with broad, patterned wings and a long, rigid proboscis. In the Cretaceous are the earliest records of the Ascalaphidae, Berothidae, Mantispidae, and Myrmeleontidae. Berothidae were particularly abundant and diverse in Cretaceous ambers. An unusual, dipterous mantispid (fMantispidiptera) is known in Cretaceous amber from New Jersey.

Coleoptera The earliest Permian forms (i.e., fTshekardocoleidae) had long, pointed, coriaceous forewings with definitive venation and arrays of small cells and pits (Fig. 4m). Beetles similar to modern cupedoids were diverse in the Upper Permian and the Mesozoic. Cupedoidea today are a small, relict group. Fossil forms were probably all wood borers as larvae and adults, like modern relatives. By the Triassic, Adephaga appeared (Carabidae, Trachypachidae) as did some basal Polyphaga (definitive Staphylinidae). By the Jurassic the first Hydradephaga (fCoptoclavidae, Dytiscidae, Gyrinidae) appeared, as well as other living families (Elateridae, Hydrophilidae, Silphidae). The earliest records of many living families are from the Cretaceous and the lower Tertiary (especially Baltic amber). Interpretation of compression fossil beetles is greatly compromised by the lack of wing venation characters and restriction to the use of simple features such as elytral structure.

Plecoptera Permian f Palaeperlidae, f Perlopseidae, Eustheniidae, and Taeniopterygidae had venation consistent with this order. Several extant families are recorded from the Jurassic and Cretaceous. fLemmatophoridae and fLiomop-teridae (Figs. 4g and 4h) had expanded parapronotal lobes (sometimes with distinctive venation like the wings) and have been placed in "Protorthoptera." These families are probably related to the Plecoptera because they had nymphs with abdominal tracheal gills and so were probably aquatic.

fProtelytroptera Found only in the Permian, this group is characterized by narrow, elytrous/tegminous forewings and with hind wings with an expansive anal lobe and radiating venation (the latter one reason they have been allied with Dermaptera) (Fig. 4j). The forewings of some species have very few veins; others have intricate reticulation. The fUmenocoleidae from the Cretaceous, formerly placed in this order, are actually blattarians.

Psocoptera The earliest putative members of this order are the Permian fPsocidiidae, but these have cerci and five tarsomeres (vs lack of cerci and generally three tarsomeres in living species) (Fig. 4i). fPsocidiidae do possess the areola postica (short, terminal branch of vein CuA), although this feature also occurs in the Zoraptera and Embioptera. Psocoptera are poorly known in the Triassic, but are diverse and abundant in Cretaceous ambers, which include many living families (e.g., Prionoglariidae, Lepidopscocidae). fLophioneuridae (Permian—Cretaceous) have traditionally been placed in this order, but the reduced wing venation (especially in Permian fZoropsocus) and (where preserved) the

FIGURE 5 Representative Mesozoic (a—f) and Cenozoic (g, h) insects (not to the same scale). (a) Primitive, oldest known thysanopteran (Triassic, Virginia). (b) tProtorhyphidae (Diptera) (Jurassic, Kazakhstan). (c) Sphecidae (Cretaceous, Brazil). (d) Oldest known zorapteran (Cretaceous amber, Burma). (e and f) Oldest definitive ants [Formicidae; Sphecomyrma (e), Kyromyrma (f)] (Cretaceous amber, New Jersey). (g) Large, extinct tsetse fly (Diptera: Glossinidae) (U. Eocene/L.Oligocene, Colorado). (h) Spoon-winged lacewing (Neuroptera: Nemopteridae) (Colorado).

FIGURE 5 Representative Mesozoic (a—f) and Cenozoic (g, h) insects (not to the same scale). (a) Primitive, oldest known thysanopteran (Triassic, Virginia). (b) tProtorhyphidae (Diptera) (Jurassic, Kazakhstan). (c) Sphecidae (Cretaceous, Brazil). (d) Oldest known zorapteran (Cretaceous amber, Burma). (e and f) Oldest definitive ants [Formicidae; Sphecomyrma (e), Kyromyrma (f)] (Cretaceous amber, New Jersey). (g) Large, extinct tsetse fly (Diptera: Glossinidae) (U. Eocene/L.Oligocene, Colorado). (h) Spoon-winged lacewing (Neuroptera: Nemopteridae) (Colorado).

narrowed, projected mouthparts indicate relationship to the thrips (Thysanoptera). fLophioneuridae lack extensive vein reduction, the marginal fringe, and the flagellum and tarsal structure distinctive to true thrips.

Mesozoic

The Mesozoic was an era when terrestrial ecosystems became modern, with the rise of cycads and ginkgos and the diversification of conifers in the Triassic and Jurassic. In the Lower Cretaceous there occurred what was probably the most profound evolutionary event: the explosive radiation of the angiosperms.

triassic (245-208 mya) This was a period when arid and semiarid savannas developed and when the first mammals, dinosaurs, and pterosaurs also appeared. Most deposits with insects are from the Upper Triassic (especially Carnian, ca. 230 mya), including South Africa; Virginia; Queensland, Australia; Tadjikistan; and France. The first evidence of a diverse freshwater insect fauna appears during the Triassic, as did the oldest living families: Cercopidae, Cicadellidae, Cixi-idae, and Membracidae (Auchenorrhyncha); Belostomatidae (Fig. 1d); Naucoridae (Heteroptera); Carabidae; Staphylinidae; Trachypachidae (Coleoptera); Anisopodidae, Chironomidae, and Tipulidae s.l. (Diptera); and Xyelidae (Hymenoptera). The first true Odonata, Heteroptera, Thysanoptera (Fig. 5a), Diptera, and Hymenoptera appeared during this time. The Triassic Hymenoptera consisted entirely of primitive symphytans; the Diptera consisted of diverse nematocerans. tTitanoptera were restricted to the Triassic and the size of some species fit their name (e.g., Gigatitan, ca. 33-cm wing span). Others were no larger than typical orthopterans, to which they are probably most closely related. They may have been Early Mesozoic analogues of the predatory mantises because their forelegs, when preserved, were spiny and apparently raptorial.

jurassic (208-145 mya) One of the more significant events during this period was the origin of birds in the Upper Jurassic. Birds and (much later) bats are the only other skilled fliers and are perhaps the most important predators of modern insects. Numerous Jurassic deposits of insects occur in Europe and Asia: Grimmen and Solnhofen, Germany (the latter famous for the earliest birds, Archaeopteryx); Dorset, England; Issyk-Kul, Kirghizstan; and, the most diverse and productive site of all, Karatau, Kazakhstan. Jurassic deposits of insects are barely known in North America and in the Southern Hemisphere. The earliest aculeate (stinging) Hymenoptera appeared in the Upper Jurassic and were of the family tBethylonymidae. Diptera in the Jurassic were diverse nematocerans (i.e., Fig. 5b), and the oldest definitive brachycerans evolved, dominated by Rhagionidae.

cretaceous (145-65 mya) In many respects, the insect fauna of the earlier part of the Cretaceous has more similarity to the Jurassic than to the later part of the Cretaceous. No doubt this is the result of the radiations of angiosperms 120-100 mya. Today, insects pollinate some 85% of the angiosperms, and so pollinating Cretaceous insects must have helped spawn the diversification of angiosperms; also, the diversification of phytophagous insects (and probably their parasitoids) was promoted by angiosperms. Radiations of some very speciose insect groups began during the Cretaceous, including the Scarabaeoidea, Cerambycidae, Chrysomelidae, and Curculionoidea (Coleoptera) and the Lepidoptera (the largest lineage of phytophagous organisms). The Yixian Formation of China (Lower Cretaceous, ca. 130 mya) has yielded important vertebrate fossils, as well as early angiosperms and nemestrinid flies with long proboscides; these are the earliest records of specialized insect pollination. Early sphecoid wasps (Fig. 5c), empidid and other flies, and some beetles were probably very important, generalized pollinators of early angiosperms. Other important Cretaceous deposits are from Koonwarra, Victoria, Australia; Orapa, Botswana; Ceara, Brazil; Purbeck, Dorset, and Weald, England; Baissa, Russia; and Llerida, Spain. Isoptera appeared first in the Cretaceous, represented entirely by the primitive families Hodotermitidae, Termopsidae, Masto-termitidae, and Kalotermitidae. True, eusocial termites and ants existed for at least 50 million years before they became abundant in the Cenozoic. Eusocial wasps and bees did not first appear until the Upper Cretaceous.

Cretaceous continental drift fragmented Gondwanaland and Laurasia into the continents seen today. One result was fragmentation of ancestral ranges, the areas most famous for this being disjunct temperate regions of the southernmost regions of Africa, South America, Australia, and New Zealand (the "Austral Region"). This region harbors many primitive, relict insect groups.

Conifers were still diverse in the Cretaceous, which produced virtually all of the amber found during the Cretaceous. The oldest amber with insect inclusions is from the Lower Cretaceous of Lebanon, Japan, and England. Highly fossil-iferous, somewhat younger amber deposits occur in northern Burma, western Canada, New Jersey, northern Spain, and the Taimyr Peninsula in northern Siberia. These have been exceptionally important in the study of smaller insects, having revealed the earliest bee (Apoidea), ants (Formicidae) (Figs. 5e and 5f), Zoraptera (Fig. 5d), and Stepsipteran, as well as the oldest definitive Embioptera and Lepidoptera and many families of insects. All Cretaceous Lepidoptera belong to phylogenetically basal families. Cretaceous ambers have also revealed a great diversity of primitive parasitoid Hymenoptera, sternorrhynchan hemipterans (especially Coccoidea), and empidoid flies. Cyclorrhaphan Diptera were rare and primitive in the Cretaceous.

Many of the oldest records of blood-sucking insects are from the Cretaceous: Ceratopogonidae, Culicidae, phle-botomine Psychodidae, Tabanidae, and a possible stem group to the Siphonaptera (tTarwinia, from Koonwarra). Unlike modern fleas, t Tarwinia did not have jumping hind legs and had long antennae, and so it is at best a very primitive relative of fleas. Apterous mecopteroids from the Cretaceous of Baissa and Transbaikalia, Russia, are also believed to have been vertebrate ectoparasites, perhaps of pterosaurs or feathered dinosaurs. Simuliidae appeared first in the Upper Jurassic but were still scarce and primitive in the Cretaceous. Vertebrate ectoparasitism probably first appeared in the Jurassic, but were fully developed in the Cretaceous.

Cenozoic (65 Mya-Recent)

The sudden radiation of orders of modern mammals occurred in the Paleocene (65—56 mya). This period is very poorly known from the insect fossil record, the most diverse deposit being the Fur Formation from Denmark, which preserved giant ants, noctuid moths, and others. The first butterflies (Papilionoidea) are known from the upper Paleocene.

The Eocene (56—35 mya) is far better known for insects, with extensive compression deposits from British Columbia, Canada (Horsefly, Merritt, Princeton); Green River, Wyoming; Gurnet Bay and Bembridge Marls, Isle of Wight, England; and Florissant, Colorado. Florissant (e.g., Figs. 5g and 5h) was an ancient lake inundated with volcanic ash and is probably the most diverse compression fossil insect deposit from the Cenozoic. The greatest diversity of fossil insects is preserved in Baltic amber, huge deposits of which occur throughout northern Europe (from Eocene to Oligocene). The Baltic amber has preserved the first diverse faunas of schizophoran Diptera, ditrysian Lepidoptera, advanced termites, bees, and ants, all of which are relatively young, very speciose groups whose greatest radiations occurred in the Cenozoic. At least 30 species of bees have been found in Baltic amber; paradoxically, the great majority of them are corbiculate bees belonging to extinct genera. The diversity of advanced eusocial bees was much greater than today. The oldest definitive muscoid flies and fleas occur in Baltic amber. Other important Eocene amber deposits are from Fushun, China, and Arkansas.

Deposits from the Oligocene (35—23 mya) and the Miocene (23—5 mya) indicate that the insect fauna was essentially modern, with virtually all species (extinct) belonging to modern genera. Particularly rich Oligocene deposits are from the Ruby River Basin of Montana (compression) and Chiapas, Mexico (amber). Rich Miocene deposits occur in Oeningen, Switzerland (compression), and the Dominican Republic (amber). The age of the Dominican amber has been cited as Eocene but is definitively Miocene. The Dominican amber forest was very similar to contemporary neotropical forests, but there were some groups now extinct from the Caribbean (meliponine and euglossine bees, certain genera of ants, and others) or even from the Western Hemisphere (Mastotermes termites and some genera of ants, acrocerid and phorid flies, and others). Dramatic extirpation of ranges has also been found in other Cenozoic deposits, such as tsetse (now entirely African) (Fig. 5g) and nemopterid lacewings (Fig. 5h, now Southern Hemisphere) from Florissant and many currently austral taxa preserved in Baltic and Cretaceous ambers of the Northern Hemisphere. Although some specimens of insects preserved in Cenozoic ambers are very similar to modern species, it is unclear (especially genetically) if these are conspecific. The average duration of insect species is difficult to estimate, but the upper limit probably extends to 10 mya.

Study of Pliocene (5-1.5 mya), Pleistocene (1.5-0.01 mya), and Holocene (10,000 years ago-Recent) deposits has been extremely useful along with that of fossil pollen in reconstructing paleoclimates and ecological succession. These remains are preserved in existing or ancient lakebeds, bogs, and tarpits. Paleoclimatic use of these remains depends on the availability of indicator taxa or readily identified extant species whose distributions are well documented. Particularly persistent and abundant in lakebeds, and therefore commonly used, are fragments of beetles (Fig. 2g)

and the larval head capsules of chironomid midges.

See Also the Following Articles

Amber • Coevolution • Endangered Insects • Nomenclature and Classification • Phylogeny • Wings

Further Reading

Carpenter, F. M. (1992). "Superclass Hexapoda," Vols. 3 and 4 of "Treatise on Invertebrate Paleontology," Part R, "Arthropoda 4." University Press of Kansas, Lawrence, and Geological Society of America, Boulder, CO.

Elias, S. (1994). "Quaternary Insects and Their Environments." Random House (Smithsonian Inst. Press), Washington, DC.

Evenhuis, N. L. (1994). "Catalogue of the Fossil Flies of the World (Insecta: Diptera)." Backhuys, Leiden.

Grimaldi, D. A. (1996). "Amber: Window to the Past." Abrams/Am. Mus. Nat. History, New York.

Grimaldi, D. A., and Cumming, J. (1999). Brachyceran Diptera in Cretaceous ambers and Mesozoic diversification of the Eremoneura. Bull. Am. Mus. Nat. Hist. 239.

Hennig, W. (1981). "Insect Phylogeny." Wiley, New York.

Kukalova-Peck, J. (1991). Fossil history and the evolution of hexapod structures. In "The Insects of Australia," Vol. 1. Cornell University Press, Ithaca, NY.

Labandeira, C. C. (1998). Early history of arthropod and vascular plant associations. Annu. Rev. Earth Planet. Sci. 26, 329—377.

Larsson, S. G. (1978). "Baltic Amber: A Paleobiological Study." Scandinavian

Sci. Press, Copenhagen. Rasnitsyn, A. P., and Quicke, D. L. J. (eds.) (2002). "History of Insects."

Kluwer Acad, Publ., Dordrecht. Rohdendorf, B. B. (1962). "Fundamentals of Paleontology," Vol. 9. "Arthropoda, Tracheata, Chelicerata." 1991 English translation of original Russian published by Amerind Pub., New Delhi.

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