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Very diverse Very diverse

Rayner et al., 1998 Jell and Duncan, 1986

a Ages are approximate.

formations of Cretaceous amber were formed when certain wood-boring insects radiated because it is well known that certain trees today produce copious resin in response to insect attacks. Since most species of insects are 3-4 mm in length or less, exquisite preservation of the myriad smaller species in amber has vastly improved our understanding of insect evolution. Also extensive formations of layered limestone were deposited during much of the Early Cretaceous, which resulted in exceptional insect Lagerstätten in Brazil, Spain, and elsewhere.

Significant Cretaceous deposits for insects are summarized in Table 2.2, with major deposits reviewed below.

Europe. The main European deposits of compression/ impression-fossilized insects are from the Early Cretaceous of Britain (the Purbeck and Wealden groups) and Spain (Montsec and Las Hoyas), and for Cretaceous amber fossils the main deposits are from northern Spain and France.

The Purbeck Group of deposits from southern Britain is of exceptional significance because it is the only major, very diverse assemblage of insects of known earliest Cretaceous age (Berriasian, 145-138 myo). The Purbeck is stratigraphi-cally well constrained (Allen and Wimbledon, 1991), the paleoclimate is well characterized (fresh and brackish water lagoons with surrounding hinterlands of Mediterranean climate and flora [Allen, 1998]), and the fossil insects are well explored (Ross and Jarzembowski, 1996; Coram and Jarzembowski, 2002; Coram, 2003). As of 2003 there were 200 named insect species for the entire Purbeck, representing some 17 orders, with over 70 species from Wiltshire alone (Ross and Jarzembowski, 1996). The great percentage of insects are isolated wings and other disarticulated remains, principally Coleoptera elytra, then Hemiptera and Diptera. An autochthonous, brackish water aquatic insect fauna is indicated by the taxonomic composition, lithology, and somewhat depauperate nature of the fauna. Approximately 700 "morphospecies" have actually been collected from the Purbeck (Coram and Jarzembowski, 2002), and these authors even made estimates using abundance-diversity curves that 1,400 species may be preserved in the Purbeck. This high estimate should be taken with caution, though because their curves showed no obvious asymptote, and thus little basis for extrapolation. Also, careful study of one group of Purbeck insects, the roaches, indicates that there is actually one-third the number of described species of these insects (A. Ross, pers. comm.).

The Wealden is an extensive series of Early Cretaceous outcrops of mud- and siltstones from southern Britain (Figure 2.52) and limestones in Belgium and Germany (the famous iguanodons from Bernissart in Belgium are from the Wealden). In Britain the 'Weald Clay Group' is divided into an Upper (early Barremian: ca. 128 myo) and a Lower Weald Clay (Late Hauterivian: ca. 130 myo). The British Wealden yields diverse remains of vertebrates (including the occasional dinosaur fragment), plants, and disarticulated insects. Unlike the Purbeck, aquatic insects are uncommmon. Stratigraphy

2.52. Outcrops of the Early Cretaceous Wealden strata in England. The Wealden group was the first intensively studied assemblage of Cretaceous insects, and the various outcrops are also well dated and so insects from here are an important source of comparison for other Cretaceous deposits. Photo: Natural History Museum, London (NHM).

2.52. Outcrops of the Early Cretaceous Wealden strata in England. The Wealden group was the first intensively studied assemblage of Cretaceous insects, and the various outcrops are also well dated and so insects from here are an important source of comparison for other Cretaceous deposits. Photo: Natural History Museum, London (NHM).

2.53. Fossiliferous limestone outcrops containing diverse insects from the Early Cretaceous of Las Hoyas, Spain. Photo: X. Martinez-Delclos.

has been discussed by Jarzembowski (1977, 1984, 1987, 1991, Worssam (1978), Ross and Cook (1995), and Cook and Ross (1996),) has discussed the insects.

The finely grained, laminated lithographic limestones of Montsec (Lleida Province) and Las Hoyas (Cuénca Province) (Figures 2.53, 2.54) yield one of the most significant Cretaceous deposits of insects in Europe besides the Wealden and Purbeck. Las Hoyas is approximately Barremian in age (130 myo) (Whalley and Jarzembowski, 1985; Martínez-Del-clos, 1989, 1991); Montsec has often been thought to be late Berriasian to early Valanginian (about 140 myo), but some investigators attribute an early Barremian age (129-125 myo) to this deposit. Both deposits have yielded a total of 13 orders and nearly 50 families of insects (reviewed in Peñalver et al., 1999). Among these are numerous aquatic insects, such as Ephemeroptera nymphs and Belostomatidae, and abundant larvae of stratiomyid flies. Insects of particular significance are diverse odonates, Hemiptera, early aculeate wasps and weevils, large kalligrammatid lacewings, early alate termites (Meiatermes: Figure 7.82), and the oldest known worker termite.

The main European amber deposits of Cretaceous age have been discovered relatively recently. The first European deposit to be seriously studied is from Cenomanian-aged strata of the Paris Basin in western France (Schlüter, 1978, 1983). More recently, amber of late Albian and early Cenomanian ages (100-95 myo) has been found in Charente-Maritime in southwest France, which is more abundant and has more diverse inclusions (Néradeau et al., 2003). The French Cretaceous amber is very similar in age and composition to amber from Álava, in the Sierra de Cantabria mountains of northern Spain, about 30 km south of the town of Vitoria-Gasteíz (Alonso et al., 2000). Álava amber is late Aptian to mid-Albian in age (115-120 myo), and its chemical composition and association with fossil pollen indicates an araucarian source. of nearly 2,000 insect inclusions in Álava

2.54. Deposits of similar age as Las Hoyas, from La Cabrua, Spain. Photo: X. Martinez-Delclos.

amber, 13 hexapod orders are known, and 50% of all inclusions are Diptera, followed by Hymenoptera (28% - almost all parasitoids). These proportions are similar to those found in the French amber, though amber from Charente-Maritime has also preserved early ants, a mole cricket, scorpion remains, and other very rare inclusions. The French and Spanish Cretaceous ambers are additionally similar in that they are turbid, resulting from a suspension of fine bubbles and organic particles. The amber must be carefully trimmed close to the surface of the inclusion for optimal observation.

Asia. Cretaceous insect deposits abound in Transbaikalia, the region of Siberia that is west of Lake Baikal, the world's largest freshwater lake (it even has an endemic species of seal). Some of these deposits are summarized in Table 2.2, and the most exceptional one is on the Vitim Plateau near a small tributary of the Vitim River, called Baissa Creek (reviewed by Zherikhin et al., 1999) (Figure 2.55). Five expeditions of Russian paleontologists to "Baissa" between 1959 and 2000 have uncovered nearly 20,000 insect specimens from strata of approximately Hauterivian age (ca. 135 myo). It is the only fossil insect locality in the world where nearly all of the pterygote orders of insects are preserved, the exceptions being Embiodea and Zoraptera. Nearly 300 species of insects have been described from Baissa thus far, and an estimated 700-1,000 species (and 200 families) are thought to exist (the estimate of 7,000 species [Vrsansky, 1999] is extremely excessive). Even an apparent louse (Phthiraptera) is preserved in this deposit, which we discuss later. Aphids comprise one

2.55. Outcrops of the Early Cretaceous deposits at Baissa, central Siberia, seen on the far shore. Compression fossil insects are extremely diverse in the Baissa deposits and are preserved with microscopic detail. Photo: Paleontological Institute, Moscow.

third of all the terrestrial insects from Baissa, which must reflect the luxuriant vegetation that is known to have surrounded ancient Lake Baissa, including dense conifer forests. Fossils from Baissa are extremely well preserved (Figures 6.10, 8.12); some Coleoptera and Heteroptea are preserved with relief (though most insects are flattened), and the cuticular remains have even preserved some sensilla. Bon-Tsagan in central Mongolia is the other major deposit of Cretaceous insects from Eurasia, deposits being approximately Aptian (120 myo) in age. Some 10,000 fossil insects have been collected by Russian paleoentomologists from this site (Zherikhin, 1978).

Siberian amber derives from outcrops of various ages on the Taimyr Peninsula in northern Sibera, the most productive of them being Yantardakh ("amber mountain"), which is Santonian (ca. 85 myo) in age. It has yielded fossiliferous amber containing some 3,000 inclusions, and is most abundant in chironomid midges and aphids. Yantardakh is located on the Maimecha River in the eastern part of the peninsula, and smaller outcrops of the same formation are known from the Kheta River. Older Siberian amber occurs likewise in the eastern part of the Taimyr, but in the Khatanga River basin (Albian to early Cenomanian, 110-95 myo) inclusions are not abundant. In the western part of the Taimyr Peninsula at Nizhnayaya Agapa River (called just "Agapa") are fairly rich deposits of Cenomanian-aged (95 myo) amber.

Middle East. Early Cretaceous amber occurs in numerous outcrops from Egypt, to Israel, Lebanon (Figure 2.56), and Jordan, the so-called "Levantine amber belt." Only amber from Lebanon has yielded insects in significant quantity and preservation, and a minor number of poorly preserved inclusions occur in Jordanian amber (Bandel et al., 1997). The Jordanian amber is approximately 10-15 my younger than the Lebanese amber, though there is significant variation in the ages of the latter depending on the formations and outcrops (see Azar, 2000). Lebanese amber is arguably the most scientifically significant amber in the world because it is the oldest amber that yields a great diversity of organismal inclusions. Ages of outcrops vary from latest Jurassic (though none of these contain insects) to upper Aptian (ca. 115 mya). Most of the outcrops yielding insect inclusions, though, come from the upper part of the Neocomian, approximately Barremian (125 myo). Lebanese amber was first seriously explored by Dieter Schlee (formerly of the Natural History Museum in Stuttgart), based on excavations from near Jezzine (Schlee and Dietrich, 1970). He discovered early bird feathers and a significant diversity of insects, some of which he and Willi Hennig had studied (e.g., Hennig, 1970; Schlee, 1970). Subsequent collections made by Aftim Acra of the American University in Beirut (also near Jezzine) and by Dany Azar of the Museum National d'Histoire Naturelle in Paris (from many other outcrops) have uncovered a trove of insect and other inclusions. Diptera comprise approximately half of all insect inclusions (most of these chironomids and ceratopogonids) (Figures 12.28, 12.30, 12.47), then Hymenoptera (mostly par-asitoids: 6-11%). Among the more significant aspects of the insect fauna are very interesting aculeate wasps, brachyceran flies, beetles (Figures 10.6, 10.39, 10.59), early termites, and Lepidoptera (Figure 13.21). Various papers have been written on some of these inclusions, many of which we cite elsewhere in this book, but a great deal more research is needed. Lebanese amber is very fractured and brittle, so it requires special embedding techniques in order to trim the amber for observation of inclusions.

Far East Asia. Rich amber deposits from Burma (presently Myanmar) (Figure 2.57) have been known to be a source of material for carvings in Peking (Beijing) for several millennia,

2.56. Strata like this one from the Early Cretaceous of Lebanon are the world's oldest source of insects in amber. Amber from the Early Cretaceous occurs throughout the Middle East but only the material from Jordan and especially Lebanon has yielded insects.

and one collection of approximately 1,200 inclusions was made in the turn of the 20th century and housed at the Natural History Museum in London (Ross and York, 2000). An excellent history of its exploitation has been written (Zherikhin and Ross, 2000). Until about 1997, Burmese amber was thought to have been abandoned or depleted, but a larger collection of 3,500 inclusions in this material has recently been made (Grimaldi et al., 2002). Burmese amber was originally believed to be Miocene to Eocene in age, but the study of insect inclusions indicate it is clearly Cretaceous (Rasnitsyn and Ross, 2000). In fact, comparison of Burmese amber insects to those from amber deposits with better dating indicate a Cenomanian age of this amber, approximately 95 myo (Grimaldi et al., 2002), which is corroborated from modest data based on pollen and an ammonite (Cruikshank and Ko, 2003 [these authors suggest a slightly older, late Albian to early Cenomanian age, 100-105 myo]). Burmese amber is the richest Cretaceous amber deposit in the world. Among the rare inclusions are an onycophoran (Figure 3.3), primitive ants (Figure 11.70), the only Mesozoic Embiodea (Figure 7.13) and Zoraptera (Figures 7.15, 7.16), the oldest Strepsiptera (Figures 10.85, 10.86), a very primitive mosquito, and several archaic taxa from the earlier Mesozoic (Meso-raphidiidae [Raphidioptera], Protopsyllidiidae [Hemiptera: Figure 8.21], and Pseudopolycentropodidae [Mecopterida: Figure 12.3]). There are also very diverse Coleoptera and Diptera, and 27 hexapod orders in total, with approximately 130 families now known, representing some 300 species or more. Clearly, future exploration of these deposits will uncover some exciting discoveries.

The Yixian and Laiyang Formations yield the most abundant compression fossil Cretaceous insects in the Far East (reviewed by Ren, 1995; Lin, 1998). The insects are extremely diverse and beautifully preserved in light lacustrine and volcanic shales (Figure 12.2), but their significance is unfortunately overshadowed by the equally spectacular vertebrate finds from this area. The most exciting vertebrates include a beautiful specimen of Jeholodens, a stem-group triconodont mammal, and an unexpected diversity of early feathered dromeosaurs that have provided unique insight into the early evolution of birds. For insects, the Yixian and Laiyang insects include a vast diversity in most orders, including spectacular Neuropterida, odonata, Mecoptera, and Hymenoptera. Unfortunately, the ages have been seriously confused. The Yixian Formation was originally promoted as latest Jurassic in age, so when beautiful angiosperm plants (Archaefructus) were discovered from the deposits, they were announced as the first Jurassic and earliest angiosperms (Sun et al., 1998). Now it is generally agreed that the Yixian Formation is Early Cretaceous, probably Hauterivian to Barremian in age, approximately 130 myo, which would place it nearly contemporaneous with the Wealden and Baissa. The Cretaceous dating is based on microfossils as well as isotopes (Barrett, 2000).

2.57. Excavations (above) of amber from the mid-Cretaceous of northern Burma, and transportation of the amber (below) in sacs to be loaded onto the elephant. Photos: Jim Davis, Leeward Capital.

This is a prime example as to how erroneous dating can seriously affect interpretations of evolution.

North America. The only truly diverse deposits of Cretaceous insects from this continent are of amber. The world's first major deposit of Cretaceous amber to be seriously studied, in fact, is from western Canada (Carpenter et al., 1937; McAlpine and Martin, 1969). McAlpine and Martin (1969) listed nearly 40 localities of Cretaceous amber from western North America (including Alaska), but the main deposits came from two localities: Cedar Lake, Manitoba, and Medicine Hat, Alberta. Since then, another major site has been

2.58. Excavations of amber from the Late Cretaceous Magothy Formation of New Jersey. Virtually all amber deposits occur in sediments rich in black, fossilized peat and lignite, shown piled here. Lignites and peat are the remains of vegetation that were buried with amber in lagoons, estuaries, and along coastlines. Photo: K. Luzzi.

2.58. Excavations of amber from the Late Cretaceous Magothy Formation of New Jersey. Virtually all amber deposits occur in sediments rich in black, fossilized peat and lignite, shown piled here. Lignites and peat are the remains of vegetation that were buried with amber in lagoons, estuaries, and along coastlines. Photo: K. Luzzi.

discovered, from Grassy Lake, Alberta (e.g., Pike, 1994, 1995). Most of the Canadian amber derives from the Foremost Formation, of Campanian age (ca. 75 myo). In contrast to most other Cretaceous amber, Canadian amber has excellent clarity, though abundant flows require that pieces be trimmed to best observe the inclusions (Figure 10.84). The insect fauna in this amber is also distinctive, with nymphal aphids being the most abundant inclusions (one third to two thirds of all insects), with Diptera a close second (nematocerans are

2.59. An excavation of Cretaceous amber in New Jersey. Cretaceous amber occurs in the Atlantic Coastal Plain of the eastern United States from Massachusetts to Georgia, with particularly rich deposits like this one known from Staten Island and central New Jersey. Photo: K. Luzzi.

abundant in virtually all ambers). Also unusual is the abundance of mites, which comprise about a quarter of all inclusions. As of approximately the year 2000, some 150 species of hexapods in 17 orders and nearly 80 families were known from Canadian amber. This amber is believed to have been formed from an extinct species of tree in the Taxodiaceae.

Surrounded by urban sprawl in central New Jersey is the other diverse Cretaceous deposit of insects for North America (Figures 2.58, 2.59). Scattered pieces of amber had been collected in Cretaceous clay pits in Staten Island and central New Jersey for more than a century, but the discovery of the first Cretaceous ant, Sphecomyrma (Figures 11.62, 11.63) brought serious attention to this amber (Wilson et al., 1967). Subsequent study in the late 1980s and early 1990s uncovered rich, localized deposits from the Turonian-aged Magothy Formation (ca. 90 myo) in Middlesex County, New Jersey (Grimaldi et al., 2000a,b). Chemistry of the amber, and its match to amber preserved in wood and cone scales of fossil conifers, indicates that it was also formed by a taxodiaceous tree, or possibly by an early pine (Pinaceae). New Jersey amber is significantly more diverse than Canadian amber, which may reflect its lower (and more tropical) paleolaltitude and climate. It contains 19 orders and approximately 120 families and 250-300 species of hexapods (Grimaldi et al., 2000a). Diptera comprised 34% of all inclusions, Hymenoptera 24%, Hemiptera 13% (most of these coccoids), and Coleoptera 8%. Among the more significant finds were the oldest fossil mushrooms, a tardigrade (Figure 3.5), early ants (including the only known Cretaceous formicine) (Figures 11.66 to 11.68), and an unexpected diversity of scale insects, Neuropterida (Figures 9.9, 9.33, 9.36, 9.37), and Lepidoptera (Figures 13.22, 13.28).

South America. The only major Cretaceous deposit of insects from South America - and arguably the largest and most diverse of the approximately 25 known gondwanan localities of insects - is from the Aptian-aged Crato Member of the Santana Formation in Ceara, northeastern Brazil (Grimaldi, 1990a). The deposit is a classic nearshore Plattenkalke deposit (Figure 2.60), except that the insects and other organisms are preserved as completely articulated permineralized replicas in remarkable relief and with microscopic detail. Even the fine structure of muscle tissues, like myofibrils, is well preserved (Figure 2.10). The Santana Formation has preserved a diverse autochthonous fauna of aquatic insects, chiefly Ephemeroptera adults (Figure 6.12) and nymphs (Figures 6.11, 6.13), nepomorphan waterbugs (Figure 2.9), and some odonates (Figures 6.39, 6.44 to 6.46), along with abundant roaches (Figures 7.70, 7.72), orthopterans (see cover), diverse terrestrial Hemiptera (Figures 8.47, 8.48, 8.79, 8.80), diverse Neuropterida, and other terrestrial groups from nearby vegetated areas. Thus far, approximately 300 species in 18 orders and approximately 100 families are known

2.59. An excavation of Cretaceous amber in New Jersey. Cretaceous amber occurs in the Atlantic Coastal Plain of the eastern United States from Massachusetts to Georgia, with particularly rich deposits like this one known from Staten Island and central New Jersey. Photo: K. Luzzi.

2.60. The Tatajuba quarry in Ceara, Brazil, containing finely laminated limestones of the Early Cretaceous San-tana (Crato) Formation. The Santana Formation is probably the richest source of Cretaceous insects from the Southern Hemisphere; the insects are remarkably preserved as detailed, mineralized replicas (e.g., Figures 2.9, 2.10, and many others in this book). Photo: J. Maisey.

2.60. The Tatajuba quarry in Ceara, Brazil, containing finely laminated limestones of the Early Cretaceous San-tana (Crato) Formation. The Santana Formation is probably the richest source of Cretaceous insects from the Southern Hemisphere; the insects are remarkably preserved as detailed, mineralized replicas (e.g., Figures 2.9, 2.10, and many others in this book). Photo: J. Maisey.

(Grimaldi, 1990a; Martins-Neto, 1999). This number will clearly change when taxonomic specialists assess the voluminous descriptions by Martins-Neto. Among the more significant aspects of this insect fauna are the the oldest known Thysanura (Figure 5.6); the earliest blattid roaches with egg cases (oothecae) (Figure 7.72); a superb early mantis (Santanmantis) (Figures 7.97, 7.98); the only Southern

Hemisphere snakeflies (Raphidioptera) (Figure 9.8); and a remarkable "long-tongued" brachyceran (Cratomyia) (Figure 14.15), which is one of the earliest specialized pollinators.

Africa and Australia. As the Santana Formation is to South America, so are Orapa to Africa and Koonwarra to Australia. Orapa was formed from the eruption of a kimberlite pipe and

2.61. Continental configurations and climate during the Late Cretaceous. For additional reconstructions during the Cretaceous of the Southern Hemisphere, see Figure 14.27.

then sedimentary filling of a crater lake in Botswana during the Turonian-Coniacian (95-87 mya). Preserved in the finegrained shales there is a significant diversity of plants, arachnids, and insects in eight orders (McKay and Rayner, 1986; Rayner et al., 1998). Of approximately 3,000 insects collected, reports exist thus far only for some Diptera (Waters, 1989a,b) and carabid beetles. Koonwarra is a shallow lacustrine deposit formed probably during the Aptian (120 mya) in South Gippsland, Victoria, Australia, thus contemporaneous with the Santana Formation. The Koonwarra deposit was nicely documented in a monograph (Jell and Duncan, 1986), which shows a significant diversity of soft-bodied invertebrates, along with 12 orders of insects. Immature Epheme-roptera and Diptera are most abundant, but Hemiptera, Coleoptera, and Diptera are most diverse. Among the more significant insects are damselfly (zygopteran) nymphs, plecopteran nymphs, mesoveliid (Figure 8.65) and gelastocorid bugs (Heteroptera), diverse adult and larval Coleoptera, and abundant blackfly larvae (Simuliidae). There is also an exceptional specimen of an ectoparasite, Tarwinia, which appears to be closely related to modern fleas (Siphonaptera) (Figures 12.19, 12.20).

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