Jurassic 207146 mya

The Jurassic was a 62 my period in the middle of the Mesozoic (207-146 mya), which is now probably the poorest sampled period for fossil insects because the great bulk of Jurassic insect deposits are Palearctic. Gondwanan Jurassic insects are extremely sparse and require significant exploration.

Abundant evidence indicates that a meteoritic impact on earth at the Triassic-Jurassic boundary caused substantial extinction of marine and terrestrial organisms. For vertebrates, this had a profound effect because the extinction of labyrinthodonts and other archaic reptiles by the end of the Triassic, some 207 mya, apparently allowed the ecological release and radiation of the dinosaurs in the Jurassic (Olsen et al., 2002). Dinosaurs became much more diverse and larger in size less than a million years into the Jurassic. There seems to have been little differentiation, though, between insect faunas of the Late Triassic and early Jurassic. Significant floristic changes of the Jurassic include radiations of the cycads, ginkgos, bennettitaleans, and especially the conifers, with modern families of the last group appearing, like the Pinaceae, Taxodiaceae, and Podocarpaceae. In the Early Jurassic there was no ice, and the poles were cool temperate, all other regions having been warm temperate to tropical (Figure 2.50). By the Late Jurassic this changed, though, and limited ice formed at the poles, and climates were slightly cooler and more seasonal, no doubt a result of extensive rifting and continental separation. By the Late Jurassic, about 155 mya, the supercontinent of Pangaea separated into Laura-sia and Gondwana. Most Jurassic insects belong to extinct families or to stem groups of basal Recent families.

Europe. As would be expected by the history of paleontology, the earliest studied Jurassic insects are from Europe, particularly

2.50. Continental configurations and climate during the Early Jurassic.

Tropical summerwet Desert

2.50. Continental configurations and climate during the Early Jurassic.

Germany and Britain (e.g., Brodie, 1845). Southern Britain has extensive deposits from the Lias (the first 27 my of the Jurassic), which vary in age within this interval. Deposits from Gloucestershire, Warwickshire, and Worcestershire are slightly older (by about 20 my) than deposits from Dumbleton, Aldertone, and other places. The best-studied deposit is from the Sinemurian-aged outcrops (ca. 200 myo) from the cliffs at Charmouth, Dorset, which has been monographed by Whalley (1985). That study was based on just 400 specimens, which had been collected over many years since the insects are rare and widely scattered in the deposits. The Dorset Jurassic insects are preserved in a marine or deltaic deposit of calcareous mudstone and were allochthonous. Beetle elytra predominate (40% of all insects), with Orthoptera second in abundance (22%) among the 11 orders and 66 species known thus far. Perhaps the most significant find from Dorset is the oldest lepidopteran, discussed later.

In continental Europe, Lias insect deposits are widely distributed through Germany, Switzerland, and Luxembourg, which have been reviewed in Ansorge (1996, 2003b). A small deposit is known from the Early Jurassic (ca. 205 mya) of Odrowaz, near Kielce, in central Poland. The most significant of the continental Europe sites are the deposits at Dob-bertin (Mecklenberg), Schandelah (Saxony), and Grimmen (Vorpommern), the last of which has been monographed by Ansorge (1996). Ansorge's monograph is a model of systematic paleoentomology because it is based on careful observations, detailed documentation, and the reexamination of old types by Geinitz (1883), Handlirsch (1906a,b, 1907, 1908, 1939), and Bode (1953). The Grimmen deposits are marine clays from the Toarcian (150 mya), with the insects preserved in carbonate concretions. As of 1996, 1,200 specimens representing 91 species were known, most of them isolated wings of small insects (<5 mm wing length), and allochthonous in origin. Like the Dorset Jurassic insects Orthoptera and Coleoptera were abundant at Grimmen, but at Grimmen Diptera are the most abundant insects, comprising 23% of all insects; Auchen-orrhyncha are also an abundant order (Ansorge, 2003b).

Fossils from the rich deposits at Solnhofen and Eichstätt, Germany, have provided some of the first views of Jurassic life, which has been nicely reviewed by Barthel et al. (1990) and Frickhinger (1994). These deposits have been made famous by the six skeletal specimens of the oldest and most basal bird, Archaeopteryx lithographica, which is one of the premier examples of transitional forms in the entire fossil record (in this case between raptor dinosaurs and true birds). The fossils from these localities include a great diversity of vertebrates (bony fish, sharks and rays, turtles, ichthyosaurs, plesiosaurs, crocodilians, lizards, beautifully preserved pterosaurs, and a dinosaur), plants (seed ferns, ginkgos, conifers), marine invertebrates (mollusks, horseshoe "crabs" [Xiphosura], jellyfish, corals, squids, ammonites, various crustaceans, and echinoderms), and insects. They are preserved in very fine-grained, layered limestone, Plattenkalke, which has been quarried for millennia, even by the Romans. The fossils were preserved in micritic mud of calcite that settled to the bottoms of isolated, anoxic, and highly saline lagoons. The terrestrial organisms wafted in or flew from surrounding land. Unlike the vertebrates and crustaceans, the Solnhofen insects are not particularly well preserved, though they are usually complete (Figures 2.1, 6.43). Among the 12 orders and at least 50 genera of insects, significant examples include an impressive diversity of dragonflies, and the large insects Chresmoda and Kalligramma. The classification of Chres-moda, discussed later, has been controversial, entirely as a result of the typically poor preservation of details in Solnhofen insects. Anton Handlirsch provided many of the early descriptions of Solnhofen insects, and other, later studies on these insects include Carpenter (1932), Kuhn (1961), Ponomarenko (1985), Tischlinger (2001), and various papers on assorted taxa.

Asia. Jurassic deposits from Asia are extensive, and have been reviewed by Rasnitsyn (1985), Hong (1998), and by Eskov (2002), so we are providing a superficial overview here (Table 2.1). Eskov (2002) mapped some 45 Asian and Eurasian Jurassic insect localities, most of which lie in central Asia and China. The Eurasian and central Asian collections alone comprise approximately 50,000 Jurassic insect specimens from 20 major localities, housed in the Paleontological Institute in Moscow. These span the Early to latest Jurassic and thus provide a unique and nearly continuous fossil record of insect life from approximately 200 to 150 mya. The most significant of all the deposits is the famous Karatau deposit (Figure 2.51), which is one of the truly great insect Lagerstatten. Without Karatau, our knowledge of Jurassic insects would be far more incomplete. Karatau is comprised of various outcrops in the Karatau range of mountains in southern Kazakhstan, which is a spur of the Tien Shan mountains. The main fossiliferous locality for insects is near the village of Aulie (formerly called Mikhailovka), from which 20,000 insect specimens alone were collected. The age is Kimmeridgian to Oxfordian, Late Jurassic (ca. 152-158 myo). Insects are preserved in dark grey shales as isolated wings or entire specimens, usually in a detail so fine that even fine setae can be discerned on tiny specimens a few millimeters long (Figures 7.68, 9.7, 9.28, 10.12, 11.16, 12.4 to 12.6). The deposit is lacustrine and has preserved diverse plants (Doludenko and Orlovskaya, 1976), including diverse ben-nettitaleans, cycads, and conifers. The insects from Karatau have been intensively studied, as monographed in Rohdendorf (1968) and numerous subsequent papers. These include 19 orders and several thousand species. Coleoptera comprise approximately half of all insects (55%), then Diptera (14%), Blattodea (10%), Heteroptera (6.6%), other Hemiptera (3.3%), Orthoptera (2.2%), Raphidioptera (2.2%), Neuroptera (1.8%),

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