Triassic 247208 mya

The Triassic was dramatically different than the Permian, with a mean global temperature (mgt) of near 22°C, compared

MID PERMIAN (265 MYA)

Tropical summerwet | cool-cold temperate

Desert

Tropical summerwet | cool-cold temperate

Desert

2.47. Continental configurations and climate during the Permian.

to the 12-15°C mgt in the first half of the Permian. No ice occurred at either pole, and floras changed from archaic lycopsids, ferns, cordaites, and pteridosperms, to radiations of cycads, ginkgos, conifers, and the angiosperm-like Ben-nettitales. Because insects are so intimately associated with plants, this floristic change probably affected the change in insect faunas in the Triassic. Though the effects of a Permo-Triassic extinction on insects is debated (which we discuss elsewhere), the first modern families like Tipulidae (Diptera), Staphylinidae (Coleoptera), Belostomatidae and Naucoridae (Heteroptera), and Xyelidae (Hymenoptera), to name a few, undoubtedly appeared during the Triassic. A review of Triassic life was presented by Lucas (1999). With the exception of the Bugarikhta Formation of central Siberia (which is latest Permian to earliest Triassic), very few insect deposits are known from the Early Triassic, ca. 247-241 mya. Most deposits, in fact, are from the Carnian or later, 231-207 mya.

Europe. Triassic insects have been known from Europe longer than in any other region, and the one most studied has been the Bundsandstein from Bavaria and Thuringia, Germany (Anisian to Carnian). The most significant European Triassic deposit, though, is the Grès à Voltzia from the mid-Triassic (Anisian: 240 mya) of the Vosges mountains in France (Gall, 1996; Marchal-Papier, 1998). Diverse insects, arachnids, myriapods, marine worms, bivalves, crustaceans, fish, and plants occur in finely laminated clay and siltstone deposited in a shallow, brackish environment (Gall, 1971, 1985). Over 5,000 specimens, representing some 200 species and 11 orders are known (Marchal-Papier, 1998), though 40% of the individuals are roaches. Papers have been published on the Orthoptera (Marchal-Papier et al., 2000), roaches (Papier et al., 1994; Papier and Grauvogel-Stamm, 1995), and the oldest mygalomorph spider (Selden and Gall, 1992). Various deposits occur throughout the Keuper Basin in western Europe, which is generally Norian (222-209 myo) in age. Near Bergamo in northern Italy, the lower Rhaetian (209 myo) Argilliti di Riva di Solto Formation has yielded diverse odonates and some Coleoptera and Orthoptera (Whalley, 1986b; Bechly, 1997). These deposits have also yielded exquisitely preserved pterosaurs, which are the earliest in the fossil record. In southern Switzerland and northern Italy the Ladinian-aged Meride limestone (234 myo) has yielded a few insects (Krzeminski and Lombardo, 2001), but this deposit is best known for the diverse vertebrates. The Triassic in Britain has yielded insects from Rhaetian-aged (209 myo) deposits from Stensham (Hereford-and-Worcester) and Forthampton (Gloucestershire) (Popov et al., 1994; Krzeminski and Jarzembowski, 1999).

Asia. The largest Triassic deposits are probably those of central Asia, in the regions of Kazakhstan, Uzbekistan, and Kyrgyzstan; vast collections from which reside in the Paleontological

2.48. The hills of Fergana Valley near the confluence of Uzbekistan, Kyrgyzstan and Tajikistan, which have yielded fossiliferous outcrops of the Triassic-aged Madygen Formation. This formation has prolificacy yielded insects. Photo: Paleontological Institute, Moscow (PIN).

Institute in Moscow. Issyk-Kul', a 225 myo lake bed in the Tien Shan mountains, has yielded over 3,000 specimens, from which B. B. Rohdendorf described 53 species of Diptera alone, though these need serious revision. This deposit has recently been reevaluated as being Early Jurassic. An extremely large and diverse deposit for insects is the Madygen Formation, from the Ladinian-Carnian (236-220 mya) of the Fergana Valley of Uzbekistan, Kyrgyzstan, and Tajikistan (Martynova, 1958; Rohdendorft, 1961, 1962; Bekker-Migdisova, 1962; Sharov, 1968; Ponomarenko, 1969, 1977b; Papier and Nel, 2001) (Figure 2.48). Ponomarenko (1995) mentioned that the Madygen Formation yielded 15,000 insect specimens. Other central Asian deposits are the Malt-sevo Formation of the Kuznetsk Basin in Siberia (Early Triassic), the Tolgoy Formation of western Kazakhstan (Norian to Rhaetian, ca. 210 mya), and the Protopivskya Formation of southern Ukraine (Carnian in age). From the Asian far east Triassic insects are known from Hon Gay and Ke Bao Island in Vietnam, from Japan (Fujiyama, 1973, 1991), and from various localities in China. The China localities included Szechuan and Guizhous Provinces, the Tongchuan Formation in Shaanxi Province (Ladinian: 235 mya), the Beishan Formation in Jilin Province, and the Shangu Formation in Hebei Province (these latter two are Rhaetian: 208 myo) (Lin, 1982, 1986). Triassic deposits containing insects are actually fairly common throughout the Far East, but the remains consist largely of beetle elytra and roach tegmina. In the Japanese deposits, Fujiyama (1991) reported some 6,000 insect specimens recovered from the Momonoki Formation (Carnian: 225 myo) at the Ominé Coal Field in Miné, Yamaguchi, Japan. over half of these are isolated tegmina and elytra of roaches and beetles, about 20% are Auchenorrhyncha, and 10 orders comprise the remaining specimens.

North America. Until recently the remains of Triassic insects from this continent were sparse and scattered. Earliest reports were of borings and galleries (Walker, 1938) in the wood of the conifer, Araucarioxylon arizonicum, the tree that

2.49. Fine-grained shales of the Late Triassic Cow Branch Formation, exposed here in the Solite Quarries near Martinsville, Virginia. This deposit has preserved the oldest definitive aquatic insect fauna, along with myriad other arthropods, preserved as two-dimensional, silvery images on a black shale (Figures 8.69, 10.26). Photo: Virginia Museum of Natural History (VMNH).

2.49. Fine-grained shales of the Late Triassic Cow Branch Formation, exposed here in the Solite Quarries near Martinsville, Virginia. This deposit has preserved the oldest definitive aquatic insect fauna, along with myriad other arthropods, preserved as two-dimensional, silvery images on a black shale (Figures 8.69, 10.26). Photo: Virginia Museum of Natural History (VMNH).

largely comprises the Petrified Forest National Monument in Arizona (Chinle Formation: Carnian, 231-222 mya). More recent reports, of similar galleries, have reported these as nests of bees and termites, for which the Triassic is far too early. These galleries are almost certainly from beetles. Lucas (1999) mentioned rare and poorly preserved insects in the Bluewater Creek Formation of New Mexico, and a poorly preserved staphylinid beetle was reported from the Norian (220 mya) of northern Virginia (Gore, 1988). Without doubt, the most significant deposit of North American Triassic insects is in Cascade, Virginia, on the Virginia-North Carolina border (Figure 2.49). Here there are exposures of the upper part of the Cow Branch Formation, which is a series of extremely fine-grained shales showing cyclical changes in sedimentation attributed to Van Houten cycles in climate (Olsen, 1986). These cycles are controlled by 21,000-year cycles of the precession of the equinoxes. The Cow Branch Formation is part of a series of Triassic- and Jurassic-aged rift basins from eastern North America called the Newark Supergroup (Olsen et al., 1978). In a rich, fossiliferous quarry at Cascade more than 30 such cycles are known, one of which has yielded diverse insects preserved in great detail as silvery two-dimensional films. Some 11 orders, 30 families, and perhaps 60 species are presently known (Fraser et al., 1996; Fraser and Grimaldi, 2003), but more excavation is still needed. The oldest Staphylinidae (Figures 10.26, 10.27) and aquatic insect fauna (e.g., Figure 8.69) are from the Cow Branch Formation.

South America. Triassic insects from South America were first known to occur in the Rhaetian-aged Potrerillos and Los Rastros Formations (uppermost Triassic: 209-207 mya) of Mendoza and Los Rastros Provinces, Argentina, which also extend into southern Brazil (Wieland, 1925, 1926). Pinto and Purper (1978) described stoneflies (Plecoptera) from this formation, and an odonate was described by Carpenter (1960). Other insects were treated by Martins-Neto and Gallego (1999), and overall diversity was reviewed by Gallego and Martins-Neto (1999). This fauna was diverse, including odonatoids, plecopterans, miomopterans, grylloblattodeans, orthopterans, auchenorrhynchans, glosselytrodeans, and various undetermined species. Apparently, the Argentinian deposits are very similar to those of Australia's Triassic Ipswich Series (Martins-Neto et al., 2003) and, no doubt, reflect a time when these continents were connected via Antarctica. Anderson and Anderson (1993) mentioned the Los Rastros deposit as being Carnian, based on paleobotani-cal evidence, though Martins-Neto and Gallego (1999) indicated a slightly older, Ladinian-Carnian age. A small deposit is also known from Rio Grande del Sul and Santa Catarina in Brazil (Pinto, 1956; Pinto and Ornellas, 1974). Most recently, Martins-Neto et al. (2003) reviewed the South American Triassic deposits.

Africa. Several vast deposits occur in southern Africa, including the Stormberg Series from the uppermost Permo-Triassic Karroo suite of Lesotho and Transvaal (Anderson and Anderson, 1993). Because this series straddles the P-Tr boundary, it is quite important for assessing the impact of the Permian extinctions on terrestrial arthropods. In Cape Province there are deposits at Birds River near Mount Fletcher, and the Molteno Beds (Carnian: 231 mya), probably the richest gondwanan Triassic insect site (Zeuner, 1961; Riek, 1974a, 1976a,b). Riek (1974a, 1976a) largely described 32 species of insects in 22 families and 11 orders, based just on 70 specimens from the Molteno Formation. Anderson and Anderson (1993) mentioned that there is vast insect diversity based on new collections from the Molteno Formation, with some 335 recognizable species in 18 orders, based on 2,056 specimens (Anderson and Anderson, 1993; Anderson et al., 1996). They estimated, however, using a Poisson distribution of species abundance, that there may actually be 7,740 species of insects preserved in the Molteno Formation! In lieu of published results it is difficult to assess the accuracy of the 335 recognizable species, which probably has a dramatic effect on the estimate. An estimate of 7,740 insect species seems extremely excessive, as few places on earth today probably harbor this kind of diversity (even the richest tropical forests), and the fossilized diversity of a region is always a fraction of the actual diversity. Molteno insects are preserved mostly as isolated wings. Oddly, there is an absence of Diptera in this formation, which are often among the most abundant orders in Mesozoic deposits, so there may be something peculiar about the taphonomy of the Molteno.

Australia. Diverse Triassic insects are preserved near Sydney, New South Wales, in mid-Triassic sandstones (Anisian: 240 mya) (Riek, 1954) and in Late Triassic-Early Jurassic shales (Etheridge and Olliff, 1890). The major Triassic deposits are near Mt. Crosby in Queensland, northern Australia, at Din-more and Denmark Hill (the Ipswich Series: Carnian) (Tillyard and Dunstan, 1916; Tillyard, 1917b, 1925; Tindale, 1945; Riek, 1955; Evans, 1956; Rozefelds and Sobbe, 1987). A small deposit occurs near Perth. Cockroaches, beetles, and auchenorrhynchans (Figure 8.42) predominate in the Australian Triassic, but there is also a unique diversity of early mecopteroids. Other orders include Neuroptera (Figure 9.15), Coleoptera (Figure 10.7), Odonata, Orthoptera, Phas-matodea, rare Hymenoptera (Figure 11.4), and the extinct order Titanoptera. In fact, some of the most spectacular insect fossils are the patterned wings of large, presumably predatory Titanoptera from the Australian Triassic (Figure 7.43). Smaller deposits of similar Triassic age occur in Tasmania (Riek, 1962).

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