Denisia, Biologiezentrum Linz, Austria Vol 0004-0037-0056

Introduction

What is amber? "... When the warm kingdom of the amber pine and its seas set, cooled and froze beneath a thick glacial mass, only amber itself survived; the living sap of a dead tree" Stefan ZEROMSKI The Sea Breeze (1922) Amber is fossilized tree-derived resin that is found in the geological record from the Devonian through the present day (GRIMALDI 1996). The oldest amber deposits containing insects come from the Middle East and are commonly known as Lebanese amber (SCHLEE 1970;ZHERIKHIN 1978), although similar amber occurs in Israel and Jordan (NlSSEN-BAUM & HOROWITZ 1992). They are dated on the Neocomian, Early Cretaceous, which means that they are 130 million years old. The Cretaceous (140 Ma to 65 Ma) is one of the most interesting chapters in the history of the Earth. It was in the Cretaceous that an explosive radiation of flowering plants, angiosperms, occurred, together with many modern families of insects. Several kinds of amber, frequently including a variety of "amberized" insects, are known from the Cretaceous: Lower Cretaceous amber from Alava (Basque Country, Spain), Lower Cretaceous amber found near Vienna and Salzburg, and Lower Cretaceous amber found in Chöshi (Honshu, Japan). Many localities of Upper Cretaceous amber are known from North America (DAHLSTRÖM & BROST 1996;GRIMALDI 1996, RICE 1987). These are Cedar Lake, Manitoba, and Medicine Hat and Grassy Lake, Alberta in Canada. Amber -'omalik' as called by Inuits -is also found in Alaska Peninsula, in the Yukon delta and on the Fox Islands (part of the Aleutian Archipelago), and in Greenland (KOSMOWSKA-CERANOWICZ 1983; DAHL-STRÖM & BROST 1996). The most famous is New Jersey amber, containing many insect inclusions. Other amber sites in the United States are located in New Mexico, Tennessee, Mississippi, Arizona, Nebraska and North Carolina, along the Atlantic coast in Maryland, on Cape Cod, Long Island and Staten Island. Another famous Cretaceous resin is the amber from Taimyr Peninsula in northern Russia (Fig. 1), of Lower Cretaceous Begichev Formation and Upper Cretaceous Kheta, Khatanga and Dolgan Formations (ZHERIKHIN & SUKACHEVA 1973, ZHERIKHIN 1978, ZHERIKHIN 6k ESKOV 1999). Upper Cretaceous amber of Asia is amber of Adzhakent in Azerbeijan, Shawarshawan in Armenia, Timmerdiak-Kaja on the Viliuj River in Yakutia (ZHERIKHIN 1978), and Kuji and Iwaki on Honshu, Japan (SCHLEE 1990). A very interesting Asian amber is Burmese amber, which is estimated by different authors to be of Miocene, Oligocene, Paleogene, post-Eocene, Eocene, or even Late Cretaceous age (ZHERIKHIN 1978, BOTOSANEANU 1981). The last estimation seems to be correct according to the latest data (ZHERIKH1N & Ross 2000). Late Cretaceous amber of the Paris and Aquitan Basin in northwestern France, very interesting and rich in inclusions, was reported by SCHLÜTER (1978). Cretaceous amber originated from the resins of the gymnosperm plants of the families Araucariaceae, Taxodiaceae, Cupressaceae and Pinaceae, and angiosperm plants of the family Hamamelidaceae (GRI-MALDI 1996).

Most of the known deposits of Tertiary amber are known from Europe (KRZEMINSKA et al. 1993;POINAR 1999). The most famous Eocene amber from the Baltic area (Fig. 2) probably represents one of the largest accumulations of amber in the world. It comes from the Tertiary deposits in the Sambian Peninsula and from accumulations in Quaternary deposits. The amber in Sambia is located in layers of the 'blaue Erde' -the "blue earth"; blue earth is actually grayish with traces of green when dry or black when wet, and composed mainly of clay, not blue clay, but rather glauconite-rich clay. During the Pleistocene, amber from Tertiary deposits was transported by glacial, fluvial or fluvoglacial action. This resulted in distribution of the Eocene Baltic amber across Latvia, Lithuania, Belorussia, Poland and Germany, up to the east coast of the British Isles and even as far as Jutland (Denmark) and the southern coast of Scandinavian Peninsula (DAHLSTRÖM & BROST 1996, KOSMOWSKA-CERANOWICZ 1998).

The tree that produced resin which became Baltic amber is the still mysterious "Pinus succinifera" (POINAR 1992, GRIMALDI 1996, ROSS 1999) -probably a collective name for resin (amber) producing tree (or trees). Modern methods of analysis of amber have raised some annoying questions. It is surprising, that the infrared spectra (infrared spectroscopy is a successful technique in comparing fossil and recent resins) of Baltic amber are not similar to those of any modern Pinaceae, but more similar to resin of the Araucariaceae tree Agathis australis (LAMB.) STEUD. that grows in New Zealand. Further analyses using pyrolysis mass spectrometry have supported the results from IR spectroscopy (POINAR & HAVERKAMP 1985). Additionally, the IR studies demonstrated some hetero-geneity, which raises the question of whether a single tree species was the amber-producing tree (POINAR 1992). Baltic amber lacks abietic acid, which chemically distinguishes pine resin, and araucarian resin does not have the succinic acid, which is distinctive of most Baltic amber. On the other hand, recent pine species, the north-western American sugar pine Pinus lambertiana DOUGLAS, is marked by a characteristic IR spectrum, with "Baltic amber shoulder" typical of Baltic amber. Some living trees in the pine tree family of the genera Ketekeria CARRIERE and Pseudolarix GORDON do indeed produce resin rich in succinic acid (GRIMALDI 1996). Pseudolarix is of particular interest, since resin in 40 Ma old cones from Axel Heiburg Island in Canadian Arctic also contains succinic acid. Pseudolarix today is found in Asia. The sole species, Pseudolarix amabilis NELSON (REHDER), is closely restricted to some mountains in south-eastern China. This may suggest that Pseudolarix might have been connected with the North, with Scandinavia during the Eocene. The Pseudolarix hypothesis is also bolstered by the fact that many other plants and insect species fossilized in Baltic amber are closely related to species now living in Asia, Australia and even Chile (GRIMALDI 1996). The "amber tree" could then be considered a rather primitive type, an early stage of developmental history of the Pinaceae, which still retained archaic characteristics in common with the Araucariaceae (LARSON 1978;MILLS, WHITE & GOUGH 1984;BECK 1999). The Pinaceae appeared in the Cretaceous, although certain pine-like ancestral plants have been recorded from the Mid Jurassic; recently the family is restricted to the Northern Hemisphere, with a sole exception. The Araucariaceae date back to the Mesozoic, when the family was abundant both in Northern and Southern Hemispheres. There are few araucarian fossils in the Northern Hemisphere, and apparently none in Baltic amber.

Another famous Tertiary fossil resin is Dominican amber (Fig. 1), which originated from leguminous (Caesalpiniaceae, Fabales) algarrobo trees, although the only one described is Hymenaea protera PoiNAR (POINAR 1991, 1992;CARIDAD 1999, POINAR andPOINAR 1999). Dominican amber is aged Oli-gocene to Lower Miocene, some deposits are regarded as originating from the Middle Eocene (POINAR 1992;KRUMBIEGEL & KRUMBIEGEL 1996a;CARIDAD 1999;POINAR & POINAR 1999). According to ITURRALDE-VINENT & MACPHEE (1996) the ambenferous deposits in the Dominican Republic were formed during the late Early Miocene through the early Middle Miocene. However, mines are scatte-lithophora fossils, is estimated at 30-45 Ma (SCHLEE 1990). Amber usually occurs in the form of discrete nodules or lumps ranging in size from a few millimeters to masses as large as 20 kilograms.

Mexican amber, also named "amber of Chiapas", is fossil resin of the same age and origin as Dominican amber, from the Hymenaea trees (Caesalpiniaceae). Chiapas amber occurs 1996, RICE 1987)).

The Quaternary fossil and semi-fossil resins also are reported from different parts of The amber trap and inclusions

Sticky traps

Stalactite

Leakage

Lava trap Drop trap

Pool trap

Amberization -changes involved in the process of forming amber from fresh resin -is a slow, gradual process which leads to the preservation of small, delicate, and soft-bodied insects into inclusion in hardened resin. It is the most complete type of fossiliiation known for insects. Fossils thus preserved can be easily compared with their extant descendants thanks to the three-dimensional form, colour pattern, and minute details of the exoskeleton (POINAR 1993). Resin originated in different pans of the tree-trunk (K.ATINAS 1971; KRZE-MINSKA et al. 1993), so insects living on different parts of trees could be entrapped in resin (Fig. 3). Production of resin differed also according to the season, and time of the day (KRZEMiflSKAetal. 1993).

The mode of preservation -taphonomyof amber insects has been discussed many times (BRUES 1933;HENWOOD 1992;PIKE 1993). There were many factors that pre-conditioned the preservation of an organism in resin, so resin was a rather selective trap. The size of an entrapped insect determines its biotic loss; decay and scavenging. Insects living on or near the amber-producing tree had higher fossilization potential than those living far from the forest. Behavior is another important factor affecting the inclusions. Flying insects, insects living on the bark or hiding in the cracks and crannies of the tree bark could be entrapped more easily. Enticing or deterring smell of resin, the colour and glaze of resin are also responsible for the bias of amber trap (KRZEMINSKA et al. 1993, KRUMBIEÜEL & KRUMBIEGEL 1996b). The "amber trap" in fact comprises four different types of traps (Figs 4-7): sticky trap, lava trap, drop trap and pool trap. Sticky traps -the stalactite-like and icicle-like leakages, rods and "baggy" leakages -entrapped active flyers and passive flyers, as well as forms wandering on the tree-trunk. Lava traps entombed non-moving or slow moving organisms. Drop traps also preserved forms living on branches, leaves, and on the ground, or even in water. Particles of detritus or litter can frequently be found among such inclusions. Pool traps encased dead insects, active and passive flyers, wandering on the ground or in the litter, in some cases also living under the bark or in the wood of "amber tree". In many amber pieces, insect inclusions are preserved in layers, as they were caught in subsequent leakages of resin.

What exactly is an inclusion? An inclusion is an object, which is trapped in amber. It is a three-dimensional, very tine mould of an insect body with all external characters. Only remains of the external skeleton and the rest of the body are to be found inside the inclusion (Fig. 8). Dehydration is the most important process in the insect tissues during creation of an inclusion. All organic remnants are highly changed by acids and other compounds included in resin, by processes of dehydration, polymerization, etc. However, tissue preserved in such a way has many characters of the structure of living tissue. Well-preserved striated muscles of insects, internal organs and hypodermis of spiders in Baltic amber were described (KORNILOVICH 1903;PETRUNKEVITCH 1935PETRUNKEVITCH , 1950)). Using scanning electron microscope exposed surfaces of the insects (MlERZE-JEWSK1 1976a, b), and ultrastructure of the pre-served tissue in Baltic amber fly of the family Mycetophilidae (POINAR & HESS 1982) were examined. Extracting DNA from amber inclusions is a relatively recent endeavor (POINAR, POINAR &. CANO 1994). Several

studies have shown that amber provides conditions conducive to the long-term preservation of amino-acids (WANG et al. 1995, POINAR et al. 1996). The first extraction and partial characterization of DNA from amber inclusions of stingless bee from Dominican amber was pre- 1993, HAMILTON 1999and SHCHERBAKOV 1996, 2000. arb.

Permian inclusion of weevil in Lebanese amber, about 125 Ma old (CANO et al. 1993). These data attest the remarkable preservative properties of amber. However, DNA from amber organisms is fragmented, degraded and strongly cross-linked with other molecules in the cell, so it is necessary to take this into consideration. In future, it may be possible to repair some of the 'ancient DNA, which would allow the retrieval of longer, more authentic sequences.

Studies with DNA from organisms preserved in amber make it possible to include extinct organisms that existed millions years ago in molecular phylogeny studies.

• Pleistocene, Holocsne + Tertiary O Cretaceous D Triasste, Jurassic H Carboniferous • Devonian Figs 1: Distribution of fossil resins worldwide

fossils (ITURRALDE-VINENT & MACPHEE 1996). The age of the oldest, based on Cocco-In recent years a large amount of Miocene fossil resin was found in Merit-Pila Coal Field, land, amber of Oise in France, rumanite from Romania and Sicilian amber (simetite) from Sicily, the northernmost in the world localities from Early Eocene of Ellesmere Island and Axel Heberg Island in the northern Arctic Ocean, amber from the Eocene Claiborn For-well as of angiosperms: Burseraceae, Dipterocarpaceae and Hamamelidaceae (GRIMALOI

Triassic Jurassic Cretaceous Tertiary Quat.

Table 1 . Described inclusions of Archaeorrhyncha and Clypaeorrhyncha in fossil resins

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