Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 178 178 Bulletin of the Amateur Entomologists’ Society Eocene world: fossil insects from Baltic amber by Martin J. F. Fowler (15910) danebury216@hotmail.co.uk Abstract An introduction is provided to a developing collection of fossil insects and other arthropods from Baltic amber that once formed part of a forest ecosystem around 45 million years ago. Introduction I guess like many people my attention was drawn to the remarkable ability of amber to preserve fossil insects, often in exquisite detail (figure 1) by Michael Crichton’s 1990s science fiction novel Jurassic Park and the subsequent blockbuster film franchise. The premise of the book is that long-extinct dinosaurs can be cloned from DNA extracted from blood-sucking insects preserved in amber (DeSalle & Lindley, 1997). As a molecular biologist, I was naturally more interested at the time in the potential of extracting and analysing DNA from insects millions of years old than in the insects themselves. Twentyfive years on, with amber pieces being readily available via the internet at relatively modest cost, my interest in amber has been rekindled. However, it is now directed towards palaeoentomology, the study of fossil insects (Penney Figure 1. Dorsal (A) and ventral (B) habitus of the biting midge Serromyia polonica Szadziewski, 1988 preserved in exquisite detail in Baltic amber. Collection reference: BA039-A. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 179 Volume 77 • September 2018 179 & Jepson, 2014), and the remarkable preservation and biodiversity of insects and other arthropods in Baltic amber that were once part of a forest ecosystem around 45 million years ago (abbreviated to Mya) (Selden & Nudds, 2012). In this article I introduce my developing collection of fossil insects by describing the nature and origin of Baltic amber, where pieces can be sourced, and the taxa of fossil insects and other arthropods that are represented in the collection. Future articles are planned to address the practicalities of imaging the often-microscopic fossils, the data management aspects of the collection, and the biodiversity of the Eocene world that is preserved in the amber pieces. What is amber? Amber is fossilised resin that was produced by trees millions of years ago (Ross, 2009). Not to be confused with sap, which transports nutrients; resin protects trees from damage by blocking gaps in the bark. Its sticky nature can also gum up the jaws of insects trying to gnaw or burrow into the bark thereby providing a degree of protection. Once the resin hardens it goes through a process of amberisation to convert it into amber. The fresh resin loses its volatile oils and undergoes polymerisation, which hardens it, to become what is known as copal. The copal becomes incorporated into the soil at its initial site of deposition, where it remains long after the tree dies and, over millions of years, it polymerises further to form amber. Many insects are attracted to tree resin and, together with other small invertebrates, can become trapped in the resin because of its stickiness. The tendency is for smaller creatures to become trapped since larger ones can be strong enough to extract themselves, albeit sometimes evidently at a cost as disarticulated arthropod legs can occasionally be found in amber. Ultimately the trapped organisms become entombed by subsequent waves of resin to form what are known as inclusions. As the amberisation process proceeds, the inclusions become dehydrated and effectively mummified. Indeed, resins are laden with various antiseptic and antimicrobial compounds that often protect the insect body from decomposition leading to occasions of exceptional preservation in the fossil record, including the occasional preservation of internal soft tissue structures. When polished, amber tends to have a yellow-orange-brown appearance (figure 2), although it can range from a whitish colour through to almost black. With a hardness similar to that of gold or silver, around 2-3 on the Mohs scale, it is easily scratched. It has a melting point in the range 200-300ºC but tends to turn black and burn. Being only slightly heavier than water, it is readily transported by rivers and tides; this can result in secondary deposits of amber that can be some distance from the original source as described below. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 180 180 Bulletin of the Amateur Entomologists’ Society Figure 2. Examples of polished Baltic amber showing a range of colours of the pieces. Insect inclusions can be seen in many of the pieces as dark spots. Baltic amber Amber is globally distributed and is found mainly in strata of Cretaceous age (around 100 Mya) or younger (Penney, 2010); with the largest known deposit in the world being located on the Samland peninsula coast in the Kaliningrad Oblast of Russia. Known as Baltic amber, it has been mined on an industrial scale at a place now known as Yantarny since the end of the 19th century, although pieces can also be found along the Baltic coastline and sometimes as far away as the sea shores of East Anglia. The most important amber-bearing horizon at Yantarny is the ‘blue earth’ sediment, part of the Middle Eocene (Lutetian) which dates from around 41-48 Mya, although two additional amber-bearing horizons underlying the main strata indicate that amber had already been transported to Samland by the Early Eocene, around 50 Mya (Weitschat & Wichard, 2010). The origin of the amber is believed to be a forest that covered large regions of the Scandinavian Peninsula, Finland, Karelia, and the Kola Peninsula (collectively known as Fennoscandia) to the north of Samland. For many years it was believed that an extinct pine tree, Pinites succinifera, was the source of the amber. However, it has recently been suggested that a relative of the umbrella pine (Sciadopitys) may have been the resin producer (Wolfe et al., 2009). After its initial deposition, the amber was washed out of the forest in streams and rivers and became incorporated as secondary deposits into the ‘blue earth’ sediments at Yantarny. Further re-deposition took place in the Pleistocene epoch that began around 2.5 Mya when ice sheets scoured the area now occupied by the Baltic Sea and transported the amber further afield. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 181 181 Volume 77 • September 2018 Sources of Baltic amber With the development of internet commerce, Baltic amber can now be readily purchased from several sources. Table 1 lists the main suppliers from which Baltic amber has been purchased for my collection, with the two suppliers based in Lithuania being responsible for over 95% of the amber pieces. Prices can range from less than £10 to £100 or more per piece and usually relate to the relative rarity or number of inclusions present, rather than the size of the piece of amber. Unsorted ‘wholesale’ amber is available from one supplier at a cost that equates to around £2 per piece and is therefore a relatively affordable way to quickly build up a collection. Whilst each piece contains at least one inclusion, you do not know what you are getting in advance; however, this is not a problem as part of the fun is discovering what you can find and occasionally a piece can reveal a relatively rare specimen. Supplier Comments MB Amber Inclusions (Lithuania) http://www.amberinclusions.eu Previews of the amber pieces and inclusions are provided on the website. Printed photographs are provided with purchased pieces. AmberTreasure4u (Lithuania) https://www.ambertreasure4u.com/ Previews of the amber pieces and inclusions are provided on the website. ‘Wholesale’ amber with inclusions is available in lots of 5, 10, 50 and 100 pieces. UKGE Ltd (UK) https://www.ukge.com Limited selection of Baltic amber pieces with inclusions but includes more recent Dominican amber (Miocene) and Madagascar copal (Pleistocene) for sale containing insect inclusions. ebay (various) https://www.ebay.co.uk/bhp/amber-insect The occasional bargain can be found but be aware that some of the specimens for sale are artificial comprising modern insects embedded in plastic or resin. Table 1. Some suppliers of Baltic amber. Observing and identifying amber inclusions Given the very high cost of particularly rare inclusions, it is not surprising that most of the pieces in my collection comprise small inclusions, mainly Diptera about 1 mm in size, and require the use of a loupe lens or microscope to reveal their full beauty. Initially I photographed the inclusions using a USB camera connected to my laptop. However, as my interest grew I found that the purchase of a relatively inexpensive stereomicroscope with a built-in digital camera was the most effective way to search for, and photograph, the various inclusions. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 182 182 Bulletin of the Amateur Entomologists’ Society Details of the practicalities of imaging of the microscopic insects will be provided in a follow-on article. In essence, for each inclusion a series of images are taken at varying depths of focus in order to overcome the relatively shallow depth of field of the microscope and then combined to form a single in-focus composite image using the freeware ImageJ package (Schindelin et al., 2015) and an Extended Depth of Field plug-in (Forster et al., 2004). A mild unsharp mask is then applied to sharpen the image and the brightness and contrast adjusted to optimise its appearance. Compared with specimens of extant species, fossil insects in amber can be difficult to identify. Since the fossil is fixed it cannot be moved or dissected. This can restrict viewing angles and opacities, and other inclusions can further obscure characteristics of interest. Differential preservation can also result in only a subset of characteristics being evident in the fossil. Nevertheless, it is usually possible to identify an inclusion to at least the level of order and in many cases to family and occasionally to genus. Ross (2009) provides several useful keys to aid identification of arthropods to family level; identification to genus and species level requires the use of more specialist keys and descriptions (e.g. Wichard et al. (2009) for aquatic insects). To manage the collection, a project has been established on the iNaturalist citizen science website, a joint initiative by the California Academy of Sciences Figure 3. Breakdown by order of a sample of 182 insect inclusions present in the collection of Baltic amber. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 183 Volume 77 • September 2018 183 Figure 4. Examples of true flies (Diptera) observed in Baltic amber. A. Non-biting midge (Chironomidae: Orthocladiinae) [BA125-A]. B. Dark-winged fungus gnat (Sciaridae) [BA108-A]. C. Scuttle fly (Phoridae) [BA007-D]. D. Long-legged fly (Dolichopodidae) [BA005-A]. E. Moth fly (Psychodinae) [BA106-A]. F. Unidentified larva [BA014-A]. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 184 184 Bulletin of the Amateur Entomologists’ Society Figure 5. Examples of other insects observed in Baltic amber. A. Ant-like leaf beetle (Coleoptera: Aderidae) [BA110-A]. B. Aphid (Aphidoidea) [BA101-A]. C. Unidentified wasp with air bubble (Hymenoptera). [BA008-A]. D. Pygmy eye-capped moth (Lepidoptera: Nepticulidae). E. Caddisfly (Trichoptera) [BA134-A]. F. Bark louse (Psocodea). Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 185 Volume 77 • September 2018 185 Figure 6. Examples of non-insect inclusions observed in Baltic amber. A. Spider (Araneae) [BA032A]. B. Prostig mite (Acari: Prostigmata) [BA031-F]. C. Larva of a terrestrial parasitengona mite (Acari: Prostigmata) (arrowed) attached to a non-biting midge (Diptera: Chironomidae: Orthocladiinae) [BA044-A/E]. D. Springtail (Collembola) [BA028-B]. E. Unidentified true moss (Bryopsida) with air bubble [BA007-C]. F. Stellate hairs of oaks (Quercus) [BA040-A]. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 186 186 Bulletin of the Amateur Entomologists’ Society and the National Geographic Society, and can be accessed via the following tinyURL: https://tinyurl.com/y95jmx5n. Images of individual inclusions are uploaded to the site and provide a record of the collection’s content that can be seen by everyone. Whilst originally intended for observations of extant species, iNaturalist has the benefit of providing a firm taxonomic basis for the collection as well as enabling others to propose identifications, which is of great assistance given the wide range of taxa being considered. At the time of writing (July 2018) the collection numbered over 250 inclusions and was growing at a rate of approximately 30 inclusions a month. Further details of the management of the collection, including the development of an off-line database to administer and analyse the collection, will be provided in a future article. Insect and other inclusions observed in Baltic amber To date, a total of 182 insect inclusions from ten orders have been observed in the collection (figure 3). Almost 70% are true flies (Diptera) and include representatives from at least 14 families, several examples of which are shown in figure 4. By far the most common are non-biting midges (Chironomidae), dark-winged fungus gnats (Sciaridae) and long-legged flies (Dolichopodidae) which collectively comprise over half the Diptera inclusions. Other families that are represented include fungus gnats (Mycetophilidae), scuttle flies (Phoridae), moth flies (Psychodinae), gall midges (Cecidomyiidae), black flies (Simuliidae) and biting midges (Ceratopogonidae). There is even an unidentified fly larva inclusion illustrating the preservation of soft tissue in amber (figure 4F). Examples of non-dipteran insects from the collection are shown in figure 5. The majority are beetles (Coleoptera), aphids (Hemiptera: Aphidoidea) and wasps and ants (Hymenoptera) which collectively represent over 50% of the non-dipteran insects. Despite being one of the most species-rich lineages on Earth, moths (Lepidoptera) are relatively rare in Baltic amber and represent just over 3% of the insect inclusions in the collection and comprise a mixture of adults and pupal cases. However, this is an over-representation of the order as the specimens have been selected for inclusion in the collection. By way of comparison, Lepidoptera have been found to comprise only about 1% of the arthropods present in an unselected sample of Baltic amber (Sontag, 2003). The remaining insect orders represented in the collection are caddisflies (Trichoptera), thrips (Thysanoptera), bark lice and book lice (Psochodea), a termite (Blattodea) and a badly damaged bristletail (Archaeognatha). Of course, insects are not the only life forms that are preserved in amber and the collection includes several other arthropods as well as plant remains Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 187 Volume 77 • September 2018 187 (figure 6). The arthropods include spiders (Araneae) and parts of their webs, mites (Acari) and springtails (Collembola). Plant remains include a fragment of moss (Bryopsida) as well as minute stellate (star-like) hairs which come from the male flowers of oaks (Quercus). The presence of the latter is a characteristic feature of Baltic amber and stellate hairs are present in over a quarter of the amber specimens in the collection. Although the current collection is relatively small and is to an extent biased through cost and choice, the observation that the majority of the inclusions are true flies from the Chironomidae, Sciaridae and Dolichopodidae families is broadly consistent with other studies of unselected Baltic amber (e.g. Sontag, 2003; Perkovsky et al., 2007). As more specimens are added to the collection, particularly from unselected ‘wholesale’ amber pieces which have not been chosen for their specific inclusions, a better indication of the numbers and range of arthropod taxa present in the collection will be obtained and insights provided into aspects of the ‘Baltic amber forest’ ecosystem. Concluding remarks If you are interested in seeing more examples of fossil insects from Baltic amber, do visit the project on iNaturalist (at https://tinyurl.com/y95jmx5n). Any comments on the identifications of the specimens uploaded so far would be greatly appreciated: you can suggest identifications and comment directly on iNaturalist if you have an account (it’s free and all you need is to think up a username and a password). New inclusions are being added monthly, so it’s well worth checking what’s new every now and then. Acknowledgements The assistance of Christel Hoffeins, Viktor Baranov, Eva-Maria Sadowski, Thilo Fisher and Bjoern Rulik in identifying several of the specimens in the collection is greatly appreciated. References DeSalle, R. & Lindley, D., 1997. The science of Jurassic Park and the Lost World. HarperCollins, London. Forster, B., Van De Ville, D., Berent, J., Sage, D. & Unser, M., 2004. Complex wavelets for extended depth-of-field: A new method for the fusion of multichannel microscopy images. Microscopy Research and Technique 65: 33–42. Penney, D. (Ed.), 2010. Biodiversity of fossils in amber from the major world deposits. Siri Scientific Press, Manchester. Penney, D. & Jepson, J.E., 2014. Fossil insects: An introduction to palaeoentomology. Siri Scientific Press, Manchester. Perkovsky, E.E., Rasnitsyn, A.P., Vlaskin, A.P. & Taraschuk, M. V, 2007. A comparative analysis of the Baltic and Rovno amber arthropod faunas: representative samples. African Invertebrates 48: 229–245. Bulletin 77(530).qxp_Layout 1 12/09/2018 13:21 Page 188 188 Bulletin of the Amateur Entomologists’ Society Ross, A., 2009. Amber: The natural time capsule. Natural History Museum, London. Schindelin, J., Rueden, C.T., Hiner, M.C. & Eliceiri, K.W., 2015. The ImageJ ecosystem: An open platform for biomedical image analysis. Molecular Reproduction & Development 82: 518–529. Selden, P. & Nudds, J., 2012. Evolution of fossil ecosystems. Manson Publishing Ltd, London. Sontag, E., 2003. Animal inclusions in a sample of unselected Baltic amber. Acta Zoologica cracoviensia 46: (Supplement - Fossil Insects) 431–440. Weitschat, W. & Wichard, W., 2010. Baltic Amber, in: Penney, D. (Ed.), Biodiversity of Fossils in Amber from the Major World Deposits. Siri Scientific Press, Manchester, pp. 80–115. Wichard, W., Gröhn, C. & Seredszus, F., 2009. Aquatic insects in Baltic amber. Verlag Kessel, Remagen-Oberwinter. Wolfe, A.P., Tappert, R., Muehlenbachs, K., Boudreau, M., McKellar, R.C., Basinger, J.F. & Garrett, A., 2009. A new proposal concerning the botanical origin of Baltic amber. Proceedings of the Royal Society B: Biological Sciences 276: 3403–3412.