Amber containing fossil arthropods presents a fascinating world in miniature. The deposits of the Lower Cretaceous are rich in fossil arthropods which have survived for some 130 million years, the much-admired stars of the film Jurassic Park, and until recently they were the oldest known preserved in fossil resin. For some time, however, we have been able to add a new element to this history, thanks to several extremely rare examples, 100 million years older, from the Dolomites near Cortina, a find of extraordinary scientific value.
The fossil resin of the Upper Triassic in the Dolomites is the jewel casket which has allowed us to antedate the geological record of animal organisms in amber, a substance known from the Carboniferous era, but, until recently, with no animal remains older than the Cretaceous. Triassic amber from the Carnia region, formed about 230 million years ago, includes a considerable quantity of fossil microorganisms. After years of patient cleaning, analysis and research on some 70,000 droplets, a group of international researchers has been able to identify the oldest examples of Arthropods in amber in the world. We are dealing here with a Dipteran (two-winged fly), and two Eriophyd mites which belong to a group still in existence today.
Part of the head, some parts of appendages, an antenna, part of the thorax, and what remains of at least four legs of the Dipteran are preserved. From analysis of these elements, it seems this is a Nematocera, or a primitive form of Brachycera (sucking insects from a humid environment). The Eriophyd mites are the very oldest fossils ever found in this group of Arachnids. Their perfect state of conservation has allowed a detailed study by the specialists David Grimaldi of New York and Evert Lindquist of Ottawa. One the the two mites is elongated and wormlike in form, with strange structures adapted for chewing or for grinding. The second has a more triangular, compact form, and possesses a mouth with a flatter contour. These two extraordinary Triassic mites provide documentary evidence that the absence of a third and fourth pair of legs, an anatomical trait which differentiates them from other Arthropods, is an ancestral characteristic which has remained unchanged for 230 million years.
Wormlike mites similar to the first specimen live today in confined spaces inside the bark, blisters, and shoots of plants, where they are protected from becoming dry. Several tougher forms have instead a more roving lifestyle, being able to live freely on the surface of plants. A similar form of behaviour is postulated for the Triassic fossils, one which made possible the entrapment of these organisms in the viscous flow of resin, and their preservation through geological time. The forests of the Triassic were populated by conifers in whose bark, or amongst whose leaves, the mites could find refuge. Analysis of the paleo-flora, found at the same level as the droplets of amber, has allowed us to identify conifers of the Cheirolepidiaceae family, plants with long trunks which were extinct at the end of the Cretaceous. The Eriophyd mites are today a group of highly specialised phytophagous Arthropods, of over 3,500 species, 97% of which feed off Angiosperms, flowering plants which emerged during the Cretaceous. Only 3% feed on Gymnospermae, such as conifers, another adaptation of ancestral origin. This discovery lays the foundation for future research, opening new windows on the coevolution of terrestrial Arthropods and the plants which have always constituted their habitat, food, and the extraordinary means by which they have come down to us.
Roghi G., Ragazzi E. & Gianolla P. (2006). Triassic amber of the Southern Alps (Italy). Palaios 21,143–154.
Schmidt A.R., Ragazzi E., Coppellotti O., Roghi G. (2006). A microworld in Triassic amber. Nature 444, 835.
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Text and pictures by Guido Roghi
A study carried out with the collaboration of:
Alexander R. Schmidt, Courant Research Centre Geobiology, Georg-August-Universität Göttingen, Göttingen, Germany
Saskia Jancke, Museum für Naturkunde zu Berlin, Berlin, Germany
Evert E. Lindquist, Canadian National Collection of Insects, Arachnids, and Nematodes, Research Branch, Agriculture and Agri-Food Canada, Ottawa, Ontario K1A 0C6, Canada
Eugenio Ragazzi, Department of Pharmaceutical and Pharmacological Sciences, University of Padova, Padova, Italy
Paul C. Nascimbene & David A. Grimaldi, Division of Invertebrate Zoology, American Museum of Natural History, New York, USA
Kerstin Schmidt, Friedrich-Schiller-Universität Jena, Institut für Ökologie, Jena, Germany
Torsten Wappler, Section Palaeontology, Steinmann Institute, University of Bonn, Bonn, Germany