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AMBARES is the acronym of “Ambares de España” (Ambers from Spain), a project chiefly funded by the Spanish Ministry of Economy and Competitiveness. AMBARES is formed by an international group of geologists and biologists aimed to study Early Cretaceous amber from Spain (~115 mya) under a multidisciplinary approach, as well as other ambers of different ages worldwide. The team is not only working on amber but also on other paleobiological fields. Although this website is focused on Spanish amber, you can also find works carried out by the AMBARES researchers, like published papers, spotlights on paleoentomology, and congress participations.

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During the Early Cretaceous, the Earth experienced a significant global warming, with average temperatures up to 22º C and local temperatures in medium latitudes from 10 to 20º C higher than today. As a result, there was a global greenhouse, prompted by a CO2 rich atmosphere (concentration ten times higher than today), CH4, and water vapour. This phenomenon is related to several paleogeographical and tectonic events associated with the fragmentation of Pangaea, the alteration of the global oceanic currents, and an increase in the volcanic activity at the central oceanic ridges.

Climatic conditions were peculiar during the Cretaceous. There was very low temperature gradient between tropic and polar areas, and a marked climatic zonation did not exist. In general terms, there was a tropical zone from the Equator up to 30º latitude and a temperate zone up to higher latitudes, with a relatively narrow dry zone between them. It is in this intertropical area that the amber-producing trees occurred, in forests ecologically similar to modern ones, but with higher temperatures and a marked dry/wet seasonality. On the other hand, oxygen isotope, pollen, and fossil plant remains studies indicate that the general humidity was high during the Cretaceous (generalized steppes or deserts were lacking), with a flat continental relief and an average altitude higher than today. Moreover, in this period there was a regular increase in the sea level that reached the maximum level known in all Earth’s history, in which emerged landmasses were not more than 10% of the global surface of the planet. This explains the formation of abundant insular areas over the entire globe, subsequently increasing global biodiversity.

Within this general context, two main factors caused a global change in the structure, distribution, and operation of continental ecosystems from the Iberian plate and their evolution during the Cretaceous. First of all, the Iberian plate was intermittently isolated from the European plate and was an island for most part of the Jurassic and Cretaceous. This had an obvious influence on the terrestrial biota, as the Iberian plate acted as a refuge for some Jurassic forms and promoted speciation leading to the establishment of endemic arthropods. On the other hand, during the Cretaceous the southern part of the Iberian plate was arid, the north-eastern part was located in a wet and warm area, and the transitional area had a paratropical/ temperate-warm regimes. The latter paleoclimatic region was where the amber outcrops were located in Spain. Due to the climatic, and presumably floristic, homogeneity of the northeastern Iberian plate during the Early Cretaceous, it was first thought that all the paleocommunities preserved in Spanish amber had a very similar composition. However, currently we know that this is not the case and the Spanish deposits formed in different paleoecosystems.

The AMBARES project seeks to integrate different disciplines related with the study of the fossil record at a global scale in order to obtain a general understanding on the evolution of the forest ecosystems in the Iberian Plate during the Early Cretaceous. This period constitutes a time of dramatic change in the ecosystems, with the substitution of the conifer-dominated forests by angiosperm-dominated ones, which caused deep changes in trophic relationships and other biotic interactions. That is one of the reasons that explains why the great crisis on insect diversity during the Cretaceous did not take place at the K-T boundary but at the middle of that period instead.

The team members have participated in the study of the geology, paleobiology, taphonomy, and biogeochemistry of multiple amber outcrops, mainly from Europe (Spain, France, Italy, Baltic region) but also from the rest of the world (India, Ethiopia, Lebanon, Myanmar, Canada, USA, Mexico, Dominican Republic, Madagascar, and Peru).

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The paleontological significance of amber is based on two factors. First, the potential for three-dimensional anatomical preservation of the amber bioinclusions allows a detailed study, not only externally but also internally thanks to synchrotron imaging. This leads to recognition of the diagnostic characters necessary for classifying the taxa, which, in turn, allows us to carry out paleoecological inferences and cladistic studies. Second, amber holds the potential to preserve biological interactions, which otherwise are scarce in the fossil record, both interspecific (like predation or parasitism) and intraspecific (like socialization or reproduction). Cretaceous amber is rare, and the Spanish deposits are some of the oldest in the world with paleobiological content, with up to 22 different arthropod orders recognized to date. Some Spanish amber taxa have crucial evolutionary significance as they represent the first known records of their respective groups or show intermediate characters between fossil and Recent forms.

The main objective of the AMBARES project is to undertake the study of the Early Cretaceous amber deposits from Spain using a multidisciplinary approach and focusing on its paleobiological content (namely, arthropod and plant inclusions), with the aid of synchrotron X-ray phase contrast microtomography and CT-scan. Spanish amber has yielded important discoveries in the field of arthropod paleobiology, and after the Lebanese amber (Berriasian-Aptian in age), is the oldest in the world providing a wide paleodiversity.

The six secondary objectives of this project are:

1

Geological characterization of the amber deposits, including sedimentology and resin production

2

Taphonomical research on amber, so the factors that controlled the formation of the amber deposits can be established in order to obtain a reliable paleoecological reconstruction

3

Biogeochemical research on the amber, focused on determining the different resin-producing trees for each outcrop, conducting isotopic studies on the amber to look for fingerprints (which could determine the spatial location of the resin secretion) and investigating if there is a relationship between the large resin outputs during the Cretaceous with important environmental changes such as the oceanic anoxic events (OAEs)

4

Taxonomic and phylogenetic studies of the amber paleobiological content, mainly insects, arachnids, and crustaceans

5

Study of pollen and meso- and macro-remains from the amber-bearing levels, and structural reconstruction of resinous trees

6

Paleoecological and paleoenvironmental study of the amber and its inclusions; in this regard, the study of organisms associated with aquatic environments and plant-insect interactions are given priority as they are especially informative. Paleoenvironmental reconstruction is paramount, as the amber forest was a most likely pervasive ecosystem during the Cretaceous with no modern equivalent, i.e., gymnosperm-dominated under a subtropical climate, with wet/dry seasons and higher average temperatures compared to those of today.

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