AMBERIA: PROJECT RESULTS
After a three-year span,
the AMBERIA research project (CGL2014-52163:
“Iberian Amber: An Exceptional Record of
Cretaceous Forests at the Rise of Modern
Terrestrial Ecosystems”) concluded on
December 31th 2017. This project represented
the first time that the AMBARES research
team was run under a coordinated framework:
one team was managed from the University of
Barcelona by Dr. Xavier Delclòs, and the
other team was managed from the Geological
and Mining Institute of Spain (IGME) by Dr.
Eduardo Barrón. The multidisciplinary team
of the AMBERIA project studied the geology (stratigraphy
and sedimentology), taphonomy, geochemistry
(including chemotaxonomy), paleobotany
(macro- and mesoremains, palynology,
microinclusions), paleozoology (systematics
and phylogeny), and paleoecology associated
to the Iberian Cretaceous amber and the
outcrops where it is found. The project was
integrated by 13 Spanish researchers and a
significant portion of foreign specialists.
As results of the project, two PhD theses
were carried out, and more than one hundred
of both specialized and outreach papers were
published, as well as several monographic
book chapters. In addition, around twenty
works were exposed in national and
international congresses and scientific
workshops.
The project AMBERIA aimed
to integrate multiple points of view in
order to reconstruct the ecological dynamics
of the resiniferous forests that gave rise
to the Early Cretaceous amber deposits from
Iberia. The main results of the project were
as follows: (i) the taxonomic and
geochemical relationships between ambers and
modern resins produced by araucariaceous
conifers were found, (ii) the taphonomic
knowledge on Cretaceous ambers was
increased, (iii) organic and inorganic
elements in Iberian ambers were recognized,
including the description of a new chemical
substance, the amberene, (iv) the study of
fungal cortices from pieces of Cretaceous
amber revealed that fungi were a main
component of the Early Cretaceous
resiniferous forest microcoenoses in Spain,
namely inhabiting the litter and soil and
playing an important role in the recycling
of organic matter, based on the abundance of
amber pieces that were strongly colonized
when the non-solidified resin felt to the
forest floor, (v) the study of the
palynomorphs that occur within amber-bearing
sediments pointed out a late Albian age
(about 105 Ma) for the Spanish Cretaceous
amber, (vi) the pollen grains found on the
surface of insect bioinclusions belonging to
multiple groups revealed the importance of
insect-mediated pollination for gymnosperms
in the mid-Cretaceous ecosystems, (vii) the
study of preserved bioinclusions of beetles
and edaphic arthropods allowed to increase
the knowledge on the Cretaceous terrestrial
ecosystems from the paleofaunistic and
paleoecological standpoints, (viii) the
occurrence of ticks included in Cretaceous
ambers confirmed the presence of
warm-blooded vertebrates in the
resin-producing forests, and, (ix) all these
results were disseminated to the public
through the comic “Vongy” (http://www.senckenberg.de), outreach magazines, the
“AMBERIA” webpage, and the temporary
exhibition “AMBERIA: the Iberian amber”. |
AMBERIA RESEARCH PROJECT
Research fields
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).
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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