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Dating fossils with molecules – innovative approach to determine the age of Baltic AMBER

Periodic Reporting for period 2 - AMBER (Dating fossils with molecules – innovative approach to determine the age of Baltic AMBER)

Reporting period: 2019-09-01 to 2020-08-31

Baltic amber from Northern Europe is an outstanding deposit due to the high diversity of well-preserved inclusions, mostly insects. Although it is one of the richest sources of fossils, science has consistently failed to define its geological age, despite applying various traditional approaches. There are several hypotheses concerning the age of Baltic amber, which is generally dated as Eocene, with an age range between 55 and 34 Ma. Difficulties in the age determination are essentially due to the repeated re-deposition of the amber, the broad range of the ancient forest, and its probable existence for several million years. It limits the scientific value of all Baltic amber fossils in evolutionary divergence time estimation. This is very unfortunate, especially because these fossils would be very important for reconstructing evolutionary events in the Eocene, which was a period of dynamic climate, with several warming and cooling events and is considered as a deep-time analogue of current climatic changes.

The core idea of my project was to apply an innovative approach of precise dating for this very important fossil deposit by using DNA, the morphology of extinct and extant species within the framework of advanced Bayesian statistics. Information contained in DNA sequences together with the morphology of both extinct and extant taxa allowed for estimating phylogenetically the age of fossils from Baltic amber, and thus the amber itself. I used a dataset from my previous project as a basis and expanded it with fossils from Cenozoic deposits worldwide.
The main result of the project is developing a method for estimating the age of fossil deposits using a total-evidence phylogenetic approach. This new approach has been used to establish the age of Baltic amber deposits.

The knowledge of the age of the Baltic amber fossils could be of use in e.g. evolutionary biology, palaeoecology, biogeography, and palaeoclimatology. It gives us an insight into the ecosystems' response to the dynamic climate changes that took place in the Eocene and shaped out the recent biota.
I began the project from collecting additional morphological data on fossils belonging to my study group, rove beetle subfamily Paederinae (Staphylinidae), from Cenozoic deposits. I visited several most important fossil collections, which gave me an overview of the Paederinae fossil material from the most diverse terrestrial Cenozoic deposits. Based on that knowledge, I chose several fossils and scored them into the morphological dataset. The matrix for further expanded with fossils from Baltic amber. At the same time, I was collecting information on the first and last occurrences of the fossil taxa and the age of fossil deposits other than Baltic amber. After gathering all this information, I ran a phylogenetic analysis of the morphological and molecular data with simultaneous divergence time estimation. I used fossils from non-Baltic amber deposits to phylogenetically estimate the age of Baltic amber fossils. All analyses were done in RevBayes, which is a statistical software package using probabilistic graphical models for estimating evolutionary parameters in a phylogenetic context and providing a flexible environment for fully integrative Bayesian analysis.

Together with my supervisor and designated postdoc, we validated the method performance and reliability by running a series of designed simulations. Simulated datasets are extremely useful tools because they can characterize the expected performance of phylogenetic methods under idealized conditions to test and validate newly implemented methods. The simulation study was run to assess whether well-dated fossil samples can be used in combination with extant samples, to date fossil samples from a deposit of unknown age.

The main results obtained in the project are the phylogeny of the rove beetle subfamily Paederinae and the estimated dates for Baltic amber deposits. The results have been disseminated via scientific publications, two already published, six more in progress. They were also presented at the 2nd Palaeontological Virtual Congress.
The results of the project significantly expand our knowledge of the Paederinae rove beetle systematics and evolution. My research shows that they are one of the oldest rove beetle subfamilies, but the main speciation events leading to the current diversity took place in Cenozoic, specifically in Eocene. My studies indicate that they were important elements in different terrestrial Eocene ecosystems, which could help us to understand the patterns and processes leading to their recent diversity and distribution. As Paederinae rove beetles are having potential in biomedical, pest management, and conservation research, expanding knowledge on their systematics and evolution have wider societal implications.

The results of using a phylogenetic approach to date Baltic amber are highly promising and show the potential of applying this newly developed method to difficult fossil deposits. Knowing the age of Baltic amber is important for reconstructing evolutionary events in the Eocene, which was a time of drastic climatic changes analogues to the current global warming. Climate change is among the most important environmental issues in the recent world, and its impact on biodiversity and ecosystems is not only of scientific interest but also stands high in the scientific and political agenda of the modern world. Baltic amber fossils with known age could be used as a tool for reconstruction of the palaeoclimate and palaeoenvironment in the Eocene in Europe. It could help us to understand the current geographic distribution of different groups and their species composition, which in turn, could indicate how the past ecosystem was reacting to these events and recovering after global warming.