Excavating the roots of the tree of life: revealing a billion year fossil record for the euglenids

Lead Research Organisation: University of Sheffield
Department Name: School of Biosciences


In establishing the theory of evolution Charles Darwin realized that life originated only once and over billions of years diversified, through evolution, into the bewildering diversity of life on Earth today. Since this monumental paradigm shift a major goal of biology has been to establish the 'true tree of life' in terms of evolutionary relationships of the different types of organism and timing of their divergence. The most problematic and least understood regions of the tree of life are its deep roots: the origin of life and its early diversification. This is because these events occurred billions of years ago in the deep past and: (i) the primary divergence into the three domains of life (bacteria, archaea, eukaryotes) involved a complicated combining of organisms in 'endosymbiotic events'; (ii) the organisms involved are unfamiliar because modern relatives, if any, have changed dramatically through time; (iii) the fossil record is poor in rocks from such ancient times; (iv) techniques such as molecular clock analyses become unreliable the further back in time one investigates.

The euglenids are a bizarre group of single-celled organisms common on the planet today. They inhabit freshwater environments where they move through the water using a unique motion called 'peristaltic movement'. Intriguingly, they either feed by ingesting matter (like animals) or through harvesting the Sun's energy (like plants). It is believed that they can do the latter because they combined with a photosynthetic unicellular green algae during a 'secondary endosymbiotic event'. Euglenoids are familiar to many of us as they are routinely examined in elementary laboratory classes, to familiarise students with the basic features of single-celled eukaryotes and the fact that some display characteristics of both animals and plants. Euglenids are particularly fascinating because studies of their anatomy and genome suggest they are among the most primitive of the earliest eukaryote organisms (that is organisms that have a true cell and evolved through the combination of more basic organisms (bacteria and archaea) that lack a true cell). Unfortunately euglenids lack a recognisable fossil record so we know little regarding their origin and evolutionary history.

In order to remedy this major problem we have trawled the literature and discovered a number of fossils that have euglenid-like characters. Our insight is that we have discovered a way of recognising whether a fossil does indeed represent a true euglenid. Modern euglenids have a unique cell wall structure, and by taking extremely thin sections of their cell walls (less that 1/10,000 mm in thickness) and examining them under a powerful Transmission Electron Microscope, it is possible to identify this unique structure. We have undertaken preliminary studies on potential fossil euglenids and demonstrated that we can observe such structure in the fossils and hence prove that they are indeed euglenids. Some of the euglenid-like fossils are a staggering 1 billion years old.

Our proposal is to analyse potential euglenid fossils from throughout the geological column and, by demonstrating which possess the characteristic euglenid wall structure, provide a continuous fossil record for the euglenids. This will place euglenids as one of the few groups of early divergent eukaryotes with a deep fossil record (and the first of the SuperGroup Excavates). This is important because it will provide evidence for the timing and nature of the diversification of the earliest eukaryotes. It will also provide an important fossil calibration point for molecular biologists that undertake molecular clock studies. Furthermore, we are addressing a highly topical research area and our findings will fuel current controversies concerning whether the eukaryotes evolved in the ocean or in fresh water and how and when euglenids acquired their secondary endosymbiotic green alga.

Planned Impact

The proposed research will make demonstrable contributions to the economy and society as the generated research-related knowledge and skills will enhance:-
Creative output
Economic competitiveness
Quality of life

It is critical to maintain a thriving UK science base and associated creative output. The proposed research addresses a long-standing and fundamental question in science. This innovative and World-leading science will enhance UK scientific prestige through the generation of key publications in top-ranking journals and presentations at international conferences (e.g. International Palynological Congress/International Organization of Palaeobotany Congress in The Czech Republic in 2020). CHW is currently Past-President of the International Federation of Palynological Societies (IFPS), who organize this conference, and will have an extensive role to play in organizing and delivering the conference. Such contributions will continue with the other international conferences during the lifetime of the grant enhancing national prestige in the wider international scientific community.

Key to the UK's economic competitiveness is both energy security and success of the UK hydrocarbon exploration/development industries. Our findings will directly impact both due to their significance for biostratigraphical consultancies that serve these industries. We are in constant contact with this sector and our results will be made available to them through publications, conference presentations and general consultation. In particular we maintain contact with 300+ alumni of the Centre for Palynology, the vast majority of who work in this sector, through an annual newsletter that is distributed electronically. The newsletters are also posted on the internet for open access to all working in this sector [http://www.sheffield.ac.uk/aps/staff-and-students/acadstaff/wellman/cpnewsletters]. Team members CHW and WAT are also integral to training of the next generation of industrial palynologists (e.g. twelve of CHWs past postgraduate students now work as industrial palynologists representing both consultancies and majors including Saudi Aramco, Shell, Petroleum Development Oman). Development of young lecturer WAT will expand UK palynological training activities and help maintain long-term national capability.

We will improve quality of life through our involvement in the University of Sheffield's extensive and committed outreach program. Fossils have an innate fascination and we ruthlessly exploit this to introduce young people to science and promote its enjoyment and importance. We plan to continue to develop these outreach activities, including events such as the Scarborough Fossil Festival.


10 25 50
Description We analysed a 440 million-year-old unicellular microfossil type to ascertain its wall ultrastructure. The wall ultrastructure is identical to that in the modern protist group euglenids (where this specific wall ultrastructure is indeed unique to this group and a defining feature of it). Thius we have proven that the microfossils are euglenids and provided the first fossil evidence for euglenids. This has also been confirmed by geochemical analysis of the wall.

Similar fossils have now been analysed back to 1000 million years ago (I billion) and are also clearly euglenids--thus proving the deep geological history of this group of organisms.

A second microfossil type we analysed to investigate if it was a euglenid turned out to be someting very different indeed and is an very exciting discovery. It is in fact a 1 billion year old multicellular organism that is probably related to some of the earliest animals as they first developed multicellularity. This fossil is also from a non-marine environment suggesting that the earliest evolution of animals may have taken place in freshwater rather than marine environments as is usually suggested.

An analysis of the evolutionary relationships (cladistic analysis) has placed our fossil euglenids within a classification of living and fossil euglenids showing where they fit into 'the tree of life'. This has provided evidence for the timing of diversification of the protists (the basal group of single-celled eukaryotes).
Exploitation Route We have already published some of our findings. These will be utilised by palynologists working in the exploration industries (water, brines, coal, hydrocarbons). Notably we have identified various microfossils as non-marine indicators that will help in studies of palaeoenvironments (palynofacies analysis).
Sectors Energy,Environment,Culture, Heritage, Museums and Collections

Description Television Interview on Sky News 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Following the publication of the paper Strother et al. (2021) in Current Biology we prepared a press release via the University of Sheffield Press Office. This generated considerable media interest including:-
(i) Numerous reports in regional (e.g. The Sheffield Star), national (e.g. The Daily Telegraph) and International newspapers.
(ii) A feature on the BBC Website (science section).
(iii) Several radio broadcasts on local and regional radio shows.
(iv) An interview on the main Sky News television broadcast that was broadcast on the midday news.

STROTHER, P. K. BRASIER, M. D., WACEY, D., TIMPE, L., SAUNDERS, M. & WELLMAN, C. H. 2021. A possible billion-year-old holozoan with differentiated multicellularity. Current Biology 31, 2658-2665.
Year(s) Of Engagement Activity 2021
Description Yorkshire Fossil Festival 2018-2020 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact We set up a stand at the 2018 and 2019 Yorkshire Fossil Festivals that were held the University of Hull (2018) and The Rotunda Museum, Scarborough (2019, 2021). The stand featured fossil and living plants and was interactive (using microscopes etc.). The aim was to highlight: (i) the importance of fossil plants (megafossils and dispersed pollen) in reconstructing past vegetation, environments and climate; (ii) the use of fossil dispersed pollen as a biostratigraphical tool used in the oil exploration industry. sadly the 2020 event was cancelled due to Covid.
Year(s) Of Engagement Activity 2018,2019,2021