Periodic Reporting for period 2 - Tetrapod Origin (Tracking our ancestors across the Devonian world: a new multidisciplinary approach to the origin of tetrapods)
Reporting period: 2023-03-01 to 2024-08-31
This project addresses the fish-tetrapod transition, by which a group of fishes evolved the ability to live permanently on land and gave rise to the tetrapods or backboned land animals - the group to which we ourselves belong. This transition took place during the Devonian period, which lasted from 419 to 359 million years ago. It was a very important event, producing an entirely new kind of animal that changed the character of land ecosystems forever: today there are more than 30 000 tetrapod species, inhabiting all environments from the tropics to the high arctic. The fossil record of skeletons shows tetrapods first appearing around 375 million years ago. In slightly older rocks from 385-380 million years ago we find so-called elpistostegalians - intermediate forms that look quite similar to tetrapods but still have fins rather than legs. This looks like a straightforward picture of the fish-tetrapod transition captured by the fossil record, but the fossil footprint record shows something quite different: the oldest known fossil tetrapod footprints and trackways are about 390 million years old. However, the dominant evolutionary scenario for the fish-tetrapod transition - the one presented in popular media - shows tetrapods evolving from elpistostegalians in an aquatic setting, and fails to take proper account of the footprint data. There is also a more general failure to place the early tetrapods in a well-defined ecological context.
Our project addresses these problems. We are undertaking fieldwork at Devonian tetrapod localities in Ireland, Latvia and Greenland, gathering data that encompass tetrapod body fossils, tetrapod trackways, non-tetrapod body fossils and trackways (arthropod as well as vertebrate), plants, and the sediments themselves. Techniques used to study the material include synchrotron microtomography (which allows us to image the fossils in three dimensions inside the rock) and isotope geochemistry (which can be applied to the sediment, to determine environmental conditions, or to the fossils themselves, to investigate their environmental preferences or the preservation of their tissues). Trackways are recorded using optical scanning, which captures three-dimensional surfaces. We aim to understand not just the tetrapods themselves, but their environmental and ecological associations, so that we can make sense of the fish-tetrapod transition in an ecosystem context as well as a series of evolutionary events.
Our project addresses these problems. We are undertaking fieldwork at Devonian tetrapod localities in Ireland, Latvia and Greenland, gathering data that encompass tetrapod body fossils, tetrapod trackways, non-tetrapod body fossils and trackways (arthropod as well as vertebrate), plants, and the sediments themselves. Techniques used to study the material include synchrotron microtomography (which allows us to image the fossils in three dimensions inside the rock) and isotope geochemistry (which can be applied to the sediment, to determine environmental conditions, or to the fossils themselves, to investigate their environmental preferences or the preservation of their tissues). Trackways are recorded using optical scanning, which captures three-dimensional surfaces. We aim to understand not just the tetrapods themselves, but their environmental and ecological associations, so that we can make sense of the fish-tetrapod transition in an ecosystem context as well as a series of evolutionary events.
We had intended to focus our fieldwork on the Middle Devonian trackway localities of Ireland and Poland (the earliest known tetrapod localities in the world), the Late Devonian of Russia, and the end-Devonian of Greenland. Regrettably, Russia's war against Ukraine has made it impossible to pursue fieldwork there, so that part of the project has been replaced by fieldwork in the Late Devonian of Latvia. Our fieldwork in Greenland has generated a very large body of new material with major implications for our understanding of tetrapod diversity and evolution. A follow-up expedition to Greenland will take place in the summer of 2024. This list presents most of our results to date. Some work-in-progress with confidential results is omitted:
South Africa: Work on the Late Devonian fossil assemblage from Waterloo Farm. We have described the giant predatory fish Hyneria udlezinye, and are studying the rich flora.
Valentia Island, Ireland: We have made optical scans of all accessible trackways, mapped the landscape-scale sedimentology and plant root horizons, collected fish body fossils, and collected volcanic tuff samples for radiometric dating.
Latvia: A two-week excavation at the tetrapod locality Pavari. We collected important tetrapod material, including a femur and skull bones. We also discovered well-preserved land plants, a first in the Devonian of Latvia, and an important contribution to understanding the ecosystem.
Greenland: in the summer of 2022, we carried out a 4-week expedition to the end-Devonian and Devonian-Carboniferous boundary of North-East Greenland (Figure 1). The results were spectacular. We discovered a rich bone bed yielding at least 4-5 different tetrapods, all new to science (Figure 2), approximately doubling the Devonian tetrapod diversity discovered during the previous 90 years in Greenland. Some specimens contain preserved soft tissue, a world first for Devonian tetrapods. We also sampled a lake deposit spanning the Devonian-Carboniferous boundary. Fossils are being imaged by synchrotron microtomography at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.
Canada: We are investigating the anatomy of a complete specimen of the near-tetrapod Elpistostege from the Late Devonian of. Québec, using synchrotron microtomography at ESRF. Two scan sessions have been completed with excellent results.
South Africa: Work on the Late Devonian fossil assemblage from Waterloo Farm. We have described the giant predatory fish Hyneria udlezinye, and are studying the rich flora.
Valentia Island, Ireland: We have made optical scans of all accessible trackways, mapped the landscape-scale sedimentology and plant root horizons, collected fish body fossils, and collected volcanic tuff samples for radiometric dating.
Latvia: A two-week excavation at the tetrapod locality Pavari. We collected important tetrapod material, including a femur and skull bones. We also discovered well-preserved land plants, a first in the Devonian of Latvia, and an important contribution to understanding the ecosystem.
Greenland: in the summer of 2022, we carried out a 4-week expedition to the end-Devonian and Devonian-Carboniferous boundary of North-East Greenland (Figure 1). The results were spectacular. We discovered a rich bone bed yielding at least 4-5 different tetrapods, all new to science (Figure 2), approximately doubling the Devonian tetrapod diversity discovered during the previous 90 years in Greenland. Some specimens contain preserved soft tissue, a world first for Devonian tetrapods. We also sampled a lake deposit spanning the Devonian-Carboniferous boundary. Fossils are being imaged by synchrotron microtomography at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.
Canada: We are investigating the anatomy of a complete specimen of the near-tetrapod Elpistostege from the Late Devonian of. Québec, using synchrotron microtomography at ESRF. Two scan sessions have been completed with excellent results.
The project has already progressed far beyond the state of the art, and will continue to do so for the remainder of the project. The end result will be the most radical overhaul of the explanatory framework of the origin of tetrapods for at least 30 years. There are four main components to this.
Firstly, we are discovering and exploring major new localities - above all in Greenland, but not only there - which cast new light on the origin of tetrapods and the development of Devonian ecosystems. For example, the tetrapod assemblage from the new end-Devonian tetrapod bed from Greenland is younger than any previously known Devonian tetrapods and consists entirely of new taxa that appear substantially unlike previous known forms from Greenland and elsewhere.
Secondly, we are undertaking synthetic overview studies of the entire ecosystems represented by these localities, enabling us to draw well-founded conclusions about the ecological role of the tetrapods.
Thirdly, we are employing a battery of cutting-edge techniques to study the material, most importantly synchrotron microtomography for imaging the fossils and various geochemical tools for analysing the composition of fossils and sediment, which allow us to extract far richer data than traditional techniques - and kinds of data that were previously entirely unobtainable.
Fourthly, some of our discoveries have very radical implications for the timing and mode of tetrapod evolution. The most dramatic of these are not yet published, and must remain confidential for now, but suffice it to say that they will completely overthrow the accepted timeline for the origin, diversification, and terrestrialisation of the tetrapods.
The results that can be predicted between now and the end of the project are those that spring from the currently ongoing analyses. By the end we will have a good understanding of the new tetrapod assemblage from Greenland and will have published descriptions of most of the taxa it contains. We will have analysed as far as possible the depositional environment and the composition of its ecosystem, to produce an overview of the end of the Devonian in the Greenland basin. We will have published descriptions of the new tetrapod material from Latvia, and of the axial skeleton and pelvic fins of the near-tetrapod Elpistostege from Québec, Canada. Most importantly, we will also have published the radical results that overthrow the established timeline for early tetrapod evolution.
Firstly, we are discovering and exploring major new localities - above all in Greenland, but not only there - which cast new light on the origin of tetrapods and the development of Devonian ecosystems. For example, the tetrapod assemblage from the new end-Devonian tetrapod bed from Greenland is younger than any previously known Devonian tetrapods and consists entirely of new taxa that appear substantially unlike previous known forms from Greenland and elsewhere.
Secondly, we are undertaking synthetic overview studies of the entire ecosystems represented by these localities, enabling us to draw well-founded conclusions about the ecological role of the tetrapods.
Thirdly, we are employing a battery of cutting-edge techniques to study the material, most importantly synchrotron microtomography for imaging the fossils and various geochemical tools for analysing the composition of fossils and sediment, which allow us to extract far richer data than traditional techniques - and kinds of data that were previously entirely unobtainable.
Fourthly, some of our discoveries have very radical implications for the timing and mode of tetrapod evolution. The most dramatic of these are not yet published, and must remain confidential for now, but suffice it to say that they will completely overthrow the accepted timeline for the origin, diversification, and terrestrialisation of the tetrapods.
The results that can be predicted between now and the end of the project are those that spring from the currently ongoing analyses. By the end we will have a good understanding of the new tetrapod assemblage from Greenland and will have published descriptions of most of the taxa it contains. We will have analysed as far as possible the depositional environment and the composition of its ecosystem, to produce an overview of the end of the Devonian in the Greenland basin. We will have published descriptions of the new tetrapod material from Latvia, and of the axial skeleton and pelvic fins of the near-tetrapod Elpistostege from Québec, Canada. Most importantly, we will also have published the radical results that overthrow the established timeline for early tetrapod evolution.