On Saturday
22nd September the British Geological Survey’s (BGS) office in
Edinburgh was opened to the public as part of Edinburgh’s Doors Open Day. This
event, held annually, had the theme of ‘hidden treasures’. There were plenty of
these to seek out as the BGS was packed with Earth science demonstrations,
talks, experiments and displays of work undertaken at home and abroad. There
were lots of hands-on activities to interest people of all ages, some 750 of
whom came through the doors.
Top: Nick Fraser (National Museum of
Scotland) and Dave Millward (BGS) talking to an interested visitor. Bottom: limb
bones from an early amphibian – an example of the superbly preserved materials
from Stan Wood’s collections.
What is the significance of the new
fossils?
This is some
very useful information from the poster that gives an overview of the project:
What
is Romer’s Gap?
When did limbed vertebrates - or tetrapods - adapt to walk on
land? How long and under what circumstances did it take to achieve this? These
are key questions that shaped the future evolution of life on Earth, including
the eventual appearance of humans. The process began about 360 million years
ago at the end of Devonian times when a mass extinction event changed the world
for ever. Many fish groups became extinct and their place was taken by modern
forms. Modern plant groups, including true ferns and seed plants, diversified.
Before the mass extinction tetrapods were essentially aquatic and fishlike, but
afterwards they emerged on to land for the first time. The animals seen later
in the Carboniferous around 340 million years ago very strongly resemble modern
forms.
Until now, the intervening 20 million years has remained almost
unrepresented for fossil tetrapods. Thus, we know little about how they evolved
adaptations for life on land, the environments in which they did so, and the
timing or sequence of these events. The evolutionary relationships among these
early tetrapods and how they relate to modern forms are also unclear and
controversial as a result of this lack of fossil information. The entire fossil
hiatus has been called 'Romer’s Gap' after the American palaeontologist who
first recognized it.
New tetrapod
fossils
Now,
for the first time anywhere in the world, new fossil localities that lie within
Romer’s Gap have been found in south-eastern Scotland. These have already
provided a wealth of new fossils of tetrapods, fish, invertebrates and plants.
During the next 4 years the TWeed project team will be the first to have the
opportunity to study these specimens and to search for others. Team members
will also investigate the environmental, depositional, and climatic context in
which this momentous episode took place.
The Early Tetrapod World
The
fossils are all from the Ballagan Formation, a distinctive rock unit that crops
out widely across the Midland Valley of Scotland, East Lothian and the Borders
through into Northumberland. The Ballagan Formation is a cyclic succession of
mudstone, with interbedded sandstone and thin beds and nodules of
'cementstone'. These rocks were deposited on an extensive, low relief, muddy floodplain
that was traversed by meandering streams flowing from the north and north-east.
Periodically, the river-derived floods submerged the floodplains generating
extensive shallow freshwater floodplain lakes including some that were more
permanent. The widespread presence of gypsum and pseudomorphs after halite,
particularly in the Midland Valley of Scotland, suggests that these were
marginal marine coastal floodplains that were subject to occasional marine
transgressions and fluctuating salinity.
Project aspirations
The collaborative nature and efforts of our team, with its wide
range of experience and expertise can, for the first time anywhere in the
world:
• Provide a coherent picture of the biological, environmental and
geological conditions during the 15-20 million years recovery period following
the mass extinction event at the end of Devonian times.
• Explore and explain the changes during this period that laid the
foundations for the emergence of modern fauna and flora, and when tetrapods underwent
a major radiation into diverse groups including predominantly terrestrial forms
for the first time.
• South-east Scotland is the only place so far known in the world
where we can obtain this quality and depth of data to understand a crucial
period of Earth history: it is of international significance.
Until next
time
Carys
