10 jul 2012
A volcanic eruption around 579 million years ago buried a 'nursery' of
the earliest-known animals under a Pompeii-like deluge of ash,
preserving them as fossils in rocks in Newfoundland, new research
suggests.
A team from the Universities of Oxford and Cambridge, in
collaboration with the Memorial University of Newfoundland, looked for
evidence of life from the mysterious Ediacaran period (635-542 million
years ago) in which the first 'animals' -- complex multicellular
organisms -- appeared.
The team discovered over 100 fossils of what are believed to be
'baby' rangeomorphs; bizarre frond-shaped organisms which lived 580-550
million years ago and superficially resemble sea-pen corals but, on
closer inspection, are unlike any creature alive today. This 'nursery'
of baby rangeomorphs was found in rocks at the Mistaken Point Ecological
Reserve in Newfoundland, Canada.
A report of the research will appear in the July issue of the Journal of the Geological Society.
The fossil remains of rangeomorphs are often described as 'fern-like'
and where exactly they fit in the tree of life is unclear. Because they
lived deep beneath the ocean where there would have been no light they
are not thought to be plants but they may not have had all of the
characteristics of animals. Mysteriously, their frond-shaped body-plan,
which might have helped them gather oxygen or food, does not survive
into the Cambrian period (542-488 million years ago).
'The fossilised 'babies' we found are all less than three centimetres
long and are often as small as six millimetres; many times smaller than
the 'parent' forms, seen in neighbouring areas, which can reach up to
two metres in length,' said Professor Martin Brasier of Oxford
University's Department of Earth Sciences, one of the authors of the
report. 'This new discovery comes from the very bottom of the
fossil-bearing rocks, making it one of the oldest bedding planes to
preserve 'animal' fossils in the whole of the geological record.
'We think that, around 579 million years ago, an underwater 'nursery'
of baby Ediacaran fronds was overwhelmed, Pompeii-style, by an ash fall
from a volcanic eruption on a nearby island that smothered and
preserved them for posterity.'
Dr Alexander Liu of Cambridge University's Department of Earth
Sciences, an author of the report, said: 'These juveniles are
exceptionally well preserved, and include species never before found in
rocks of this age, increasing the known taxonomic diversity of the
earliest Ediacaran fossil sites. The discovery confirms a remarkable
variety of rangeomorph fossil forms so early in their evolutionary
history.'
The find reinforces the idea that 'life got large' around 580 million
years ago, with the advent of these frond-like forms, some of which
grew up -- in better times -- to reach almost two metres in length.
Professor Brasier said: 'We are now exploring even further back in
time to try and discover exactly when these mysterious organisms first
appeared and learn more about the processes that led to their
diversification in an 'Ediacaran explosion' that may have mirrored the
profusion of new life forms we see in the Cambrian.'
