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| February 2010 |
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Decomposing fish sheds light on fossil ancestryRevelations of rotting fish provide scientists with clearer picture
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 Picture credit: Mark Purnell, Rob Sansom, Sarah Gabbott,
University of Leicester |
Decaying corpses are usually the domain of forensic scientists, but
palaeontologists have discovered that studying rotting fish sheds new light on
our earliest ancestry.
The researchers, from the Department of Geology at the University of
Leicester, devised a new method for extracting information from 500 million year
old fossils -they studied the way fish decompose to gain a clearer picture of
how our ancient fish-like ancestors would have looked. Their results indicate
that some of the earliest fossils from our part of the tree of life may have
been more complex than has previously been thought.
Dr Rob Sansom, lead author of the paper explains: “Interpreting fossils is in
some ways similar to forensic analysis – we gather all the available clues to
put together a scientific reconstruction of something that happened in the past.
Unlike forensics, however, we are dealing with life from millions of years ago,
and we are less interested in understanding the cause or the time of death. What
we want to get at is what an animal was like before it died and, as with
forensic analysis, knowing how the decomposition that took place after death
altered the body provides important clues to its original anatomy.”
This is something that palaeontologists sometimes overlook, according to
Sansom, “probably because spending hundreds of hours studying the stinking
carcasses of rotting fish is not something that appeals to everyone.” But the
rewards are worth the discomfort.
Fish-like fossils from half a billion years ago are recognised as being part
of our evolutionary history because they possess characteristic anatomical
features, such as a tail, eyes and the precursor of a backbone. Sansom
continues: “It seems contradictory, but decomposition is an important part of
the process by which animals become preserved and fossilized, so by knowing how
these important anatomical features change as they rot, we are better able to
correctly interpret the most ancient fossils representing the lowest branches of
our part of the evolutionary tree.”
“These fossils provide our only direct record of when and how our earliest
vertebrate ancestors evolved” adds Dr Mark Purnell, one of the leaders of the
study. “Did they appear suddenly, in an evolutionary explosion of complexity, or
gradually over millions of years? What did they look like? – in what ways did
they differ from their worm-like relatives and how did this set the stage for
later evolutionary events? Answers to these fundamental questions - the how,
when and why of our own origins - remain elusive because reading the earliest
vertebrate fossil record is difficult.”
The scarcity of branches in this part of the evolutionary tree could reflect
rapid, explosive evolution or the simple fact that, because they lacked bones or
teeth, the earliest vertebrates left few fossils.
This is the area in which Dr Sarah Gabbott, who with Purnell conceived the
Leicester study, is an expert: “Only in the most exceptional circumstances do
soft-tissues, such as eyes, muscles and guts, become fossilized, yet it is
precisely such remains that we rely on for understanding our earliest
evolutionary relatives: half-a-billion years ago it’s pretty much all our
ancestors had.”
The results published in Nature, show that some of the characteristic
anatomical features of early vertebrate fossils have been badly affected by
decomposition, and in some cases may have rotted away completely. Knowing how
decomposition affected the fossils means our reconstructions of our earliest
ancestors will be more scientifically accurate. - NERC
More information:
You can watch a video of rotting primitive fish here:
http://www.youtube.com/watch?v=zKk1OFYDPEU
University of Leicester: http://www2.le.ac.uk/about/facts
NERC: www.nerc.ac.uk
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