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Testing the fossil record

How good is the fossil record? And does it paint an accurate picture of the history of life? Those are the long-standing questions that geobiologist Bjarte Hannisdal at the University of Bergen’s Centre for Geobiology is trying to answer.

How good is the fossil record? And does it paint an accurate picture of the history of life? Those are the long-standing questions that geobiologist Bjarte Hannisdal at the University of Bergen’s Centre for Geobiology is trying to answer.

Palaeontologists have developed methods to try to identify and correct for bias and incompleteness in the fossil record. A new study, published on 4 September 2014 in the journal Nature Communications, suggests that some of these correction methods may actually be misleading. The work is led by Dr Alex Dunhill (University of Leeds, formerly at the Universities of Bath and Bristol), together with Hannisdal (University of Bergen) and Professor Michael Benton (University of Bristol).

Back to the origin of animals:

“The Earth keeps changing. Life keeps evolving. And there is a link between the two, where both can influence one another,” says Hannisdal. “These types of issues are central to my research in general and also underpin this particular study.”

The trio have compared biodiversity through the last 550 million years of the British fossil record against a number of geological and environmental factors including the area of sedimentary rock, the number of recorded fossil collections and the number of named geological ‘formations’. All of these measures had been used as yardsticks against which the quality of the fossil record could be assessed – but the new study casts doubt on their usefulness.

This map shows the geology of Great Britain spanning the past 550 million years. Image credit: Dr Alex Dunhill, University of Leeds

This map shows the geology of Great Britain spanning the past 550 million years. Image credit: Dr Alex Dunhill, University of Leeds

The case of Great Britain:

The British rock and fossil records were used as a case study, because the British Isles have been extensively mapped and documented by geologists for over 200 years.

“We suspected that the similar patterns displayed by the rock and fossil records were due to external factors rather than the number of fossils being simply dictated by the amount of accessible rock. Our work shows this is true. Factors such as counts of geological formations and collections cannot be used to correct biodiversity in the fossil record,” says Alex Dunhill.

The study benefits from the application of advanced mathematical techniques that not only identify whether two data sets correlate, but also whether one drives the other. The results show that out of all the geological factors, only the area of preserved rock drives biodiversity. Therefore, the other geological factors; counts of fossil collections and geological formations, are not independent measures of bias in the fossil record.

“We can learn more by analysing old data in new ways, than by analysing new data in old ways,” says Hannisdal.

A new view of the fossil record:

The discovery fundamentally alters the way we view the fossil record of life through time. It shows that both the preservation of rock and the preservation of fossils were probably driven by external environmental factors like climate change and sea level. This better explains the similarities between the rock and fossil records, as both responding to the same external factors. The alternative idea, that rock preservation was driving the fossil record is now strongly queried by this study. Perhaps the record of biodiversity in the fossil record is more accurate than previously feared.

Michael Benton from the University of Bristol, another co-author of the study, said: “Palaeontologists are right to be cautious about the quality of the fossil record, but perhaps some have been too cautious. The sequence of fossils in the rocks more or less tells us the story of the history of life, and we have sensible ways of dealing with uncertainty. Some recent work on ‘correcting’ the fossil record by using formation counts may produce nonsense results,” says Michael Benton.

University of Bergen

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