Rotten fish & fossils

Resolving the riddle of our earliest vertebrate ancestors

Rotten fish

Introduction

The questions of how, when and why our earliest fish-like ancestors evolved are fundamental to understanding our place in evolution. However, answers remain elusive because we don’t know how to read the earliest vertebrate fossil record.

The experiments behind this exhibit – which involve rotting existing primitive vertebrates and their near-relatives – reveal how the characteristic features that allow us to recognise and identify fossil vertebrates are transformed and then lost during decay. Visitors will learn how this affects our ability to correctly read the fossil record and how understanding patterns of decay provides a much clearer view of our evolutionary origins.

How does it work?

The deepest roots of our vertebrate family tree predate the evolution of skeletons, so our earliest fish-like ancestors lacked bones and teeth. Amazingly, fossils do exist from this critical period of vertebrate evolution, preserving traces of soft tissues such as muscles and cartilage, but there are very few identifiable species.

Is this rarity because evolution was occurring rapidly? Or because the animals lacked easily fossilisable hard parts and just rotted away? The answer depends on being able to correctly read the fossil record, and scientists have taken a new approach to this by studying how the bodies of similar, currently existing primitive vertebrates rot away after they die. The results provide a ‘photofit’ resource of body parts in various states of decay which can be compared with those of the rare fossils from half a billion years ago.

These experiments have revealed that the characteristics which are most useful in placing primitive vertebrates and their relatives in the correct order on the tree of life – are also the ones which decompose quickest. This means that some fossils may be interpreted as more ‘primitive’ than they actually are because parts of their anatomy rotted away before fossilisation. For further information please see the University of Leicester website.