Fossil CSI: what can a 100 million year old crime scene tell us about the past, and the future?

Written by Caitlin Syme (@taphovenatrix), PhD Candidate, The University of Queensland

for the National Science Communication Challenge

Fossil crocodile with most of the skull missing, from Isisford (tail at top of photo) Image: Caitlin Syme

Fossil crocodile with most of the skull missing, from Isisford (tail at top of photo) Image: Caitlin Syme

When you look at a fossil, you're peering into the past.

A fossil represents a once living creature, and shows us what life on Earth looked like thousands, millions, or even billions of years ago.

It is almost like looking at another planet, very different to modern day Earth as we know it.

The only evidence of these once living, breathing creatures are their skin and bones which have been turned to stone.

It is the job of those who study fossils (Palaeontologists) to recover as much information as they can from each fossil.

Who or what was this creature?

When and where did it live?

And why did it die?

The science of taphonomy – what happens after an animal dies and how its body becomes a fossil – can help answer these questions.

A fossil skeleton embedded in rock is a bit like a modern day ‘crime scene’ photograph

A fossil can hold clues to the mystery of why the animal died. Like a very ancient episode of CSI, palaeontologists try to solve the mystery of an animal's death.

Did a predator kill it? Did it drown in a flood? Did it die from an ancient disease?

We can look for evidence such as bite-marks on bones, the pose of the body, or broken bones, and sometimes most importantly, whether any part of the body is missing.

I am currently studying an ancient 'crime scene' preserved near the town of Isisford in central-western Queensland.

The victims? Dinosaurs, crocodiles, and fish.

Their time of death? 100 million years ago during the Cretaceous period.

These fossils are very well preserved, but some have missing limbs and, in one case, a missing head.

My research suggests that the Isisford dinosaurs, crocodiles and fish died in a river delta near a giant inland sea

The rock the specimens are preserved in contain river sand, with chemical tests showing that a mixture of freshwater and marine water was present, like in a modern-day delta.

The fossils don't have any bite marks and are almost completely intact, so they were not killed or eaten by a large predator. If smaller animals ate soft tissue from the bones, they have left no trace.

The fossils also have no broken bones, so they may have instead died from disease or starvation.

When an animal dies in water, its body can float for a few days before sinking to the bottom. While it floats, bits of the body can fall off. The Isisford animals were buried before this could happen.

So, what about the missing parts of the fossils?

As it turns out, they were most likely still present when the animal carcasses were buried, but were later eroded after the fossils had formed. These clues tell us that there was a sandy river delta at Isisford during the Cretaceous period, and animals were buried under thick layers of sand before larger predators could eat their remains.

We can use these same techniques to understand how life might be preserved in rocks on other planets in our universe. And from those extra-terrestrial remains, we could get a clearer picture of how those organisms lived and died in their alien environments.

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