The words "zombie fossils" may conjure up images of undead dinosaurs lurching around the ancient forests and grasslands some 65 million years ago, leaving a trail of rotting flesh and destruction in its wake. Or it might make you think of the questionable B-movie released just last year in which this is a major plot point.
But for researchers studying long-dead animals that have become turned to stone, the idea of zombie fossils is actually one of importance. Specifically, how fresh carcasses rot and decay before they become fossilized, and how this might affect which bits are preserved and thus how they once looked and behaved.
When palaeontologists dig up the fossil remains of long-dead animals, it can often be tricky to understand exactly what they’re looking at. They have to figure out to what extent decay has altered the remains, how much is missing, and then where the bits they do have go to piece together the original animal. This is all made even trickier if the animal in question was largely soft-bodied, as many of the earliest life forms once were.
Because of this difficulty in interpreting fossil remains, there are plenty examples of when our understanding of long-extinct animals has had to change as new evidence comes in. One of the most famous examples is that of the Iguanodon: original reconstructions placed a large spike on the end of its nose based on fossils found, until it was realized that this was in fact a thumb spike and likely used for defense and foraging.
“As soon as an organism dies, it starts to decay, and this process of decomposition inevitably involves changes in how features or body parts look: they may collapse, alter their shape or position; all too soon they liquefy and are eaten by bacteria until nothing remains,” explained Professor Sarah Gabbott, co-author of a new study exploring zombie fossils published in Palaeontology.
To do this, a team of scientists from the University of Leicester took up up the unenviable task of, well, watching things rot. From primitive eel-like fish such as hagfish and lamprey to insects and worms, they hoped to get a better understanding of how the decaying process alters the shape and appearance of the animals, and as such how this can then be misinterpreted if fossils are then dug up.
“One consequence of this decay is that palaeontologists have to work with incomplete fossils," said Professor Mark Purnell. "Some of the features that are present don't look anything like they did when the animal was alive, and many features are missing completely. The trick is to be able to recognize partially-decomposed features, and where body parts have rotted away completely.”
Unfortunately, this means that Z-Rex might have to stay firmly in our imaginations, for now.
