New fossil reveals origin of defensive strategy

For the first time, scientists have been able to pinpoint the very first animal to roll itself up defensively, thanks to a new fossil find.

Researchers from the University of Cambridge's Department of Earth Sciences have discovered that a very early group of tribolites known as olenellids were able to enrol.

Until now, palaeontologists were unable to pinpoint exactly when this defence mechanism originated, but these new findings indicate that the strategy is in fact just over 510 million years old.

According to the university, the fossilised remains of sea-dwelling tribolites, one of the first complex animals, are abundant due to their hard, protective shells. Until now, however, it was generally thought that they were simply unable to enrol.

Lead researcher, Javier Ortega Hernández, says: "No-one had ever seen an enrolled fossil of this very early trilobite group, so it was assumed that they did not have enrolling ability at this stage of evolution.

“We now realise that… when they died their muscles would relax and their bodies stretch out again. We needed to find olenellids that had been rapidly buried shortly after death and were still enrolled."

Javier discovered two tiny but highly significant specimens during field research in Jasper National Park in Alberta, Canada.

"The first specimen is unusual for an olenellid, as the tail covers the underside of the head completely - a typical characteristic of enrolment," he explains.

"The second shows overlapping segments in the body. Taken together, these are an exciting find, as it is clear evidence that, despite their limitations, olenellids were capable of rolling themselves up effectively."

According to the findings, which have been published in the journal, Biology Letters, the seafloors inhabited by the olenellids would have been relatively predator-free during the Cambrian period - 545 million years ago.

Simply being able to curl up would have been enough to avoid predators, researchers say. Over the next several million years, however, the complexity of life developed rapidly and better defences were needed.

Findings suggests that olenellids developed a larger tail to cover the soft underside of their heads when they were enrolled. Later tribolites also had locking devices which meant that their bodies could not be pulled apart or twisted open when enrolled.

Credit: Javier Ortega Hernández