Prehistoric Crab’s Death March Fossilized

Roughly 150 million years ago, an unfortunate horseshoe crab found itself in a stagnant lagoon in what is now Germany after a harsh storm. Unable to survive, the crab began its 31-foot death march before finally succumbing, leaving its tiny mark on the world in the form of a fossil.

That story may not sound all that interesting on its own, but the mark that the prehistoric horseshoe crab left wasn’t just its fossil. In 2002, the fossil of the animal was discovered in a layer of limestone in Bavaria, Germany. Remarkably, the crab’s “death march”–or mortichnia–was also visible in the layer, and it was surprisingly well preserved.

It’s not terribly uncommon for a creature’s last steps to be fossilized, researchers say, but it’s very rare to find such a long trackway with the creature preserved along with it. Needless to say, the fossilized 31-foot death march, and the 150 million year-old horseshoe crab at the end of it, is a spectacular find.

“When I first laid my eyes on this specimen in 2008, while on display, I realized how special this fossil truly was. It’s not particularly rare to find these horseshoe crabs at the end of their short traces, but nothing quite as substantially large and scientifically important as this; trackways and tracemakers preserved together in the fossil record is rare,” said Dean Lomax, lead author on the research published August 29 in Ichnos: An International Journal for Plant and Animal Traces.

Speaking to the BBC, Lomax said that the lagoon the crab found itself in was anoxic–near the bottom, there was no oxygen–so the crab was doomed as soon as he reached the bottom. It was able to get up and walk after reaching the bottom, as evidenced by the fossil, but it didn’t last long.

“We started to study the specimen closer and saw that the walking patterns and the animal’s behaviour started to change. The leg impressions became deeper and more erratic, the telson (the long spiny tail) started being lifted up and down, up and down, showing that the animal was really being affected by the conditions,” Lomax said.

“Discoveries such as this provide unique insights into the behaviour of extinct species – in this example during the last throes of its life and the environmental conditions that led to its demise.”