Death March Recorded In Fossil
September 10, 2012

Horseshoe Crab’s Death March Recorded In Stone

Brett Smith for - Your Universe Online

An unusually complete fossil unearthed in Bavarian Germany was found to depict the tragic last moments of a prehistoric horseshoe crab as it stumbled for its life over 150 million years ago.

The crab´s fossilized track, which is over 31 feet in length, displays both the beginning and end of its death march that was the result of the arthropod falling into a stagnant lagoon, according to a recent report published in the journal Ichnos.

The rare fossil was discovered in 2002 in the Solnhofen Lithographic Limestone of Bavaria in Germany, where the famous Archaeopteryx fossil was found.

“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 lead author Dean Lomax, a curator of paleontology at Doncaster Museum and Art Gallery in England.

A violent storm or an encounter with a predator could have driven the crab into the deadly water, the researchers hypothesized. They noted that the quality of preservation that the murky lagoon provided allowed them to reconstruct the animal's final minutes.

"The lagoon that the animal found itself in was anoxic, so at the bottom of these lagoons there was no oxygen and nothing was living," Lomax told BBC News.

"This horseshoe crab [Mesolimulus walchi] found itself on the lagoon floor and we can tell by looking at the trace that the animal righted itself, managed to get on to its feet and began to walk," he explained.

Lomax said that close examination of the detailed fossil showed that the walking patterns and the animal's behavior started to change after the animal landed in the water. The leg impressions made by the crab became deeper and more erratic as it progressed along its death march.

“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 added.

Horseshoe crabs are considered to be an ancient species, a holdover from a time when the earliest animal started to walk around 450 million years ago. Today, only four living species exist and the typical horseshoe crab can grow over 24 inches in length. The fossilized specimen appears to be a juvenile about 5 inches long.

Commercially, horseshoe crab are caught and used for bait to catch eel or whelk. Some states, like New Jersey, Delaware, and South Carolina, have either banned or put restrictions on catching the arthropods because they are seen as a vital cog along the coastal ecosystem of these states.

Last month, New Jersey artist and marine biologist Christopher Wojcik created a 47-foot-long, 25,000-pound concrete horseshoe crab sculpture to be placed underwater and function as a unique habitat for fish, crabs, lobsters, mussels and other marine life.

Image 2 (below): Credit Dean R. Lomax / Christopher A. Racay)