Believe it or not, the author of a Death Dictionary learned a new morbid word yesterday! I was familiar with the concept of trace fossils* (as opposed to body fossils), since I have some fossilized bird footprints. But I didn't know of a "mortichnia" in the fossil record, which is the trackway of the animal's final moments. The mortichnia, or death march, above represents the last 32' (9.7m) movement of a horseshoe crab 150 million years ago. From it, researchers Dean Lomax and Christopher Racay pieced together the likely circumstances of the crab's demise. The
animal was somehow flung into a lagoon during a storm and sank to the bottom. Unfortunately, the lack of oxygen put it in distress, although it managed to right itself and begin to
walk. Soon, though, it began to struggle. "We started to study the specimen closer and saw that the walking patterns and the animal's behavior 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," describes Lomax. The creature died and was preserved in the lithographic limestone of Bavaria, Germany (photo here), where fossils of the Archaeopteryx have also been found. The find is of interest because the fossil of the animal itself is present at the end of the trackway, where the animal died. Says Lomax, "It's not particularly rare to find these horseshoe crabs at the end of short traces, but nothing quite as substantially large and scientifically important as this." (Follow links for more trace fossils of horseshoe crabs: in Tennessee, U.S., New Jersey, U.S., and Nova Scotia, Canada.)
*Geological records of biological activity, also called "ichnofossils."
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Various posts about paths:
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