Some 150 million years ago, a squid-like creature that lived in a coil-shaped shell, also known as an ammonite, died. Its shell drifted to the bottom of a tropical lagoon, dragging along in the current nearly 28 feet before settling into it final resting spot.
Millions of years later, as Helen Briggs reports for the BBC, scientists have unearthed the mark along with the shell in a stone quarry in Solnhofen, Germany. They published a paper this week describing the find this week in the journal PLOS One.
“The fossil is perhaps one of the most unlikely of fossils to have ever been preserved, let alone be discovered," Dean Lomax paleontologist from the University of Manchester who led the study in the journal tells Briggs. “[It’s] a real chance find…[that] provides a snapshot of a moment that is captured in time—it really tells a story.”
The ammonite owner of the shell likely died between 163 and 145 million year ago, according to the study. These creatures jetted around the oceans from roughly 240 million years ago until about 65 million years ago.
As Stephanie Pappas at LiveScience reports, Lomax and his colleagues made a 3D model of the ammonite and its track using a method known as photogrammatry, which involves taking and combining hundreds of photos of a subject from many different angles. The resulting model shows that at its tip, the "death drag" is a mere 0.3 inches wide and is composed of two grooves. But as the shell was pulled along by the current the impression widened, till 18 ridges become visible before the ammonite plopped over.
Lomax tells Pappas it's likely that the water was between 65 and 200 feet deep, and that the current was strong enough to propel the shell, but not strong enough to disturb the sandy bottom. “If the current was very fast, then the ammonite would likely have bounced as opposed to drifted,” he says.
This isn’t the first ammonite marks found in the limestone, though it is by far the longest. According to the study, researchers first interpreted such impressions as claw marks, ripples from fish or paths made by turtles or coelacanths. But this track and the other like it—drag marks, roll marks and bounce trails—are helping researchers interpret the origins of other mysterious tracks paleontologists unearth.