If fearful people have nightmares about being naked in public, a fearful ammonite might have dreamed of swimming around without its shell, exposing its soft body to the elements and the grinning eyes of predators.
For an unfortunate ammonite in the late Jurassic, this was not a dream but a harsh reality. The animal died completely unclothed outside of its lively shell and was buried in this way. According to a study recently published in the Swiss Journal of Paleontology, the death of the ammonite made it an extraordinary fossil – one of the few records of soft tissue in a creature most commonly immortalized as a clam.
“We know of millions and millions of ammonites obtained from their shell, so something extraordinary had to happen here,” said Thomas Clements, a paleobiologist at the University of Birmingham in England who was not involved in the research. “It’s like finding -” said Dr. Clements and fell silent. “Well I don’t even know how to find it, it’s so bizarre.”
René Hoffmann, ammonitologist at the Ruhr University Bochum in Germany, who reviewed the study, described the fossil as a “paleontological jackpot that you only have once in a lifetime”.
To the untrained eye, the fossil looks more like an impressionist painting than an ammonite: a pink, bean-shaped smear surrounded by bulges, veins, and ovals. It was discovered in the southern German region of Solnhofen-Eichstätt, which at the time of the ammonite around 150 million years ago was an archipelago that was littered with calm lagoons without oxygen. These conditions made it possible for soft, dead creatures to sink into the mud unscathed by predators or bacteria, says Christian Klug, paleontologist at the University of Zurich in Switzerland and first author of the paper.
When Dr. Cleverly seeing the fossil for the first time, he knew that it represented the soft tissues of an ammonite, but exactly which soft tissues he did not know. He left it alone for months until Helmut Tischlinger, a fossil collector and author of the paper, sent him photos of the fossil taken with ultraviolet light, which revealed the tiny bumps and mineral stains in the fossil.
Dr. One by one, Klug reconstructed the creature’s anatomy, from the most visible organs to the darkest. First, he identified the aptychus, a Shelly mandible that indicated the fossil was an ammonite. Behind the jaws, he found the chitinous layer of the esophagus and then a lump that indicated a digestive tract with a cololite fecal matter (he used another word) “still in the intestine,” noted Dr. Cleverly clear.
“For the most part, the soft body reconstruction makes perfect sense,” said Margaret Yacobucci, a paleobiologist at Bowling Green State University in Ohio who was not involved in the research.
Solving the fossil’s other riddle – how the ammonite was separated from its shell – was far more difficult. The soft tissues were so intact that they still appeared to be wrapped. The authors propose several alternative endings for the life of the ammonite, each possible but uncertain. The soft tissues of a dead ammonite are believed to have slipped out as the tissue connecting its body to its conch began to disintegrate.
Another, more elaborate explanation imagines a predator breaking the ammonite’s shell from behind and sucking its body out to drop the naked ammonite. “The best explanation is that some squid-like organism pulled the soft tissues out and couldn’t find them,” said Dr. Smart.
Dr. Clements finds the clumsy predator theory “great,” if unlikely; probably an eaten ammonite body would show more visible damage. But he doesn’t have a good alternative. The interpretation of a fossil always raises doubts, and Dr. Clements predicts that the unarmed ammonite will be reanalyzed using robust chemical analysis in the future.
Strangely enough, the fossilized ammonite has no arms, leaving one of the outstanding puzzles of ammonite anatomy unsolved. “Did you have lots of thin, delicate arms like modern nautilus or a few strong arms like modern coleoids?” Asked Dr. Yacobucci. “If I got access to a time machine, the first thing I would do would be to go back to the Jura to see what kind of weapons ammonoids had.”
If a squid-like predator had actually freed the ammonite from its shell, it might have chewed the creature’s unknown amount of weapons as a consolation prize, and fed both the ancient cephalopods and the scientists who study them.
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