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If anxious humans have nightmares of being naked in public, an anxious ammonite may have dreamed of swimming without her shell, her limp body exposed to the elements and the peeping eyes of predators.
For an unfortunate Upper Jurassic ammonite, this was not a dream but a harsh reality. The animal died completely naked, out of its whorled shell, and was buried that way. According to a study published recently in the Swiss Journal of Palaeontology, the death of ammonite has made it an extraordinary fossil – one of the very few soft tissue records in a creature that is most often immortalized in the form of a shell..
“We know of millions upon millions of ammonites that have been preserved from their shells, so something exceptional must have happened here,” said Thomas Clements, a paleobiologist at the University of Birmingham in England who did not participated in the search. “It’s like finding…” Dr Clements said, pausing. “Well, I don’t even know what it’s like to find, it’s so weird.
René Hoffmann, an ammonitologist at Ruhr University in Bochum, Germany who reviewed the study, called the fossil a “paleontological jackpot that you only have once in your life.”
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 Solnhofen-Eichstätt region of southern Germany, which was, during the ammonite era, around 150 million years ago, an archipelago dotted with serene and private lagoons oxygen. These conditions allowed limp, dead creatures to sink into the mud unharmed by predators or bacteria, according to Christian Klug, a paleontologist at the University of Zurich in Switzerland and first author of the article.
When Dr Klug first saw the fossil, he knew it represented the soft parts of an ammonite, but exactly which soft parts he didn’t know. He left it alone for months until Helmut Tischlinger, a fossil collector and author on the paper, sent him photos of the fossil taken under ultraviolet light, which revealed the tiny elevations and mineral specks in the fossil.
Dr. Klug reconstructed the creature’s anatomy sequentially, from the most visible organs to the most obscure ones. He first identified the aptychus, a lower jaw shell which indicated that the fossil was an ammonite. Behind the jaws, he found the chitinous layer of the esophagus, then a lump that suggested a digestive tract with cololitis – fecal matter (he used a different word) “that’s still in the gut,” the gut said. Dr Klug.
“For the most part, 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 other mystery of the fossil – how ammonite was separated from its shell – was much more difficult. The soft parts were so intact that they still seemed coiled. The authors propose several alternative endings for ammonite life, each possible but uncertain. It is suggested that the soft parts of a dead ammonite slipped off when the tissue connecting its body to its conch began to break down.
Another, more elaborate explanation imagines a predator smashing the ammonite shell from behind and sucking its body only to drop the bare ammonite. “The best explanation is that some squid-like organisms removed the soft tissue and couldn’t get it back,” Dr Klug said.
Dr. Clements finds the clumsy predator theory “great” so unlikely; presumably, a scraped ammonite body would show more visible damage. But he has no good alternative. There is still some doubt about the interpretation of a fossil, and Dr Clements predicts that unarmed ammonite will be analyzed again in the future with robust chemical analyzes.
Oddly enough, the fossilized ammonite is missing its arms, leaving one of the outstanding mysteries of ammonite anatomy unanswered. “Did they have many thin, delicate arms, like modern nautiluses, or a few strong arms, like modern coleoids?” Asked Dr. Yacobucci. “If I had access to a time machine, the very first thing I would do would be go back to Jurassic to see what kind of weapons ammonoids had.”
If a squid-like predator did release the ammonite from its shell, it may have nibbled at the creature’s unknown amount of weapons as a consolation reward, feeding both the ancient cephalopods and the scientists studying them. .
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