Ammonite Perseverance
AAAS: “Against all odds, a curious sea creature survived the dino-killing asteroid.” It was some 66 M yrs ago that a 14-km asteroid struck near the Yucatán Peninsula in southeastern Mexico. This ejected millions of tons of debris, “creating a tsunami 4.5 km high and engulfing the world in caustic ash and flames.” Three-quarters of life perished from the impact + coupled volcanic eruptions, including the nonavian dinosaurs that had ruled unchallenged for 160 million years. “Ammonites, which formed elegant spiral shells from a few mm to ~ 3 m across, were long considered a textbook victim of the end-Cretaceous asteroid.” For over 350 M yrs, they thrived in ancient Earth’s oceans…but after the asteroid struck, they seem to all have swiftly disappeared.
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“Whether ammonites survived [beyond the Cretaceous] has been debated for about 2 decades,” says Kyoto University paleontologist Amane Tajika, an ammonite expert who led the 2023 study. In 2025, to resolve the uncertainty, Marcin Machalski, a paleontologist at the Polish Academy of Sciences and the new study’s lead author, directly studied “the sediments surrounding ammonite fossils from the Stevns Klint limestone beds in eastern Copenhagen, some of them apparently deposited after the end-Cretaceous extinction.” Scanning electron microscopes scrutinized the sediments surrounding 10 fossil ammonites from 3 different genera to precisely determine which layers of rock they came from. “It convincingly shows that some ammonite species did indeed survive the asteroid impact before disappearing for good,” says Margaret Yacobucci, an ammonite expert at Bowling Green State University.
“Ammonites would have been extremely vulnerable to ash-clouded skies, with high metabolisms as adults and a larval stage that relied on photosynthetic microbes for food.” Nonetheless, Machalski and his colleagues estimate they survived for at least 68,000 years after the cataclysm, finally falling victim to falling sea levels + their diminished diversity — which would have made ammonites a “dead clade walking,” unable to bounce back. Sounds like an old western movie soundtrack, does it not?
