Ammonites, the ancient creatures that survived the asteroid that killed the dinosaurs, but how?

Fossils Reveal These Creatures Withstood the Asteroid That Wiped Out Dinosaurs (Image: Canva)

A new study published in Scientific Reports suggests ammonites did not vanish immediately after the asteroid impact 66 million years ago. Fossils from Denmark indicate some survived for up to 200,000 years. Researchers say long-term ecosystem disruption, rather than the impact itself, likely caused their eventual extinction, reshaping understanding of this mass extinction event.

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Scientists have long believed ammonites vanished alongside dinosaurs 66 million years ago. New fossil evidence now challenges that long accepted extinction timeline. The findings were published recently in the journal Scientific Reports. Researchers report ammonites survived well beyond the asteroid impact. The study reshapes understanding of Earth’s last mass extinction.

New fossils challenge ammonite extinction timeline

Ammonites were spiral shelled marine animals dominating ancient oceans. They survived for more than 340 million years. These creatures endured three previous mass extinction events. Their fossils appear across Europe, Africa, and other regions. Scientists believed the asteroid impact caused their rapid extinction. That impact triggered ocean acidification and food chain collapse. Fossil records appeared to support this sudden disappearance. New discoveries now question that interpretation strongly.

The evidence comes from Stevns Klint in Denmark. The site is recognised by UNESCO for fossil preservation. Researchers examined limestone layers from the early Paleogene period. Professor Marcin Machalski led the research team. He works at the Polish Academy of Sciences. The team reported ten ammonite fossils in those layers. These layers formed tens of thousands of years later.

What the Denmark discovery reveals about survival

The fossils belonged to three known ammonite genera. These included Hoploscaphites, Baculites, and Fresvillia. Most fossils showed no signs of reburial. Researchers found preserved voids where shells dissolved naturally. This indicated fossils formed within those younger layers. One genus, Fresvillia, had not appeared locally earlier. Its presence suggests post extinction migration occurred.

The dating shows ammonites survived up to 200,000 years. This survival followed the catastrophic asteroid impact. Scientists now believe extinction was delayed, not immediate. This pattern matches a concept called Dead Clade Walking. It describes species surviving disasters but failing later.

Ammonite specimens were collected from the main part of the Cerithium Limestone Member, as defined by Störling et al.31, at Stevns Klint. Panels (a, b, h, i) show Baculites vertebralis (OESM 13290) from the top of the unit, with (h, i) presenting field photographs. Panels (c, d) display Fresvillia sp., including part and counterpart (OESM 13291). Panel (e) shows Baculites sp. (OESM 13293), panel (f) shows Baculites vertebralis (OESM 11541), and panel (g) shows Hoploscaphites cf. constrictus johnjagti (OESM 13287). Specimens in panels a–e and g–i are from Sigerslev quarry (with a–d, g–i from the sampled basin and e from a different basin), while specimen f comes from Rødvig (Nature).

Why ammonites vanished despite surviving the impact

Post impact oceans eventually regained chemical stability. However, marine ecosystems remained badly disrupted. Ammonites relied heavily on plankton based food webs. These food sources recovered slowly after the catastrophe. Reproduction and genetic diversity may have been limited. These weaknesses likely prevented long term population recovery.

Their relatives, nautiloids, survived and still exist today. Nautiloids lived deeper and reproduced more slowly. These traits may have protected them from instability. Ammonites lacked similar ecological flexibility.

For decades, Paleogene ammonite fossils were dismissed. Scientists believed they were redeposited older specimens. The Stevns Klint fossils are well preserved. Their geological placement makes reworking unlikely.

The study highlights limits of fossil record interpretation. It shows extinction timelines can shift with evidence. Researchers say future discoveries may refine this picture further.