Ammonites were not in decline prior to end-cretaceous extinction: new study suggests
Ammonites, the marine mollusks renowned for their coiled shells, have long been thought to have experienced a decline leading up to their complete extinction at the end of the Cretaceous period. However, a recent study by a team of paleontologists from the UK and the US has challenged that narrative. The researchers analyzed the fossil record of ammonites throughout the Late Cretaceous epoch (100.5 to 66 million years ago) and found evidence that suggests ammonoids were still thriving in the Late Cretaceous, contrary to previous beliefs.
During their research, the team encountered obstacles when attempting to understand the changes in biodiversity over time. Dr. Joseph Flannery-Sutherland, a paleontologist from the University of Birmingham and the University of Bristol, acknowledges that the fossil record can sometimes be an unreliable storyteller. Patterns of diversity may simply reflect the patterns of sampling, rather than the true biological history of ammonites. This led the researchers to assemble a comprehensive database of Late Cretaceous ammonite fossils, drawing from museum collections and ensuring a more accurate representation of their biodiversity.
Analyzing their newly compiled database, the team examined how ammonite speciation and extinction rates varied across different geographic regions. Contrary to expectations based on the prior assumption of decline, the researchers discovered that the balance of speciation and extinction changed both geologically and among regions. Dr. James Witts, a paleontologist from the Natural History Museum in London, emphasizes that the misunderstandings surrounding the Late Cretaceous story of ammonites stem from variations in their diversification across the world. Their fossil record in certain areas, such as North America, may have led to the misconception of struggle, while they actually thrived in other regions. The researchers determined that the chance event of their extinction was not an inevitable outcome.
To further understand the sustained success of ammonites during the Late Cretaceous, the scientists investigated potential factors influencing their diversity. They explored whether environmental conditions, such as ocean temperature and sea level, or biological processes, including predator pressure and ammonite competition, drove speciation and extinction rates. One key finding was that the causes of ammonite speciation and extinction mirrored the variability of the rates themselves, dependent on the geographical location where they resided.
The study's findings offer fresh insights into the evolutionary history of ammonites, challenging prevailing assumptions about their decline preceding extinction. By overcoming limitations of the fossil record and considering divergent global patterns, this research sheds new light on the complex story of ammonoid diversity. The study, published in Nature Communications, provokes a reevaluation of our understanding of the factors influencing the rise and fall of ancient marine creatures like ammonites.