{"id":14902,"date":"2025-06-16T10:00:00","date_gmt":"2025-06-16T10:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=14902"},"modified":"2025-06-13T05:20:53","modified_gmt":"2025-06-13T05:20:53","slug":"cretaceous-mass-extinction-ocean-biodiversity-fossil-record-recovery-june-2025","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/cretaceous-mass-extinction-ocean-biodiversity-fossil-record-recovery-june-2025\/","title":{"rendered":"Ancient fossils show how the last mass extinction forever scrambled the ocean\u2019s biodiversity"},"content":{"rendered":"\n\n\n
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\n Even bivalves looked different during the time of the dinosaurs, as these fossils of an ultra-fortified oyster, left, and armored cockle show.\n Smithsonian Institution<\/span><\/span>\n <\/figcaption>\n <\/figure>\n\n Stewart Edie<\/a>, Smithsonian Institution<\/a><\/em><\/span>\n\n

About 66 million years ago \u2013 perhaps on a downright unlucky day in May<\/a> \u2013 an asteroid smashed into our planet.<\/p>\n\n

The fallout was immediate and severe. Evidence shows that about 70% of species went extinct<\/a> in a geological instant, and not just those famous dinosaurs that once stalked the land. Masters of the Mesozoic oceans were also wiped out, from mosasaurs<\/a> \u2013 a group of aquatic reptiles topping the food chain \u2013 to exquisitely shelled squid relatives known as ammonites<\/a>.<\/p>\n\n

Even groups that weathered the catastrophe, such as mammals, fishes and flowering plants, suffered severe population declines and species loss<\/a>. Invertebrate life in the oceans didn\u2019t fare much better.<\/p>\n\n

But bubbling away on the seafloor was a stolid group of animals that has left a fantastic fossil record<\/a> and continues to thrive today: bivalves<\/a> \u2013 clams, cockles, mussels, oysters and more.<\/p>\n\n

What happened to these creatures during the extinction event and how they rebounded tells an important story, both about the past and the future of biodiversity.<\/p>\n\n

Surprising discoveries on the seafloor<\/h2>\n\n

Marine bivalves lost around three-quarters of their species<\/a> during this mass extinction, which marked the end of the Cretaceous Period. My colleagues and I<\/a> \u2013 each of us paleobiologists studying biodiversity \u2013 expected that losing so many species would have severely cut down the variety of roles that bivalves play within their environments, what we call their \u201cmodes of life.\u201d<\/p>\n\n

But, as we explain in a study<\/a> published in the journal Sciences Advances, that wasn\u2019t the case. In assessing the fossils of thousands of bivalve species, we found that at least one species from nearly all their modes of life, no matter how rare or specialized, squeaked through the extinction event.<\/p>\n\n

Statistically, that shouldn\u2019t have happened. Kill 70% of bivalve species, even at random, and some modes of life should disappear.<\/p>\n\n