About 66 million years ago, on what could be described as a particularly unfortunate day in May, an asteroid collided with Earth.
The consequences were both immediate and drastic. Research indicates that 70% of species went extinct. This catastrophic event didn’t just affect the well-known dinosaurs; it also led to the disappearance of various geological formations and marine life, including the remarkable Mosasaur, a group of marine reptiles, and Ammonites.
Even resilient groups like mammals, fish, and flowering plants suffered severe declines in population and species. Invertebrate life in the oceans faced dire conditions as well.
Yet, at the ocean’s depths, certain less fortunate animals managed not just to survive but to thrive. A remarkable fossil record has persisted through the ages, including groups like clams, which include various species like cockles, mussels, and oysters.
The survival and recovery of these organisms post-extinction reveal critical insights into both the history and future of biodiversity.
Incredible Finds on the Seabed
During this mass extinction, marine bivalves experienced a loss of about a quarter of their species, marking the close of the Cretaceous period. My colleague and I have been studying biodiversity, considering how such an extensive loss affects the diverse roles that bivalves play in their ecosystems, something we term “the mode of life.”
However, as we explained in our research featured in the Journal Sciences Advances, despite the catastrophic loss, fossils of thousands of bivalve species revealed that at least one species from nearly every lifestyle managed to persist through extinction.
Statistically, this is puzzling. In a random extinction event, we would expect 70% of bivalve species to vanish.
Related: Five Major Extinction Events That Shaped Earth’s History – And a Sixth Is Happening Now
Most bivalves burrow into substrates and feasting on phytoplankton. However, others have formed relationships with chemosymbionts and photosymbionts—bacteria and algae that derive nutrients through chemical processes and sunlight in exchange for shelter. Certain species even consume detritus and eat meat. Some groups, like oysters, can create severe cement that hardens the surrounding water, while mussels cling to rocks with silken threads.
Initially, I believed that such specialized lifestyles would be severely impacted by the asteroid’s effects, like dust obscuring sunlight and disrupting the bivalve food chain composed of photosynthetic algae and bacteria. In fact, biodiversity shifted, allowing many organisms to persist as new ecological opportunities arose. While formerly dominant species faced challenges, emerging species adapted and flourished.
The reasons behind the survival of some species over others raise many intriguing questions. Phytoplankton feeders suffered significant losses, whereas species that subsisted on organic debris and were less reliant on solar energy fared better. It’s possible that certain geographical distributions or metabolic differences contributed to these patterns of extinction.
Biodiversity Rebounds
Life has rebounded after each Big Five Mass Extinction. Historically, this has led to a resurgence of diversity that surpasses prior levels. A well-preserved fossil record and the incredible ecological variety of bivalves provide us with an opportunity to study these recoveries and understand how ecosystems can rebuild amid extinction.
The asteroid impact led to the collapse of numerous thriving ecosystems and created possibilities for others to thrive in the subsequently altered landscape.
Many mourn the loss of the dinosaurs, yet our research focuses on Rudists.
These uniquely shaped bivalves, which resemble gigantic ice cream cones, can grow over 3 feet (1 meter) tall and dominated shallow tropical Mesozoic oceans, forming large clusters. Like modern corals, they fostered growth by hugging light algae that provided essential nutrients.
Currently, a giant clam (Toridakuna) and its relatives occupy some of the ecological niches once held by rudists, but the spectacular diversity of rudist species is no longer present.
The mass extinction clearly reshaped the environment. Today, our ocean floors are primarily covered in sand and mud, populated by Quahogs, cockles, and their relatives, a stark contrast to the vibrant ecosystems of 66 million years ago.
Emerging Winners in a Reshuffled Ecosystem
Ecological traits alone fail to completely explain extinction patterns or recovery dynamics. Simply surviving numerous extinction events does not guarantee a resurgence of species; diversification often occurs in novel or traditional modes of life. Many of these new strategies are now the dominant features of today’s ecological landscape.
Like the rudists, the trigoniid bivalves—once highly diverse—were remarkably specialized before the catastrophic event. These intricately patterned clams relied on their shells for protection like a rainbow pearl, with hinges designed to hold the two valves together.
Nevertheless, despite having survived the extinction, trigoniid bivalves didn’t reclaim their former dominance. Instead, species with similar ecological niches have risen to prominence, relegating this once-revered group to a handful of species found mainly off the coast of Australia.
Lessons for Today’s Oceans
The unexpected survival and extinction patterns can yield valuable insights for the future.
Fossil records reveal a significant breakpoint in biodiversity following mass extinction events, paralleling emerging trends in climate and environment. The loss of species impacts not only individual organisms but also the broader ecological context.
Many scientists are currently observing a biodiversity crisis, known as the sixth mass extinction, driven by human actions that disrupt ecosystems and alter global climates. Almost a quarter of known marine species face risks, exacerbated by mass bleaching events occurring due to climate change. Furthermore, ocean acidification from increased carbon dioxide levels weakens the shells of key marine organisms vital for food webs.
Our findings indicate that future rebounds from extinction events are likely to generate entirely different combinations of species and marine lifestyles, potentially not meeting human needs if species essential to ecosystem services become genetically or functionally extinct.
The oceans and their inhabitants are remarkably intricate, and our recent research indicates that biodiversity trends are complex and less predictable, even under reduced extinction pressures.
Billions of people depend on the oceans for food. Historical records reflecting bivalve diversity illustrate that the dynamics of species within each ecological role do not necessarily ensure a future capable of supporting human needs.
This edited article has been republished from The Conversation under the Creative Commons license. Please read the original article.
Source: www.livescience.com