Smithsonian Institution
Even the bivalves were different during the time of the dinosaurs, as these fossils of an ultra-certified oyster show on the left, and a shielded brindle.
Ancient fossils show how the last mass extinction has forever altered ocean biodiversity.
About 66 million years ago, possibly particularly unlucky, the infamous asteroid who created the chicxulub crater collided with our planet.
The consequences were immediate and severe. Evidence shows that approximately 70% of species They were extinguished at a geological moment, not just the famous dinosaurs who once dominated the earth.
The masters of the oceans of Mesozoic have also been eliminated, since the mosassauros – A group of aquatic reptiles at the top of the food chain – even relatives of Lula with exquisite shells known as ammonites.
Even groups that survived The catastrophe, such as mammals, fish and flowers with flowers, suffered serious population declines and species losses.
Inverted life in the oceans There was no better luckexplains or paleobiologist Stewart EdieCurator of Paleobiology of the Smithsonian Institution, in an article in.
But the bubbling under the sea was a group of animals that left a fantastic fossil record and continues to prosper today: os bivalves – clams, beerbigons, mussels, oysters and others.
What happened to these creatures during the extinction event and how they recovered tells an important storyboth about the past and the future of biodiversity.
Surprising discoveries at the bottom of the sea
Marine bivalves lost about 3/4 of their species during this mass extinction, which marked the end of the Cretaceous period.
Edie and colleagues, paleobiologists who study biodiversity, hoped that the loss of so many species severely reduced the variety of functions that bivalves perform in their environments – which they call “modes of life”.
But, as researchers explained in a recently published magazine Sciences Advances, This is not what happened.
In evaluating the fossils of thousands of bivalves species, they found that at least A kind of almost all of your life modesno matter how rare or specialized, managed to survive to the extinction event.
Statistically, this should not have happened. Eliminate 70% of bivalves species, even randomly, should make Some modes of life have disappeared completely.
Most bivalves bury happily in the sand and mud, feeding on phytoplankton that filter from the water. But Others adopted chemosymbrocers and photosypends – bacteria and algae that produce nutrients for bivalves from chemicals or sunlight in exchange for shelter.
Some have even become carnivores. Other groups, including oysters, may deposit a resistant cement which hardens underwater, and the mussels cling to the rocks weaving silk wires.
Edie and colleagues thought that certainly these more specialized ways of life would have been eliminated For the effects of the impact of the asteroid, including dust and debris that probably blocked sunlight and disturbed a large part of the bivalve food chain: photosynthetic and bacteria algae.
Instead, most persistedalthough biodiversity has been permanently altered as a new ecological landscape emerged. Species that were once dominant fought to survivewhile evolutionary newcomers rose in their place.
The reasons why Some species survived, and others nothey leave many questions to explore.
Those that filtered phytoplankton from the water column suffered some of the Largest Loss of Speciesbut the same happened with species that fed on organic remains and did not depend so much on solar energy.
Geographical distributions restricted and different metabolism may have contributed to these extinction standards.
Biodiversity recovers
Life has recovered from each one through the history of the earth, eventually surpassing the previous peaks of diversity.
The rich fossil record and spectacular ecological diversity of bivalves gives us an excellent opportunity to study these recoveries and understand how ecosystems and global biodiversity if rebuild after extinction.
The extinction caused by the impact of the asteroid toppled some modes of life Prosperous and opened the door for others to dominate the new landscape.
While many people mourn the loss of dinosaurs, malacologists (scientists who, as Edie, study mollusks) miss the rudowsan extinct group of bivalves, very different aspects of those currently.
These bivalves in a bizarre way seemed huge ice creamsometimes reaching more than 1 meter in size, and dominated the shallow and tropical seas of Mesozoic as massive aggregations of contorted individuals, similar to current coral reefs.
At least Some housed photosybiotic algaethat provided them with nutrients and encouraged their growth, much like modern corals.
Today, the giant clams (Three -time) and their relatives fill part of these unique photosybiotic lifestyles once occupied by ruders, but lack the impressive diversity of species of ruders.
Mass extinctions clearly change thehow. Now our ocean funds are dominated by clams buried in the sand and mud, the mercenaries, Berbigons and their relatives – A very different scenario from the sea bottom 66 million years ago.
New winners in an altered ecosystem
The ecological characteristics in themselves did not completely foresee extinction patterns, nor do recovery fully explain.
We also see that Simply survive an extinction In mass it did not necessarily provide an advantage as species have diversified within their old and sometimes new ways of life – and few of these new modes dominate the ecological landscape today.
Like ruders, the Trigoniide Bivalves They had many different species before the extinction event.
These highly ornate clams built parts of their shells with a Super resistant biomaterial shabad nacar – similar to an iridescent pearl – and had fracturally interconnected hinges holding their two valves.
But Although they survive the extinctionwhich should have placed them in a privileged position to accumulate species again, their diversification stagnated.
Other types of bivalves that lived in the same way proliferated instead, relegating this once powerful and global group a handful of species now found only on the coast of Australia.
Lessons for today’s oceans
These unexpected extinction and survival patterns can offer lessons for the future.
Fossil registration shows us that Biodiversity has breakthrough definitive, usually during a perfect storm of climate and environmental agitation. It is not just that species are lost, but the ecological landscape It is knocked down.
Many scientists believe that current biodiversity crisis It can evolve into a sixth mass extinction, this time driven by human activities that are changing ecosystems and the global climate.
Os coralwhose reefs house almost a quarter of known sea species, they faced events as ocean water heating puts their future at risk.
A, as they absorb more carbon dioxide, can also weaken the shells of organisms crucial to the ocean food chain.
Discoveries such as the study of Edie and his colleagues suggest that, in the future, the RECOVERY OF EXTINCTION EVENTS probably will result in very different mixtures of species and their ways of life in the oceans.
E The result may not align with human needs If the species that provide most ecosystem services are led to genetic or functional extinction.
Global oceans and their inhabitants are complex and, as shown in the study by Edie, It is difficult to predict the trajectory of biodiversity while it recovers – even when extinction pressures are reduced.
Thousands of millions of people depend on the ocean for food. As shown in the history of bivalves, the change in the hierarchical order – the number of species in each way of life – will not necessarily establish itself in an arrangement that can feed so many people next time.
