What most likely happened to a species that became extinct and are only found as fossils?

Millions of years from now, paleontologists may dig into Earth and uncover fossils from our own time. They may, like scientists today, construct a chronology of what came before them, watching past species popping into—and later out of—existence. Today, humans are continually driving species to extinction—by one estimate, almost 500 vertebrate species have gone extinct in the past 100 years—but will those future scientists be able to tell? New research suggests that it might not be easy: Only a small proportion of these human-caused extinctions will leave behind a fossil trace—and the most threatened species are the ones least likely to be preserved for posterity.

The history of life on Earth is punctuated by what researchers call the “Big Five” mass extinctions, a group that includes the dinosaur-killing Cretaceous-Tertiary extinction and several other, even more severe, events. Many scientists now want to add a sixth: the one that humans are causing all over the globe today. But it’s hard to gauge just how severe the current extinction crisis is, compared with others in Earth’s sometimes tumultuous history. Modern extinctions are documented, sometimes in real time. But the Big Five are measured using only the fossil record, a history of those species that were buried and preserved by sediments over time.

That’s why Roy Plotnick, a paleontologist at the University of Illinois, Chicago, and lead author of the study, thinks about far-flung scenarios involving future paleontologists. “We really need to look at modern day extinctions as if they were in the fossil record already, in order to make a comparison,” he says. So he and his colleagues searched fossil databases for modern mammal species—both those threatened by extinction and those that aren’t—to see how many modern extinctions would be detectable by relying only on fossils.    

Explanation:

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.