The study reveals the changes of extinction and origin patterns after the mass extinction
since the 1980s, evolutionary biologists have been debating whether mass extinction and its subsequent recovery have strengthened the selection criteria of normal periods – or fundamentally changed a series of characteristics marking the destruction of species groups. The new study found evidence of the latter in a comprehensive analysis of most marine fossils over the past 500 million years
the study authors wrote that whether and how the evolutionary dynamics changed after the global mass extinction “has a far-reaching impact not only on understanding the origin of the modern biosphere, but also on predicting the consequences of the current biodiversity crisis”
Pedro monarrez, a postdoctoral scholar and lead author of the school of earth, energy and Environmental Sciences at Stanford University, said: “Finally, we hope to be able to look at the fossil record and use it to predict what will go extinct and, more importantly, what will come back. When we carefully observe the extinction and recovery in the world’s oceans over the past 485 million years, it seems that there is indeed a pattern according to the size of some groups.”
this study is based on a recent study at Stanford University, which studies the body size and extinction risk of marine animals in groups called genera, one classification level higher than species. The study found that on average, genera with smaller bodies are equally or more likely to die out than their larger close relatives.
the new study found that there is a long gap between mass extinctions For some time, this pattern was true in 10 species of marine animals. However, mass extinction changed this rule in an unpredictable way. In some categories, the extinction risk of smaller genera became greater, while larger genera lost their advantage in other categories.
the results showed that in mass extinction events, smaller genera called crinoids were extinct In contrast, there were no detectable size differences between victims and survivors during the “background” interval. In trilobites, a diverse population with a long-distance relationship with modern horseshoe crabs, in the “background” During the interval, the probability of extinction decreases slightly with the increase of body size, but during the mass extinction, the probability of extinction increases about 8 times with the doubling of body length.
when they focus on the extinct marine genera and consider the earliest similar genera and species, the author finds that the body size pattern changes more greatly before and after extinction Changes. In the “background” During the interval, the newly evolved genera and species tend to be slightly larger than the previous genera and species. During the recovery of mass extinction, this pattern has reversed, and the originators of most categories have become more common than the reserved species that survived the catastrophe.
including sea snails in The Gastropoda genus in is a few exceptions. They are based on a smaller model. The Gastropoda genus produced in the recovery period is often larger than that of the survivors of the previous catastrophe. The authors write: “regardless of the direction, the selectivity for body size is more obvious in the mass extinction event and its recovery period than in the background period.”
professor Jonathan Payne, senior author of the study and professor of the school of earth, energy and Environmental Sciences of the University, said: “our next challenge is to determine why so many ancestors are small after mass extinction.”
scientists do not know whether these reasons may be related to global environmental conditions, such as low oxygen levels or rising temperatures, or factors related to the interaction between organisms and their local environment, such as lack of food or lack of predators. According to Payne, “Determining the reasons for these patterns may help us not only understand how our current world is formed, but also predict the long-term evolutionary response to the current extinction crisis.”
this is the latest in a series of papers by Payne research group. These papers use statistical analysis and computer simulation to reveal the evolutionary dynamics of body size data in marine fossil records. In 2015, the team recruited high school interns and undergraduates to help calculate the body sizes and volumes of thousands of marine species from photos and illustrations. The resulting data sets It includes most invertebrate fossil genera known to the scientific community, which is at least 10 times larger than the compilation of any previous animal fossil body size.
since then, the team has expanded the data set and conducted in-depth research on its model. In other results, they found that larger body size has become one of the biggest determinants of the extinction risk of marine animals, which is very important for life on earth In this new study, monarrez, Payne and Noel Heim, research co-author of Tufts University, used body size data from marine fossil records to estimate that the probability of extinction and origin was related to body size for most of the past 485 million years. By comparing their body size data with public paleontological databases “This data set enables us to record how evolutionary patterns change when mass extinctions occur in different animal groups,” Payne said
other paleontologists have observed that after mass extinction, smaller animals become more common in the fossil record – commonly known as the “Lilliputian effect”, which is based on Jonathan Swift’s novel Gulliver’s travels in the 18th century The results of this new study show that animal physiology provides a reasonable explanation for this model. The author found a classic shrinking model in most marine animal categories with low activity level and slow metabolism. If the species in these categories evolved immediately after mass extinction, they often play a more important role than those during the background interval The original species have smaller bodies. On the contrary, when new species evolve in marine animal populations with faster and more active metabolism, they tend to have larger bodies after extinction and smaller bodies in normal times.
“Extinction partially changed the world, not just by removing a large number of organisms or species, but by removing them in a variety of selective patterns. Then, recovery is not just equal to every surviving species. A new set of prejudices entered the recovery model,” Payne said. “Only by combining the two can you really understand the world we got 5 million or 10 million years after the extinction.”