When Extinction Knocks, Size Doesn’t Really Count

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When Extinction Knocks, Size Doesn’t Really Count

Did you know that new findings on the Permian-Triassic mass extinction challenge prior assumptions that large organisms are vulnerable in times of extermination as compared to small organisms? A recent study conducted by scientists from Chengdu Center of the China Geological Survey, in collaboration with the University of Bristol, showed that the extinction of species does not depend on their size. These findings are founded on thorough research carried out on the Permian-Triassic mass extinction, which is regarded as the largest life sweep in history.

For the study, the research team investigated existing data that covered a time before and after the Permian-Triassic mass extinction. They carried out a set of computational models to determine patterns of time and account for mishaps that may result from the fossil data quality.  

The Mass Extinction

Researchers were particularly focused on the evolution of bony fishes at the time of the Permian-Triassic mass extinction. The extinction is attributed to the largest species death that wiped out about 90% of all life on earth.

The mass extinction was an aftermath of the massive volcanic eruptions in Russia. At the time, volcanic gases erupted, causing atmospheric warming and acid rains. Plants were killed while soils were washed into the oceans. More so, ocean temperatures increased, causing deaths and creatures to flee from the tropics.

Evidence from the Study

Researchers used prior data from all available information on fish fossils in the last 100 million years in their investigations. The time frame encompassed a time before and after the mass extinction. By using data on the body sizes of more than 750 fishes, researchers made numerous calculations to determine the shape variations as well as ancestry and exact dates of all the study species.

Findings from the study revealed that the body length had no role in the extinction of the non-teleostean actinopterygian fish species, regardless of the massive reduction in their diversity during the extinction. However, it was revealed that phylogeny played a big role in early Triassic as compared to late Permian.

Other Factors to Consider

The study further reveals that unlike the aspect of size, the evolutionary history of organisms had a significant role in the extinction. This is evident during the extinction aftermath where species like the Ordovician brachiopods exhibit a high phylogenetic influence.

If body size is ruled out, the question of a fall in diversity needs to be answered. To do this, the researchers revealed that phylogeny had a hand in the decreasing diversity of fish species. The findings showed that patterns of diversity show a high phylogenic signal in species like the Actinopterygii. Based on the outcome of the study, the researchers argue that after the mass extinction, taxa were reduced in size. However, the reduction in size is not necessarily a means of selection against taxa with larger body sizes but as a result of the aftermath of extinction.

Prior research attributed body size, as a major factor in other mass extinction before the concept of phylogenic analyses. However, these studies show that the size of an organism is not significant in selectivity during mass extinctions, whether phylogeny is considered or not. To further their claims, the researchers marked lineages that gave rise to less than ten descents after the mass extinction as extinct. There was no proof of body size as evidence for selection. However, there was evidence that both big and small body sizes are vulnerable to extinctions.

Professor Michael Benton, one of the researchers from the University of Bristol says "The methods are based on a detailed evolutionary tree so, unlike most previous work in the field, we paid attention to the relationships of all the species under consideration." These findings were surprisingly different when compared to factors that affect modern taxa. This is because body length is a major contributor of extinction in this era as a result of climate change factors. However, these modern intricacies on body size selectivity and extinction also result from various human factors.


Results from the findings affirm that there is no evidence of the impact of body length of bony fishes regarding selectivity during the Permian-Triassic mass extinction. Although the study did not consider other ecological traits like diet and palaeolatitude, these and other significant traits may have been factors of selectivity.  

Dr. Mark Puttick, the lead researcher of the study, says "These results continue the trend of recent studies that suggest body size played no role in determining which species survive or go extinct. This is the opposite result we would expect, but provides increasing support for previous studies that show body size plays no role in extinction selectivity."

Before the study, the assumption that body size is a key factor in extinction was very pronounced due to factors like starvation stress.  However, the new findings have reshaped the understanding of critical extinction and biodiversity threats.  











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