New research suggests periods of high extinctions, as opposed to adaptation, created the animal diversity we see today.
The findings reveal the mass extinction among some groups of amniotes (land vertebrates) are closely linked with large diversifications in other closely related groups, the University of Lincoln reported. The study disputes the idea of a close relationship between the evolution of "key innovations" in a group and the rapid increase in its number of species, and suggests this relationship has only been circumstantial.
To make their findings, the researchers looked at fossil records from between 315 and 200 million years ago. This period experienced some of the most intense changes in climate and largest mass extinction events seen in all of history. The team focused on adaptive radiation, which is an "extremely rapid increase in the number of species in a group," that gives them an advantage over competitors.
To make their findings, the researchers used statistical methods to identify which of the amniote groups present during this early period were more species-rich than their relatives. They found that differences in diversity between two close groups are most often caused by more species evolving in the larger group, as opposed to more species in the smaller group going extinct. This means a new innovation in the larger group does not cause a proliferation in species until a major extinction occurrs.
"It appears that these 'key innovations' do not promote massive increases in species richness, but instead buffer against extinction when times get tough," said Neil Brocklehurst, a postdoc at the Museum für Naturkunde in Berlin.
For example, dicynodont therapsids (a group of extinct plant-eaters) evolved a toothless beak and a back-and-forwards motion of the lower jaw to help them munch on plant matter about 270 million years ago, it was not until a major extinction event 10 million years later that the creatures developed significant diversity.
"Surprisingly, when these early terrestrial vertebrates evolved a novel structure or function, they did not undergo a dramatic increase in species number. Instead, an adaptive radiation usually occurs much later in the history of these groups, during one of the many extinction events or during times of climate stress," said co-author Jörg Fröbisch, Professor for Palaeobiology and Evolution at the Museum für Naturkunde and Humboldt-Universität zu Berlin
The findings were published in a recent edition of the journal Scientific Reports.
