The first insects that we have evidence lived in the Devonian, a little over 400 million years ago. Since then, they have become the most successful animals on Earth, at least if we focus on their numbers. Experts from the Royal Entomological Society of London estimate that, on average, in every square kilometer of the planet we could find 10,000 million of them. So far, more than 750,000 species have been described , but some researchers, such as Terry Erwin, an entomologist at the Smithsonian Institution, are convinced that there may be as many as 30 million. Why such evolutionary success?
The discovery of two large sets of fossils in China could shed some light on this matter. In fact, one of the first conclusions reached by scientists who have studied the remains, coordinated by a team of paleobiologists from the Nanking Institute of Geology and Paleontology, is that, after the mass extinction that took place 252 million years ago years, the longest that has taken place, in which 70% of terrestrial vertebrates and 90% of marine species perished, there was an explosion of diversity among these animals. This coincided with a similar phenomenon that affected the plants that many of those insects fed on and that contributed to pollination.
Life makes its way
Before the aforementioned Great Dying, there were already very different varieties, such as beetles or dragonflies, but it is not easy to know which ones survived the cataclysm – this could be due to excessive volcanic activity or the impact of a large space rock. The anatomical structures of these animals are not as well preserved as the cochas or bones , so there are not many fossils with which to study this question. However, paleontologists from the aforementioned Chinese institution and their collaborators found two enclaves in the northwest of the Asian country in which all kinds of remains could be clearly seen, from larval envelopes to wings. These had been imprinted on the layers of sandstone and other sedimentary rocks that covered the beds of what had been two lakes. In total, some 800 fossils were collected, a real treasure for specialists in this field.
In a study published in the journal Science Advances , the researchers point out that in the oldest site, some 237 million years old, the most varied remains appeared, belonging to 28 families of insects. In the most recent, 230 million years old, fossils from 10 families were recovered. In both cases they were animals with a life cycle similar to that of many of their current relatives, with four different stages – the most archaic had only three, like cockroaches.
Born survivors
In their conclusions, these scientists point out that certain insects, such as some beetles, survived extinction, but that many others evolved soon after. This would have happened much earlier than experts have suspected. For example, remains of some aquatic insects have been found that, according to the most widespread hypotheses to date, were believed to have diversified 130 million years ago. This finding takes that moment back considerably.
Image: Fossil of a fulgoromorphic insect. Zheng et al. Science Advances (2018) .
Reference: Middle-Late Triassic insect radiation revealed by diverse fossils and isotopic ages from China. Daran Zheng et al. Science Advances (2018). DOI: 10.1126 / sciadv.aat1380
