About 180 million years ago! Chinese fossils reveal the oldest insect "marriage flight" behavior

In 1974, villagers in Xiyang Village, Lintong District, Shaanxi Province accidentally discovered the fragments of terracotta figurines while digging a well, which marked the beginning of the excavation of the Terracotta Warriors and Horses of Qin Shihuang...

In April and May 2021, in the Xiwan Basin of Hezhou City, Guangxi Zhuang Autonomous Region, fossils of the family Pseudocoptera were discovered for the first time by scientists from the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences. These fossils are the "Terracotta Warriors" in the field of insect fossil research.

The scientific expedition team inspected the strata along the steep slope

Image source: Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences

The first discovery of the fossil of the family Psammothidae is of great significance. It not only reveals the oldest insect mating flight behavior, but also provides important evidence for our in-depth understanding of the characteristics and evolutionary process of Mesozoic lake ecosystems, as well as the connection between water and land ecosystems.

Part 1

The "collective wedding" of mayflies

The fossil of the insect of the family Psammoptidae was discovered in the Shiti Formation of the Lower Jurassic in the Xiwan Basin, Hezhou City, Guangxi Zhuang Autonomous Region. Scientists named it Jurassic Psammoptidae (Jurassephemera zhangi Zhang et al., 2022). Currently, there are only four species recorded in this family worldwide.

The appearance of a colony of Zhang's Jurassic sandflies when it was first "unearthed"

Image source: Photographed by Zhang Qianqi

The new genus and species discovered in Guangxi are somewhat different from the other three species, mainly because the branch of the MA vein on the forewing of the new genus and species is closer to the base. In addition, Zhang's Jurassic sandfly also has the characteristics of a large number of preserved insects, a complete body, and clear forewings.

A partial enlarged view of the mayfly fossil

Image source: Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences

The fossils discovered this time preserve the most detailed morphological and taxonomic evolutionary information known so far on the extinct group of Psammothidae.

The unearthed mayfly cluster composed of Zhang's Jurassic sand mayflies contains hundreds of individuals, and the wings of the mayfly insect fossils are intact, with their bodies facing different directions. They are deposited in situ after the insect cluster died during its nuptial flight, which is very similar to the "Terracotta Warriors". Therefore, it is not an exaggeration to say that they are the "Terracotta Warriors" in the field of insect fossil research.

In addition to being well preserved, the discovery of the mayfly insect fossil is more significant than that. It also shows us a collective wedding spanning billions of years.

If nature is a camera, then the mayfly insect fossil is a "film" left by nature to mankind. This fossil "film" directly shows the vivid scene of insects reproducing in groups after emerging from their shells at a lake in southern my country about 180 million years ago. This biological phenomenon also has a poetic term - "nuptial flight".

The mayflies in the fossil "film" are bustling about, in various postures, and looking at each other from head to tail. It is obviously a spectacular scene that they died quietly after completing reproduction. It was not rediscovered by scientists until today, 180 million years later.

Social insects go through the process of nuptial flight to reproduce and form new colonies, which continue endlessly and make up the colorful nature.

Restoration map of the Early Jurassic ecosystem in the Xiwan Basin

Image source: Drawn by Yang Dinghua from the Institute of Southern Paleontology, Chinese Academy of Sciences

Nuptial flights are actually very common in daily life. In spring and summer, groups of flying insects gather in an area and fly around, which is actually "nuptial flights".

"Nude and famine" is widely present in today's terrestrial ecosystems, and the earliest fossil records of this phenomenon are mostly reported in Cretaceous fossils, such as the Jehol Biota.

By "developing" this "negative", scientists have a clearer understanding of the mayfly fossils. Combined with the geological age of this output, scientists say that the mayfly cluster fossils in the Xiwan Basin represent the oldest known insect mating flight behavior.

Part 2

The oldest insect resource pulse phenomenon

The mayfly cluster fossils in the Xiwan Basin are the oldest known insect nuptial flight behavior and also the oldest insect resource pulse phenomenon.

So what is the insect resource pulse phenomenon?

In nature, resource fluctuations sometimes occur in pulses, characterized by low frequency, high intensity, and short duration. A resource pulse is an event in which a large amount of resources become available in a short period of time.

Resource pulses are an important mechanism for the transfer of energy, nutrients, and biomass between ecological domains. Although this phenomenon is widespread in modern ecosystems, we know little about similar records in the ancient Earth billions of years ago.

Therefore, the mayfly cluster fossils found in the Xiwan Basin can help us understand the ecosystem billions of years ago.

The mayfly fossils discovered this time

Image source: Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences

The resource pulse effect revealed by the mayfly cluster fossils in the Xiwan Basin can be reflected in two aspects: as food and as fertilizer.

Let's first look at the first aspect - as food. Aquatic insects play an important role in the food web, being decomposers and consumers of aquatic plants, and at the same time becoming food for fish and other predators.

Coincidentally, the living habits of mayflies determine that they are born in water and spend their lives above the water. When the "grouped" mayflies emerge from the water, spread to land and look for mates, they become an important part of the terrestrial food web.

This resource pulse effect is confirmed by the large number of multi-category fossils (invertebrates, shark egg cases and plants, etc., which are collectively called the Xiwan Biota) found in the Shiti Formation strata.

In addition to providing food for predators in the biota, the sudden appearance of mayfly swarms also has a "fertilization effect" on plant communities near lakes and streams, bringing a large amount of available resources to terrestrial ecosystems in the form of a pulse. Simply put, the death and decomposition of these insect swarms can be transformed into fertilizer for the ecosystem.

This insect resource pulse effect may lead to huge changes in the ecosystem flux of the waterfront habitat, thereby affecting the basic ecology and biogeochemical cycles.

The "Terracotta Warriors" of mayfly clusters discovered in the Xiwan Biota represent the oldest known insect resource pulse event formed after the emergence of insects. This insect resource pulse also shows that one of the important channels for energy transfer in Mesozoic lake ecosystems is from aquatic to terrestrial ecosystems.

A tiny mayfly, born in the morning and dead in the evening, has come to us through the power of nature across billions of years, and in its own way has told us that a tiny body can also create huge value. The research conducted by researchers in related fields is a dialogue across time and space, and will ultimately affect the development of the present and the future.

Produced by: Science Popularization China

Author: Zhang Qianqi, Wang Bo (Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences)

Producer: China Science Expo

Editor: Wang Tingting

The article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

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