Some scientists not only don't take a holiday, but are also ready to tell you about a discovery that took them ten years to develop.

Author: Liu Yun, Wang Bo, Shi Gongle (Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences)

The article comes from the Science Academy official account (ID: kexuedayuan)

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Warm reminder: Some of the insect images in this article have been hidden. Readers who are seriously afraid of insects can click to read without worry.

As we all know, Labor Day is a good time to work hard (obviously not). Scientists are even more aware of this, and have found a researcher who advocates "studying hard during the holidays" to share with you a discovery that took ten years to develop.

This discovery is the Zhangpu Biota, a tropical rainforest fossil deposit in Fujian. Over the past decade, a joint team of 30 researchers from multiple disciplines, led by Wang Bo and Shi Gongle from the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, has conducted detailed research on the diversity, paleoecology and paleoclimate significance of this biota.

Field outcrops and various fossils of the Zhangpu Biota (Photo credit: Nanjing Institute of Geology and Paleontology)

From the Middle Miocene Climate Optimum

The past is the key to understanding future environmental changes, and fossils are undoubtedly the most important key. In 2010, the Zhangpu Biota was discovered in the Fotan Group strata in Zhangpu County, southeastern coastal Fujian. As a set of interbedded sedimentary and volcanic rocks (i.e., two types of rock formations appear repeatedly), it is mainly distributed in Zhangpu County and Longhai County in southern Fujian, and Mingxi County and Ninghua County in western Fujian. The geological age (about 14.7 million years ago) is in the late period of the Middle Miocene climatic optimum period.

The Middle Miocene Climatic Optimum, which occurred in the middle Miocene 17 to 14 million years ago, was a strong warming event in geological history. At that time, the carbon dioxide content in the atmosphere was significantly higher than the current level, and the global average annual temperature was 3 to 7 degrees Celsius higher than today, which is very similar to the climate environment currently predicted for 2100. Therefore, understanding the changes in climate and biota during this optimum period is of great significance for predicting future changes in climate and biota under the background of global warming, and can help humans cope with future environmental crises more efficiently.

Although many fossil taxa from the middle Miocene have been discovered, our understanding of tropical biota during this period is still very limited. The Zhangpu Biota can provide rich fossil data for related research. So, how did these fossil data survive?

The world's most species-rich fossil repository of Cenozoic tropical rainforests

In the geological history, when there were flash floods or heavy rains, some plant leaves that fell in autumn would be washed into streams and eventually flow into rivers or lakes. When the lake was quickly buried, the sediments would cover it. In very rare cases, these leaves would be preserved and become what we call plant fossils today. These plant fossils are the main signs for dividing and restoring the ancient continents, ancient climates and plant geographical divisions in the geological history period.

After 10 years of continuous field collection, the research team has obtained more than 25,000 insect-containing ambers and more than 5,000 plant compression/impression fossil specimens. Among the ancient flora, the groups with the highest diversity and the richest fossil specimens include Dipterocarpaceae, Fabaceae, Lauraceae and Luteaceae. Other pan-tropical families include Annonaceae, Anacardiaceae, Oleaceae, Euphorbiaceae, Melastomataceae, Moraceae, Myristicaceae and Myrtaceae. Plants from these families are the dominant groups in the tropical rainforests of Southeast Asia today. Among them, plant leaf fossils include 2 species of ferns, 3 species of monocots, 78 species of dicots, in addition to more than 20 species of fruit and seed fossils. Based on the species of animal and plant fossils that have been discovered, the Zhangpu Biota has become the world's most species-rich fossil repository of the Cenozoic tropical rainforest.

Representative plant fossils of the Zhangpu Biota (Photo credit: Nanjing Institute of Geology and Paleontology)

Bling bling amber collection

In addition, a lot of amber has been found in the Zhangpu biota. Amber is a very special fossil formed by the long geological process of ancient plant resin buried underground. The inclusions in Zhangpu amber are very rich and have important research significance. The Zhangpu amber found so far comes from the Dipterocarpaceae plant. The resin of the Dipterocarp tree dripped and was brought into the lake, where it was deposited and preserved together with plants and clay.

my country is a country with extremely rich fossil resources. However, amber (especially insect amber), as a special fossil, is rarely found in my country. There is only one well-known amber production area in Fushun. It is the wish of every paleoentomologist to discover the world's top amber biota in their own country. Since Mr. Bingzhi first carried out Chinese amber research in 1931, after the efforts of several generations of Chinese paleoentomologists, this wish was finally realized 90 years later.

In 2014, the amber research team of Nanjing Institute of Geology and Paleontology reported the appearance and composition of Fushun amber biota (Current Biology, 2014), making it one of the most species-rich amber biotas in the world, filling the gap of Asian continental amber biota in the Eocene period, indicating that there was extensive biological exchange between the two ends of Eurasia 50 million years ago; the team also reported the appearance characteristics of the late Cretaceous Tilin amber biota in Myanmar for the first time in 2018 (Nature Communications, 2018), which filled the gap of 24 million years of insect fossils, and greatly helped scientists understand the evolution of insects before and after the mass extinction event at the end of the Cretaceous. Today, Zhangpu amber biota is the third amber biota that has been completed by the team through multidisciplinary and systematic research. This biota is the richest amber biota newly discovered in the past century and one of the four major amber biotas in the world. This discovery also shows that my country is a country rich in amber resources.

Ecological restoration map of Zhangpu biota (Image drawn by Yang Dinghua, Nanjing Institute of Paleontology)

Zhangpu amber contains a large number of animal and plant fossils. In terms of arthropod diversity, the Zhangpu amber biota currently ranks third in diversity with 250 families discovered, second only to the Kachin amber biota in Myanmar (Middle Cretaceous, about 100 million years ago; nearly 600 families) and the Baltic amber biota (Eocene, about 48-34 million years ago; nearly 600 families), and higher than the Dominican amber biota (Middle Miocene, about 20-15 million years ago; about 200 families).

Insects are the most abundant in amber, including at least 20 orders and 200 families. The most common order is Diptera, accounting for about 55% of the total; followed by Hymenoptera (various bees and ants); then Coleoptera (beetles) and Hemiptera (aphids, cicadas, stink bugs, etc.). In addition, amber also contains a large number of feathers, plants, gastropods and microbial fossils.

Representative plants and animals in Zhangpu amber (Photo credit: Nanjing Institute of Geology and Paleontology)

Unlike most other ambers, Zhangpu amber has precise geological age and paleoclimate data, which can be used to clearly understand the environmental background of the amber biota. Most of the arthropods in the Zhangpu amber biota (especially ants, bees, springtails, crickets, mosquitoes, etc.) are living genera, providing a good time correction point for molecular systematic studies of various groups. The stability of genus-level elements shows that the Asian tropical rainforest biota had reached its current ecological structure as early as 15 million years ago, which also supports the view that "tropical rainforests are museums of biodiversity."

More importantly, the Zhangpu amber community is also the richest amber community collected for scientific research (non-commercial mining), which completely preserves the initial paleoecological and taphonomic information, providing valuable comparative data for the paleoecological restoration and taphonomic (fossil formation) deviation correction of other amber communities.

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Representative insects in Zhangpu amber (Photo credit: Nanjing Institute of Paleontology)

Various types of ants in Zhangpu amber (Photo credit: Nanjing Institute of Paleontology)

History provides lessons for understanding climate change

According to the research and analysis, the flora composition and leaf phase composition of the flora in Zhangpu represent a tropical monsoon forest, and its leaf phase composition is very similar to the vegetation in central Thailand, central India and the Ganges Delta today. The paleoclimate analysis of the leaf phase of plant fossils shows that the Zhangpu area was located at the northern edge of the tropics in the Middle Miocene, with an average annual temperature of 22.5 ± 2.4 °C, an average summer temperature of 27.1 ± 2.9 °C, an average winter temperature of 17.2 ± 3.6 °C, a growing season of about 12 months, and a growing season precipitation of 1929 ± 643 mm. Spring is the driest season. The summer temperature in the Middle Miocene in Zhangpu area quantitatively reconstructed by leaf phase analysis was about 10 °C higher than that in winter, which is lower than the seasonal temperature difference in Zhangpu today (about 15 °C). In addition, the difference in seasonal precipitation in Zhangpu area in the Middle Miocene is close to that of today.

At the same time, the fossils of the Zhangpu Biota contain a large number of typical Southeast Asian tropical biological groups, such as some flowering plants, mosses, snails, spiders, and many insects such as ants, bees, crickets, and beetles, which are currently only distributed in the tropical rainforests of Southeast Asia (even in northern Oceania). Under the background of the greenhouse effect in the middle Miocene, the minimum winter temperature in the Zhangpu area rose significantly, weakening the winterkills effect, which may be the most important factor leading to the northward migration of tropical biota. The "Northern Expedition" of tropical biota brought a large number of invasive species and caused changes in the local food chain, biogeochemical cycle, and climatic conditions, which may have strongly affected the original biological groups in East Asia and further shaped the current East Asian biota.

"Ten years of hard work to make a sword", this research result is the result of ten years of hard work and selfless dedication of all the team members. This study is the preliminary result of the Zhangpu Biota, focusing on the overall appearance of the Zhangpu Biota, but there are still a large number of fossils that need to be identified in detail (for example, only more than 8,000 insect ambers have been identified so far). The research team will continue to conduct in-depth taxonomic, phylogenetic and paleoecological studies on some important animal and plant groups. This study also provides an important reference for understanding the evolution of modern Asian tropical rainforest ecosystems and how they respond to future climate warming.

The relevant research results were jointly completed by an international research team consisting of Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Institute of Zoology, Chinese Academy of Sciences, Sun Yat-sen University, China Agricultural University, Capital Normal University, Linyi University, Qufu Normal University, University of Hong Kong, Open University, University of Göttingen, University of Munich, Senckenberg Natural History Museum, Musée d'Histoire Naturelle, University of Rennes, Indiana University-Champaign, American Museum of Natural History, University of Kansas, University of Gdansk, Poland, and Lebanese University. The relevant research was published online in Science Advances on April 30, 2021.

The research was funded by the Chinese Academy of Sciences, the Ministry of Science and Technology, and the National Natural Science Foundation of China. The Fujian Institute of Geological Survey and the Zhangzhou Binhai Volcano National Geopark provided important support for the research. Mr. Zhu Li, a fossil enthusiast, discovered many new amber deposits and carried out long-term collection work, grinding more than 20,000 specimens, providing important support for this insect amber research. Mr. Shen Huazhu provided a lot of support for the Zhangpu fossil collection.

References:

[1] Wang Bo*, Shi Gongle*, Xu Chunpeng, Spicer RA, Perrichot V., Schmidt AR, Feldberg K., Heinrichs J., Chény C., Pang Hong, Liu Xingyue, Gao Taiping, Wang Zixi, Ślipiński A., Solórzano-Kraemer MM, Heads SW, Thomas MJ, Sadowski E.-M., Szwedo J., Azar D., Nel A., Liu Ye, Chen Jun, Zhang Qi, Zhang Qingqing, Luo Cihang, Yu Tingting, Zheng Daran, Zhang Haichun, Engel MS (2021) The mid-Miocene Zhangpu biota reveals an outstandingly rich rainforest biome in East Asia. Science Advances, 7: eabg0625. https://doi.org/10.1126/sciadv.abg0625.