Translation. Region: Russian Federation –
Source: Novosibirsk State University –
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Associate Professor of the Department of Historical Geology and Paleontology Faculty of Geology and Geophysics Igor Kosenko, a candidate of geological and mineralogical sciences from Novosibirsk State University, spoke about the formation of modern ecosystems and the unique biota of Jehol, which forever changed scientists' understanding of dinosaurs and other prehistoric creatures that inhabited our planet 120 million years ago. His lecture, held as part of Darwin Week—a popular science marathon traditionally held by NSU in February—explored the world at the end of the Mesozoic Era, the Cretaceous Period. This year, the event was held for the first time on the new NSU campus.
The origin of life on the planet
Terrestrial ecosystems of the Cretaceous were very different from those of today. However, the origins of modern terrestrial ecosystems date back to the first half of the Cretaceous. Modern terrestrial ecosystems support a wide variety of plants, from mosses and lichens to giant sequoias and angiosperms. Currently, angiosperms predominate, although gymnosperms also thrive. Among animals, higher vertebrates, namely mammals and birds, are of great importance. And among freshwater vertebrates, bony fishes predominate. But this was not always the case.
Our planet formed approximately 4.5 billion years ago. Life also emerged on it relatively quickly, by the standards of its history. The first ecosystems were composed of cyanobacteria, which appeared approximately 3.8 billion years ago. Today, their remains are stromatolites—the fossilized remains of cyanobacterial mats. These primitive organisms, whose cells lacked a nucleus, possessed the ability to photosynthesize, releasing oxygen. Hundreds of millions of years later, the accumulation of oxygen in the Earth's atmosphere eventually killed off all organisms adapted to anoxic conditions, but it gave rise to new inhabitants of the planet, who formed ecosystems from the first multicellular marine organisms, known as the "Ediacaran biota." This occurred at the end of the Proterozoic Era, approximately 630 million years ago. These creatures did not yet have a mineral skeleton, so only rare traces of them have survived to this day in a handful of locations with special conditions. They are found on every continent. Such sites have also been discovered in our country—in the White Sea and in Eastern Siberia. All the fossil remains that scientists have discovered are quite diverse, representing the imprints of soft-bodied organisms. It is believed that most of this biota left no descendants, although some organisms are considered the ancestors of certain modern groups of organisms, such as arthropods.
Then, approximately 538 million years ago, the Cambrian explosion occurred, when the soft-bodied Ediacaran biota was suddenly replaced by a multitude of organisms with mineral skeletons: mollusks, echinoderms, brachiopods, and chordates. The world changed. Suddenly, the fossil record became filled with numerous fossils with mineral skeletons. Admittedly, the first organisms were quite primitive. For example, the earliest chordates looked like lancelets and led a bottom-dwelling lifestyle. They are our most distant Cambrian ancestors. Then, ecosystems gradually began to become more complex.
During the Ordovician period—460-443 million years ago—corals, an important group of organisms, emerged. They became the primary reef builders, leading to a rapid expansion of biodiversity. All these events in the evolution of the biosphere were linked to global geological events, including the constant drift of continents, the opening and closing of oceans, and fluctuations in sea levels. The evolution of the biota was largely a response to the geological evolution of our planet.
Land development
Then, in the Silurian—443-420 million years ago—a crucial event for terrestrial ecosystems occurred: the appearance of the first land plants, the rhyniophytes. They presumably evolved from algae and inhabited coastal areas of bodies of water. Although they did not yet venture far from the coast, they were nonetheless the first plants to colonize land.
Many important events related to the colonization of land by animals occurred during the Devonian period. Approximately 400 million years ago, animals related to arachnids began to emerge onto land, and the first amphibians, descended from lobe-finned fishes, appeared.
"The Carboniferous period, which lasted from approximately 359 to 299 million years ago, was critical for coal accumulation. Terrestrial ecosystems began to occupy all of Earth's surface, and numerous forests of giant ferns, club mosses, and horsetails emerged, reaching gigantic sizes—growing as large as modern trees. The emergence of numerous plants increased atmospheric oxygen levels, leading to the growth of arthropods, which eventually reached gigantic proportions," said Igor Kosenko.
The lowlands were filled with forests of giant tree-like horsetails, ferns, and club mosses. Two-meter-long centipedes called Arthropleura inhabited the land, and giant dragonflies called Meganeura soared through the air. Overall, the Carboniferous period was characterized by an increase in the diversity of terrestrial vertebrates. The first representatives of the group of higher vertebrates, the synapsids, appeared, becoming the ancestors of mammals. The appearance of diopsids led to the emergence of reptiles, and ultimately, the formation of birds. Initially, these animals were not very large.
New conditions
During the Permian period of the Paleozoic Era—from 299 to 252 million years ago—continental drift resulted in the formation of the single supercontinent Pangea. As a result, a humid climate gave way to an arid one, and organisms adapted to the new conditions began to thrive. Gymnosperms dominated the plant kingdom, while amphibians were supplanted by reptiles, which became highly diversified. Remarkably, they developed an important advanced trait: the egg, protected from the external environment by a shell, enabling the embryo to survive in arid conditions. Furthermore, reptiles abandoned intermediate stages of development (such as tadpoles in frogs), enabling them to more successfully colonize arid landscapes. The group of higher vertebrates—the synapsids—distinguished themselves from another group, the diapsids, by their skull structure. Incidentally, humans are also synapsids.
"The Paleozoic era ended with the Permian-Triassic extinction, the largest in Earth's history. Compared to that, the giant meteorite impact that occurred 66 million years ago, which wiped out most of the dinosaurs, was relatively minor. The Permian-Triassic extinction was associated with catastrophic volcanic eruptions in what is now Siberia approximately 252 million years ago. The scale of this event was such that 57% of organism families, 83% of genera, 81% of marine species, and 70% of terrestrial species became extinct. Modern scientists estimate its duration at approximately 60,000 years," explained Igor Kosenko.
After the disaster
Then began a new frontier in the evolution of our planet's biosphere—the Mesozoic Era. In its first period, the Triassic, the Earth's ecosystems gradually began to recover from a catastrophic extinction. New marine ecosystems formed, where the dominant groups of the Paleozoic (such as brachiopods) were replaced by new groups of organisms—bivalves, which were more sophisticated and better adapted to changing environmental conditions. Reptiles dominated among terrestrial vertebrates, while relatively advanced groups appeared among conifers, such as pines, araucarias, and cypresses. Ferns continued to evolve. While the Permian was the age of the mammal-like synapsids, the Triassic saw an order of magnitude increase in the diversity of diapsids. At the end of the Triassic, the first dinosaurs appeared. Moreover, two main groups—the saurischians and the ornithischians—appeared almost simultaneously. At first they were very modest in size, but later they developed into real giants.
The Triassic period also saw the first successful attempt by reptiles to master the air, and flying animals emerged. The first representatives of these animals were slightly larger than a modern house mouse. They continued their development in the Jurassic, followed by the Cretaceous, which scientists gained a detailed understanding of thanks to the discovery of the unique Jehol Fauna.
The first birds
The Jehol Biota is a complex of fossil organisms dating back to the Cretaceous period, 133–120 million years old. They are preserved in continental deposits in northeastern China. It was here that scientists discovered unique finds—feathered dinosaurs, birds, mammals, the first flowering plants, and other exquisitely preserved fossils.
"The study of the Jehol biota sheds light on the origins of modern ecosystems. Detailed paleontological research has allowed us not only to reconstruct what the East Asian world looked like 133-120 million years ago. Representatives of the Jehol biota were first discovered in Liaoning Province. We now know that many dinosaurs were covered in feathers. We know what these dinosaurs ate. And thanks to modern paleontological methods, we've even been able to reconstruct dinosaur coloration. This uniquely preserved fossil site has allowed scientists to completely revise their understanding of Mesozoic terrestrial ecosystems. We have a better understanding of the diversity of the Early Cretaceous world," explained Igor Kosenko.
The first discovery was made in the mid-1990s. The footprints of a small, bipedal predatory dinosaur, Sinosauropteryx, were discovered. Feathers can be discerned along the contours of this creature's tail. It was this footprint, the first feathered dinosaur known to science, that sparked researchers' interest in the Jehol Biota. Numerous similar discoveries were subsequently made. The same deposits later yielded footprints of various Cretaceous birds, which perfectly preserved not only their plumage and skeleton, but also their stomach contents. Now paleontologists could not only determine what the animal looked like but also what (or what) it ate.
The remains of ancient mammals, which had already occupied various ecological niches by that time, also deserved special attention. These included arboreal and marine animals, as well as predators. Thanks to these finds, scientists learned that these predators preyed on dinosaurs.
Typical representatives of the fauna
Igor Kosenko introduced the audience to key representatives of the Jehol Biota. The most striking of these was Sinosauropteryx, a bipedal dinosaur with short upper limbs. Using modern microscopic and chemical analysis techniques, its coloration was reconstructed. It turned out that Sinosauropteryx's body was reddish, with white stripes on its tail. Its abdomen was noticeably lighter than its back, and its head was two-toned, reminiscent of the mask of a modern raccoon. This feathered dinosaur fed on small vertebrates, insects, and reptiles—bones of the latter were found in the stomach cavities of Sinosauropteryx.
"The name 'Jehol Fauna' was first proposed by the American paleontologist Amadeus Grabau back in 1923. The term 'Jehol Biota' was codified in 1962 by the Chinese scientist J.-W. Gu. Scientists noted that three organisms are very common in Mesozoic rocks in northeastern China: the bivalve freshwater crustacean conchostracans, the larvae of dipteran mayflies, and the bony fish Lycoptera. The state of preservation of these specimens astounds scientists—every scale on the fish, every leg on the larvae, and even the eggs inside the conchostracans, which died 125 million years ago, can be seen in exquisite detail," explained Igor Kosenko.
Another typical representative of the Jehol biota is Psittacosaurus. Interestingly, the skeletal remains of these primitive horned dinosaurs are found in abundance in today's Kuzbass region. These animals were widespread in Siberia and East Asia—in Mongolia, China, and even Thailand.
Two quite different groups of animals inhabited the air: birds and feathered dinosaurs. Among the birds of the Jehol Biota, Confuciusornis, which lived in northeastern China, is notable. It was named after the Chinese philosopher Confucius. Confuciusornis differs from primitive birds in that it lacks teeth in its beak. Scientists are now discovering beautifully preserved birds. A pair of Confuciusornis was discovered, one with a luxuriously long tail, the other without such a tail ornament. Researchers have concluded that these birds, like modern birds, exhibited sexual dimorphism, and that millions of years ago, a male and female were frozen in stone.
"For their time, Confuciusornis were quite advanced birds, as, for example, Archaeopteryx had a toothed beak and a long tail consisting of numerous vertebrae. Pterosaurs were another group of animals that mastered the air. They varied greatly in size and diet. Interestingly, some pterosaur remains have also been found to have hair-like coverings, suggesting that pterosaurs weren't scaly, naked reptiles like snakes, lizards, or turtles. Like mammals and birds, they also had hair, which likely served to maintain body temperature," noted Igor Kosenko.
A very common animal in the Jehol Biota was the small, feathered flying dinosaur Microraptor. Remarkably, it had four wings, not just two! This was another attempt by vertebrates to colonize the air. Admittedly, it wasn't entirely successful—Microraptor survived for several million years before becoming extinct. Its appearance has also been reconstructed from perfectly preserved imprints, and melanosomes in fossilized feathers have revealed that its plumage was black.
Some discoveries have shed light on the behavior of ancient animals—impressions in stone have provided scientists with information that was impossible to extract from even the best-preserved skeletal remains, much less individual bones. They discovered clusters of Psittacosaurus juveniles, including one adult, and concluded that these dinosaurs were herd animals, with "nannies" watching over their young. The fact that ancient mammals hunted dinosaurs was also established by paleo-discoveries from the Jehol Biota. One such hunter was Repenomamus, and its prey were the same Psittacosaurus, which, incidentally, was herbivorous. How did the scientists reach this conclusion? They found the skeletal remains of Psittacosaurus juveniles in the stomach cavities of this predator. But there was another unique find—the skeletons of a Repenomamus and a Psittacosaurus, locked in a deadly fight that proved fatal for both the predator and its prey, said Igor Kosenko.
General interest
As the scientist mentioned, Chinese people show a keen interest in paleontology. This is common among both scientists and laypeople. As soon as an interesting discovery is made, massive research begins. Years of research are conducted, and large-scale excavations begin. Paleontological discoveries are popularized, sensationalized, and reported on in the press and news feeds. Every significant discovery becomes a sensation.
"Excavations are conducted over large areas, so the number of finds increases. Enormous museums are being built at excavation sites, which are highly sought after by both local residents and numerous tourists. Despite the admission fee, the number of visitors is high. They are interesting for both children and adults. A striking example is the museum in Chaoyang (Liaoning Province), where some of the first organisms of the Jehol biota were discovered. Surrounding the museum are sculptures of key vertebrates of this biota—dinosaurs and other ancient animals. Visitors have the opportunity to tour the excavations and see the rock layers in which the paleontological finds were made, as well as the finds themselves, which are displayed under glass," added Igor Kosenko.
These places are so rich in paleontological finds that imprints of prehistoric fish and various invertebrates are abundantly displayed in numerous souvenir shops. Chinese residents eagerly buy and collect them. Tourists also rarely leave empty-handed, as such souvenirs are inexpensive.
Promising Transbaikalia
Igor Kosenko described the joint work of scientists from the Institute of Petroleum Geology and Geophysics (IPGG) SB RAS with Chinese paleontologists in both China and Transbaikal, Russia. It turns out that these areas share a similar geological history during the Cretaceous, which explains the similar biota. Studying excavation sites in northeastern China and comparing them with those in Transbaikal, the scientists noticed clear similarities.
For several years, researchers from the Mesozoic and Cenozoic Paleontology and Stratigraphy Laboratory at the IPGG SB RAS have been studying the continental Mesozoic of Transbaikalia and participating in work at the Turga section (also known as the Middendorf outcrop). During the Cretaceous, freshwater lakes were present here; today, much of the outcrop consists of grassy slopes. Nevertheless, many interesting finds have been made here, including the remains of fish, conchostracans, and insects of the same species that make up the Jehol biota. In terms of preservation, these are comparable to specimens discovered in northeastern China: the fish have all their scales intact, and the crustaceans have microscopic eggs.
Together with our Chinese colleagues, we studied this section and obtained zircon grains of volcanic origin. This means that their age is the same as the age of the layer in which they were discovered. So, we were fortunate to be able to date our paleontological finds. Dating using the radioactive decay method showed that they are 124 million years old. This means that the Transbaikal and Chinese sites of prehistoric flora and fauna are contemporaneous. This means that Transbaikal, along with northeastern China, was the center of origin of the Jihol biota. Therefore, it is quite possible that it could be a treasure trove of feathered dinosaurs. In this regard, we continue to study the Mesozoic continental sections of Transbaikal, attempting to make new discoveries, reconstruct the habitats of fossil animals, and compare them with classic sites. We can already say that in some sections of Transbaikalia, the diversity of fish exceeds what we observe in classical sections of China. In 2024, during a joint expedition to Transbaikalia, our colleague from China discovered a chain of fossilized dinosaur footprints. This means that we still have many interesting discoveries ahead, shedding light on our planet's distant past, concluded Igor Kosenko.
Material prepared by: Elena Panfilo, NSU press service
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