Once a paradise for all kinds of marine life to thrive together, today, it gives us a glimpse into the world of marine life 200 million years ago with a large number of beautifully preserved fossils.
In the southwest region of Guizhou, there is a treasure trove of rare fossils in the world known for preserving a large number of perfect marine reptiles and marine lilies, which is the Guanling biota. The discovery of the Guanling biota is another major discovery of the paleobiota in China after the Chengjiang biota and the Rehe fauna.
Since 1929,
There are many Chinese and foreign paleontologists who have conducted detailed studies of ammonites, bivalves and tooth-shaped stones in Guanling and its neighboring areas. In the 1990s, a large number of exquisite sea lily fossils found here attracted the world's attention, and the final knock on the door of this fossil treasure house was a ichthyosaur fossil that was inadvertently discovered.
As early as 1998, two geologists found a strangely shaped fossil in a strange stone market in Guizhou, which was later identified as a rare ichthyosaur fossil.
This discovery has attracted the attention of paleontologists at the Yichang Institute of Geology and Mineral Resources of the China Geological Survey. In 1999, the institute organized a group of experts to go to the Guanling area to carry out work.
On the first day of excavation, experts excavated ichthyosaur fossils, and the next discovery stunned everyone: marine reptiles such as ichthyosaurs, sea dragons and turtle-like cornstys; vertebrates have amphibians and fish; invertebrates, in addition to a large number of beautifully preserved sea lilies, there are a surprising number of cephalopods, bivalves, sea cucumbers, brachiopods and tooth-shaped stones; in addition to a large number of well-preserved plant fossils. Although experts had predicted that there must be fossils of other creatures besides ichthyosaurs and sea lilies, they were still shocked by such a spectacular sight.
Why did such a prosperous marine life kingdom exist in the Guanling region 200 million years ago?
In the Middle and Late Triassic, about 220 million years ago, the Guanling area is still a crystal clear bay. To the southwest is the entrance to the bay, connected to the Gutesian Ocean and the Nanpan River. The river carries a large amount of land-based material into the bay, bringing rich nutrients to the filter-eating animals in the bay, making it a paradise for all kinds of vertebrates and invertebrates. The river enters the bay with a large number of plant stems of different lengths and sizes, which provide ample living space for the sea lilies to live in the camp. A large number of sea lilies are fixed on these drifting logs, forming an underwater "forest" in which various fish species shuttle through. Sea dragons can also be found in the bay, sometimes frolicking and preying in the sea and sometimes soaking up the sun on the beach. Ichthyosaurs living in the open oceans,
During the breeding season, they also enter the bay in droves, where they make love and breed offspring. The little ichthyosaurs weave through the "forest" of sea lilies, which for them are both a rich place to eat and an excellent hiding place.
Together, a variety of marine life forms a thriving biological kingdom. so. Who is the ruler of this kingdom?
The "royal family" in the Guanling biota: Ichthyosaurs
The ichthyosaurs in the Guanling biota are not only huge (the longest body length is more than 10 meters), but also have a vast living area and can freely travel between shallow seas and open oceans. At the same time, they are also the most ferocious animals in the Guanling fauna, including sea dragons, many marine reptiles and individual huge fish (the largest fish fossils with a body length of more than 2 meters) are their delicacies, they are at the top of the marine biological chain, known as the "royal family" in the Guanling biota.
Ichthyosaur was first discovered in 1699 , although it was thought to be a fish at the time. It wasn't until 1821 that Koening, a researcher at the British Museum, officially named the fish-like reptile the Ichthyosaurus. Ichthyosaurs had a streamlined shape and paddle-shaped limbs, similar to dolphins and whales today.
There are 4 genera and 4 species of ichthyosaurs in the Guanling biome, namely the small and medium-sized Ichthyosaurus of the Zhou dynasty, the beautiful Panjiang Ichthyosaurus and the Wollongong Kalovi Ichthyosaurus, and the large Gangusast Ichthyosaurus. The discovery of these ichthyosaurs is of great significance for studying the evolution of ichthyosaurs.
Zhou's Qianyu Dragon
The Zhou ichthyosaur is the most abundant of ichthyosaur fossils found in the Guanling area, ranging from juvenile to adult, in the thousands. The Zhou ichthyosaur is a small and medium-sized ichthyosaur with a body length of 2-3 meters. Compared to other ichthyosaurs, this ichthyosaur has a shorter snout, accounting for only 55% of the head. The orbit is round and occupies 40% of the head. The cheeks are extremely narrow. The teeth are tapered and do not develop longitudinal ornaments on the surface. The dorsal spine is bent upwards and the mid-posterior part of the tail is significantly bent downwards. The forelimbs are slender paddle-shaped, and the hindlimbs are thick and short.
Among the discovered ichthyosaurs of the Zhou dynasty, there are also very rare ichthyosaurs with embryos, and the number of embryos is about 13. The vast majority of reptiles are oviparous, laying their eggs in sand or nests. Ichthyosaurs have become very specialized and have lived in water all their lives, so where do they reproduce? It was not until the discovery of fossils of ichthyosaurs with embryos in the Jurassic formation near Hosmaden in southern Germany that it was known that Ichthyosaurs were oviparous. The eggs of the ichthyosaur hatch into pups in the mother's body and are then produced. However, there are different views on whether the ichthyosaur is produced first out or tail first out. Most people now believe that the tail of the ichthyosaur pups give birth to the mother before the head, because only in this way can the ichthyosaur pups surface in the shortest possible time after birth and complete the first breath. Fossils found in Guanling prove that Triassic ichthyosaurs were also oviparous.
Wollongong Carlovis Ichthyosaurus
Wollongong Carlovis Ichthyosaurus is slightly smaller than the beautiful Panjiang Ichthyosaurus, and its body length generally does not exceed 6 meters. The overall morphology is similar to that of the beautiful Panjiang Ichthyosaurus, with the main difference being the head features. The snout of Wollongong's Carovis Ichthyosaurus is more slender, with smaller and sparse teeth. Studies have shown that Wollongong's Kalovi Ichthyosaurus is more closely related to Saarstahlosaurus and may be a more evolved ichthyosaur.
Gangusast Ichthyosaurus
Gangusast Ichthyosaurs are not only the largest ichthyosaurs in the Guanling biota, but also the largest animals, with a body length of up to 10 meters. Before the discovery of the Gangusast Ichthyosaurus, there was little information about the Sastay Ichthyosaurus. Studies of Gangusast Ichthyosaurus show that Sastay was a very special type of ichthyosaur: a large body but a small head; a very short snout but large eyes; no teeth; a spine that rapidly enlarged backwards, reaching its maximum before the belt; a relatively short tail that did not bend; and short limbs.
Saarstahlosaurs have no teeth, so what do they feed on and how do they eat? This question has been plaguing scientists. A study of the fossils of Gangusast Ichthyosaurus found that the hyoid bones of the ichthyosaurs were so developed that it appeared that their mouths could be opened wide. Without teeth, they may only be able to devour cephalopods in the ocean by sucking, similar to a type of whale in the modern ocean. This unique way of eating may have been an adaptive evolution of the environment, as in the Late Triassic, when the world's oxygen content was at its lowest, this massive animal needed to inhale as much oxygen as possible to meet its own needs.
Beautiful Panjiang Ichthyosaurus
The beautiful Panjiang Ichthyosaurus is a medium to large ichthyosaur, with a body length of about 6 meters and a maximum length of no more than 7 meters. The head of this ichthyosaur is huge, with a length of about 1 meter. The snout is thick. It accounts for 65% of the head. The teeth are tapered and have longitudinal ornamentation on the surface. The upper teeth are numerous and closely arranged, and the lower teeth are sparse. The tail is slightly bent downwards.
Very rare gastrolithic specimens have been found in the body of the beautiful Panjiang ichthyosaur. Gastrolithia refers to a certain amount of gravel that an animal swallows into the body. Although countless ichthyosaur fossils have been found around the world, this is the first time that gastrolaria have been found in the body of an ichthyosaur. Prior to this, gastrolithia was often found in another class of marine reptiles, plesiosaurs.
The gastrolithic stones found in the body of an ichthyosaur clearly reflect the process from death to its eventual burial: first. After death, the body of the ichthyosaur begins to swell, and the abdomen floats upside down on the surface of the sea; then, the body slowly decays, the belly ruptures, the gas in the body cavity is removed, and some of the internal organs overflow out of the body; finally, the body of the ichthyosaur sinks vertically to the bottom of the sea, and when it reaches the bottom of the sea, the body falls to the right, and is finally buried and preserved by the sediment.
The "turk" in the Guanling biota: the sea dragon
If ichthyosaurs are the "royal family" in the Guanling biota, then the sea dragons are the "turks" among them. Why? Because the sea dragons do not have the specialization of ichthyosaurs, they also retain some characteristics of terrestrial reptiles, their swimming ability is not strong, and they can only live in shallow seas, unlike ichthyosaurs who can swim freely in the vast ocean and can only live in place.
Among the marine reptiles of the Guanling biota, the number of sea dragons is the largest. However, despite the large numbers, the genus species are very single. So far, the sea dragons that have been found are 2 genera and 3 species: Huangguoshu Anshunlong, Sun's Xinpulong and Bamaolin Xinpulong.
Sea Lily "Forest"
A large number of exquisitely preserved sea lily fossils have been found in the Guanling area, and under normal circumstances, sea lilies are easily scattered by seawater because of their special structure, and it is difficult to preserve them intact in the formation.
In the past, sea lilies with stem and root structures were thought to be typical shallow benthic organisms, but studies of sea lilies in the Guanling area, especially those of sea lilies fixed on driftwood, have shown that sea lilies do not grow solidly, but live on drifting trees by attaching root-like vine branches that grow from roots. They use the swing of their wrists and feathers to obtain food from the water. In order to resist the impact of the waves, they also have spines attached to their wrist branches, and the thorns are connected to form a rough net, which not only enhances the firmness of the body, but also filters out the detritus particles in the food.
"Civilians" in the Guanling biota: cephalopods, bivalves, and brachiopods
The Guanling biota also includes countless cephalopods, bivalves and brachiopods, which are like "civilians" in the Guanling biota.
Cephalopods are dominated by ammonites, with a small amount of nautilus. Ammonite appeared in the Devonian Period, 390 million years ago, but did not reach its peak until the Mesozoic Era, between 250 million and 65 million years ago. The Nautilus has lived in the ocean until now, and is very similar in form and structure to its ancient ancestors, so it is called a "living fossil". The nautilus moves in a very peculiar way: it swims backwards in the sea by the reaction force generated by spraying water forward.
Bivalves are found all over the world, from the equator to the poles, from saltwater to fresh water. Because the closed shell muscles of bivalve animals lose their function after death, the two halves of the shell are opened by the action of ligaments, so they are easily washed away by the current. Most of the bivalves in the Guanling biota are preserved intact, indicating that they were buried by sediments soon after their deaths.
Brachiopods only float freely in the sea during the larval stage, and in this way expand their living territory, and then inhabit the seafloor for a lifetime and live on solids.
Extinction stories
Studies of the Guanling biota show that 220 million years ago, in the Middle and Late Triassic, a large number of marine organisms flourished in Guanling and showed a vigorous vitality. But 220 million years later, in the mid-to-late Triassic Carney period, the creatures of the region's oceans suddenly and bizarrely converged on extinction. Apparently, this paradise of marine life suddenly collapsed! So, what caused the extinction of the Guanling biota?
The Guanling biota was formed with the recovery of marine life and the restoration of ecosystems following the global extinction at the end of the Permian. However, by the late Kani period, with the further uplift of the southern Chinese continent, the Yangtze Sea gradually became smaller, and the environment in which the Guanling biota lived gradually changed from an open ocean to a semi-enclosed bay, and even became an almost closed limited basin. Although with the change of seasons, from time to time there is fresh water into the bay, due to the poor flow of water, the bottom water body is in a state of hypoxia for a long time, which is conducive to the preservation of biological remains, and the accumulation of biological corpses is bound to lead to excess storage of organic matter in the basin, and the decomposition of these organic matter undoubtedly greatly consumes the oxygen in the seawater, so that the hypoxia event occurs inside the basin. However, the lack of oxygen on the seabed alone is not enough to cause the extinction of animals such as fish, ichthyosaurs, nautiluses and other animals in the Guanling biota that live in large quantities on the surface of the ocean, swimming or floating. Therefore, there must be another reason for the extinction of the Guanling biota. Through a detailed investigation of the Late Triassic strata buried with a large number of fossils of the Guanling biota, three "suspects" were identified: storms, volcanoes, and earthquakes. So, who is the culprit responsible for the lack of oxygen in the surface waters of the oceans, which leads to the death of a large number of organisms?
Huge storms are enough to hang individual giant ichthyosaurs, or cause oxygen-starved ocean bottom currents to rush into the ocean surface, causing temporary oxygenation of the ocean surface water flow and causing large-scale suffocation of organisms. However, the storm rocks found in the Guanling area belong to distant source storm rocks, that is, the Guanling area was far away from the storm at that time, and the impact of the storm on the oceans inhabited by the Guanling biota was not very serious.
Volcanic activity has been shown to be responsible for the collective extinction of the Rehe biota, and the results of the survey show that volcanic activity in the Guanling region during the Triassic period was also very frequent.
However, the most intense period of volcanic activity in the Guanling area coincided with the late Middle Triassic period when the Guanling biota began to diverge, and the period of final demise of the Guanling biota was tens of millions of years. Therefore, from the perspective of the distribution era of volcanic rocks and the life course of the Guanling biota, volcanic activity is not the culprit of the demise of the Guanling biota, on the contrary, it may also be one of the important triggers for the early formation and development of the Guanling biota.
The Middle and Late Triassic period was an important period of frequent global crustal activity and Indochinese orogeny. The discovery of seismic rocks in the Guanling biota confirms the natural relationship between seismic activity and extinction of the Guanling biota. Earthquakes can not only change the circulation pattern of ocean currents, causing the hypoxic water flow on the ocean floor to surge to the surface of the sea, resulting in a lack of oxygen in the surface seawater, but also may lead to the entry of deep crustal material into the ocean, further depleting the oxygen in the ocean, resulting in a serious lack of oxygen in the marine environment, resulting in the death of a large number of organisms in the ocean.
At present, why the Guanling biota, a once vibrant marine biological kingdom, suddenly disappeared is still a question that geologists are diligently pursuing.