About 90 million years ago in the late Cretaceous period, the layout of the continents had become more similar to what it is today, and these two maps show the Arctic and Antarctic at that time: the Atlantic Ocean separated the New World—the Americas—from the Old Continents of Europe, Asia, and Africa, and most of the Asian continents, with the exception of India, which were important puzzle pieces, had been pieced together. Australia remains linked to Antarctica, while India remains inseparable from Madagascar.
Late Cretaceous Map 1
Map of the Late Cretaceous Period 2
1 From California to Alaska The west coast of the United States continues to subduct (the plates of the Earth's crust sink under another piece), in the process of which a series of crust fragments form a series of crust fragments of the earth collide with Baja California in northern Mexico, forcing the formations in this area to move north along the western edge of the American Road, some of which are even more than 3,000 kilometers away, until Alaska stops.
2 Self-contained Australia The formation of a mid-ridge in the southeastern Indian Ocean between Antarctica and Australia has led to the formation of oceans between the two continents. As new seafloor formed and expanded along both sides of the ridge, Australia was slowly pushed north.
3 The Great Migration of the Malvinas Islands (Falkland Islands) The Falkland Islands drift between continents. Today geological studies clearly show that the archipelago was once located at the southwestern tip of South Africa. But in the middle of the Cretaceous period it was pulled toward South America, and as the South Atlantic and the Southern Ocean formed, the islands were rotated 180 degrees.
4 Madagascar becomes an island Madagascar is still connected to India, which has long since separated from Africa. A hot stream of melting material erupting from madagascar's mantle withdrew from the crust, which eventually cracked and lava poured onto the Earth's surface. This rupture caused India to begin to separate from Madagascar.
5 Antarctica By the middle of the Cretaceous Period, the ancient southern supercontinent Gondwana continent fell apart. The three continents that were once stitched together, South America, Africa and India, are now separated. Australia and Antarctica, on the other hand, are only connected by slender road bridges. The decomposition of the continent of Gondwana has its roots, namely a series of expanding mid-ocean ridges that gradually encircle Antarctica and push other continents northward.
6 Oceans Connected The Atlantic Ocean and the Pacific Ocean are connected on a narrow sea lane between South and North America and to the east by the Tethys Ocean, which leads to the separation of the South American continent from the North American continent and Africa from the European continent and the Asian continent.
7 Oceans Across the Midwest The sea level remained high in the mid-Cretaceous period, with water flowing from the Gulf of Mexico through North America to the Arctic Ocean. This sea route runs through the United States, separating the plains in the east from the Rocky Mountains in the west.
During the middle and late Cretaceous period, the ocean changed, forming a greenhouse environment, and organisms continued to develop rapidly and diversely in the ocean. During the mid-Cretaceous Period, about 100 million years ago, the formation of new oceans in the southern hemisphere (such as the Southern Ocean, South Atlantic) drove crustal movement, and these oceans and new seafloor itineraries, in turn, were driven by changing convective patterns within the mantle.
The continent of Gondwana continues to divide, with India separating from Madagascar and then moving north. As the Tasman Sea connected the eastern edge of Eurasia; in Europe, the Atlantic Ocean drifted northward, forming the Gulf of Biscay and dividing the islands of Britain, Labrador and Newfoundland, and later Norway and Greenland.
Ocean changes Geological evidence suggests that the frequency of volcanic activity in the middle Cretaceous period was extremely high, particularly in the mid-ocean ridge region. The mid-ocean ridge rises high from the ancient ocean, causing the surrounding deep seabed to rise. As a result, sea levels around the world rose to a height of 200 metres above today's sea level, causing flooding worldwide and falling again by the end of the Cretaceous period.
Late Cretaceous oceans
Before the end of the period, the sea temperature rose sharply, then fell, and then partially rose. These changes are the result of the fluctuating patterns of ocean circulation at the time of continental division. Over a period of time, ocean temperatures rise rapidly and oxygen is depleted. Appears to have led to the extinction of marine life.
Creatures of the Mid-To-Late Cretaceous Period Dinosaurs still dominated the Earth during this period and continued to diversify. The theropod dinosaurs of the middle and late Cretaceous periods were varied, such as Rex Tyrannosaurus rex of the genus Tyrannosaurus, smaller carnivores, dinosaurs, and ostrich-like birds, as well as dracopods, duck-billed dragons, and triceratops.
Middle and late Cretaceous
The creatures that dominate terrestrial ecosystems today, such as floppy plants, birds, and mammals, thrive explosively and rapidly in the greenhouse environment of the middle Cretaceous. Mammals range in size from shrews to cats and are mostly nocturnal. The earliest angiosperms were flowering plants, most likely shrub-like miscellaneous trees, whose range and variety grew rapidly, growing under the sky of a pine forest. Flora of the late Cretaceous period includes banyan trees, willows, poplars, magnolias, and plane trees. With the expansion of angiosperms, insects are also rapidly diversifying around the world.
During the Cretaceous period, the most abundant carnivores in the Red Deer River region were the Beautiful Toothed Dragon (a theropod like a bird). Langston's lizard Thief of the Family Chironidae and the Serpent-haired Female Monster Dragon of the Family Tyrannosaurus. Tyrannosaurus rex was the largest theropod , with a length of 14 meters and an upright body of 5.5 meters. These huge creatures have large heads, short and muscular necks, long and powerful legs, and an upright tail to balance the body, and their forelimbs are small, with two short fingers, and the short ones can't even touch the mouth, which seems useless and confusing.
Tyrannosaurus rex In the late Cretaceous period, tyrannosaurs (such as Rex Tyrannosaurus rex) were commonly distributed in North America and Central Asia. This skull diagram of Rex Tyrannosaurus shows in detail the animal's curved, jagged, dagger-like teeth.
Rex Tyrannosaurus
It is widely believed that tyrannosaurs were animals capable of running quickly, but it has recently been found that they could not move quickly at all, and British biologist Robin McNeil Alexander deduced from its weight and leg length and pace that the top speed of tyrannosaurs was 30 kilometers per hour. Another American expert, Jim Farlow, pointed out that if such a tall and weighted animal falls, its head will violently hit the ground, causing the skull to shatter, so the large tyrannosaurus can not run fast, otherwise there will be a fatal danger.
Tyrannosaurus rex
Scavengers Although it is widely believed that tyrannosaurus dinosaurs were an active carnivore, in fact, it may have been a scavenger that fed on carrion. Such a lifestyle doesn't require too much speed, which reduces the risk of injury, but it's still just speculation.
Maastricht's behemoth Cretaceous sediments are made up of plankton chalk-like skeletons, a major product of the late Cretaceous period and abundant in Europe. People have been mining this soft limestone for thousands of years in search of flint, and in recent times, this chalk has been mainly used to produce lime. This mining has unearthed many amazing fossils, but none of them can match the behemoths of Maastricht. The name is based on the Dutch town where fossils were found.
Discover the Maastricht behemoth
This carving is found to record a large piece of the jaw of The Dragon of Hochsch was excavated in 1786 in a limestone mine on St. Peter's Hill in Maastricht. This discovery caused a huge sensation in the European scientific community.
The dragon fossil caused a lot of controversy at the time, when people did not know that animals would go extinct, nor did they know Darwin's theory of evolution. Initial doubts focused on the identity of the animal. Dutch naturalist Pierre Camper concluded in 1786 that it was a whale. His theory has caused more controversy, especially on the side of the French scholar Fajah Stadson, who believes it to be a crocodile. But in 1800 Campbell's son Adrian claimed it was a large lizard. He told the French paleontologist Baron Georges Cuvier of his ideas. George Cuvier named it "Canglong", meaning "lizard from the Meuse River".
The jaws of the trophy Maastricht behemoth have been damaged during fossil formation and are now preserved in the Natural History Museum of Paris, seized from the Netherlands in 1795 by Napoleon's army.
Napoleon's booty
Fear in the Cretaceous Ocean Huo's Canglong is not only the last type of marine reptile, but also the tallest in the evolutionary process and the largest. The dragon was a carnivorous reptile that left land and returned to the sea, filling the ecological niche left by the early marine carnivorous reptile, Ichthyosaurus, after the decline of its early marine carnivorous reptile.
Huo's Dragon
The body of Huo's dragon could be more than 15 meters long and had a large jaw. Its skull is harder than its ancestors, its eyes are quite large, its power is relatively good, but its vision is limited, so the sense of depth is poor. In addition, there is evidence that its taste is also not sensitive.
The jaws of The Dragon were covered with large, conical curved teeth with jagged edges, which were powerful and effective. The jawbone has an active node that is used to concentrate all efforts on eating large prey. The edges of its teeth are the most advanced of all marine reptiles, and each crown has a knife edge and friction surface. The animal's terrifying jaw and large size suggest that most of the marine life of the time was his potential prey.
Fossils of a dragon
A large number of fossils of Canglong have traces of the healing of jaw fractures, and there are many tooth marks on the shell of the huge Hoh's heterogeneous turtle, which indicates that the dragon may want to eat the Heterogeneous Turtle of Huo, which is really a non-picky carnivore. Another possibility is that they have fought to the death with males of the same species. Some survived fractures of the jaws, suggesting that they recovered quickly, much like crocodiles today.
As a group, these massive animals, widely distributed in the oceans of the late Cretaceous period, evolved into large sizes and diverged from about 70 species in 20 genera worldwide. But they perished at the end of the Cretaceous period 66 million years ago and survived only 25 million years. By the Cenozoic, their place in the global ocean was replaced by marine mammals.
Dragon restoration diagram
K-Pg boundary The end of the Cretaceous period heralded many major changes around the world, with the highest peak of the extinction of many life species on land and in the sea. Today's dinosaur fossils are found in rocks 66 million years ago, a point in time that borders the Cretaceous and Paleogene periods. By the end of the Cretaceous period, dinosaurs and other close relatives of the ocean were extinct, including plesiosaurs, dragons, flying pterosaurs, and many groups in the Mesozoic Era. In contrast, mammals and birds multiplied in large numbers during the Cenozoic. More than 100 years ago, scientists first recognized the great reversal of these creatures. This time is more pronounced the K-Pg boundary, with K representing Kreide (german for chalk) and Pg representing Paleogene in paleogene.
Clues to the mass extinction The cause of the K-Pg border mass extinction has been a mystery for many years. In the 1970s, American geologist Walter Alvarez discovered iridium in thin clay that marked the border between the Cretaceous and Paleogene periods. This element can be detected in many parts of Europe and North America. Iridium is one of the platinum metals found in meteorites and meteor dust, and Alvarez believes that many of the changes that occurred during the K-Pg boundary period were caused by the impact of giant meteorites (possibly asteroids or comets) on Earth.
Some scientists believe that such a large impact could have a huge impact on the earth, throwing dust and debris into the atmosphere and blocking sunlight for several years, leading to mass extinction. The buried crater was eventually discovered in Cicosulub, on mexico's Yucatan Peninsula, which may have been the site where the meteorite hit Earth when it hit the K-Pg boundary. This crater stretches for several kilometers up to the Gulf of Mexico.
Little stars hit the earth
Collisions from outer space At the end of the Cretaceous Period 66 million years ago, a large object crashed from space to Earth, bringing devastating disasters, and an extraterrestrial planetary impact of this scale was not the first and would not be the last. Over the past 500 million years, there have been more than 500 major impacts from outer space. But the planetary impact in Chicxulub, near present-day Yucata Peninsula in Mexico, was a turning point in biological history. Before this catastrophic impact, dinosaurs and their reptile relatives dominated the landings, oceans and skies. Immediately after the catastrophe, they went extinct, opening the way for mammals and birds to rule the world.
The star is about ten kilometers wide, and it hit a crater on Earth spanning a thousand kilometers and twelve kilometers deep, instantly destroying all life within a radius of thousands of square kilometers. A total of about 50,000 cubic kilometers of limestone was crushed into powder, which later turned into dust, small pieces of lava and microcrystals and were lifted into the atmosphere. Tiny Chicxulub rocks have been found in K-Pg boundary sediments thousands of kilometers away. The impact also threw thousands of tons of sulfur into the air, which mixed with water, creating a large amount of acid rain.
One theory is that ten minutes after the impact, the heat from the explosion swept through the Forests of the Americas and ignited in an instant. Thick smoke and soot blanketed the sky, and large amounts of vegetation were burned around the world, forming a lot of charcoal, which subsequently formed a layer of soot in the rock layer. The dust from the explosion mixed with the smoke from the fire, which filled the sky and caused the temperature to drop. Ten hours after the impact, huge waves of the tsunami reached the eastern coast of the Americas and spread deep into the interior, drowning the animals that survived the explosion.
After the meteorite impact
The search for the K-Pg boundary impact site continued for several years, and finally deformed quartz particles and tsunami sediments near the Caribbean Sea helped determine the impact site of Chixulub.
The Road to Destruction it was discovered through geological analysis that the star was moving at a speed of thirty kilometers per second and was hitting the Earth at a small angle from the southeast. At that time, South America was still separated from North America.
Meteorite impact angle speculation
Crater section The impact squeezed around the crater to form a circle of 8,000 meters high circular edges, which were extremely unstable, and soon collapsed into the crater. This, in turn, led to a massive earthquake, followed by the collapse of the crater, which spread 150 kilometers away.
Boundary Clay Layer Found in the thin clay layer of this stratigraphy in Colorado, it marks the boundary between the Cretaceous and Tertiary periods. This soil layer is rich in iridium produced by the hit of the Chicxulub meteorite.
Boundary clay layer containing iridium
Tsunami sediments Contain rare fine sand hard soil layers in the K-Pg boundary sediments of the Brazos River in Texas, USA, which belong to the K-Pg boundary era and are significantly different from the upper and lower soft sediments. Some scientists believe that this layer of fine sand was deposited 66 million years ago by a tsunami caused by the impact of the Chicxulub meteorite.
Shock Quartz The quartz particles found in Montana, USA, are placed under a microscope, and in the polarized light, its lattice can be seen distorted by the pressure of the shock wave. This mineral particle is found in a clay layer just above the K−Pg boundary. They are hit by the K−Pg boundary formation and are so widely distributed that they are part of the same impact-generated ejecta as the molten glass called "glass meteorites".
Montana quartz granule facets
Named after the meteorite Hicksulub Crater was first discovered in the 1970s but was soon forgotten, in part because it was buried deep in sedimentary layers and was permanently located below the surface of the water. In the 1990s, the site was investigated again and found that the time it was formed coincided very well with the time of the K-Pg boundary. The image of the crater is made by integrating seismic data from a computer and then enhancing the image quality, and the blue area at the bottom of the image represents the groove that was created when the stars struck.
Even if a meteorite impact during the K-Pg border period was an accident, this time it is not necessarily the root cause of the mass extinction. Plants did not go extinct on the K-Pg border, dinosaurs declined gradually, and many environmentally sensitive animals, such as amphibians and turtles, survived with minimal losses.
There was also a massive volcanic eruption, accompanied by a large amount of carbon dioxide being emitted into the atmosphere. This may also have accelerated global warming and contributed to the extinction of many flora and fauna on the road, so volcanic eruptions provided the background for mass extinctions, and meteorite impacts dealt a fatal blow to plants.
Basalt of the Deccan Plateau A river valley that cuts across the Benna Mountains in India exposes the overflowing basalt of the Deccan Plateau. In the late Cretaceous period, as India drifted away from the island of Madagascar, this basalt erupted from a hot spot deep in the mantle to form this basalt, and the toxic gases emitted by the volcanoes that followed exacerbated climate change and mass extinction.
Basalt of the Deccan Plateau
The end of the Cretaceous period was a critical period in the history of animal life. Dinosaurs and a large number of other animals disappear forever at this time. Many different theories have been proposed to understand the extinction events of dinosaurs, from disease to meteorite impacts, but no fossils formed by the large number of bones accumulated between the Cretaceous and Tertiary periods have been found at the K-Pg boundary. A careful study of the fossil record of this period has revealed that the timing of this extinction event is not as obvious as previously expected, and may not have been caused by a cataclysmic event.
Dinosaurs in Decline Many major dinosaur species, such as the large plant-eating dinosaur sauropods, ankylosaurs, and prismatic dinosaurs, began to decline before the end of the Cretaceous period. Comparing two fossil sites in western North America, 75 million years old sediments from the Judith River in Alberta, Canada, and 66 million years old from Hell Creek in northeastern Montana, USA – this is already evident: 32 different dinosaurs were preserved in the older Judith River sediments, while only 19 species were preserved in the Hell Creek sediments at the end of the Cretaceous period. The decline in dinosaur species suggests that dinosaurs were already in decline before the Great Impact event.
Found in North America, the last dinosaurs included large plant-eating animals such as the rhinoceros-shaped horned dinosaurs. But Triceratops and Oxeratops were the only two remaining of the five species of horned dragons that survived to the end of the Cretaceous period. Similarly, there are only two species of duck-billed dragons in the Hell Creek Formation, namely Duck-apatosaurus and Edmontonosaurus, while there are seven species in the earlier Judith River formations.
Edmonton Dragon
The last small plant-eating dinosaurs, including the spiny ankylosaurs with spiny epidermis. The creature's tough epidermis is attached to heavy osteomatomas and spines, and there is a huge bone rod at the caudal end. Its contemporaries were also those of the Stegosaurus , a dinosaur of the family Plesiosaurs , who were only two meters long , belonging to the order Ornithischia.
Another major dinosaur species, the order Sauropodidae, includes large plant-eating sauropods and carnivorous theropods. Sauropods disappeared from much of North America during the late Cretaceous period, and only a few still lived in other areas, such as the Mongol Namogai touosaurus. Theropod dinosaurs, on the other hand, flourished, especially in the family Tyrannosaurus. But not all of them were as large as tyrannosaurs, weighing eight tons (elephants weighing only 4.5 tons). Alberta dragons weighed 2.7 tons, and the smaller dracopods weighed only 200 kilograms, about the same size as modern adult males.
Some theropod dinosaurs did decrease in numbers and species during the last million years of the Cretaceous Period, the most important of which were the swift ostrich-like ornithischians. If the hard and long tail is also counted, its body length can reach four meters. Only three ornithopods persisted until the end of the Cretaceous period, and other theropod dinosaurs, such as the swift carnivorous chiliosaurs, who were members of the family Chilonga and Leptosaurus, became extinct at the end of the Cretaceous period.
Flying reptiles also declined sharply in the late Cretaceous period, and marine reptiles were not spared. Ichthyosaurs and plesiosaurs disappeared long before the K-Pg boundary. 66 million years ago, when the Earth was hit by meteorites, great changes were already brewing.
Some scientists believe that most of North America's vulnerable animals, including massive sauropods and top predators, went extinct a week after the explosions. The animals themselves are already relatively small in number. Due to acid rain falling from the sky and lack of sunlight, plants also began to die. But perhaps it wasn't until 100,000 years after the disaster that the dinosaurs eventually went extinct. Ammonite mollusks lived for another 200,000 years after this. As climate and ocean circulation re-form orderly connections with animals, animals and plants, the global environment returned to normal after 2.5 million years.
Peak fern growth Fossil evidence suggests that the North American continent was covered with broad-leaved evergreens and ferns before the K-Pg boundary mass extinction. The peak growth period of ferns appeared immediately after the K-Pg boundary in Neogene rocks. The sudden abundance of ferns suggests that ferns similar to extant ferns survived tenaciously and did not appear to be affected by the impact. Over time, fossils of other plants became apparent, and even today, whenever the land is destroyed by volcanic eruptions, ferns are always the first plants to grow and can form before other flora can grow again. This discovery, along with events 66 million years ago, suggests that plants at the end of the Cretaceous period suffered a heavy blow.
Ferns sprout
After Earth was hit by a star, tiny phytoplankton in the oceans may be the first to die. Their deaths disrupt entire marine ecosystems. However, there is evidence that, possibly due to the dramatic changes in ocean currents, they began to decline before the meteorites struck, and the meteorites merely accelerated the process. It is estimated that the impact not only blocked the light from shining, but also caused massive wildfires and acid rain, which adversely affected land plants.
As can be seen from the Hell Creek Rock Record in Montana, usa, more than 75% of plants in North America are extinct. Overall, newly evolved angiosperms suffered the most from other Mesozoic plants such as ginkgo biloba and cycads, although ferns survived and conifers slowly thrived. Surprisingly, the land plants of the southern hemisphere were almost unaffected by this impact, suggesting that the impact was not as devastating as some scientists claim.
The end of the age of dinosaurs Plants have recovered, while many animals have not been so lucky, and the most interesting thing is that dinosaurs, flying pterosaurs, large marine reptiles and plesiosaurs are extinct. There is much controversy as to why dinosaurs went extinct, but vertebrates such as bony fish (12% extinct), frogs (no extinction), salamanders (no extinction), lizards (6% extinction) and mammals with a platform (14%) did not become mass extinct.
Life in the Late Cretaceous Period In the final Cretaceous period, a wide variety of animals lived in the vast rivers and swamps of North America, including horned triceratops, scaly ankylosaurs, and dinosaurs of the Edmonton dragon, Lyceosaurus, Parachloros, and duck-billed dinosaurs. The huge aeolian pterosaurs in the pterosaurs had a wingspan of up to 12 meters, and none of these animals survived to the Cenozoic. But many mammals have done so, including primitive marsupials.
Aeolian Pterodactyl
Horned plant-eater Triceratops roams the wilderness of western South America, and its name implies that it had three horns on its face. Its horns and neck shields play an offensive and defensive role in battle, often used to fight with other male Triceratops for territory.
Triceratops roams the wilderness of western America
The age of dinosaurs came to an abrupt end, and the so-called abrupt end, in which the timeline means 100,000 years. It is now impossible to judge by rock that the mass extinction event lasted for several years or a long time. Although meteorite impacts now appear to have played an important role in extinction events, the influence of other factors cannot be ignored.
Before the mass extinction, the reptiles of the late Cretaceous period included tortoises, crocodiles, lizards, and snakes in 45 families, in addition to dinosaurs. Fish and crocodiles are the most affected, but animals that survive like plants have also adapted quickly to their new environment. To this day, there are still more species of reptiles than mammals.
The decline of reptiles provided an opportunity for the rapid expansion of mammals, although mammals also suffered a tragic fate in the mass extinction. Of the early Cretaceous mammals (20% of which are extinct), marsupial mammals were the most affected.
During the K-Pg boundary period, about 75% of species went extinct. Many species are originally rare and are facing extinction, but the jury is still out as to why some species have gone extinct and some have survived. Some scientists believe that it was only luck that survived.
Skull of " Apatosaurus " was a small dinosaur that lived in the late Cretaceous period , and its remains were found in Mongolia. The broad eye sockets and curved fangs of the " L. orniosaurus " suggest that they were typical predators.
Fossil skull of Apatosaurus
This fossil of the cubs of the duck-billed dragon " Was found in Montana, USA. The cubs were so small that they were not suitable for survival, so adult dinosaurs had to look after them like adult birds. The care of parents can be seen from the name, which means "good mother".
Fossil embryo of Dracopoda
Bivalve fossil triangular clams are prevalent in the warm waters of the Mesozoic Tethys Ocean. The hard, ridged shell protects them from the onslaught of waves, and one of the tropical triangular clams survives to this day.
Cretaceous bivalve fossils
Mongolian Desert Some formations in Mongolia's dry desert are rich in dinosaur fossils. Over the past 80 years, thousands of organisms have been recovered from these Mesozoic sediments.
Origin of Mongolian dinosaur fossils
Witnessing a Lost World For paleontologists, digging up Mongolia's rich fossils is an exciting experience. In 1994, an expedition organized by the American Museum of Natural History found more than 500 intact Cretaceous remains on the hills of Uhatoka. Professor Michael Novacek, the leader of the expedition, wrote: "We seem to have broken into the large cemetery, as if these animals had only recently lost their last breath. Walking into this world and seeing such a group of extinct animals, we have never been so close to them in time.
After patient excavations, a team of paleontologists finally unearthed part of the body skeleton of the skull of a dinosaur in the family Tyrannosaurus, an extremely rare discovery.
Fossil megafauna are discovered
Dinosaurs with scales " Baotou " was one of the larger ankylosaurs , with a skull protected by bone fragments and scales around its eyes. Its bone spurs and bone pieces protect the head, neck and shoulders.
Fossils of Baotou dragons with scales and horns
Extinction of ammonites At the end of the Cretaceous, marine life went extinct on a larger scale than terrestrial organisms, including ammonites that lived in the ocean for nearly 300 million years.
Extinct ammonite fossils
Surviving shelled animals . Tortoises and turtles belong to the same kind of reptiles, turtles. They have long been classified as omnivores that can reproduce in both water and on land, yet they all have similar shells, a trait that may help them survive the K-Pg boundary mass extinction event.
Surviving animals