Dinosaur Extinction

Quck answer

Dinosaur Extinction occurred at the end of the Cretaceous period, approximately 65 million years ago. There are several theories about what caused the extinction, including a massive asteroid impact, volcanic activity, and climate change. The most widely accepted theory is that a large asteroid impact caused a global catastrophe, leading to the extinction of the dinosaurs and many other species. The extinction of the dinosaurs paved the way for the rise of mammals, including humans. Today, scientists continue to study the dinosaur extinction in order to better understand the history of life on Earth.

Extinct Animals

As per the paleontologists, Dinosaurs became extinct by the end of the Cretaceous Period. The reason and how it happened is still a mystery which is being solved by studying fossils and rock formations. Since these fossils and rock formations don’t provide all the facts, scientists have to make educated guesses. Even after seeing the same material, different scientists come up with different conclusions, resulting in many theories.

Some of the paleontologists believe that the extinction was caused due to a catastrophe like a meteorite or a comet hitting the earth or a giant volcano erupting. However, some believe that a more gradual process was responsible. Some theories suggest that the competition between dinosaurs and mammals was the cause of extinction, or possibly climate changes. However, the time required for the extinction to take place is still a topic of disagreement. Some believe it happened in several days, while others argue that it took from hundreds of generations to over half a million years. Any extinction theory must account for the extinctions that occurred in the sea, including some types of clams and coiled mollusks.

The extinction event did not kill all animals and plant life, and many kinds of animals survived, including fishes, frogs, turtles, crocodilians, birds, and mammals. However, scientists must take the fossil record and find reasons for all extinctions.

The Cretaceous Extinction Event

Triceratops lived until the end of the Cretaceous Period

Canadian Museum of Nature

The extinction event that killed the dinosaurs was worldwide and affected many plant and animal groups, both on land and in water. Dinosaurs were only a small part of the extinction, and the disappearance of other living things was so great that scientists knew about the extinction 30 years before the first dinosaur was described.

The Cretaceous extinction victims included dinosaurs, ammonites (mollusks related to the octopus and the chambered nautilus), pterosaurs, and certain plant groups. But many other animal groups, even some large-bodied reptile groups like champsosaurs, were not affected.

The image of the last majestic dinosaurs passing away and leaving a world of shrew-like mammals and cold-blooded reptiles is false. Instead, many of the major modern land animals were already living in the Cretaceous, and dinosaurs shared their last million years with modern creatures.

Since more than just dinosaurs became extinct, reasons that only explain why dinosaurs died can be ruled out. For instance, there is one theory that disease caused the extinction of dinosaurs. But a disease could not have caused the extinction of plants and animals over the whole world.

Fossil Record Information

Museum Victoria Research Associate and Monash University PhD student Erich Fitzgerald inspects the skull of a 25-million-year-old fossil from southeast Australia identifying a new family of small, highly predatory, toothed baleen whales with enormous eyes

AFP/Getty Images

The relationship between plants and animals that became extinct at the end of the Cretaceous is important in understanding dinosaur extinction. The reasons for extinction in all these different groups are related. Understanding why another group became extinct may give us clues about dinosaur extinction.

Plants and certain animals have a more complete fossil record than dinosaurs, and they provide insight into climate that dinosaur fossils cannot. Foraminifera, a type of marine protozoan, have shells that indicate the temperature of the water in which they lived. By analyzing the chemical composition of these fossils, researchers can determine the temperatures of prehistoric seas and observe changes in ocean temperature, which reflects climate. This information can reveal what the climate was like before, during, and after dinosaurs became extinct.

Unlike other scientists, paleontologists cannot conduct experiments in a lab. They can only study fossils to piece together history. Unfortunately, the fossil record is often incomplete, with insufficient data.

Studying the fossil record is like watching a mystery movie, but with missing parts. Paleontologists have developed a measure of “stratigraphic completeness” to determine how much of the fossil record is present. This information is necessary to estimate the duration of dinosaur extinction. The completeness of rock formations containing the last dinosaur fossils and the boundary between the Cretaceous and the Tertiary have been studied. Incomplete rock units make it difficult to estimate the time frame. In marine rocks, the record is more complete, and evidence for an extraterrestrial cause of dinosaur extinction has been found. The stratigraphic completeness in marine rocks is smaller and more accurate, allowing for shorter intervals to be studied.

However, the fossil record is not always reliable. Fossils may be collected out of place, leading to inaccurate conclusions. For example, some dinosaurs may have survived beyond the Cretaceous period and into the early Tertiary, but their fossils were collected with early Tertiary mammals.

According to many paleontologists, the fossils discovered in the Early Tertiary era were already fossils before being reburied with the remains of Tertiary mammals due to the process of “reworking” or secondary deposition. Despite appearing to have lived at the same time, these animals lived millions of years apart, and scientists must study each specimen carefully.

Theories on Extinction

Two groups of extinction theories exist: catastrophic extinction and gradual extinction. Catastrophic extinction would have been caused by a sudden external event, such as the collision of the earth with an asteroid or the eruption of a series of gigantic volcanoes. Gradual extinction, on the other hand, would have been the result of changes in the earth’s land mass and climate shifts. It could also be due to new and better animals winning in the struggle for existence.

Before recent theories about extraterrestrial collisions, some scientists believed mammals beat dinosaurs in the struggle to survive. One theory suggests that mammals killed dinosaurs by eating their eggs, while other scientists believe that dinosaurs caused their own extinction. This theory suggests that too many meat-eating dinosaurs evolved, eating all the plant-eaters, causing all dinosaurs to die. These theories have the same pitfall, explaining dinosaur extinction but ignoring the extinction of other groups.

Theories on Climate Change

Leigh Van Valen and Bob Sloan proposed a more complex theory, suggesting that during the Late Cretaceous period, the continents were moving, and new mountain chains began to rise, resulting in many shallow Mesozoic seas drying up. This change caused the world’s climate to change, with evidence from fossil plants suggesting that it got about ten centigrade points colder. This temperature decline would have affected the earth, with colder temperatures in the mountains and new plants replacing warm-weather plants.

Van Valen and Sloan argued that dinosaurs were at a disadvantage in the new forests of coniferous trees. So, they left the mountains and moved towards the tropics, where the climate was better. This theory suggests that the dinosaurs survived longer in the tropics than in the mountains. However, something else must have caused dinosaur extinction in these areas since plants in the tropics survived. One suggestion is that placental mammals became abundant in the mountains as they no longer competed with dinosaurs. Later, the mammals escaped these regions and went into the tropics, where they drove dinosaurs to extinction. However, there is no evidence that dinosaurs lasted longer in one area than another. Although competition between animals may explain the extinction of many living things at the end of the Cretaceous, other groups, especially the foraminifera, seem to have disappeared without competitors.

According to recent research, the sex of certain reptiles, such as turtles and crocodiles, is determined by the temperature of their nest. This has led to a theory that dinosaur extinction may have been caused by cooling temperatures in the Late Cretaceous, resulting in all the young being of the same sex and the inability for the species to continue.

Another theory suggests that an extraterrestrial body hit the earth, causing the Late Cretaceous extinctions. Evidence for this theory was found in Cretaceous clay from northern Italy, which contained a high concentration of the rare element iridium, commonly found in meteorites and comets. Further studies revealed the iridium only in a narrow layer that matched the Cretaceous-Tertiary boundary, leading scientists to believe that a large extraterrestrial body had hit the earth, causing the extinction of dinosaurs.

The impact of such a large asteroid would have caused major changes to the earth’s atmosphere, including a giant hole, dust and debris covering the earth, and a drop in temperature, which would have harmed green plants and ocean plankton, the bottom of the world’s food chain. The dust cloud would have taken weeks or months to settle, causing climate changes worldwide for several years.

During the Late Cretaceous period, it’s possible that animals died due to a lack of oxygen or starvation. The herbivores would have been affected first, followed by the carnivores. The resulting dust cloud may have caused global warming by trapping the Earth’s heat, as it would not have been able to escape through the thick layer of dust in the upper atmosphere.

Since the original study by the Alvarez team, various pieces of evidence related to the iridium layer have supported the idea that an extraterrestrial impact was responsible for the end of the Cretaceous period. This evidence includes the discovery of an impact structure off the Yucatan peninsula and the presence of shock-fractured quartz grains. Additionally, a high concentration of fern spores was found, which is typically the first plant to regenerate in an area that has been devastated by a natural disaster.

The Alvarezes proposed that the dust cloud caused by the impact would have killed all animal and plant life, not just dinosaurs. Paleontologists believe that marine extinctions lasted for thousands of years, indicating that the marine and land extinctions may not have occurred simultaneously. Some scientists speculate that numerous smaller meteors or comets may have struck the Earth over a longer period of time.

FAQ

1. What caused the extinction of dinosaurs?

There is still much debate among scientists, but the most widely accepted theory is that a large asteroid impact caused the extinction of dinosaurs. This impact would have caused massive fires, a nuclear winter effect from the dust and debris in the atmosphere, and a loss of food sources. Other theories suggest that volcanic activity, climate change, or disease may have also played a role.

2. When did the dinosaurs go extinct?

The most commonly accepted date for the extinction of dinosaurs is around 66 million years ago, at the end of the Cretaceous period. This date is based on the geological record and the discovery of a layer of iridium-rich rock that is thought to have been caused by the asteroid impact.

3. Did any dinosaurs survive the extinction event?

While the non-avian dinosaurs (all dinosaurs except birds) did not survive the extinction event, some birds are descended from theropod dinosaurs and are therefore considered to be living dinosaurs. Other animals that survived the extinction event include crocodiles, turtles, and various mammals.

4. Were all dinosaurs huge and fearsome predators?

No, not all dinosaurs were huge and fearsome predators. In fact, some dinosaurs were quite small and harmless, such as the tiny Compsognathus which was only about the size of a chicken. Other dinosaurs, such as the duck-billed Hadrosaurs, were herbivores and had no predatory abilities.

5. How do we know what dinosaurs looked like?

We know what dinosaurs looked like based on fossil evidence. Fossils can include bones, teeth, and even imprints of skin or feathers. By studying these fossils, scientists can learn about the size, shape, and appearance of different dinosaurs.

6. Did humans ever coexist with dinosaurs?

No, humans did not coexist with non-avian dinosaurs. Dinosaurs went extinct millions of years before humans evolved. However, humans have found and studied dinosaur fossils for thousands of years, often interpreting them as mythical creatures or dragons.

7. Are there any living descendants of dinosaurs?

As mentioned earlier, birds are considered to be living descendants of theropod dinosaurs. While they have evolved and changed significantly over millions of years, they still share many traits with their dinosaur ancestors, such as feathers and a wishbone.