The end of the dinosaurs: not only from outside?

BBC, many thanks for this folder. More on their website.

The final days of the dinosaurs, a very successful species of animals that lived on this planet for about 165 million years (from about 230 million (the Triassic area) until about 65 million years ago (the end of the Cretaceous period)) has fascinated people since the first discovery and recognition of their remains. It is still not known whether their disappearance happened quite abrupt or was spread over a longer period and thus people still wonder what caused their end. A number of possibilities are circulating, the best known too the public is that a comet crushed into the Earth and resulted in a quick disappearance from this planet. Others suggest increased volcanic activities or failure to adapt to changing environments caused a slower decline.

(This article is partly a summary of what is known but to be better informed you should read more detailed articles. However, I am not sure whether scientists already thought about the internal factors. If yes, they can comment about their newest findings; if not then maybe it may help scientists to think about its possibilities.)

External factors

Meteorite

One theory is that an extremely large meteorite collapsed with the Earth around Mexico, resulting in the Chicxulub crater which can still be seen as part of a large circle in Mexico while the other half is covered with water from the sea. The impact might have resulted in (1) megatsunamis that destroyed large parts of land but also might have brought many fish on land to die, (2) shock waves travelling through the Earth (earthquakes) maybe even increasing the spread of continental drift, (3) a heatwave because of the impact (smaller animals living under the ground and in water could have escaped as well as small groups of isolating living dinosaurs (e.g. in valleys between mountains) although I think the heat travelled not more than a few tens of kilometres because heat dies quickly off) and (4) afterwards a cooling of the Earth's atmosphere as large amounts of debris were thrown in the atmosphere, blocking the sun. These events resulted directly in the death of many animals and plants and the death of plants resulted indirectly in the death of herbivorous dinosaurs because these large animals needed plenty of food. As herbivorous dinosaurs died, carnivores started to die and within a short time the dinosaurs disappeared (although there is evidence some continued to live a few thousand of years afterwards such as some Neanderthals did after most of them disappeared). The only dinosaurs that survived even to the present day were birds.
Is it known whether only one meteorite or more meteorites hit the Earth, maybe because we flew through a group of meteorites or maybe because the very large meteorite broke in smaller pieces when it entered the Earth's atmosphere and the pieces fell at different places on the Earth?

Volcanoes

Other scientists claim increased volcanic activities released many particles in the sky, some poisonous such as sulphur killing life directly while other particles blocked the sunlight, reducing the photosynthesis of plants and thus plants grew slower and as a result there was less food for dinosaurs. Only a very long and/or very large eruption could have resulted in these dramatic events. But such an event took place in India, the so-called Duccan Traps flood basalts, large volcanic activities that lasted over two million years. I think the gases released mainly killed local animals while particles blocking sunlight would have an effect on the whole planet.

When the volcanic activities took place around the same time as the impact from the meteorite, the effect could be strong enough to kill most animals and plants, including the dinosaurs (so-called Cretaceous-Paleogene extinction event). Maybe the impact of the very large comet caused instabilities in the Earth's crust (remember, the core of the Earth is quite liquid and we all know what happens when we hit a bath with water that is covered with plastic: the plastic moves because of the water underneath and it takes a while before it returns to its resting position). Maybe the shock waves after the impact resulted in volcanic activities although I think these volcanoes might have lasted only a short period until the Earth's surface returned to a new stability? Furthermore, volcanic activity often results in increased diversity except when it destroys everything (indeed, mammals flourished after the dinosaurs disappeared). Fox news reported that the diversity in dinosaurs boomed after the formation of the Rocky Mountains and the emergence of a prehistoric sea, formed due to geological forces and it is known that many volcanoes were active during the time dinosaurs roamed the Earth. Why did those volcanoes had not that much effect, although after a certain period of active volcanoes the composition of the air changes (less oxygen). The eruption of Mount St. Helens destroyed large parts of nature, but 30 years later scientists discovered life flourished because some animals survived (e.g. frogs during winter sleep and fish) while most of the predators were killed and plants (= food) grew well because of the minerals. Of course, when the whole planet burns, then nothing can survive although that did not happen because other animals survived.

Inability to adapt to changing environment

It is also thought that changes in the environment resulted in the decline in dinosaurs. Indeed, flowering plants started to take over and dinosaurs might not have been able to eat or digest these plants. As the change might have happened quite quick, the dinosaurs, very large animals, might not be able to change and die from starvation in a world full of food.

Questions

I do not question the impact large events have on the struggle to survive for plants and animals. However, I think particles in the air after the fall of a comet or active volcanoes only last a few years. As mentioned above, these particles can cause climate change, in general a cooling down of the Earth and thus lower yields of food (that can even lead to starvation at places far away from the disaster). But we also know that in general these effects caused by particles released in the air by volcanoes only last a few years (but sometimes long enough to kill many). Indeed, I think that as a result of the particles in the atmosphere there will be more rain although a cooler climate results in less rain. The particles in the air are ideal as core around which moisture condenses to form water droplets to form rain. Normally, water evaporates to form water vapour that is light and rises into the sky (warm water evaporates more quickly). High in the sky it is cooler and as a result water vapour condenses and forms small water droplets that come together to form larger droplets until they become too heavy and they fall downwards. Water vapour condenses quicker when there are dust particles in the sky, and as a result the condensed water brings the particles back to the Earth. Thus, during volcanic activities, there are many particles in the sky and therefore water vapour can condense more easily to form rain that brings down the volcanic dust particles, spreading minerals over large parts of the Earth, fertilising the Earth. Thus, I think that as a result of volcanic activity it will rain more, clearing the sky from the particles. Certainly when dust particles are the result from the impact of a comet (a short-lived phenomenon while volcanic activity can continue for many years) I think the sky was quickly released from dust particles. And if the volcanic activity was the result of the impact of the comet on the Earth's surface, I think the volcanic activity will only last a few years and then settle. Thus, the impact of a comet on the Earth can be very great but I think it is insufficient to destroy most life as the increase in mammals afterwards demonstrated. Of course, if the impact also caused an increase in radioactivity, the effects can be much worse. But this short period of impact would also explain why many other animals, including mammals, did not disappear. The cooling of the Earth and partly darkening would affect large animals much more than smaller ones. Of course, two million years of volcanic activity would cause long lasting effects.

Internal factors?

Did they die because of self-made starvation?

I sometimes wonder if the events described above were really so big it destroyed almost all dinosaurs (except birds). Not only dinosaurs died but also other groups of animals and plants and thus something happened around that period that killed mainly larger animals. Still, I wonder whether the dinosaurs themselves may have been partly to blame for their disappearance while the other events were a few too many?

Fern plants.
Examples of the diverse group of flowering plants.
The first dinosaurs where quite small but over millions of years on this planet they continued to become bigger and bigger (the largest dinosaurs measured up to 60 000 kg (60 tons)). One of the reasons why they grew so big was because of the plants they eat at that time. These were mainly pteridophyte (amongst them ferns) and gymnosperms, plants that are quite hard to digest if you compare them with plants we eat. Larger animals digest their food more efficiently than smaller animals whereby the food stays longer in the body and thus larger dinosaurs yielded more energy from these plants because the food remained longer in their bodies together with stones to grind the plants. Other advantages of being large is that large animals use less energy, they are better protected against predators (more about this later) and in general they live longer. Although large dinosaurs were more energy efficient, these animals still needed to eat enormous amounts of plants. As dinosaurs became one of the most successful multicellular animals on Earth (they conquered the whole planet and remained here for 165 million years while modern humans, although we also conquered the whole world, are here for only about 200 000 years and already we call ourselves successful), they consumed large amounts of plants and probably because of their seize also destroyed lots of their habitats. I can imagine that this resulted in a decline in the plants they eat. This might have resulted in climate change (plants evaporate water and that results in cloud formation, thus as many plants and trees disappear less water evaporates and less rain is formed), and thus the Earth became dryer and even fewer plants grew. Around that time, other types of plants (flowering plants or angiosperms) started to be able to dominate which were probably not suitable for dinosaurs to digest while they were probably easier to digest by other animals such as mammals whose numbers started to increase. These plants probably existed already for a longer period but the decline in the other plants allowed these flowering plants to conquer the Earth. Thus I think the increase in numbers of mammals is not only due to the decline in dinosaurs but also to an increase in availability of more nutritional food.

Large herbivorous dinosaurs were not only better in digesting their food but they were also less likely to be killed by predators than smaller ones and thus their size continued to increase as mainly the larger animals survived. As the size of herbivorous dinosaurs increased, carnivores also became bigger if only to be able to kill the large dinosaurs but certainly because the death of one herbivorous animal provided plenty of food. But, maybe conditions for these large carnivores were too good as large groups of herbivorous dinosaurs were present and thus their numbers increased too quickly. Of course, they probably killed younger animals first (who then can't give birth to other dinosaurs) and as the numbers of carnivorous dinosaurs increased, too many herbivores and smaller carnivores might have been killed, maybe even without eating them. This might have caused a decrease in the number of herbivores and thus of carnivores. Remember, one of the largest carnivores ever, Tyrannosaurus rex (T. rex), lived near the end of the period of the dinosaurs and some carnivores were even bigger. These large predators could have killed many dinosaurs, even a few too many.

Did dinosaur numbers decline because they were killed by diseases?

When many animals live together, chances increase that diseases spread and kill, certainly when many animals of the same species live together (diseases also spread easier when many plants of the same species grow together). This doesn't mean that small populations are better protected because in those circumstances one disease can kill all individuals (e.g. Ebola can kill all people who live in one village). But too many animals in one large area spread diseases easily over that large areas (compare with the plague during the Middle Ages killing many people in Europe).

I think the best are medium-sized populations spread over large areas. This means plenty of animals are alive and when a disease kills many some animals will survive and become immune. Other populations live far away and do not come in contact with the disease and thus their population remain large. When these two populations meet after the disease disappeared, they can breed and increase the population while the surviving ones could spread their resistance gene. However, when too many animals live together over large areas and certainly when the disease is very deathly, many animals will die or become weak. Then other diseases will get a chance and kill the weaker animals. When animals try to escape the diseased area (animals run away when they smell death) they will spread the diseases to other areas.

Thus, diseases easily spread because large numbers of dinosaurs lived together could have resulted in a decrease in the number of dinosaurs, and as diseases are often specific, other species including mammals might have escaped the disease. Even when only herbivorous dinosaurs were affected, it would have had a major effect on all dinosaurs because the weakened dinosaurs would have been an easy target for their predators and thus numbers went down and as a result also the numbers of carnivorous dinosaurs. The only dinosaurs that survived until today might have been those that could escape from the diseased area: healthy birds could fly away from the smell and reach areas with still large populations and thus continue to grow in numbers.

Bringing all factors together

These factors, (1) a decline in plants that were eaten by herbivorous dinosaurs due too overconsumption, (2) too many large carnivorous dinosaurs that would mainly kill weaker and younger dinosaurs (thus those couldn't reproduce) and (3) easy spreading of diseases due too overpopulation might have started the decline of the dinosaurs. Scientists are still discussing whether the decline in dinosaurs was gradually or fast and I would argue for a slower decline with a sudden stop.

If I am correct, these factors could have resulted in a downwards spiral: firstly the plant shortages resulted in weaker and dying herbivorous dinosaurs which were more vulnerable to diseases while the numbers of (large) predators would continue to increase for a short time because plenty of food was available (weakened or death herbivorous dinosaurs) until the numbers of herbivorous dinosaurs felt too sharply. Then the carnivores would turn their attention to smaller dinosaurs and mammals and even towards each other (meat eaters kill each other, certainly during food shortages), causing a further decline in numbers at an increasingly high speed. But, although also the numbers of carnivorous dinosaurs started to decline, they would continue killing other animals including dinosaurs as they would be very hungry, preventing other species to recover. Also increasing volcanic activities might have resulted in weaker animals, more prone to diseases. Finally, a meteorite and more volcanic activities might have been the killing knife to remove the dinosaurs (and many other animal and plant species) from the Earth because when numbers become too small and animals too weak, they are no longer able to adapt to a changing environment. Certainly when other plants were better adapted to the new environment (e.g. cooler environment) and continued to conquer the Earth and thus prevented the return of plants eaten by dinosaurs. This new environment and fewer dinosaurs would allow other animals, i.e. mammals, to increase in numbers, some of which were carnivorous and might have hunted the weakened dinosaurs until they finally disappeared.

There is evidence some dinosaurs survived for a short period after the events described above and while many scientists think these are artifacts, I think they may be real. These dinosaurs might have escaped the terrible events because they lived in protected areas but because of changes in their environment (e.g. invading new species) and too small numbers they might not have been able to adapt and thus disappeared (unless we may one day discover some animals are surviving dinosaurs (e.g. some mammals lay eggs, but are they real mammals?).

The only dinosaurs that escaped extinction where birds. Indeed, surviving healthy birds could move away from disaster areas to areas where more birds where present and thus mate to increase their numbers. Secondly, birds are much smaller and thus they need less food, important when food is scarcely available.

Summary

I wonder whether this story sounds plausible and whether my internal factors are additions to the reasons why dinosaurs disappeared. Indeed, dinosaurs became too greedy and too big, destroying their environment, changing climate and finally destroying themselves. In this case, external factors such as meteorites and/or volcanoes only resulted in the final blow while during previous periods when dinosaurs were smaller and more adaptable, disasters resulted in larger diversities of dinosaurs species.

Thus, maybe dinosaurs became too successful and this drove them to extinction because they depleted the resources and this made them more vulnerable to external factors. After they were gone, plants could grow again without being eaten while as the carnivorous monsters were death fewer animals were killed and thus planet Earth could recover.

Final remark: oil find its origins in the remains of dinosaurs. Thus, would we find more dinosaur bones in oil fields?

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