But it was not only flying insects that became huge: giant , , and other arthropods also lived in the Carboniferous, such as mayflies with half-meter wingspans. The (more than two meters long) has been featured in popular culture as a nightmare creature, although it was vegetarian. The lived in the Carboniferous and reached seven meters long. The high-oxygen hypothesis is challenged for and giant animals in general, and the controversy will probably continue for many more years.
What was most relevant to humans, however, was the almost-complete extinction during the Kellwasser event of the tetrapods that had come ashore. Tetrapods did not reappear in the fossil record until several million years after the Kellwasser event, and has even been referred to as the Fammenian Gap (the is the Devonian’s last age). The Kellwasser event also appeared to be a period of low atmospheric oxygen content, and some evidence is the lack of charcoal in fossil deposits. Recent research has demonstrated that getting wood to burn at oxygen levels of less than 13-15% may be impossible. Because all periods of complex land life show evidence of forest fires, it is today thought that oxygen levels have not dropped below 13-15% since the Devonian, but during the “charcoal gap” of the late Devonian, when the first landlubbing tetrapods went extinct, oxygen levels reached their lowest levels since the , which must have impacted the first animals trying to breathe air instead of water. During the , there is no charcoal evidence at all, which leads to the notion that oxygen levels may have even dropped below 13%. This drop may be related to severe climatic stresses on the new forests, which are probably related to the ice age that the forests helped bring about due to their carbon sequestering. That is an attractively explanatory scenario, but the continues. The first seed plants probably appeared before the Kellwasser event, but it was not until after the Fammenian Gap that seed plants began to proliferate.
Sauropods seem to have . Until relatively recently, animals as agents of ecosystem change and maintenance was a marginal idea. But today, is thought to be a seminal geophysical event in the Cambrian, and those huge sauropods probably had an ecosystem impact like what elephants have today in Africa. Elephants today break up woods as they feed, as they knock over trees and uproot them. That damage transforms the biome and provides opportunities for other kinds of herbivores and their predators. Elephants also and are considered , which have an outsized impact on their environment. Today, there is a “” to the overkill hypothesis regarding megafauna extinctions soon after humans appeared; such people minimize the impact of humans (their position has an inherent conflict of interest, as those ) and attribute the extinction of elephants of the Western Hemisphere (, ) to climate change and resulting changes in vegetation. If the current situation with African elephants is relevant, it is likelier that those vegetation changes were a of elephant extinction, not a cause. Elephant extinctions would have affected many other kinds of plants and animals, and could have precipitated . Similarly, those huge sauropods would not just have nibbled at vegetation and been relatively harmless browsers, but their vast bulk would have been ideal for pushing over trees to get at their foliage and other devastations of trees in particular, which would have dramatically impacted biomes. Giant dinosaurs probably had keystone species impacts on their environments, particularly the vegetation. Dinosaurs were not the only huge organisms in those days. The appeared in the Jurassic, and would have been immune to dinosaur browsing when they grew large enough. Below is an artist's conception of a typical Jurassic landscape (just as an allosaur and stegosaur are about to cordially interact). (Source: Wikimedia Commons)
The coincided with a and the in what became Central Asia. Ammonoids, bivalves, and other marine denizens were hit hard, and on land it was nearly the final exit for therapsids ( and ), and what would have been the chief diapsid competitor to early sauropods, , suddenly went extinct, possibly by losing their . Extinction specialist Michael Benton has argued that the mass extinction at 230 mya was greater in ways than the extinction, which is considered one of the . The rise of dinosaurs to dominance coincided with the mid-Triassic mass extinction, and mammals first appeared a few million years later. Although the “slate's being cleared” by a mass extinction may well have given dinosaurs their opportunity, they also left many contemporaries far behind. Mammals would be rat-like, largely nocturnal fringe dwellers for 160 million years after they first appeared, while dinosaurs ruled Earth. Stony corals also first appeared after the mid-Triassic extinction, and about 220 mya.
In the 19th century, the Jurassic was called the Golden Age of Dinosaurs, but that moniker is arguably most applicable to the late Cretaceous, and it was a golden age clear up until a bolide impact brought it all to an end. One of the uglier disputes in paleontology’s history was a bent on outcompeting each other in finding and describing dinosaur fossils. However, the dinosaur extinction is probably the largest and most contentious controversy in the history of paleontology. Again, the , due to Lyell’s and Darwin’s prevailing uniformitarianism, until my lifetime. The hypothesized bolide event, , was a kind of a bolide event inflicted on paleontology. Acrimonious disputes ignited that still burn, but it made studying mass extinctions respectable. Initially attacked and dismissed, the bolide impact hypothesis is by far today’s leading hypothesis for explaining the . However, at the same time, India was speeding toward its Asian destiny, and its movement is associated with . Also, , so the bolide event has some theoretical competition as a causative agent.
The idea that the American mastodon was killed off by hunting was first proposed by in 1799, and , an early evolutionist, thought that humans exterminated the extinct ice age mammals. By 1860, wondered whether anything humans could have caused that mass extinction. Therefore, when first proposed his Overkill Hypothesis in 1966, it was by no means novel, but he started the modern debate and the controversy quickly focused on North America, beginning about 15 kya.
Earth had never before hosted anything like behaviorally modern humans. Nothing came close. They wielded fire and began using it for offensive purposes, to . They had sophisticated stone tools and weapons, they mastered language and could engage in group behaviors that no other land animal remotely accomplished. They probably had sophisticated projectile weapons, and if the , they may have also . One !Kung arrow can bring down a 200-kilogram antelope in less than a day. What kind of animal in the Western Hemisphere and Australia, that had never seen anything like a human before, and would have been the of the invaders, and the large ones all reproduced slowly, could have withstood that onslaught? None that I can think of. Neanderthals were ambush predators of megafauna that were wary of humans, and whatever projectile weapons they may have had, they would have been inferior to those that behaviorally modern humans left Africa with about 60-50 kya. Neanderthals still lived off of those animals, with suffered during hunts. That would have been nothing like what the invaders of the Western Hemisphere and Australia encountered. They could have walked right up to all of those animals with no conditioned fear of humans and stuck their spears into them, maybe not even needing to use projectile weapons, much less poisoned ones. That scenario has been called the , but it would not have seemed a rapid event to the invaders. It would have been a butcher shop’s version of the Garden of Eden. Farther than they could imagine, in every direction, were animals with no fear of humans that could be killed so easily that it may have literally become child’s play. One argument by human-agency skeptics is that continental animals were subject to predation and would have begun fleeing fast. That seems like a weak argument, and here is why.
To my knowledge, nobody has ever invoked a climate change hypothesis for the mass extinction of South American mammals when the land bridge formed that , even though the formation of that land bridge probably triggered the current ice age and the North American invasions of South America. Most South American mammal species quickly went extinct when that had survived many millions of years of intercontinental invasions. It was a purely Darwinian event in which animals with greater carrying capacities prevailed. There was no big picture awareness of events by the invaders or invaded, just as there had never been during life’s history on Earth. They all just tried to survive, and previously isolated South American mammals quickly lost the game. The survivors were able to live in niches that no North American animals did, such as .
The genetic testing that has been performed on humanity in the past generation has shown that the founder group’s pattern of migration was to continually spread out, and once the original settlement covered the continents, people did not move much at all, at least until Europe began conquering the world (and there were some ). There is little sign of warfare in those early days of migration, and the leading hypothesis is that people moved to the next valley rather than be close enough to fight each other. Any conflict would have been easily resolved by moving farther out, where more easily killed animals lived. Also, in those virgin continents, people need not have roamed far to obtain food. Today, an !Kung woman will carry her child more than 7,000 kilometers before the child can walk for himself/herself. If an !Kung woman bears twins, it is her duty to pick which child to murder, because she cannot afford to carry two. That demonstrates the limitations of today’s hunter-gatherer lifestyle, but in those halcyonic days of invading virgin continents (which had to be the Golden Age of the Hunter-Gatherer), those kinds of practices probably waned and bands grew fast. When they they split, and the new group moved to new lands where the animals, again, never saw people before. Unlike the case with humans, there would not have been a grapevine so that animals told their neighbors about the new super-predator. The first time that those megafauna saw humans was probably their last time. It is very likely, just as with all predators for all time, and as can be seen with historical hunting events such or , that those bands soon took to killing animals, harvesting the best parts, and moving on. To them it would not have been a “blitzkrieg,” but more like kids in candy stores. After a few thousand years of grabbing meat whenever the fancy took them, or perhaps less, those halcyonic days were over as the far coasts of Australia were reached and the easy meat was gone. When that land bridge formed to Tasmania about 43 kya, people crossed and were able to , until all the megafauna was gone on Tasmania. They also may have worked their way through the food chain, in which the first kills were the true mother lode. Nobody even deigned to raise a spear at anything less than a until they were gone. Then they started killing smaller prey, which eventually did wise up and were harder to kill, so humans had to work at it again and the brief golden age was over. The as they shaped the new continent to their liking, maybe recreating the savanna conditions that they left in Africa, may have also been used to flush out animals if they began to avoid humans.
Except for New Guinean highlanders, initial European contact with all of those relict populations was universally disastrous, just as and elsewhere for centuries. Those initial contacts happened in anthropology’s early days, and studied the Andamans in the early 20th century, when they were tattered remnants of the people of a century earlier. The people were also devastated by European invasion. When the Dutch invaded what became South Africa, the Southern San were driven to extinction while the !Kung survived in the . Andamans, !Kung, and Aboriginal Australians all had/have strikingly similar religious ceremonies, which were marathon singing and dancing sessions that could last all night. Some rituals lasted for months. Their rituals are very likely what the first religions looked like, which were strenuous ordeals in which people reached frenzied states that left them exhausted. Today’s leading hypothesis is that those rituals created group cohesion that held their society together. The social glue of monkey and ape societies is grooming, but humans seem to have , and those early rituals further cemented the bonds.