The Megafauna of the Pleistocene
In the geological era preceding the current one, animals that developed on Earth had nothing to envy of the most ancient dinosaurs. Why did they get so big? Why did they become extinct? And did gigantism also affect Man?
"Megafauna" is an aptly chosen paleontological term that refers to all those animals which, for reasons not entirely understood, developed unusually large sizes during their time on Earth. For instance, megafauna included giant dragonflies, scorpions, millipedes, and cockroaches that inhabited the Earth between the Devonian and Carboniferous periods, before the arrival of vertebrates; megafauna also included the famous dinosaurs, about which much is known (or believed to be known); and finally, megafauna are those animals from the Tertiary and Quaternary periods that reached enormous sizes and about which, unfortunately, few people can say much.
It is regrettable that Science does not direct its attention to these gigantic beings that lived only a few hundred thousand years ago, an infinitesimal span of time on the geological scale. These gigantic animals, in almost all cases, came into contact with early humans, indelibly marking the collective memory of our species. Fossil discoveries certainly tell us a global story, a phenomenon of gigantism that affected the entire planet, as megafauna were present on all continents, including the remote and isolated Australia. The reference period is between the Pliocene and, especially, the Pleistocene, the penultimate geological era of Earth (the last being the current Holocene). The Pleistocene conventionally begins 1.8 million years ago and ends about twelve thousand years ago: during this period, Earth was characterized by four major glaciations and as many interglacial periods.
At this very moment, truly mighty animal species were born, comparable in size to the dinosaurs that lived sixty-four million years earlier. After the extinction of the great reptiles (although scientifically it should be noted that they were not reptiles), the Tertiary period witnessed the dominance first of large predatory birds and then of mammals. It was these mammals that, in the last million years, developed absolutely incredible varieties, ranging from gigantic carnivores to herbivores like veritable mountains of flesh, virtually invulnerable to the weapons available to humans of the time, namely bows, arrows, and spears.
Colossal Animals
The list of giant mammals from the Pleistocene is astonishing for the variety and power of these animals. We all know the mammoth, the woolly rhinoceros, the cave bear, and the saber-toothed tiger: these are prehistoric species often depicted alongside our ancestors in Stone Age reconstructions. However, the proportions are often wrong, and we don't realize their actual size. The cave bear, for example, was as tall as a modern grizzly but much more robust and competed with humans due to its habit of seeking shelter in caves. This difficult coexistence led humans to become prey to the bear's terrible claws, even though its diet was predominantly vegetarian.
Certainly not vegetarian was the Smilodon, or Saber-Toothed Tiger. To be precise, this term is also attributed to other species of the Machairodont family, such as Machairodus and Homotherium, fearsome felines characterized by their significantly elongated front fangs. The Smilodon was up to four meters long, much longer than the modern tiger (with which, despite the name, it was not related), stood one and a half meters tall at the shoulder, and had 20 cm long canines, used like real knives. These felines were extremely robust and courageous, attacking prey larger than themselves, weighing half a ton; they would inflict deep wounds and then leave their targets to die from blood loss. Like the cave bear, the Smilodon also became extinct 10,000 years ago.
In America, there also existed a giant coyote, the Dire Wolf, weighing 100 kg, which coexisted with much smaller but more socially organized wolves. Other fearsome predators include Dinofelis, a jaguar with elongated teeth that preyed on Australopithecines in Africa, and the Cave Lion, often depicted in cave paintings as a human adversary, three and a half meters long and weighing 350 kg.
Predators of such size were matched by even larger herbivores. The Mammoth, in its largest species, reached four meters in height at the withers, six to seven meters in length, and weighed eight tons, making this mammal a true living tank. Its tusks, five meters long, also provided it with great active defense. A direct competitor of the mammoth was the woolly rhinoceros, four meters long, two meters tall at the withers, and weighing over two tons. It had two horns on its forehead, the longer of which measured one meter. Even larger was the Elasmotherium, the mythical unicorn of legends: a colossus six meters long, 2.5 meters tall at the withers, and weighing five tons. The Elasmotherium had a single horn two meters long, and although it was closely related to the rhinoceros, it had a slender build and long legs suited for fast running. Despite its size, it was an agile animal, and a charge from a herd of Elasmotheria could even scare off mammoths.
Other colossal animals were the deer: the Giant Deer was impressive for the size of its antlers, which spanned up to three and a half meters. The animal had a body proportionate to its antlers, standing over three meters tall. This is a key characteristic to understand the Pleistocene megafauna: they were not proportionate beings but rather like enlarged versions of current animals (or more accurately, current animals are scaled-down versions). An example is given by the Castoroides, also known as the Giant Beaver, which was two and a half meters long and weighed one hundred kilograms; its incisors were fifteen centimeters long and capable of gnawing even sequoias. Apart from its size, the modern beaver has the same proportions, being a charming animal sixty centimeters long and weighing about ten kilograms! Similar examples can be made for the Splendid Armadillo, which was two meters long, the Argentine Giant Sloth, and the Southeast Asian Emperor Rat, which was as large as a bull.
Not to mention the birds: from the Elephant Bird of Madagascar to the Moa of New Zealand, including the Haast's Eagle. The first two birds, similar to ostriches but weighing half a ton, reached three to four meters in height and had thighs like those of a Tyrannosaurus. Their eggs had a circumference of one meter. Haast's Eagle, on the other hand, was the predator of the moa, diving on them at a speed of 100 km/h with the power of a modern missile, given its weight and four-meter wingspan, comparable to that of a hang glider.
Haast's Eagle is certainly not the only example of a gigantic bird, as it was surpassed by the Osteodontornis, a type of albatross that lived 12 million years ago with a six-meter wingspan, and the Argentavis, a bird of prey as large as a small plane that lived in the Andes until the mid-Pleistocene. In Hawaii, starting three million years ago, there lived a giant duck, the Moa-nalo, two meters tall, while in Peru, there was a giant penguin, 1.8 meters tall, with a spear-like beak twice the length of its skull.
Reptiles deserve a separate discussion, as the forms of gigantism created frightening beings that, in some cases, still exist today, such as the anaconda, the Galápagos giant tortoise, and the reticulated python.
Giants under the Ice
It is clear, therefore, that gigantism was a phenomenon that affected many species, and scholars hypothesize that the cause of this generalized enlargement is due to a biological law, Bergmann's Rule, which states that in cold climates, animals tend to enlarge to better preserve internal heat. Contrary to what one might think by observing humans living in cold climates, such as the Inuit who are small and slender, animals with a large body surface relative to their mass can better retain heat and stay warmer internally. This is the opposite of tropical climates where a large mass requires "radiator" devices to dissipate excess heat. This theory would explain megafauna as a consequence of the Pleistocene glaciations. But what foundation does this hypothesis have?
We live in the Holocene, the last geological era that began at the end of the last glaciation. We are thus witnesses to an interglacial period in which fauna and flora are reorganizing after the climatic upheavals of the last glaciation, which certainly profoundly influenced humans, passing into collective imagination as the Great Flood. Indeed, we must remember that during the Pleistocene, the level of all the seas on the planet dropped to 130 meters below the current level. Ten thousand years ago, the sudden melting of immense ice masses, such as the one that occupied the North Sea, gave rise to cataclysmic floods, which might even have shifted the Earth's axis.
This was an epochal event, but certainly not the first and only one in Earth's history. At least four other glacial periods have occurred in the history of our planet. The first originated in the very distant eon known as the Proterozoic, 2.7 billion years ago, and lasted four hundred million years. But it was the second glaciation that was truly memorable (and devastating): 800 million years ago, during the Cryogenian, the Earth froze completely, up to the equator. This formed what geologists call "Snowball Earth." This glaciation lasted 200 million years, and at its end, the explosion of life in the Precambrian filled the seas with organized multicellular species. But the causes of that apocalyptic freeze have not yet been discovered.
The third glaciation was certainly smaller and occurred during the Ordovician, an era spanning from 460 to 430 million years ago. The fourth glaciation occurred between the Carboniferous and Permian periods, from 350 to 280 million years ago, paving the way for the gigantism of dinosaurs and their related animals. Then nothing more until about 30 million years ago when the temperature began to drop across the globe.
The fifth glaciation is a succession of smaller glacial epochs, interspersed, as mentioned, with warmer interglacial periods. Regarding the Pleistocene, the last million years saw four more significant cold epochs and three less imposing ones. The main ones are named Günz (from 780,000 to 620,000 years ago), Mindel (from 455,000 to 240,000 years ago), Riss (from 200,000 to 120,000 years ago), and Würm (from 70,000 to 10,000 years ago). The last glaciation is also called the Würmian and is particularly important for its presence in the ancient history of mankind. Now, what caused these cold periods? The theories are numerous and controversial: it is probably a combination of several factors, including an increase in carbon dioxide and methane, the precessional movements of the Earth around the Sun, encounters with layers of interstellar clouds during the Sun's orbit in the Milky Way, the absence of sunspots, and even the arrangement of the continents and the interruption or continuation of warm currents like the Gulf Stream, possibly induced by shifts in the geographical poles. Some suggest that massive eruptions cooled the Earth, such as the Toba catastrophe, which some believe generated the Würmian 75,000 years ago. Whatever the reason, the Pleistocene glaciation brought the average temperature down to 14°C, from the 22°C that the Earth currently has.
However, it is clear that tropical areas were reduced but did not disappear entirely: at the equator, the climate was not different from the current one, and despite official theories and Bergmann's Rule, it is surprising to find enormous animals even in the tropics or in warm areas like Australia.
Gigantism of Australian Fauna
Australia, 70,000 years ago, had a warm climate, not desert-like but similar to the modern African savanna. Its isolation led to the creation of giant species from those present: thus, the giant koala developed, along with various species of giant kangaroos (including one that stood three meters tall), the giant parrot, and even the small wombats, which are today the size of a squirrel but were as large as calves back then. But other species also emerged, far more terrifying than the current ones: such as the Marsupial Lion, a carnivore comparable in size to modern lionesses and a relative of the Tasmanian Tiger, which went extinct in 1936.
The largest Australian animal was the Megalania, a species of Komodo Dragon that was eight meters long and, in a sense, a reenactment of the lizards of the Mesozoic Era, weighing two tons. Another colossus was the Diprotodon, a marsupial halfway between a koala and a hippopotamus, two meters tall, three meters long, and weighing four tons; not to mention the Genyornis, called the Thunder Bird by the Aboriginal people, the Australian version of the Moa. The Quinkana, on the other hand, was a land crocodile, an adept walker, ten meters long; the Meiolania was a horned tortoise three and a half meters long, the size of a small car. Like other reptiles, it became extinct very late, about two thousand years ago. But there are countless examples of cyclopean Australian fauna.
If megafauna developed even in warm and fertile Australia, it is evident that gigantism was not caused by the cold, but by another global factor. The causes of the disproportionate growth of animal and plant organisms can be attributed to two fundamental extreme factors: the first of these is reduced gravity.
Reduced Gravity?
An American catastrophist scholar, Ted Holden, has attempted to analyze the gigantism of dinosaurs to understand what caused it. Scientists have always told us that dinosaurs were immense due to two main reasons: the enormous amount of food and the presence of a humid climate, with lakes and rivers supporting the oversized bodies of these giants. However, the discovery of terrestrial footprints by even the largest herbivores, which in the case of the Amphicoelias reached sixty meters in length, has rendered this hypothesis entirely incorrect. Dinosaurs were not amphibians, but terrestrial, warm-blooded, and likely had fur; they probably also had the ability to reproduce like mammals.
But if we analyze their muscular structure, as Holden argues, we realize that it was inadequate to move the bulk of those animals, while it would be suitable for a planet with gravity equal to 1/3 or 1/4 of the current gravity. Some catastrophists suggest that gravity is not constant, as stated by Physics, but is variable, according to the typical view of the Electric Universe Theory. Although interesting, the hypothesis of an electromagnetic origin of matter has shown various gaps and is not currently sustainable: moreover, reduced gravity would have led to the overflowing of the oceans and the submersion of all emerged lands.
Furthermore, catastrophist theories do not account for the periodicity of megafauna: let's not forget that after the disappearance of dinosaurs, for millions of years, the sizes of animals were tiny. The second factor triggering gigantism is radiation. Radiation, for example, causes anomalies in the production of growth hormone, and it is no coincidence that in the Red Forest of Chernobyl, affected by the radioactive cloud that escaped from reactor number 4 of the nuclear plant in 1986, plants developed leaves and stems twice as large as normal, only to die later. The fauna was also affected by deformities and mutations, but control measures implemented by authorities and researchers prevented these new life forms from interbreeding with uncontaminated animals.
Was global gigantism caused by radiation? The explosion of the Vela X supernova exactly in 10000 BCE caused a shower of radiation on Earth that severely affected all animals, but it does not seem that this caused the extinction of all giant species: many, even among the largest, survived for several thousand years in our era.
Giant Humans
The presence of giant humans in the myths and legends of all the peoples of the world would seem to confirm what should be a logical consequence. Faced with such beings, modern humans would have had no chance, yet surprisingly in the past of our species, we find ancestors who were tall, robust, and extremely strong. Consider the Neanderthal, relatively short (1.70 m) but massive and powerful; consider the Cro-Magnon, over two meters tall and probable builders of the megalithic temples; and even Homo Erectus, wrongly considered nothing more than a large ape, but actually an intelligent being equipped with effective weapons, fire, organized language, and a worthy adversary of mammoths and saber-toothed tigers.
The existence of humanoid giants is confirmed by science through the last representative of the megafauna, the Gigantopithecus.
This primate was 3-3.5 meters tall and weighed 500 kg, living in central-southern Asia and sharing its habitat with Homo Erectus. The Gigantopithecus was related to the orangutan and fed like the modern panda on bamboo shoots; surviving specimens might have given rise to the legends of Yetis and Bigfoot. Naturally, the existence of giants of our species would have been equally possible, and there are numerous pieces of evidence to support this, although official history categorically denies it.
Nonetheless, according to tradition, the giants were exterminated by various peoples, such as the Amorites who were defeated by the Israelites of Moses with the help of the Ark of the Covenant. In Italy, the indigenous Lestrigons, depicted as cannibals and savages, were defeated by the Sicani. These legends have led many scientists to speculate whether humans might have been the cause of the extinction of the large animals as well. The diet of our ancestors was certainly omnivorous, with a significant portion of calories coming from animal sources, but hunting megafauna was not a simple task. In the case of the Giant Deer, which survived a few thousand years into the Holocene in Ireland and the Isle of Man, the cause of its disappearance was due to a calcium deficiency in the bones, which led to progressive osteoporosis in the males.
However, humans did not inhabit those lands permanently before 7000 BCE, making extinction due to artificial causes impossible. The Moa survived in New Zealand for eleven thousand years and coexisted with the Maori until its disappearance around the 14th century. The reality is that it was a combination of these factors that caused the end of the megafauna. The end of the Pleistocene suspiciously coincides with the Vela X supernova, of which today remains a large, faint nebula and a pulsar in the namesake constellation. Therefore, there may be a connection, but it is necessary to consider how the supernova's radiation shrank living beings, instead of enlarging them. So, could it be that we, the "small" ones, are the anomaly?
