Did megatheans, mastodons and other giant mammals become extinct because of humans?

A kind of spear point, carved in stone and commonly called “Fishtail”, is capable of causing very serious injuries in large animals.

It has long been known that these 11,000- to 13,000-year-old points, found at multiple archaeological sites in South America, were contemporaries of the South American megafauna. However, the theory that humans could be responsible for a paleontological event as transcendental as their extinction – postulated in a previous investigation – required more specific evidence.

A new study carried out by scientists from the National Council for Scientific and Technical Research (CONICET), evaluates this hypothesis and its results provide an answer.

The main argument in favor of this idea is given by an interesting chronological coincidence: the disappearance of this fauna began 12,900 years ago, just a little after the 13,000 years in which the Fishtail points are located in time, which would indicate that They were used for hunting. Added to this is another geographic overlap, since the projectiles analyzed come from the same sites where the megafauna inhabited. But what was the central limitation of the hypothesis so far? The little direct evidence, that is, the few fossil remains found with clear signs of having been hunted with these weapons.

“For us, this issue is only apparent and does not represent any inconsistency with the hypothesis,” says Luciano Prates, CONICET researcher at the Faculty of Natural Sciences and Museum of the National University of La Plata (FCNyM, UNLP) and first author of the work. . “What happens in terms of direct evidence is that it is very difficult to find it because these events happened in a very short period of time to be visible in the fossil record. In addition, there are very few well-preserved archaeological sites, so the finding should combine both factors of space and time”, describes the expert.

In this scenario, the main question to be answered in the new study was raised: were the Fishtail points specifically designed, developed and used to kill these large animals? In order to find out, they evaluated the morphological and functional characteristics of these and other weapons from the same region and compared them with the dimensions of the animals that inhabited this territory during the mentioned period, even reaching up to 7,000 years before the present, when it ends. extinction of the last specimens. What they discovered is revealing: the size and damage capacity of the tips vary at different times and places, and in turn these changes are related to the weight and volume of the different prey available in each one.

Recreation of the first humans in America cooking in the shell of a glyptodont, represented in a wall painting in the central hall of the Museo de La Plata. (Image: courtesy of the researcher)

Diego Rivero, CONICET researcher at the Institute of Historical Studies (IEH, CONICET-CEH), was in charge of carrying out the analysis of the materials; about 130 Fishtail projectile points from 60 archaeological sites, as well as about 300 other types. To evaluate its efficiency and lethality, the specialist used indices that take into account the width and thickness of the tools. “The wider the tip, the more damage it causes to the tissue and produces significant bleeding that causes the animal to quickly collapse. Now, if a point is too wide and too thin it becomes brittle and then when it hits it breaks, so it takes a great deal of skill and expertise to get an efficient ratio of width to thickness that gives the maximum benefit to the weapon. . In that sense, the study showed that the Fishtails had optimal efficiency and those who made them were excellent carvers”, he comments.

The researchers estimated for the Fishtail a minimum penetration range of 20 centimeters and up to 25 percent more damage capacity than the rest of contemporary and later points, which makes them the most lethal of all. “Regarding the size variation, we found that the smallest were located in Patagonia, where there were American horses, camelids and milodons, evolutionary relatives of the current sloths. On the other hand, the largest coincide with the Pampas and Andean regions, areas precisely inhabited by larger species such as mastodons, similar to mammoths, and megatheriums, giant herbivores that existed at that time,” says Rivero.

The measurements of the tips analyzed range from 5 to 6.3 centimeters long, 2.5 to 3.03 wide, and a thickness of 0.56 to 0.66. The largest found is far from that average: it is 18.8 centimeters long by 7.2 wide and 1.1 centimeters thick. “At the same time that the megafauna disappears, the trail of these spikes is also lost, and those that replace them are much smaller, just like the animals that remain,” adds Prates. According to what the authors of the study postulate, the humans of those times would not have acted as predators on all the megafauna -of which some 80 genera have been described-, but specifically against 6 or 7 main species and that this, added at a very slow rate of reproduction, it could have generated a disaster in the entire food chain.

“This work strongly suggests that these points were a specific revolutionary technology to hunt megafauna”, emphasizes Iván Pérez, a CONICET researcher at the FCNyM and another of the study’s authors, and continues: “When these species disappear, the Fishtails are replaced in each region by points that not only have less damage capacity, but also vary according to the size of the new prey available, for example vicuñas and guanacos.” These results – the specialists emphasize – “in some way are in line with the idea that the human being, through the use of these spear or javelin points, was a central actor in the extinction of these large South American mammals at the end of the Pleistocene , a geological epoch that is located between 2.59 million years and 11,700 years old.

The study is titled “Changes in projectile design and size of prey reveal the central role of Fishtail points in megafauna hunting in South America”. And it has been published in the academic journal Scientific Reports. (Source: Mercedes Benialgo / CONICET. CC BY 2.5 AR)