Today only three species are left – but once there was an enormous variety of elephants, mastodons and co. What led to the rise and fall of the more than 180 species of proboscis in evolutionary history and what role humans played in the final decline is now highlighted a study. Geological events such as the shifting of continental plates and global environmental changes were therefore behind the evolutionary success, but also the failure of the massive herbivores. In the late Pleistocene, the “human predator” only met the last survivors of a major wave of extinction, the scientists report.
The trunk animals still have a record holder to offer: the African elephant is the largest land mammal of our time. There are also two other species – the Asian elephant and the forest elephant. But this is only the modest remainder of the once great diversity of the proboscidea, which, in addition to the elephants, also included the well-known groups of mammoths, mastodons, stegodons and deinotheria. More than 180 species of proboscis are known from fossil finds that once inhabited Eurasia, South America and North America. It was already becoming apparent that the development of these animals, which lasted around 60 million years, was marked by ups and downs.
An international team of paleontologists has now devoted the most detailed analysis to date to this topic. The scientists evaluated fossil collections from museums around the world – from the Natural History Museum in London to the Paleontological Institute in Moscow. By taking into account numerous known influencing factors in the history of the earth, they finally developed models for the development of the proboscis, from which tendencies and their backgrounds emerge.
Career after continental union
As the researchers report, in the first 30 million years of their history the proboscis were restricted to Africa and Arabia, which at that time formed a common continent that was not connected to Asia as it is today. Until then, these animals had evolved slowly, and the few species that existed were quite similar ecologically. “Most of the proboscis during this period were inconspicuous herbivores that often only reached the size of a wild boar. A few species were already as big as a hippopotamus, but none of them looked much like elephants, ”says co-author Zhang Hanwen from the University of Bristol.
The great career of this group of animals only began with the connection of Afro-Arabia to Eurasia about 22 million years ago, report the paleontologists. So the proboscis could spread and fan out. “If the connection between Afro-Arabia and Eurasia had not taken place or had taken place at a different point in time, the evolutionary history of the proboscis would have been radically different,” says co-author Fernando Blanco from the Museum für Naturkunde Berlin. The new challenges that the animals faced outside of Afro-Arabia resulted in them giving birth to many new species. It was the golden age of the proboscis, in which they also grew into giants, say the researchers.
“At some times more than 30 species of these giants lived on the planet at the same time, and many ecosystems were so productive and ecologically complex that it was not uncommon for three or more species of proboscis to live together in the same ecosystem,” says lead author Juan López Cantalapiedra from Alcalá University in Madrid. A special feature of the biodiversity was the extremely diverse tooth shapes, including strange, shovel-shaped tusks. “The diversity reduced the competition between the species and enabled several of them to coexist in the same ecosystem,” says Blanco.
How the golden age ended
The paleontologists report that the end of the great diversity will be seen around seven million years ago. At that time, savanna ecosystems spread across all continents and so many of the proboscis, which were adapted to life in forested areas, disappeared. In addition to the losses, there were also new developments: Species emerged that were able to feed on less nutritious plant material such as wood and, above all, grass, as is typical for savannahs. Today’s elephants are among the evolutionary newcomers of this era, the scientists report.
But the beginning of the Ice Ages presented the proboscis again about three million years ago with challenges that many representatives were not up to: In Eurasia and Africa the extinction rate quintupled due to climatic changes. This trend then intensified again sharply 160,000 and also 75,000 years ago in Eurasia and America. The surviving species were forced to adapt to the new, barren habitats. The most extreme example was probably the woolly mammoth. “It is important to note that the times do not date specific extinction events, but rather represent points at which the proboscis were exposed to a higher risk of extinction,” says Cantalapiedra.
But did people play a role in this? According to the researchers, their data reveal the major influence of environmental changes: the analyzes show that the various phases of extinction were associated with the decline and rapid fluctuations in global temperatures as a result of the ice ages, and not with the appearance of humans. “However, that does not mean that we have conclusively refuted human involvement. In our models, however, it becomes apparent that modern humans only settled on the respective land masses after the risk of extinction for proboscis had already escalated, ”says Zhang. In the end, however, the “human predator” could well have represented another critical factor: “The influence of our ancestors probably at least contributed to the extinction of the few surviving species, such as the woolly mammoth,” says Cantalapiedra.
Source: University of Bristol, Museum für Naturkunde Berlin, specialist article: Nature Ecology & Evolution. doi: 10.1038 / s41559-021-01498-w