A new study from the University of Helsinki reveals a striking example of how changing environmental conditions drive evolution. In this case, it involves elephant teeth.
The experts found that the evolutionary journey of proboscideans – the group that includes today’s elephants and their ancient kin – has been largely influenced by shifts in climate over the past 26 million years in East Africa.
In particular, the experts identified bursts of teeth evolution among elephants approximately 10 million years ago that coincided with major climate changes.
For thousands of years, the vast landscapes of East Africa have witnessed transformative changes. Among them, the cheek teeth of proboscideans stand out as a testament to adaptability.
These elephants, along with their ancestral counterparts, tweaked their diets based on the changing vegetation patterns and the climate of their habitats.
The evidence suggests that some proboscidean lineages, like choerolophodonts, began shifting to grass-rich diets as early as 23 to 11 million years ago, much sooner than previously assumed.
This dietary evolution finds a marked period around 7 million years ago in the Lake Turkana region of East Africa. Here, the burgeoning savannas – drier and flush with grasses – became the primary feeding grounds for the earliest true elephants.
“This supports the hypothesis of such regions as ‘species-factories’ where evolutionary adaptation to changing environmental conditions first centered around,” explained study lead author Juha Saarinen.
Grasses, laden with mineral-rich grains called phytoliths, pose a significant challenge. These grains lead to extensive wear and tear on teeth.
However, the choerolophodonts of the Early and Middle Miocene periods managed to adapt to these grass-rich diets with only minor modifications to their dental structures.
Fast forward to roughly 10 million years ago, and a significant climate upheaval reshaped East Africa. The true elephants, or Elephantidae, underwent a more profound dental evolution.
Their teeth, especially molars, saw increased crown heights and more ridges.
“We were able to show that the strongest peaks of drying of the East African climate during the last 7 million years correspond with evolutionary bursts in the increase of tooth crown height and the number of ridges on the molar teeth, while these evolutionary changes did not reverse during periods of less harsh climatic conditions,” said Saarinen.
“This supports earlier suggestions that adaptive traits in organisms are adaptations to extreme rather than average environmental conditions.”
A comparative analysis of vegetation and elephant diets over the past 7 million years revealed an ascending dominance of grassland habitats and grass-feeding elephants with intricate dental adaptations. Yet, this trend saw a shift roughly 100,000 years ago.
Likely due to significant global climatic fluctuations, only the modern African savanna elephant, with its less specialized teeth, endured in East Africa.
A similar ecological adaptability may explain the Asian elephant’s survival in Asia. Meanwhile, the African forest elephant found sanctuary in the forested territories of Central and Western Africa.
“The ecologically quite versatile modern elephants were the sole survivors of the tumultuous climate changes of the late Pleistocene,” said Saarinen.
“Now it’s us humans that threaten the last surviving species of this ecologically important group of animals, and we should work hard to keep them from being lost forever.”
The research is published in the journal Nature.
Proboscideans are a group of large mammals that include elephants and their extinct relatives. They are characterized by a long trunk (or “proboscis”), large tusks, and a massive body. Here are some key points about proboscideans:
Today, there are three extant (or currently living) species of elephants: the African bush elephant, the African forest elephant, and the Asian elephant.
These are two of the more famous extinct relatives of modern elephants. Mammoths were more closely related to the Asian elephant, while mastodons were a separate lineage.
The trunk is a notable feature of proboscideans and is a highly versatile organ used for breathing, smelling, grasping, and making sounds. Their tusks, which are elongated incisors, can be used for digging, lifting, gathering food, and as weapons.
Most proboscideans are herbivores, primarily eating grass, leaves, and fruits. Their molars are adapted to grind up tough plant material.
Elephants, the living representatives of proboscideans, are known for their complex social structures. Female elephants and their young live in closely-knit family groups led by a matriarch, while adult males may roam more independently or in smaller bachelor groups.
Elephants are currently facing threats from habitat loss, human-elephant conflict, and poaching for their ivory tusks. Efforts are ongoing to conserve these magnificent creatures and their habitats.
Proboscideans have a rich fossil record that traces back millions of years. Throughout their evolutionary history, they’ve exhibited a wide range of sizes, from the small-sized Palaeomastodon to the gigantic imperial mammoths.
While today’s elephants are limited to parts of Africa and Asia, proboscideans once roamed a much wider range, including North America, Europe, and other parts of Asia.