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11-28-2023

How elephants got their incredible iconic trunks

Researchers have recently shed light on how ancestral elephants developed their dexterous trunks, a significant evolutionary adaptation. The study offers valuable insights into the feeding behaviors of extinct longirostrine elephantiforms — elephant-like mammals known for their elongated lower jaws and tusks.

Evolution of longirostrine gomphotheres

Longirostrine gomphotheres, part of the proboscidean family, are known for their prolonged evolutionary phase featuring an exceptionally elongated lower jaw.

This fascinating study was crucial for understanding the dynamics behind the evolution of the extended lower jaw and lengthy trunks in these elephant-like animals. Longirostrine gomphotheres lived during the Miocene epoch, approximately 11-20 million years ago.

“During the Early to Middle Miocene, gomphotheres flourished across Northern China,” says lead author Dr. Chunxiao Li, a postdoctoral researcher at the University of Chinese Academy of Sciences, Beijing, China.

The research offers persuasive proof of the variety in these “trunk” features among longirostrine gomphotheres, as well as their probable adaptive responses to worldwide climate shifts.

Li continued, “Across species there was huge diversity in the structure of the long mandible. We sought to explain why proboscideans evolved the long mandible and why it subsequently regressed. We also wanted to explore the role of the trunk in these animals’ feeding behaviors, and the environmental background for the co-evolution of their mandibles and trunks.”

Studying elephant trunk evolution

Li and colleagues employed comparative functional and eco-morphological investigations, along with a feeding preference analysis. From this, they reconstructed the feeding behavior of three major families of longirostrine gomphotheres: Amebelodontidae, Choerolophodontidae, and Gomphotheriidae.

Examining crania and lower jaws from different museums revealed variations in mandible and tusk structures, indicating diverse appetites.

The team’s analysis of enamel isotopes helped identify the ecological niches of the three families. Choerolophodontidae lived in relatively closed environments. Amebelodontidae family members, like Platybelodon, inhabited open habitats like grasslands. Finally, Gomphotheriidae occupied a niche between these environments.

Implications of elephant trunk evolution

A Finite Element analysis provided insights into the advantages and disadvantages of mandible and tusk structures among the three family groups. This effort revealed specializations for cutting different types of vegetation.

The study also found variations in the evolutionary stages of the trunk among these families. Additionally, they uncovered implications for their feeding abilities and ecological adaptations. The trunk’s development paralleled the mandible’s evolution, indicating a co-evolutionary relationship.

Furthermore, the Mid-Miocene Climate Transition, which led to regional drying and expansion of open ecosystems, had a significant impact on these species. The study suggests that Platybelodon’s coiling and grasping trunk allowed it to thrive in open environments. This trait is not developed in other trunk-bearing animals like tapirs.

Further elephant trunk research

Co-author Ji Zhang is associate professor of structural engineering at Huazhong University of Science and Technology, Wuhan, China. Zhang highlights the importance of using modern computational mechanics and statistics in paleontological research, bringing a cross-disciplinary approach to understanding these ancient creatures.

“Our cross-disciplinary team is dedicated to introducing multiple quantitative research methods to explore paleontology,” says Zhang. “Modern computational mechanics and statistics have injected new vitality into traditional fossil research.”

The main limitation in their research is the lack of comparison with the development of gigantism and long limbs in proboscideans from the same period. Further analysis could enhance understanding of how changing feeding behaviors related to differences in body shapes and sizes.

Evolutionary journey of proboscideans

Dr. Shi-Qi Wang is the senior author and professor at the Key Laboratory of Vertebrate Evolution and Human Origins of the Chinese Academy of Sciences. He concludes that multiple eco-adaptations contributed to the diverse mandibular structure in proboscideans. The elongated mandible initially served as the primary feeding organ, paving the way for the development of the long trunk.

“Our findings demonstrate that multiple eco-adaptations have contributed to the diverse mandibular structure found in proboscideans,” concludes Wang. “Initially, the elongated mandible served as the primary feeding organ in proboscideans, and was a prerequisite for the development of the extremely long trunk. Open-land grazing drove the development of trunk coiling and grasping functions, and the trunk then became the primary tool for feeding, leading to the gradual loss of the long mandible. In particular, Platybelodons may have been the first proboscidean to evolve this grazing behavior.”

The evolution of open-land grazing led to the modern day elephant trunk becoming the primary tool used for feeding. Over time, this adaptation resulted in the gradual loss of the long mandible. Platybelodons may represent the first proboscideans to evolve this grazing behavior.

In summary, today’s elephants use these versatile organs for a myriad of tasks, including breathing, communicating, grasping objects, and drinking. They have millions of years of evolution to thank for their amazing and iconic trunks.

The full study was published in eLife Sciences.

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