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Proboscidea: the story on HearLore | HearLore
Proboscidea
The earliest known member of the order Proboscidea, Eritherium, was no larger than a rabbit and lived in Africa approximately 60 million years ago during the Paleocene epoch. This tiny creature, weighing only around 10 kilograms, represents the humble beginning of a lineage that would eventually produce the largest land mammals to ever walk the Earth. Fossils of Eritherium were discovered in Morocco and date back to the very dawn of the Paleocene, shortly after the extinction of the non-avian dinosaurs. Despite its small size, Eritherium possessed the first hints of the specialized dental and skeletal features that would define its descendants. It had a short snout and simple teeth, lacking the massive tusks and trunks of modern elephants, yet its existence marked the first step in a 60-million-year evolutionary journey. The discovery of Eritherium in 2009 by Eric Gheerbrant fundamentally changed the understanding of proboscidean origins, pushing the timeline of the group's emergence back to the earliest days of the Paleocene and suggesting that the ancestors of elephants were once small, shrew-like creatures navigating the forests of ancient Africa.
The Giants of the Miocene
By the late Eocene, some proboscideans like Barytherium had grown to considerable sizes, reaching an estimated mass of 2 tonnes, while others like Moeritherium were suggested to have been semi-aquatic. The Miocene epoch, beginning around 23 million years ago, witnessed a dramatic expansion of proboscidean diversity and size, with groups like deinotheres, mastodons, and gomphotheres spreading across Eurasia and North America. A major event in this expansion was the collision of Afro-Arabia with Eurasia during the Early Miocene, around 18 to 19 million years ago, which allowed proboscideans to disperse from their African homeland. This geological shift opened new territories for these animals, leading to the evolution of specialized forms such as the shovel-tusked Platybelodon and the massive Stegodon. The largest known land mammal, the mammutid Mammut borsoni, is thought to have surpassed 10 tonnes in body mass, with shoulder heights exceeding 4 meters. These giants developed increasingly large tusks, with the longest ever recorded belonging to Mammut borsoni found in Greece, measuring over 4 meters in length. The evolution of these massive creatures was driven by the need to survive on vegetation with low nutritional value, leading to longer limbs, broader feet, and more specialized teeth capable of processing tough grasses and leaves.
The Trunk and The Tusk
The development of the trunk and tusks was a defining characteristic of later proboscideans, transforming them from small, shrew-like ancestors into the iconic giants of the fossil record. The skull grew larger, especially the cranium, while the neck shortened to provide better support for the massive head. The number of premolars, incisors, and canines decreased, while the cheek teeth became larger and more specialized. In Elephantiformes, the second upper incisor and lower incisor were transformed into ever-growing tusks on the upper and lower jaws, while in Deinotheriidae there were only tusks on the lower jaw. The tusks are proportionally heavy for their size, being primarily composed of dentine. In primitive proboscideans, a band of enamel covers part of the tusk surface, though in many later groups including modern elephants the band is lost, with elephants only having enamel on the tusk tips of juveniles. The upper tusks were initially modest in size, but from the Late Miocene onwards proboscideans developed increasingly large tusks, with the longest ever recorded tusk being over 4 meters long belonging to the mammutid Mammut borsoni found in Greece. The lower tusks are generally smaller than the upper tusks, but could grow to large sizes in some species, like in Deinotherium, where they could grow over 2 meters long. The evolution of the trunk allowed these animals to reach food and water sources that were previously inaccessible, giving them a significant advantage in their environments.
When did the earliest known member of the order Proboscidea live?
The earliest known member of the order Proboscidea, Eritherium, lived in Africa approximately 60 million years ago during the Paleocene epoch. This tiny creature represents the humble beginning of a lineage that would eventually produce the largest land mammals to ever walk the Earth. Fossils of Eritherium were discovered in Morocco and date back to the very dawn of the Paleocene, shortly after the extinction of the non-avian dinosaurs.
What was the largest known land mammal in the order Proboscidea?
The largest known land mammal in the order Proboscidea is the mammutid Mammut borsoni, which is thought to have surpassed 10 tonnes in body mass with shoulder heights exceeding 4 meters. The longest ever recorded tusk belonging to Mammut borsoni was found in Greece and measured over 4 meters in length. These giants developed increasingly large tusks to survive on vegetation with low nutritional value.
When did the last surviving proboscideans on Wrangel Island die out?
The population of small woolly mammoths on Wrangel Island persisted until about 4,000 years ago, making them the last of their kind. This survival was likely due to the isolation of the island, which protected them from human hunting and environmental changes that had wiped out their mainland relatives. Mammoths were among the last surviving proboscideans, with their latest survival occurring long after the extinction of other mammoth species on the mainland.
How did proboscideans disperse from their African homeland to other continents?
A major event in this expansion was the collision of Afro-Arabia with Eurasia during the Early Miocene, around 18 to 19 million years ago, which allowed proboscideans to disperse from their African homeland. Later, around 16 to 15 million years ago, they crossed into North America across the Bering Land Bridge. This geological shift opened new territories for these animals, leading to the evolution of specialized forms such as the shovel-tusked Platybelodon and the massive Stegodon.
What is insular dwarfism in the context of the order Proboscidea?
Insular dwarfism is a phenomenon where large animals evolve to become much smaller due to limited resources and the absence of large predators. This occurred primarily during the Pleistocene, when some elephant populations became isolated by fluctuating sea levels, although dwarf elephants did exist earlier in the Pliocene. Elephas falconeri of Malta and Sicily was only about 1 meter tall and had probably evolved from the straight-tusked elephant.
Several species of proboscideans lived on islands and experienced insular dwarfism, a phenomenon where large animals evolve to become much smaller due to limited resources and the absence of large predators. This occurred primarily during the Pleistocene, when some elephant populations became isolated by fluctuating sea levels, although dwarf elephants did exist earlier in the Pliocene. Elephas falconeri of Malta and Sicily was only about 1 meter tall and had probably evolved from the straight-tusked elephant. Other descendants of the straight-tusked elephant existed in Cyprus, while dwarf elephants of uncertain descent lived in Crete, the Cyclades, and the Dodecanese. The Columbian mammoth colonized the Channel Islands and evolved into the pygmy mammoth, which reached a height of about 1.5 meters and weighed around 1,000 kilograms. These dwarf elephants likely grew smaller on islands due to a lack of large or viable predator populations and limited resources. By contrast, small mammals such as rodents develop gigantism in these conditions. The discovery of these dwarf species has provided valuable insights into the adaptability of proboscideans and the unique evolutionary pressures that shape island ecosystems. The pygmy mammoth, for example, survived on the Channel Islands of California until about 13,000 years ago, demonstrating the remarkable resilience of these animals in isolated environments.
The Last Mammoths
Mammoths were among the last surviving proboscideans, with their latest survival being on Wrangel Island around 4,000 years ago, long after the extinction of other mammoth species on the mainland. At the end of the Early Pleistocene, around 800,000 years ago, the elephantid genus Palaeoloxodon dispersed outside of Africa, becoming widely distributed in Eurasia. By the beginning of the Late Pleistocene, proboscideans were represented by around 23 species, but they underwent a dramatic decline during the Late Pleistocene as part of the Late Pleistocene megafauna extinctions. All remaining non-elephantid proboscideans, including Stegodon, mastodons, and the American gomphotheres Cuvieronius and Notiomastodon, became extinct, along with Palaeoloxodon. Mammoths, however, managed to survive in relict populations on islands around the Bering Strait into the Holocene. The population of small woolly mammoths on Wrangel Island persisted until about 4,000 years ago, making them the last of their kind. This survival was likely due to the isolation of the island, which protected them from human hunting and environmental changes that had wiped out their mainland relatives. The discovery of these late-surviving mammoths has provided scientists with a unique opportunity to study the genetics and biology of these iconic animals, offering insights into the factors that led to their eventual extinction.
The Social Herds
It has been suggested that members of Elephantimorpha, including mammutids, gomphotheres, and stegodontids, lived in herds like modern elephants, with analysis of remains of the American mastodon suggesting that herds consisted of females and juveniles and that adult males lived solitarily or in small groups. Adult males periodically engaged in fights with other males during periods similar to musth found in living elephants, and these traits are suggested to have been inherited from the last common ancestor of elephantimorphs. Musth-like behavior is also suggested to have occurred in gomphotheres, indicating that social structures and reproductive behaviors were already well-established in these ancient animals. All elephantimorphs are suggested to have been capable of communication via infrasound, as found in living elephants, allowing them to communicate over long distances. Deinotheres may have also lived in herds, based on tracks found in the Late Miocene of Romania. Over the course of the Neogene and Pleistocene, various members of Elephantida shifted from a browse-dominated diet towards mixed feeding or grazing, adapting to changing environmental conditions. The social structure of these animals, with females and juveniles forming the core of the herd and adult males living on the periphery, suggests a complex social dynamic that was crucial for their survival and reproduction. The ability to communicate via infrasound would have been particularly important for coordinating movements and maintaining social bonds within the herd.
The Evolutionary Tree
Over 180 extinct members of Proboscidea have been described, forming a complex evolutionary tree that includes families such as Deinotheriidae, Mammutidae, Stegodontidae, and Elephantidae. The earliest members of Proboscidea like Eritherium are known from the Paleocene of Africa, around 60 million years ago, and the earliest proboscideans were much smaller than living elephants. By the late Eocene, some members of Proboscidea like Barytherium had reached considerable size, with an estimated mass of around 2 tonnes, while others like Moeritherium are suggested to have been semi-aquatic. A major event in proboscidean evolution was the collision of Afro-Arabia with Eurasia, during the Early Miocene, around 18-19 million years ago, allowing proboscideans to disperse from their African homeland across Eurasia, and later, around 16-15 million years ago into North America across the Bering Land Bridge. Proboscidean groups prominent during the Miocene include the deinotheres, along with the more advanced elephantimorphs, including mammutids, gomphotheres, amebelodontids, choerolophodontids, and stegodontids. Around 10 million years ago, the earliest members of the family Elephantidae emerged in Africa, having originated from gomphotheres. The Late Miocene saw major climatic changes, which resulted in the decline and extinction of many proboscidean groups such as amebelodontids and choerolophodontids. The earliest members of modern genera of Elephantidae appeared during the latest Miocene-early Pliocene around 6-5 million years ago. The elephantid genera Elephas, which includes the living Asian elephant, and Mammuthus, the mammoths, migrated out of Africa during the late Pliocene, around 3.6 to 3.2 million years ago. Over the course of the Early Pleistocene, all non-elephantid proboscideans outside of the Americas became extinct, with the exception of Stegodon. Gomphotheres dispersed into South America during this era as part of the Great American interchange, and mammoths migrating into North America around 1.5 million years ago. At the end of the Early Pleistocene, around 800,000 years ago, the elephantid genus Palaeoloxodon dispersed outside of Africa, becoming widely distributed in Eurasia. By the beginning of the Late Pleistocene, proboscideans were represented by around 23 species. Proboscideans underwent a dramatic decline during the Late Pleistocene as part of the Late Pleistocene megafauna extinctions, with all remaining non-elephantid proboscideans and Palaeoloxodon becoming extinct, with mammoths only surviving in relict populations on islands around the Bering Strait into the Holocene, with their latest survival being on Wrangel Island around 4,000 years ago.