An extinct species of dwarf elephant from Sicily halved in height and shrank by almost 85 per cent in body mass over a period of just 350,000 years after evolving from one of the largest land mammals that ever lived, researchers have found.
Palaeoloxodon mnaidriensis, which became extinct around 19,000 years ago, lost more than 8000 kilograms in weight and almost 2 metres in height after diverging from the much larger straight-tusked elephant Palaeoloxodon antiquus, which was almost 4 metres tall and weighed 10,000 kilograms.
An international team of researchers analysed molecular evidence from the remains of a dwarf elephant unearthed in Puntali cave in Sicily, Italy, to calculate the dwarfing rate of the species.
The specimen is thought to be between 50,000 and 175,000 years old. The researchers examined a piece of petrous bone – part of the skull that holds the inner ear – which is known to preserve DNA better than other parts of the skeleton.
They found that the dwarf elephant reduced in weight and height by up to 200 kilograms and 4 centimetres per generation, over a maximum period of about 352,000 years.
To put this in context, the researchers say the size reduction of P. mnaidriensis is comparable to modern humans shrinking to approximately the size of a rhesus monkey.
“The magnitude of dwarfing resulting from this rapid evolutionary process is truly striking, resulting in a loss of body mass of almost 85 per cent in one of the largest ever terrestrial mammals,” says team member Axel Barlow at Nottingham Trent University, UK.
“As the descendants of giants, the extinct dwarf elephants are among the most intriguing examples of evolution on islands,” he says.
P. antiquus lived on the European mainland between 40,000 and 800,000 years ago and is thought to have colonised Sicily some time between 70,000 and 200,000 years ago.
The researchers believe that the dwarfing process began once the Sicilian elephant diverged from its mainland relative. Living in an insular and isolated environment accelerated the process of evolution for the island creatures and a new species, P. mnaidriensis, soon emerged.
“By combining ancient DNA with palaeontological evidence, we can show the timing of observable evolutionary changes with greater accuracy,” says Barlow.
Previous research suggests that mammals on islands evolve around three times as fast as their continental counterparts. This rapid evolution could be explained by small initial populations and conditions that create different selection pressures than those experienced on the mainland.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2021.05.037
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