Island life
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Like in the TV series Lost, when you live on an island, things can get more than a little weird. We’re not talking about spooky supernatural stuff here, but the unexpected appearance of giants and dwarves.
The idea that when confined to an island, small species can get big and big species can get small, is known as Foster’s rule. In a paper published in the journal Nature in 1964, mammologist J. Bristol Foster compared over 100 island species to a mainland equivalent and found that the species in some families (mainly rodents) appeared to be larger on islands while others, like ungulates and carnivores, ended up smaller.
This so-called insular gigantism, he proposed, would occur when a species found its way to an island only to discover an absence of predators, while insular dwarfism would be the consequence of a species ending up on an island where the resources just weren’t enough to keep them in the manner, size-wise, to which they’d become accustomed.
Some of the most interesting cases of island gigantism and dwarfism were found by Welsh palaeontologist Dorothea Bate, who got a job at the Natural History Museum in 1898 and was probably the first woman ever employed as a scientist by the institution.
In a skirt, boots and a wide-brimmed hat, Bate worked her way through the deposits in mountain and coastal caves on Mediterranean islands to reveal evidence of peculiar Pleistocene animals, including a species of unusually large mouse on Crete, a huge, possibly flightless swan on Malta with a wingspan of around 3 metres, massive, fiercely-toothed shrews on Corsica and other islands, and a giant dormouse on Majorca that would have been about the size of a grey squirrel.
Even more exciting – not to mention cute – were Bate’s descriptions of island dwarves. In 1902, Bate was in Cyprus looking for fossils in the Kyrenia hills, which run along the north coast of the island.
“Every day she climbed and crawled into dozens of caves, peering by the light of her candle into crevices and fissures, or scraped in hot sunshine in crumbled rock and earth at the foot of cliffs,” wrote Karolyn Schindler in her biography, Discovering Dorothea.
After weeks of searching, Bate came across a tiny tooth. Then a small, curiously curved tusk. She had discovered the preserved remains of a mini elephant. Its ancient ancestor presumably reached Cyprus as a full-sized, straight-tusked elephant-like beast when sea levels were low, but being trapped in this minimalist mountainous environment natural selection quickly whittled it down to size. A fully grown adult Cyprus dwarf elephant would only have reached up to your waist and probably weighed around 200 kilos - just 2% of the body mass of its 10-tonne elephantine ancestor.
The remnants of other similarly dwarfed elephants and hippopotami have been found on just about every island in the Med. These make for wonderful summer holiday destinations, but I think we can all agree the experience would be better still if the tiny elephants and hippos that roamed these rugged landscapes until around 11,000 years ago were still with us today.
Analysis of ancient DNA recovered from the remains of different extinct dwarf elephant lineages paints an intriguing evolutionary picture. Based on comparing fragments of a gene called cytochrome B, Bate’s Cyprus dwarf elephant appears to be most closely related to Indian elephants, while the dwarf elephant from Crete is clearly some kind of mammoth.
This suggests that there weren’t just pygmy elephants but pygmy mammoths too, meaning that the dwarf species that once lived on the Mediterranean islands could each be independent illustrations of the evolutionary imperative to downsize. It was only the smallest individuals, with the most restrained ecological footprint, that were able to survive long enough to reproduce.
Based on a significant haul of fossils from the Spingallo caves in the east of Sicily, it looks like the secret to the evolution of these mini elephants may have been reaching sexual maturity very quickly, at 3- to 4-years-old, rather than 11 to 15, as is the case for African elephants.
This so-called progenesis was probably also accompanied by a shorter pregnancy of six months, compared with almost two years for modern elephants, and popping out litters of several baby dwarves rather than the typical singleton. From the abundance of juvenile bones in the Spingallo deposits, it looks like calf mortality was high, but natural selection clearly favoured those elephants that bought more tickets in the reproductive lottery, increasing the chances that at least some of them would be winners.
At the same time as Dorothea Bate was travelling in the Mediterranean in search of over- and undersized mammals, another colourful character was finding examples of island dwarfism without even setting foot on a boat.
Baron Ferenc, or Franz, Nopcsa von Felső-Szilvás was a Hungarian aristocrat born in 1877, who grew up in Transylvania, in what’s now Romania.
Gifted with a scientific mind and an adventurous spirit, Nopcsa not only gained a PhD in geology, focusing on mapping the area surrounding his family estate, but also found time to smuggle weapons for the Albanian resistance fighting against the Turks, work undercover as a spy in the World War One, be the first person in history to hijack an aircraft, and jack in his job as head of the Hungarian Geological Institute to ride around Europe on a motorbike with his male lover (who he also hired as his secretary) looking for fossils.
But it was the strange ancient bones he found on his family estate back in 1895 that cemented his ideas about island dwarfism. The fossils turned out to have come from a sauropod dinosaur from the late Cretaceous period, of the same family as well-known giants like Diplodocus, Brontosaurus and Apatosaurus. These are huge, pillar-legged, necky beasts more than 25 metres long and estimated to have weighed almost 15 tons. Nopcsa’s Magyarosaurus - literally translated as Hungarian lizard - were tiny by comparison. Think of a dinky Diplodocus, with adults measuring just 6 metres long and weighing in at around 1 tonne.
Nopcsa was way ahead of his time in suggesting that his ancestral home had once been an island, leading to downsized dinos. But there is now compelling evidence that in the Late Cretaceous when Magyarosaurus was a thing, most of what we now call Europe was submerged beneath a body of water known as the Tethys Ocean with today’s higher ground forming islands, including the ancient island of Hateg where tiny dinosaurs once roamed and on which Nopca’s well-heeled ancestors built their home.
But while both Bate and Nopcsa were convinced of the theory of insular dwarfism, they may have been surprised to know that the transforming effects of island life might have come closer to our own species than anyone expected.
In 2004, scientists announced the discovery of some very small, very old, but very human bones in a cave on the Indonesian island of Flores. Homo floresiensis – aka “the Hobbit” – was just one metre tall and weighed less than 30 kilos. This and another haul of some much older bones suggests these small hominids were present on Flores for a long time, between hundreds of thousands and tens of thousands of years ago.
Even more recently, another diminutive human has turned up on a southeast Asian island, Luzon in the Philippines. It’s hard to put a height on Homo luzonensis, as it’s known, from just a handful of hand, foot, and thigh bones and teeth, but like the pint-sized elephants on the Mediterranean islands, its existence does suggest that human species – when isolated on islands – may have shrunk more than once.
Still, we should be wary of assuming that every example of an island-dwelling giant or dwarf has come about because of the demands of island life. Take the hulking giant tortoises of Galapagos. With a carapace typically a metre or more in length and some of the island populations able to extend their limbs and stretch their necks to reach to a browsing height of almost two metres, the Galapagos tortoises are frequently cited as a case of island gigantism.
The story goes that some small tortoise-like ancestors reached the islands several million years ago and, in the absence of any serious predators to worry about, evolved into today’s gentle giants. But Gisella Caccone, a geneticist at Yale University who has examined the genetics of Galapagos tortoises in forensic detail, thinks there is another explanation.
Although the Galapagos tortoises’ closest living relative is the more modestly sized Chaco tortoise from Argentina and Bolivia, the fossil record tells us that there were giant tortoises pretty much everywhere until relatively recently.
“The direct ancestors of Galapagos tortoises were likely giants themselves, possibly even larger than the giant tortoises of today,” Caccone says. What’s more, “small tortoises may be less equipped to survive the long journey necessary to colonise remote oceanic islands,” she adds.
So giant tortoises may have been the norm, with their size being a useful adaptation to reduce predation. It’s not that they got large in the Galapagos, it’s just that these are the only refuges where giant tortoises dodged extinction.
But in spite of the odd exception, the island rule seems to be pretty robust. The only thing left to do is to set the historical record straight. Both Bate and Nopcsa had clearly worked out Foster’s rule more than half a century before Foster himself.
