by Tim Flannery
Recent DNA research shows that songbirds, parrots and falcons are related, and that this highly successful group originated around the time of the dinosaur extinction in the Australian section of Gondwana. That falcons and robins are more closely related to each other than are falcons and hawks seems nonsensical. But the avian body plan is highly restricted by the requirements of flight, so convergent evolution, in which unrelated creatures develop similar characteristics, is common.
The songbirds are by far the largest and most successful birds. Their 5000 species, divided between 40 orders, comprise 47 per cent of all bird species. Eighteen of Britain’s most abundant avian species are songbirds, as is the most abundant wild bird on Earth, Africa’s red-billed weaver bird, of which 1.5 billion are thought to exist. That said, the great majority of songbirds fall into just one order, the perching birds, or Passeriformes, which take their name from the Latin word for the sparrow. All of the little birds that forage among leaves are perching birds, as are crows and magpies—and one thing that sets them apart is the possession of a hind toe operated by an independent set of tendons.
The first inklings about the origin of the songbirds came in the early 1970s. Charles Sibley, an ornithologist working at the University of California, discovered that if he purified and boiled double-stranded bird DNA, the strands would recombine when the mixture cooled. If he mixed the DNA of closely related species, the bond between the strands was stronger than for more distantly related pairs.4 Since Sibley’s day, genetic studies have become immensely more sophisticated. In 2002 it was demonstrated that New Zealand’s wrens sit at the base of the songbird family tree. Other studies show that the second oldest branch of the songbird family tree includes Australia’s lyrebirds and scrub birds, while the third oldest includes Australia’s tree-creepers and bowerbirds. None of these branches has many species, and all are exclusively Australasian. This abundance of early types, along with the discovery in Australia of the oldest songbird fossils in the world, provides convincing evidence for the point of origin of songbirds: Australia.
Australia has repeatedly acted as a fountainhead for songbirds that have colonised Eurasia. One of the more recent immigrant groups is the orioles, which arrived in Eurasia from Australia/New Guinea around seven million years ago. Australian ecologist Ian Low thinks that Australia’s songbirds are so successful because they exploited a new ecological niche that developed courtesy of Australia’s infertile soils, which cause Australian plants to tend to hoard what nutrients they can get.5 Nectar requires few nutrients to produce, and Australia’s eucalypts produce abundant nectar in simple flowers. Visitors to Australia can easily see the consequences: flowering gum trees pulsate with lorikeets and the raucous cries of half a dozen species of honeyeaters. Relatively small species like songbirds have triumphed in this melee by becoming highly social, aggressive, and intelligent. If this is correct, the songbirds do not so much disprove Darwin’s ideas about migration—which after all is premised on the idea that elevated competition drives evolution faster—but reveal an unexpected dimension of it.
Many mysteries remain concerning Europe’s first 60 million years, but none is as vexing as the origin of one of its most extraordinary survivors. Known to Slovenes as the ‘human fish’ (and to the rest of the world as the olm), this blind, pink salamander grows to about 30 centimetres in length and is the only European vertebrate that spends its entire life in caves. In 1689, Johann Weikhard von Valvasor announced its existence in his book The Glory of the Duchy of Carniola. The dutchy, long since incorporated into Slovenia, was a small region, but Valvasor felt strongly that the world did not know enough about it. Glory filled 15 volumes with 3532 large-format pages, 528 copperplate engravings, and 24 appendices. The work was meticulously researched and scientifically accurate by the standards of the day, and to produce it, Valvasor installed a copperplate printery in Bogenšperk castle where he lived. The Glory bankrupted him, and he was forced to sell his castle, printery and estates. The Bishop of Zagreb took mercy on the patriot, purchasing his library and graphics for a handsome sum. But it was not enough and in 1693 Valvasor died a broken man, having survived the publication of his Glory by just four years.
There is something essentially European about Valvasor’s grand obsession. After graduating from the Jesuit school in Ljubljana, he spent 14 years travelling Europe and North Africa, seeking the company of learned men. Edmund Halley proposed him as a member of the Royal Society, and in 1687 he became a Fellow. His amor patriae is evident in his great work, which must take its place among those volumes that from the time of Herodotus have sought to explain the nature of Europe, or some part of it. Thanks to the likes of Valvasor, Europe is alone among all the continents in having such a deep and rich written record of its natural history, the cost of which has all too often been paid in lives as well as fortunes.*
Valvasor’s account of the olm stated that, after heavy rains, the creatures were flushed to the surface from underground caverns. The local people, he said, believed them to be the offspring of a cave dragon. Valvasor himself, however, characterised the olm as ‘a worm and vermin, of which there are many hereabouts’. In his Origin, Darwin was moved by the olm to exclaim, ‘I am only surprised that more wrecks of ancient life have not been preserved’. By the nineteenth century a sort of olm-keeping mania had developed in Europe. Thousands of the creatures were exported, and some released into caves in France, Belgium, Hungary, Germany, Italy and possibly England.
The animal occurs naturally in certain caves and waters in Slovenia, Croatia, Bosnia and Herzegovina. Each population is slightly different, and nobody can agree on how many species there are. In 1994 scientists announced that they had found a black olm, which possesses eyes, and is restricted to the underground waters in a small area around Dobličica in the White Carniola region of Slovenia. Just how the olm got to Europe is mysterious. The Proteidae family to which it belongs includes just six species, five of which are North American. Fossils are rare, the oldest, from North America and dating from the end of the age of dinosaurs. The oldest European fossils are about 23 million years old.6
One thing everyone agrees on is that olms are bizarre. For a start, their entire life is lived in the slow lane. A batch of 64 eggs that was laid in Postojna Cave, Slovenia, took four months to hatch, and the young take the same amount of time as a human—about fourteen years—to reach sexual maturity. Nobody knows how long olms live, but at least a century seems a fair bet. And they can be hardy. One olm survived in captivity for twelve years without eating.
We have not treated olms well. For over a century they have been horrendously over-collected, and even used by farmers as pig-food. Today, the survivors are threatened by metal poisoning from industrial waste.7 What a way to treat a national treasure!
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* The Glory of the Duchy of Carniola was originally published in High German. It was never republished, and for centuries was all but forgotten. Between 2009 and 2012, it was finally translated into Slovene by a team put together by Tomaž Čeč.
CHAPTER 15
The Marvellous Miocene
Extending from about 23 to about 5.3 million years ago, the Miocene was named by Charles Lyell.* It means ‘less new’ in Greek, and Lyell gave it that name for the mouth-stretchingly mundane reason that he considered that fewer Miocene species survived into modern times than those of more recent epochs. Because of its favourable climate and diverse fauna and flora, the Miocene is arguably Europe’s most enchanting epoch. A growing land area, enhanced migration corridors, and a favourable climate conspired to create an unprecedented diversity of mammals, some of which would go on to become successful colonisers of Asia and Africa. No longer solely a destination for immigrants, Europe’s fauna was beginning to influence surrounding continents.
Evidence of life in the Miocene is not evenly distributed across Europe. Greece is spectacularly rich in reptile fossils, and Spain, France, Switzerland and Italy have exceptionally good rec
ords from both marine and terrestrial environments. Switzerland has yielded some of the best-preserved fossil insects, and Germany some of the most informative fossil plants. The British Isles, in contrast, which were a mainstay as we examined the Eocene and Oligocene, have almost no fossils of Miocene land mammals and plants.
The global cooling trend that began about 54 million years ago continued through the Miocene, though there were some striking reversals. For example, between 21 and 14 million years ago, conditions became as warm as they had been in the preceding Oligocene. When I think of Europe during this warm phase I imagine a sort of Côte d’Azur on the Seine. In the warmer conditions the seas rose, so the region that is now Paris was much closer to the coast than it is today. As the warming reached its height, much low-lying land became inundated, re-creating an island archipelago reminiscent of (though far more connected than) the one that had existed towards the end of the age of dinosaurs.1
Overall, however, the trend was towards more land, and greater connectivity. A serious phase of mountain-building commenced during the Miocene, and as the Alps and other mountains grew, the landmass of Europe convulsed, causing volcanoes to erupt across the south, doubtless triggering many earthquakes. Some mountains must have risen with (from a geological perspective) astonishing speed: analysis of isotopic ratios of water and oxygen have revealed that the highest peaks of the Swiss Alps had reached their current elevation by the middle Miocene, some 15 million years ago.2 The driving force behind this unrest was the vice-like grip created by Africa as it pushed north. And it was not just the Alps that were rising. As the land buckled, whole new islands and mountain ranges, separated by wide basins, rose.*
Among the most notable of these new mountain ranges was the Baetic Cordillera, which originated as a mountainous island incorporating the region around present-day Cadiz in southern Spain, the Sierra Nevada, the Rock of Gibraltar and the Sierra Tramuntana of Majorca (where the Majorcan midwife toad found refuge). To the north, the Pyrenees received a major uplift, as did Italy’s Apennines. And further east, arcs of mountains developed from Albania right through to Turkey.
Many of Europe’s most famous volcanic regions originated in the Miocene, as a result of great slabs of crust being driven into the molten mantle, where the rock was melted to magma. One important volcanic arc extends from Tuscany (Monte Amiata) to Sicily, where Etna, among other volcanos including Stromboli, remain active enough today to be major tourist attractions. Other potentially dangerous volcanic fields are dormant, including a large area south of Rome, which last erupted about 25,000 years ago. A second major volcanic region exists in Greece, where Methana, Santorini and Nìsyros are considered active. During the Miocene, volcanic activity was far more widespread, with major volcanic provinces in the south of France, for example, during the epoch’s beginning and closing phases.
Another defining feature of the European Miocene is extensive migrations. Following la grande coupure east–west migrations were often relatively unimpeded by topography. But extensive migration corridors also opened between Africa and Europe, which were at times so ample that, about 12 million years ago, the faunas of Kenya and Germany became almost indistinguishable.
Europe’s vegetation continued to evolve, though much of the continent continued to be dominated by a subtropical forest rich in members of the laurel family, known as the laurophyllus forests. If you want to experience a laurophyllus forest, the Macaronesian archipelagos of Madeira and the Canary Islands are worth visiting. Macaronesia is Greek for ‘islands of the fortunate’, and indeed these are fortunate isles, because on them a slice of ancient Europe survives to this day. The forested zone that occurs halfway up the mountains of Gran Canaria is a fine example, being dominated by four members of the laurel family, including the Canary and Azores laurel, the stinkwood and a relative of the avocado, all of which are ancient types growing alongside members of the ebony and olive families.
Another ancient vegetable relic surviving in Macaronesia is the legendary dragon tree, whose sap, marketed as dragon’s blood, was in past times much prized as a medicine, as incense and as a dye. The dragon tree is not part of the laurophyllus forests; it is from a drier habitat that was beginning to establish itself in parts of Europe during the Miocene. These habitats were most evident on the Iberian Peninsula where, by 15 million years ago, members of the thorn-rose genus (Neurada), esparto grass, honey mesquite and nitre bush (Nitraria) flourished in arid shrublands.3
Sadly, Macaronesia’s laurophyllus forests are almost devoid of the animal life that thrived in Miocene Europe. This is because the Macaronesian islands originated as volcanoes sprouting from the ocean floor, or as pieces of ocean crust that were pushed above the surface of the sea. The ancestral laurophyllus forests must have arrived as seeds in the guts of birds, or by floating over the ocean. With one important exception, land-based creatures could not cross the sea—and had you been a Carthaginian seafarer under the command of Hanno the Navigator in the centuries before Rome razed your great city, you may have seen those exceptional creatures with your own eyes.
Imagine being one of the first people to set foot on fabled Macaronesia. It is about 500 BCE, and back then, as today, the great peak of Teneriffe was so lofty that it was often lost in the clouds. But unlike the dry, rocky lowlands of Tenerife today, the island you experience is a verdant paradise, its trees filled with birds, including the soon-to-be-famous canary, which show no fear as you approach. Just one kind of large land creature exists there. Upon entering the forest, you see a huge reptile. The Tenerife giant lizard, Gallotia goliath, was a one-metre-long herbivore, with powerful jaws.
Today, all we have to remind us of its existence are bones and a single mummified head and chest found in a lava cave. Lizards nearly as large, but belonging to other species, lived elsewhere in the Canaries, but one by one they were exterminated when humans colonised the islands bringing with them predators such as dogs and cats. For a century it was believed that the giant lizards were no more. But then, at the very end of the last millennium, a remnant population was rediscovered.
For over a century the La Gomera giant lizard (Gallotia bravoana) was thought to be extinct. But in 1999 Spanish biologist Juan Carlos Rando discovered six individuals clinging to life on two inaccessible cliffs on the island. They had found a precarious refuge from predators and had somehow managed to subsist for many generations after their relatives, who had abounded throughout the island, had succumbed. A decision was made to bring a few of these last survivors into captivity, and today, courtesy of a painstaking recovery program, there are about 90 La Gomera giant lizards in wild and captive colonies. Perhaps one day, with a little help from humans, their progeny will reclaim their island home.
Lizards are known for their ability to reach islands, often by floating on rafts of vegetation, so it is not surprising that the gallotias colonised Macaronesia. Members of Europe’s most diverse lizard family, the lacertids, their relatives include the wall lizards that can be seen throughout temperate Europe. The Canary Islands are also home to six species of smaller gallotias, which are similar in size to wall lizards, and survive in good numbers. They are remarkable for being among the world’s smallest herbivorous lizards.
Biologists have long pointed to the giant gallotias as an example of the propensity of small-bodied creatures, when isolated on islands, to become giants. But a chance fossil discovery made near Ulm in Germany proved this to be wrong. The near-complete skeleton of a 22-million-year-old ancestral, gigantic, carnivorous Gallotia shows that when they reached Macaronesia, the lizards must have turned vegetarian, and many became dwarfs.4
Just after Macaronesia’s laurels reached their island refuge, Europe’s ancient forests began to change. Some of the best evidence of what happened comes from Germany, where the silicified trunks of about 80 species of trees have been found preserved in what was once a great lagoon fringing the northern slopes of the rising Alps. Dating from about 17.5 to 14 million years ago, they reveal the p
resence of a subtropical forest whose composition was shifting rapidly.5 In the oldest layers of the deposit, the most abundant type of silicified wood comes from a relative of the cannonball mangrove (Xylocarpus granatum). A member of the mahogany family, the cannonball mangrove is today found in the tropical, coastal regions of Africa, Asia and Australasia, extending far into the Pacific.
In swamps nearby, palms and a relative of the Chinese swamp cypress known as Glyptostrobus europeaus, thrived. Some botanists consider the European fossil swamp cypress and the living Asian tree (Glyptostrobus pensilis) to be identical: ‘it is possible that the tree now on the verge of extinction in China is the Tertiary species unchanged’.6 The Chinese swamp cypress is deciduous, and it occurs naturally only on riverbanks and in swamps. Decay resistant, and with scented wood, it has been logged into near extinction.
On firmer ground away from the shore in Miocene Germany, a mixed forest of ancient relatives of the beech and myrtle trees grew. Just what clothed the higher slopes of the Alps we cannot know for sure, because no fossils are preserved. But it’s a fair bet that towards the highest peaks, three kilometres or more above the sea, an alpine or subalpine flora was becoming established. Today, 350 of Europe’s 4500 alpine plant species, including beauties like the saxifrage du Mercantour and the alpine poppy, are found nowhere else, suggesting that they have experienced a long period of evolution in their alpine home.
By the time the next layer of driftwood was being deposited in the ancient German lagoon, just a million or two years later, the climate had cooled and become drier. In this layer, the silicified trunks indicate that relatives of the acacias and members of the laurel family dominated a very diverse forest that included dipterocarps, which are among the tallest trees in the forests of Borneo today. In a more recent layer, which was formed in an even cooler and drier climate, oaks and laurels predominate, while in the most recent sediments (dating to around 14 million years ago) locust trees (Robinia), and members of the acacia family similar to the Kalahari Christmas tree (Dicrostachys), dominate.