Europe
Page 6
The name Eocene (meaning ‘new dawn’) was coined by the father of modern geology, Charles Lyell. His three-volume work Principles of Geology was published between 1830 and 1833, and in the last volume he defined the Eocene on the basis that one to five per cent of its species still exist. The epoch lasted for 22 million years—between 56 million to 34 million years ago—and at the time of its beginning a great landmass existed where once the European Archipelago had spread. There were still plenty of islands about, including proto-Britain in the west and Iberia in the south, but stretching from the Turgai Strait in the east to Scandinavia in the north, a European proto-continent was beginning to take shape, one that no amount of rising seas or shifting tectonic plates has divided since.
For ten million years after the last dinosaurian jaws were stilled, the vegetation of Europe grew unchecked. Europe’s forests had become as cathedral like—and yet more dense, gloomy and still—as the great forests of Borneo when first penetrated in the nineteenth century by the Italian explorer Odoardo Beccari. To him it seemed that the Bornean rainforests, the tallest on Earth, were places that had: ‘remained untouched and unchanged since remote geological epochs, and where the vegetation has continued to flourish uninterruptedly for hundreds of centuries since the period when that land first emerged from the ocean.’3 If we picture ourselves among the huge trunks, the gloom lit with luminescent insects and fungi, and a pervasive stillness and silence broken only by the odd, scurrying creature, we gain some idea of what the untrammelled forests of Europe were like.
Just prior to the great warming, a slight cooling caused sea levels to drop about 20 metres, opening a land bridge between Europe and North America, and allowing an American giant to enter Europe. Coryphodon was the largest creature to exist following the extinction of the dinosaurs. Descended from rat-sized North American ancestors of 10 million years earlier, Coryphodon belonged to an ancient, now-extinct order. Lumbering creatures, 2.5 metres in length and weighing up to 700 kilograms, with brains that weighed just 90 grams, they were probably rather unpleasant to look at—resembling overstuffed shrews.
Coryphodons were bulk-feeders on vegetation in the swampy woods of the New World, which then grew as far north as Greenland, functioning somewhat like dim-witted bulldozers and composters. Their impact, upon reaching Europe, was predictable. They found themselves in a larder that was 10 million years in the making. Too large to be attacked by any predator, and ‘oversexed, overpaid, and over here’ (to borrow a phrase), they feasted and wreaked havoc until eventually they exhausted their food supply.
As seedlings and understorey plants were eaten and older trees died without replacement, the timeless, umbrageous canopies of the ancient forests opened up, allowing sunlight to reach the forest floor—creating opportunity for lower-growing plants. Trails linking swamps and feeding places would have been trampled through the forest, with nutrients and seeds dumped along the way in piles of Coryphodon dung. With sunlight and a handy means of seed transport available, a far more varied canopy was established, and a greater variety of plants than ever before coexisted.
The Coryphodon invasion was just one event in a complex series of migrations that occurred around the dawn of the Eocene. We owe a great deal of our knowledge about these migrations to the work of Dr Jerry Hooker. By the time I caught up with Jerry in June 2016 he had been studying fossil mammals at the Natural History Museum in London for more than 50 years. As he explained it, his work has involved a lot of sieving. So much, in fact, that his hips had given out. Help, however, was on the way—he was expecting a pair of titanium hips, courtesy of the National Health Service. Given his sacrifices, I would have thought that a gift of gold-plated ones would have been appropriate.
The sieving that palaeontologists like Jerry do is arduous, involving agitating cumbersome sieves filled with sticky clay and sediment, usually while standing in a freezing pond, in an effort to remove the fine sediment and concentrate the fossils. After some time, all that remains is rock fragments—and with any luck between three and seven tiny teeth for every tonne of clay Jerry washes. Jerry will sieve anything—from clay nearly 200 million years old to fresh stuff formed just a few million years ago—as long as there’s the prospect of finding a fossil.
One of his finest moments was the discovery of the bones of the world’s oldest mole. He recovered the relics from 33–37-million-year-old sediments on the Isle of Wight.4 The creatures’ teeth had been described decades earlier, and while teeth can tell you what an animal ate, they don’t tell you whether it burrowed or bounded through the bushes. Jerry persisted in working the site, washing its sediments through very fine sieves until he had recovered minuscule foot and limb bones whose spade-like features demonstrated that the creature was the earliest known true burrower. The revelation opened the possibility that moles first evolved in Europe, a view supported by DNA studies, and the discovery in European rocks of fossils moles that live in North America today.5
In my opinion, Jerry Hooker is both a national treasure and a saint. Over his career he has found enough minute fossils to fill a few cigarette packets. A mechanically minded friend, who had watched too often as his mate bent over and sieved muck in a freezing pond, took mercy on him. After a bit of back-shed fiddling, he came up with a fossil ‘washing machine’. I saw it whirring away in the yard at the Natural History Museum, shuddering and flushing muddy water as it concentrated the fossils. All Jerry had to do was put sediment in the top, and retrieve the concentrate from the bottom, which would be dried and then sorted through later. It’s a tremendous piece of kit. Not as sophisticated as the Mars rover, but every bit as effective for exploring distant worlds.
Jerry’s work has revealed that about 54 million years ago migrants poured into Europe from all points of the compass. From smallest to largest, the North American immigrants were ancestral shrews, squirrels, primitive ferrets, extinct otter-like creatures, pangolins, primitive carnivores and ancestral ungulates. From Africa came a modest contingent of primitive carnivores, while from Asia came the first even- and odd-toed ungulates, along with Europe’s first primates and the ancestors of the modern carnivores.6
As a result of the arrival of these advanced mammalian lineages, the European fauna that had been evolving in isolation since the bolide impact was devastated. The frog-like Hainin beasts and their relatives, along with almost all the other mammals from Hainin, vanished. Extinction following invasion is of course a common occurrence in Earth’s history and, indeed, it has happened repeatedly in Europe during the past 100 million years, but the European extinctions of 54 million years ago were exceptionally severe.
Among the victims were Europe’s elephant shrews.7 Elephant shrews are now found only in Africa, but the oldest African fossils do not appear until five million years after the first European ones. Elephant shrews are small, specialised creatures with noses like miniature elephant trunks. They feed mostly on insects, and they make pathways through vegetation, which they race along at high speed. Some are credited with being the fastest mammals for their size on Earth. Oddly, they are one of the very few mammals, humans being another, to have a menstrual cycle.
Their unexpected presence in Europe offers a small diversion. Elephant shrews belong to a great division of mammals known as Afrotheria, which includes elephants, aardvarks, sea cows and a variety of lesser types. Afrotherians are so diverse in size and body shape that nobody suspected they were related until, in 1999, a DNA study revealed their affinities. But there were clues in their reproduction: all afrotherians have unusual placentas and produce more foetuses than can be nurtured in the womb.
It was long assumed that the afrotherians arose in Africa. But it seems odd that elephant shrews, alone among the Afrotheria, should have made the journey north into Europe at such an early stage. Alternatively, the afrotherians may have originated in Europe, and an elephant-shrew like creature crossed into Africa and gave rise to the great diversity of afrotherians—from elephants to golden moles—that inh
abit the continent today. If so, then the Afrotheria are the sole survivors among the European mammals that evolved during Hainin times.
While Europe’s mammals were devastated by the new invaders, its birds continued to thrive. As is to be expected of an island archipelago, there were many large, flightless species, among which was a two-metre-tall giant known as Gastornis.8 The first fossils of the creature were discovered in the 1850s in the sediments of the Paris Basin by Gaston Planté, who went on to become a famous physicist, best known as the inventor of the lead-acid battery. So impressed was the palaeontologist Edmond Hébert by the ‘studious young man full of zeal’ who turned up at the Paris museum with his finds that he named the creature in Gaston’s honour.
Gastornis evolved in Europe from goose-like ancestors that had become flightless in their island environment. When the land bridge to North America opened, Gastornis crossed onto the continent, and the recent discovery of fossils in China indicate that they reached Asia as well.* Gastornis had a massive beak capable of crushing hard objects, and generations of palaeontologists believed them to be predatory: many older illustrations show the great birds catching and consuming early horses. But a recent analysis of calcium isotopes indicate that Gastornis was exclusively herbivorous.9 By 45 million years ago, these gigantic birds had become extinct in North America and Asia, and then subsequently vanished from their last stronghold—their ancestral European homeland.
Modern skinks and more amphisbaenids arrived.10 Meanwhile common frogs and toads came and went. The true toads had arrived in Europe about 60 million years ago (presumably from Asia) only to disappear, before recolonising about 25 million years ago. Beginning around 34 million years ago, the green frogs (Ranidae) arrived, perhaps from Asia or Africa.11 Flittering in at around this time, from parts unknown, came Europe’s first bat.12 It is astonishing that bats appear to have been absent from Europe, Asia and North America before this. So where did they come from? The world’s oldest bat fossils are found in Australia, but no possible bat ancestors or near relatives are known from that continent. The origin and spread of the bats remains one of the greatest mysteries of palaeontology.
Jerry Hooker’s work revealed that 54 million years ago, a second migration occurred, just 200,000 years after the first. The great warming caused the sea to rise 60–80 metres during just 13,000 years, severing the land bridges to Asia and Africa. But due to volcanic activity, the land bridge to North America remained open, and marsupials, early primate-like creatures and some primitive carnivores used it to reach Europe. At the same time, something unprecedented happened: European creatures, including the ancestors of the dogs, horses and camels, all of which had arrived in Europe from Asia just 200,000 years earlier, made a mass migration into North America.
In a sense, this great migration laid the foundations of the modern world, for it enabled the evolution, in North America, of horses, camels and dogs which, in our hands, would help transform our planet. It also foreshadowed Europe’s future: the biological wealth of Asia had been poured into the European proto-continent, and then a way to the Americas was discovered.
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* In North America, it was long known as Diatryma.
CHAPTER 10
Messel—a Window into the Past
Thanks to one of the world’s most extraordinary fossil deposits we know more about life on the proto-continent of Europe a few million years after the great warming than any earlier period. The deposit, formed 47 million years ago, is exposed in an old lignite mine at Messel, near Frankfurt in Germany. Fossils from Messel can look like the remains of animals that have been pressed between the pages of a book, with impressions of hair, skin, and even stomach contents often present. This is about as far from the solitary teeth that people like Jerry Hooker study as imaginable, making the Messel fossils immensely valuable.
Marvellous fossils were being discovered at Messel as early as 1900, but in the 1970s the burghers of the town proposed that the site be used for landfill. Not since Pope Sixtus V suggested turning Rome’s Colosseum into a wool factory to provide employment for the city’s prostitutes (a fate avoided only by the pontiff’s premature death) have the heritage values of Europe been so ignored. The authorities came to their senses in 1991 and purchased the pit to secure scientific access. Between 1971 and 1995, however, amateur collectors had had free access to the priceless fossils, and therein hangs a tale of human frailty and greed that chills the bones of palaeontologists.
On 14 May 2009, a press release headed ‘World Renowned Scientists Reveal a Revolutionary Scientific Find that Will Change Everything’ was received at news offices around the globe.1 At a press conference held the following day, at the Natural History Museum in New York, it was claimed that a missing link in human evolution had been found at the Messel pit, a treasure that compared in heritage value with the Mona Lisa. The research team making the claims was led by Jørn Hurum of the University of Oslo’s Natural History Museum. He bestowed the nickname Ida (after his teenage daughter) on the fossil. Hurum claimed that, ‘This specimen is like finding the lost ark…It is the scientific equivalent of the holy grail’.2 The fossil ‘missing link’, it transpired, was an exquisitely preserved 58-centimetre-long skeleton of a small primate, surrounded by traces of fur and replete with its last meal. In a scientific paper published two days later, researchers claimed that the small creature, which they named Darwinius masillae*, was an intermediate form between the more primitive primates known as prosimians and the simians, the group that includes monkeys and humans. If this was indeed true, it would rewrite our understanding of early primate evolution. Until Darwinius came along, it was generally believed that simians derived from tarsier-like creatures.
Scientists do not like spectacular claims being made in the popular press, especially if they are announced before the supporting evidence is published in a reviewed journal. A newspaper headline ‘Origin of the Specious’, published shortly after the announcement, should have warned Hurum and his coauthors of what was to come.3 Nils Christian Stensteth, one of Norway’s leading biologists, called the claims ‘an exaggerated hoax’ that acted to ‘fundamentally violate scientific principles and ethics’.4 Moreover, analysis showed that Hurum’s team was wrong. Ida is not on the human lineage, but is an early primate known as an Adapiform, which is similar to lemurs.
The specimen had been unearthed by an amateur fossicker in the Messel pit in 1983. Because of the way fossils are preserved at Messel, the skeleton came in two parts—a slab containing the bones (a ‘positive’, if you like) and a counterpart containing impressions (the ‘negative’). The negative surfaced at a private museum in Wyoming, USA, in 1991, but was soon shown to have been partly faked: it was a composite, made up of the remains of two different creatures.* In 2006, the positive impression was offered to Hurum for US $1 million. He bought it for $750,000, a price that would put pressure on most museum budgets. And with financial pressure comes the need to maximise publicity and significance. A contract was signed for a popular book, and the History Channel reportedly paid more for the story than they had for any other program.5 Unregulated amateur digging at sites like Messel and paying of vast amounts for fossils can create a toxic hazard for researchers. Had the good burghers of Messel realised in 1971 what a treasure they had in the old lignite pit, and immediately protected it, the farce might have been avoided.
The Messel deposits formed 54 million years ago at a time when the descendants of the creatures that had reached the European proto-continent were diversifying and adapting to local conditions. Among them were the ancient palaeotheriids, early relatives of the rhinos, tapirs and horses. A variety of strange and primitive ungulates belonging to six artiodactyl families, including the duiker-like anoplotheriids and the rabbit-sized dichobunids, also flourished. All of these families were unique to Europe, and all were small creatures.6 Like Nopcsa’s dwarfish dinosaurs, Europe’s Eocene mammals had adapted to life on a tropical island by reducing in siz
e.
At that time, Germany was located 10º south of its present location, and was a volcanic, tectonically unstable place. The Messel pit was then a lake surrounded by luxuriant rainforest, at the bottom of which, in an oxygen-free environment, formed the lignite and oily shale later mined there. The nearby volcanoes made the lake a perfect future fossil site. They would occasionally belch CO2, which, being heavier than air, would sink to the lowest point in the landscape—the lake surface—and hang there. Any bird or bat flying over the lake, or creature coming down to drink, would lose consciousness and sink to the bottom, where the anoxic chemistry of the sediments would prepare it for eternity as expertly as any mummy-maker.
In some of the Messel fossils, there is enough detail to give the impression of an old black-and-white photograph of a vanished creature. But even colour is preserved in some small beasties, such as jewel beetles. And sometimes the fossils bring the ecological fabric of the forest to life: the impressions of an ants’ jaws on a leaf fragment led researchers to surmise that the ant had been afflicted with a parasitic fungus that alters behaviour, urging its host to climb to a high place and hang there until it is dead, so that the fungus can then release its spores into the breeze.
Among the most extraordinary of Messel’s treasures are nine mating pairs of pig-nosed turtles (a creature found in the dinosaur-age Charentes deposits). As a student of the fossil record, I can assure you that it’s not often that creatures are transformed, in flagrante delicto, into memento mori. Among the many mammals from Messel is the tapir-like Propaleotherium. Bodies of the 10-kilogram creatures have been found complete with near-term foetuses, and the contents of their last meal (berries and leaves) in their stomachs. There are also some surprises such as Eurotamandua, a scaleless pangolin that looks astonishingly like a South American anteater. But it is Messel’s birds that constitute the true treasure of the site. For birds, lacking teeth, make poor fossils and are difficult to classify from other fragments. At Messel an entire avifauna is preserved, as if in aspic.