- Email: [email protected]
Instant Expert: Fossils are not just bones and stones
COLOURING in THE PAST ”You can reconstruct the colour and patterning on the feathers of ancient birds and dinosaurs”
imaginechina/corbis
In 2008, graduate student Jakob Vinther, then at Yale University made an extraordinary discovery. He found that you can reconstruct the colour and patterning on the feathers of ancient birds and dinosaurs by looking at the shape of the fossils’ pigment organelles, called melanosomes. These may contain melanin, which creates black pigmentation – or, in its absence, white – or other pigments that produce greys, rusty
reds, browns, yellows, oranges, greens and blues. Each pigment gives the melanosome a distinctive shape. The arrangement of the pigments within a feather refracts light, generating colours or iridescence like that found in starlings and hummingbirds. The first feathered dinosaur to be coloured in this way was a 150-millionyear-old Anchiornis huxleyi from Liaoning province in China. When a team led by Vinther and Li Quanguo of the Beijing Museum of Natural History examined samples of the fossilised feathers under a scanning electron microscope, they discovered that the animal was extravagantly coloured, with spots, stripes and a red crest of feathers down its skull (Science, vol 327, p 1369). Such dazzling colour could have been used to attract mates, the team suggest.
Show piece: was Anchiornis huxleyi trying to attract a mate?
MAMMALS AND MORE One of the most exciting sites is in Messel, Germany. Here, fine-grained rocks preserve a 47-million-yearold ecosystem in exquisite detail, including some animals that are very rarely fossilised, such as the earliest pangolin, bats, anteaters and insects. Many of these fossils come complete with stomach contents, fur and skin alongside the hard parts more commonly preserved, such as skeletons, beaks and teeth. The site was declared a UNESCO World Heritage site of exceptional importance to palaeontology in 1995. The variety of life preserved at Messel is staggering and includes fish, snakes, turtles, lizards, crocodiles and alligators, birds, two types of early horse and some of the first carnivores. In 2009, an extraordinary primate fossil was added to the list. Although not the ancestor of all humans as first suggested, Darwinius masillae, nicknamed Ida, is important as a very early higher primate similar to modern lemurs. The extraordinary preservation at Messel is down to the ancient environment. The landscape jonathan blair/corbis, right mike segar/reuters
Minute detail: armoured Jurassic fish in the fine limestone at Solnhofen
iv | NewScientist | 4 August 2012
featured a lake surrounded by rainforests through which rivers wound, creating a wet habitat with lots of sedimentation. Periodically, the oxygen-deprived mud on the bottom of the lake was stirred up, releasing lethal carbon dioxide and killing many animals nearby. As at Solnhofen, Germany, these sediments were devoid of life, allowing organisms to fossilise rather than simply decay. All that remains today is a damp oil shale, which deteriorates as it dries. To preserve the fossils, the shale has to be delicately removed from one side, before a synthetic resin is added. This seeps into the bones and hardens them. The shale next to the fossil is then reinforced with a layer of lacquer, before the whole process is repeated on the other side.
NOT JUST BONES AND STONES Fossilisation usually involves the consolidation of sediments under pressure, and the replacement of organic material by silica or other minerals, known as petrification. These processes take time and most tissues decay and disintegrate before they can occur, which is why it is so rare to find intact organisms and fossilised soft tissues. Sites where tissues such as skin, muscles and internal organs are regularly preserved are called lagerstätten, which translates as “storage place” or “warehouse”
EARLY BIRDS One of the best-known lagerstätten is at Solnhofen in Germany, where the pale, fine-grained limestone has been quarried since Roman times. It formed during the late Jurassic, some 151 million years ago, from sediments precipitated out of the water and onto the bottom of a shallow lagoon. Without currents to mix the salty water of the lagoon with that of the adjoining Tethys Sea, salinity rose and the sediment became devoid of oxygen – perfect conditions for preserving entire organisms. Any dead animal or plant that ended up in the sediment, whether falling in from the banks or sinking from the waters above, lay undisturbed by currents, scavengers and bacteria that cause decay. The potential of the Solnhofen limestone as a fossil site was revealed in 1860 with the discovery of a fossilised feather, belonging to the first specimen of the earliest known bird, Archaeopteryx lithographica. Preserved alongside Archaeopteryx are thousands of other organisms. These include wonderful pterodactyls with their leathery, furry wings intact; a small running dinosaur called Compsognathus; marine crocodiles; insects including dragonflies and beetles; various fish; crustaceans such as horseshoe crabs; squid; jellyfish and plants.
FEATHERED DINOSAURS
Insulating fluff: 130-million-year-old juvenile Dromaeosaur
In the past two decades, Liaoning province in China has been one of the most important sites for fossil hunters. Many species new to science have been found here, but it is feathered dinosaurs, which date from between 130 and 120 million years ago, for which Liaoning is most famous. In 1996, photos of Sinosauropteryx prima, the first feathered dinosaur to be discovered, shocked the world by providing key evidence that birds evolved from dinosaurs. Since then, 30 species of feathered dinosaurs have been discovered, including juvenile specimens of Tyrannosaurus rex. Most come from Liaoning. Fabulously detailed preservation reveals a range of feather types. Some specimens, including
Sinosauropteryx, have hairy, unbranched fluff or proto-feathers. Others, like the oldest feathered dinosaur Anchiornis, have recognisable feathers but could not have flown because their wings were not large enough. Then there is Microraptor gui, which had four feathered wings, one on each limb. Despite putting models of this animal in wind tunnels, no one has been able to work out how it got around. These fossils have forced us to consider that feathers evolved for a function other than flight. Possibilities include display, as some of the feathers were brightly coloured, and insulation against extreme heat or cold as in the Dromaeosaur (pictured). 4 August 2012 | NewScientist | v
imaginechina/corbis
In 2008, graduate student Jakob Vinther, then at Yale University made an extraordinary discovery. He found that you can reconstruct the colour and patterning on the feathers of ancient birds and dinosaurs by looking at the shape of the fossils’ pigment organelles, called melanosomes. These may contain melanin, which creates black pigmentation – or, in its absence, white – or other pigments that produce greys, rusty
reds, browns, yellows, oranges, greens and blues. Each pigment gives the melanosome a distinctive shape. The arrangement of the pigments within a feather refracts light, generating colours or iridescence like that found in starlings and hummingbirds. The first feathered dinosaur to be coloured in this way was a 150-millionyear-old Anchiornis huxleyi from Liaoning province in China. When a team led by Vinther and Li Quanguo of the Beijing Museum of Natural History examined samples of the fossilised feathers under a scanning electron microscope, they discovered that the animal was extravagantly coloured, with spots, stripes and a red crest of feathers down its skull (Science, vol 327, p 1369). Such dazzling colour could have been used to attract mates, the team suggest.
Show piece: was Anchiornis huxleyi trying to attract a mate?
MAMMALS AND MORE One of the most exciting sites is in Messel, Germany. Here, fine-grained rocks preserve a 47-million-yearold ecosystem in exquisite detail, including some animals that are very rarely fossilised, such as the earliest pangolin, bats, anteaters and insects. Many of these fossils come complete with stomach contents, fur and skin alongside the hard parts more commonly preserved, such as skeletons, beaks and teeth. The site was declared a UNESCO World Heritage site of exceptional importance to palaeontology in 1995. The variety of life preserved at Messel is staggering and includes fish, snakes, turtles, lizards, crocodiles and alligators, birds, two types of early horse and some of the first carnivores. In 2009, an extraordinary primate fossil was added to the list. Although not the ancestor of all humans as first suggested, Darwinius masillae, nicknamed Ida, is important as a very early higher primate similar to modern lemurs. The extraordinary preservation at Messel is down to the ancient environment. The landscape jonathan blair/corbis, right mike segar/reuters
Minute detail: armoured Jurassic fish in the fine limestone at Solnhofen
iv | NewScientist | 4 August 2012
featured a lake surrounded by rainforests through which rivers wound, creating a wet habitat with lots of sedimentation. Periodically, the oxygen-deprived mud on the bottom of the lake was stirred up, releasing lethal carbon dioxide and killing many animals nearby. As at Solnhofen, Germany, these sediments were devoid of life, allowing organisms to fossilise rather than simply decay. All that remains today is a damp oil shale, which deteriorates as it dries. To preserve the fossils, the shale has to be delicately removed from one side, before a synthetic resin is added. This seeps into the bones and hardens them. The shale next to the fossil is then reinforced with a layer of lacquer, before the whole process is repeated on the other side.
NOT JUST BONES AND STONES Fossilisation usually involves the consolidation of sediments under pressure, and the replacement of organic material by silica or other minerals, known as petrification. These processes take time and most tissues decay and disintegrate before they can occur, which is why it is so rare to find intact organisms and fossilised soft tissues. Sites where tissues such as skin, muscles and internal organs are regularly preserved are called lagerstätten, which translates as “storage place” or “warehouse”
EARLY BIRDS One of the best-known lagerstätten is at Solnhofen in Germany, where the pale, fine-grained limestone has been quarried since Roman times. It formed during the late Jurassic, some 151 million years ago, from sediments precipitated out of the water and onto the bottom of a shallow lagoon. Without currents to mix the salty water of the lagoon with that of the adjoining Tethys Sea, salinity rose and the sediment became devoid of oxygen – perfect conditions for preserving entire organisms. Any dead animal or plant that ended up in the sediment, whether falling in from the banks or sinking from the waters above, lay undisturbed by currents, scavengers and bacteria that cause decay. The potential of the Solnhofen limestone as a fossil site was revealed in 1860 with the discovery of a fossilised feather, belonging to the first specimen of the earliest known bird, Archaeopteryx lithographica. Preserved alongside Archaeopteryx are thousands of other organisms. These include wonderful pterodactyls with their leathery, furry wings intact; a small running dinosaur called Compsognathus; marine crocodiles; insects including dragonflies and beetles; various fish; crustaceans such as horseshoe crabs; squid; jellyfish and plants.
FEATHERED DINOSAURS
Insulating fluff: 130-million-year-old juvenile Dromaeosaur
In the past two decades, Liaoning province in China has been one of the most important sites for fossil hunters. Many species new to science have been found here, but it is feathered dinosaurs, which date from between 130 and 120 million years ago, for which Liaoning is most famous. In 1996, photos of Sinosauropteryx prima, the first feathered dinosaur to be discovered, shocked the world by providing key evidence that birds evolved from dinosaurs. Since then, 30 species of feathered dinosaurs have been discovered, including juvenile specimens of Tyrannosaurus rex. Most come from Liaoning. Fabulously detailed preservation reveals a range of feather types. Some specimens, including
Sinosauropteryx, have hairy, unbranched fluff or proto-feathers. Others, like the oldest feathered dinosaur Anchiornis, have recognisable feathers but could not have flown because their wings were not large enough. Then there is Microraptor gui, which had four feathered wings, one on each limb. Despite putting models of this animal in wind tunnels, no one has been able to work out how it got around. These fossils have forced us to consider that feathers evolved for a function other than flight. Possibilities include display, as some of the feathers were brightly coloured, and insulation against extreme heat or cold as in the Dromaeosaur (pictured). 4 August 2012 | NewScientist | v