Bettles Airport, Alaska: A U.S. Army CH-47D Chinook helicopter has just landed to fill up with kerosene. The pilots take the opportunity to once again examine the satellite photographs of their destination. The aircraft and B Company, 4th Battalion, 123rd Aviation Regiment, whose soldiers form the crew, prepare for one of the most difficult missions since the Viet Nam war. The objective is to recover a marine reptile fossil, an Ichthyosaur, that lived during the dinosaur era in the Arctic Circle.
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| Reconstruction of Ichthyosaur. |
The stopover complete, the flying machine heads north. Once arriving at the fossil site, the crew sets up camp. There is no road or home within 200 km (124 miles). Army representatives, accompanied by scientists and headed by an expert on polar dinosaurs, Dr. Gangloff, extract the fossil and protect it for transport. Despite difficult weather conditions, on the fifth day the precious stone is hoisted aboard the helicopter under a sun that never sets at these latitudes at this time of year.
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| The fossil collected during this operation. |
Shortly after this expedition is completed, a similar one is arranged.
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| Members of the second trip. |
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| Chinooks, equipped with skis for landing, flying over the Arctic Ocean toward their new goal. |
This time, the expedition brings back different dinosaur fossil specimens, including three Pachyrhinosaurus skulls weighting a ton.
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| Young Pachyrhinosaurus dinosaur. Once adult, this herbivore was about 5.5 meters (18 feet) long and 2 meters (6.5 feet) high. |
Why so much effort to transport the skeletons of creatures extinct since antediluvian times? One reason is that studying them provides indications of the climate that reigned on Earth at the time they lived. For example, it is surprising to realize that dinosaurs lived in the Arctic Circle, which is an inhospitable region today. This suggests to paleontologists that a very different climate existed there than at present. Because CO2 levels during the Mesozoic Era—the period when the dinosaurs lived—were up to 12 time higher than they are today, this period permits study of a world characterized by an important greenhouse effect, perhaps similar to the one created by humans by use of fossil fuels that produce greenhouse gases by combustion.
THE MEMORY OF PLANTS
How do scientists know the atmospheric levels of carbon dioxide existing tens of millions of years ago? One way is the study of magnolias! If these plants are exposed to significant levels of CO2, the shape of their leaves becomes different. Since magnolias existed at the time of the dinosaurs, scientists can look at their fossils and deduce from them the concentration of carbon dioxide when these plants were alive.
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| A magnolia flower. Because these plants first appeared before bees even existed, their flowers evolved to be pollinated by beetles! (Beetles are insects, such as ladybugs, distinguished by their special hard wings. Today, this is the animal order with the greatest number of species.) |
Another way to determine ancient levels of CO2 is also provided by plants. The latter harness this gas and to assimilate it they have microscopic holes in their leaves known as stomata.
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| This photograph, taken with a microscope, shows a stoma, one of the many tiny ‘’mouths’’ of leaves of plants that permit them to absorb carbon dioxide. |
If the concentration of this substance increases in the atmosphere, plants will need less of these orifices to use it and so their number will decrease. Thus, stomata on fossilized leaves can be counted to gauge the level of CO2 at a given time.
GIGANTIC DINOSAURS BECAUSE OF CO2?
This high level of carbon dioxide also had another effect on vegetation. The latter generally grow better in an atmosphere enriched with this gas because plants use it as discussed above, so one can imagine that herbivorous dinosaurs had a lot of food. According to some scientists, that explains why dinosaurs became so big. To test this assumption, Ginkgos biloba, trees that existed at the time of dinosaurs and have persisted to the present day, were placed in an atmosphere enriched with carbon dioxide and oxygen to re-create an atmosphere similar to that of ancient times. The trees grew up to three times faster than they do in current conditions!
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A ginkgo tree in Hiroshima in Japan. In 1945, it grew about 1 km (0.6 mile) from the epicenter of the atomic bomb dropped on this city by the United States. The temple that was originally next to it was blown up by the explosion. A new building was built and its stairs were separated to leave a gap for the trunk. Ginkgos biloba appeared hundreds of millions of years ago. They were found throughout the Mesozoic Era (the age of dinosaurs) in vegetation very different from that found at present. Grass, for instance, did not exist. Yet, after this, they gradually started to disappear as other species of trees evolved. They finally came to be located in a region of China where monks patiently grew them for 1 000 years. This tree is now associated with Buddhism, and one can see it around temples. Some of these plants are as much as 3 000 years old! |
Not all scientists share this view. For example, Jorn Harald Hurum, a paleontologist at the University of Oslo in Norway, notes that "All dinosaurs were not big. Moreover, huge animals are known throughout the last 200 million years. Even today, such creatures can be found, including whales, elephants, and giraffes.” Christopher R. Noto, a researcher who specializes in dinosaurs at Stony Brook University in the United States, thinks that "We must take into account different phenomena that can, despite higher levels of CO2, lead to decreases in the plants’ production. For example, there are the questions of soil exhaustion, of greater plant sweating due to an increase in temperature, and of difficulty for plants accessing light because of the others around it. Let us also note that an increase in CO2 can cause plants to have less nutritional content, or even to be no longer edible. This is the case for plants that use CO2 to synthesize elements that serve as defense for the plant," continues this scientist. Dr. Lionel Cavin, curator of the Department of Geology and Paleontology at the Museum of Natural History in Geneva, Switzerland, also sees no direct connection between plants that grow faster and big animals: "Today, the areas with the largest quantities of vegetation are found in the tropical forests. Yet it is not there, but in the savannas, where big animals live." One can imagine that it should have been the same during the dinosaur era, because large animals have difficulty moving between the trees in a forest. As we shall see later, these issues play a role in the reconstruction of Mesozoic climate.
THE DINOSAURS’ CLIMATE
In what ways did the dinosaurs’ world differ from ours? The first difference is that Earth was generally warmer than today because of astronger greenhouse effect, so the distribution of climates was not the same.
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| This map shows Jurassic climates, a period during the era when dinosaurs lived. Yellow: humid climates in summer; pink: deserts; light pink: humid climates in winter; green: temperate climates; blue: cold climates. Note the absence of ice at the poles. |
The continents were configured differently than at present. This is because, at the beginning of the Mesozoic, all continents were joined, forming a single supercontinent called Pangaea, before they gradually separated. “Whereas dinosaurs initially all lived on the same continent, due to its breakup, these animals were separated from each other,” says Dr. Lionel Cavin. ”As they evolved to be better adapted to their specific environment, over time they became more and more typical of a certain geographical area." continues this researcher specialized in the Mesozoic fauna. Christopher Noto stresses that this era lasted a very long time, allowing for major evolution. "The Tyrannosaurus rex was more distant in time from the dinosaur Allosaur than it was from man!”
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| A Tyrannosaur skeleton. At 13 meters (43 feet) long, 5 meters (16 feet) high, and 7 tons in weight, it is one of the largest carnivores that ever lived on this planet. A less gigantic ‘’version’’, Allosaur, existed before Tyrannosaur. |
As far as climatology is concerned, the equator today is generally characterized by a climate with warm temperatures and heavy rainfall throughout the year. "At the time of the dinosaurs, the situation was different, because this region [in yellow on the map
] was not humid all the time," explains Christopher Noto, who participated in the writing of the article showing this map.“This resulted from a climatology marked by huge monsoons, but the later did not occur in this region of the globe." The tropics are bordered to the north and the south by deserts (in pink on the map). As one advances toward the poles, seasonally wet climates (in light pink) are again encountered, then temperate climates (in green), and finally cool regions near the poles (in blue). How do we know this?
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The first map shows plant diversity in the Jurassic era (the bigger the circle, the greater the number of plant species known at this location, as indicated by fossils). The second lists the places where coal (black circles) and evaporates, a type of rock, (white circles) can be found. The last shows where the dinosaurs were located (a larger circle denotes a greater number of species). |
"Coal provides an indication about the climate, since it is formed in wet conditions. Evaporites, a type of rock, occur in environments characterized by strong evaporation, indicating dry climates," says Professor Noto. We notice that animals are not necessarily located where there is the most vegetation. This, as we have seen above, can be explained and is a phenomenon also observable today. Regarding flora, some plant species grow in warm climates, others in wet environments, and so on, so their fossils also provide indications about their environment and are included in the map showing climates. Concerning the distribution of dinosaurs, we can see that it was different from present-day distributions of animals. Whereas today the largest concentration of animal species is in the equatorial region, the latter seems to have been little inhabited during the Jurassic. Terrestrial life was found mostly at middle latitudes, with the highest biodiversity in the northern hemisphere.
A LOST WORLD OF TROPICAL FORESTS?
Christopher Noto calls for caution in interpreting such information. "The fact that fossils are scarce in equatorial regions does not necessarily mean that these regions did not support diverse species. Indeed, even assuming that there was a rainforest, we would not necessarily find traces of it." This is because hot, humid forests are not conducive to fossilization. In such an environment, bones rapidly deteriorate, and plants use the minerals leached from bones for their own metabolism. Furthermore, carcasses are not covered, as happens, for example, in a river, where pieces of rock, transported by water, come to rest over them. Another aspect is that dead animals are eaten by carnivores or scavengers. Small bones are eaten and therefore destroyed. As we saw above, forests are populated by small- to medium-sized animals, which are less likely to be fossilized than bigger ones. In addition, a large bone will be more well preserved than a small one since nature needs more time to degrade it. "It is therefore possible to imagine that a world similar to the current tropical forests existed in the equatorial regions but that no indication of them was preserved," concludes Christopher Noto. Concerning tropical regions, another problem may also be the difficulty with which these areas are accessed, which limits possible fossil discoveries. For example, this is the case for the Sahara, the third largest desert after Antarctica and the Arctic, with an area larger than that of the United States! Michael Arthur Paesler, a physicist at North Carolina State University (the United States), is preparing an expedition to search for fossils in this geographical region . . . with a dirigible. This scientist developed a radar system that makes it possible to detect fossils that will be carried by the aircraft. "As we will have to work in an environment where it is difficult to operate computers, the information collected with the radar will be sent to a satellite. The satellite will transmit the data to the United States, where they will be analyzed," explains Professor Paesler, who is delighted at the idea of the potential discoveries that such an enterprise can bring. Indeed, this place was far from lifeless. We know that episodic but significant rains happened, thanks to the signs that such events have left in the ground. The fossils give us information about the fauna that lived here.
For example, herbivores were generally 6 to 15 meters (20 to 50 feet) long. It is therefore possible to imagine this desert as it was 100 million years ago!
THE SAHARA DESERT, 100 MILLION YEARS AGO
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| This flying reptile, with a wingspan of about 70 cm (2 feet), is a pterodactyl. |
One night a pterodactyl put its long beak on the ground. In the calm of the night, it fell asleep, but suddenly it heard a noise. Moving with the help of its wings, the reptile went to the edge of the mound that served as its refuge. It saw a herd of Ouranosaurus nigeriensis dinosaurs moving around down in the plain.
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| The Ouranosaur was a desert dinosaur that resembled a camel. After sunset, the crest on its back was used to emit excess heat absorbed during the day. It probably also had a mechanism to cool its brain during the day by circulating blood through vessels passing through its nasal region. |
The pterodactyl watched them, motionless, from the top of its rock. At each step the dinosaurs were sinking into the sand. They were walking slowly and with a heavy tread. A baby that had certainly hatched not long before was struggling to keep pace. Everything about the Ouranosaurs suggested tiredness. It had not rained for weeks and it was never possible to know when the next rain would happen. The dinosaurs were looking for a watering hole, but these had gradually gone dry. The flying reptile gazed at the landscape bathed in the moonlight, under a starry sky. Already the first light of dawn was appearing. As soon as the sun began to rise in the sky, the air became hot. Soon the temperature reached 50 °C (122°F). The dinosaurs lay down, orienting themselves facing into the sun to minimize exposure. The pterodactyl spread its wings and jumped up and down to leap into the void. Gathering speed, it soared above the sands and the stones. Soon it could feel the effects of hot air currents rising up from the blazing ground on its wings. Its brain, surprisingly large enough to analyze positions and precise balance necessary for flight, allowed it to move with remarkable agility in the air. Starting to soar in circles, it used these movements of the atmosphere to rise up without flapping its wings. Far from the ground, the heat was more tolerable. Large dark clouds were coming up on the horizon; it would finally rain. In anticipation, the pterodactyl landed and found shelter between some rocks. Soon the wind began to blow the sand while the sky darkened. A sheet of rain moved forward, and lighting, intermittently lighting up the plain, could be seen in the far distance. Then a torrential rain started, creating streams. The pterodactyl dipped its beak in a puddle that reached to its feet, then lifted its head to quench its thirst. A few hours after the storm had died down, flowers emerged from the desert soil as far as the eye could see. The Ouranosaurs walked over this carpet of flowers, feeding from it.At the end of the day, the pterodactyl flew off again. It noticed a particular perfume, that of one of the first flowering plants living on the planet. Feeling the warm air of the evening flowing past its wings, it flew over this boundless arid region, which was lying under the orange colors of the sunset.
THE POLAR DINOSAURS
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| Polar Dinosaurs |
Another geographical area that is interesting by virtue of the climate that reined there as well as the solutions that life found for adapting to them are the Polar Regions. These parts of the globe had environments that no longer have an equivalent on Earth. As we have seen above, the poles were colonized by reptiles. In the southernmost latitudes, although they were less cold than today, temperatures fell below 0 °C (32°F) during part of the year, as shown by traces in strata indicating frozen ground at that time. A question then arises: were the dinosaurs cold-blooded animals like the reptiles living today? "It is difficult to imagine that dinosaurs could have survived at such latitudes if this were the case. In the present cold climates, the only animals that are active, such as birds and mammals, are warm-blooded. Besides, [fossils of] dinosaurs of most groups are found in the polar regions," explains Dr. Thomas Hewitt Rich, curator of vertebrate paleontology at Museum Victoria in Melbourne (Australia). He is also one of the world’s most preeminent polar dinosaur specialists. There are indications that certain dinosaurs were actually active year-round, even though the South Pole was plunged into a polar night for three months of the year. For instance, this is the case with Leaellynosaura, a dinosaur with large eyes and very developed optical lobes in its brain. "Thanks to that, it was probably able to discern even small creatures in the darkness of the polar winter,” continues this paleontologist, co-author of the book
Dinosaurs of Darkness.
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Leaellynosaura, a 60–90 cm (2–3 foot) dinosaur. It was discovered by Thomas Rich and his wife, paleontologist Patricia Vickers-Rich and named after their daughter Leah.
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This is not true, however, for all dinosaurs at these latitudes. For example, at least one dinosaur, Timimus hermani, hibernated!
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| The 3.5 meter (11.5 foot) Timimus dinosaur was also discovered and named by the Riches. |
One reaches this conclusion by observing this dinosaur’s bones. "Growth-arrest lines, which reflect periods during which the animal stopped eating, are visible on them," says Dr. Rich. This is a phenomenon similar to the growth rings in cross-sections of tree trunks, which represent a time when the plant no longer grew in the winter. These patterns are nonexistent in other dinosaurs, such as Leaellynosaura, that were active during cold seasons. Reptiles also lived in the Arctic Polar Circle. For example, Svalbard is an island halfway between Norway and the North Pole swept by the winds of the Arctic Ocean. Jorn Hurum is excavating a sea monster’s skeleton, a 15 meter (50-foot)-long Pliosaur with teeth longer than those of a Tyrannosaur, at this place!
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| The large animal is a Pliosaur, a sea reptile that lived during the dinosaur era. |
This island had already given up other secrets; we know that dinosaurs lived here, since their tracks have been found. Although this region was less northward when the footprints were left, it was part of the Arctic Circle. "There was probably snow in the winter," Professor Hurum speculates.
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| The first map is the one we saw earlier. The second resulted from using a climate model. The color code for both maps is the same (yellow: humid climate in summer; pink: deserts; light pink: humid climate in winter; green: temperate climate; blue: cold climate). |
The model predicts the succession of climates that we saw on the first map. Going from the equator to the poles, one finds a tropical zone that is humid during the summer, deserts, temperate climates, and cold climates. The temperate climates (in green) represented in the equatorial region cannot be confirmed or invalidated, since the conditions existing in these areas are unknown. The most blatant error is that too much area shows up as cold climates (in blue) in the high latitudes in the version generated by the model, particularly in the Southern Hemisphere. The problem is that the model’s prediction of heat transfer is too low between the low latitudes and the poles; thus it calculates temperatures that are too cold, for instance, for areas where giant herbivores lived. This could be because the model does not take vegetation into account. Climatologists use this information to improve their models, and more accurate predictions of future climates will most likely be provided.
“CLIMATE CHANGE COULD CAUSE A NEW EXTINCTION”
Beyond the climate change issue, another question is the repercussions of a major increase in the level of carbon dioxide for animal life. As we previously saw, life evolved for 40 million years on this planet in an atmosphere enriched with CO2. Animals adapted to a distribution of climates very different from ours, as we saw in the examples of Ouranosaurus, Leaellynosaurus, and Timimus dinosaurs. Can we thus deduce that life and a lot of CO2 can also coexist in the future? According to Lionel Cavin, "Warmer climates are a normal situation for our planet.” As for Jorn Hurum, he considers that many animals appeared during past global warming events but that these were not the cause of mass extinctions. "These occur in the case of a cooling event. Of course, this does not correspond to the message that one generally hears today,” points out this fossil hunter. Lionel Cavin also believes a correlation exists between temperature and biodiversity: “For instance, we observe in past eras that the warmer the oceans, the higher the fish biodiversity.” Jorn Hurum concludes that the problem essentially concerns humans, since they live in areas that will be flooded if the polar ice melts. For his part, Lionel Cavin stresses the importance of the question of transition from one climate to another: "In the case of a shift to a climate 5 °C [about 9°F] warmer than present, this would not pose any long-term problems. On the other hand, the stage of moving from one equilibrium climate to another could be dangerous.” Thomas Rich shares this point of view by explaining that this change could be disastrous because animals adapted to conditions characterized by an important greenhouse effect are not those that currently exist. "Rapid variations cause problems for living organisms," he adds. Christopher Noto adheres to this idea: "CO2 concentration changes have already occurred in the past, but during much longer periods than what we see today.” According to this scientist, animals evolved, adapted, or disappeared during these events. When they happen in too short a period of time, fauna can’t change. "This leads to widespread extinctions," he adds.
Gaëtan Dübler
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