Wild climate swings -- persisting tens of millions of years -- were too much for the dinos, University of Utah paleontologist and colleagues discover 
 
 SALT LAKE CITY, June ­15, 2015 ­- For more than 30 million years after dinosaurs first appeared, they remained inexplicably rare near the equator, where only a few small-bodied meat-eating dinosaurs eked out a living. The age-long absence of big plant-eaters at low latitudes is one of the great, unanswered questions about the rise of the dinosaurs. 
 
 And now the mystery has a solution, according to an international team of scientists who pieced together a remarkably detailed picture of the climate and ecology more than 200 million years ago at Ghost Ranch in northern New Mexico, a site rich with fossils from the Late Triassic Period. 
 
 The new findings show that the tropical climate swung wildly with extremes of drought and intense heat. Wildfires swept the landscape during arid regimes and continually reshaped the vegetation available for plant-eating animals. 
 
 "Our data suggest it was not a fun place," says study co-author Randall Irmis, curator of paleontology at the Natural History Museum of Utah and assistant professor at the University of Utah. "It was a time of climate extremes that went back and forth unpredictably and large, warm-blooded dinosaurian herbivores weren't able to exist nearer to the equator - there was not enough dependable plant food." 
 
 The study, led by geochemist Jessica Whiteside, lecturer at the University of Southampton, is the first to provide a detailed look at the climate and ecology during the emergence of the dinosaurs. The results are important, also, for understanding human-caused climate change. Atmospheric carbon dioxide levels during the Late Triassic were four to six times current levels. "If we continue along our present course, similar conditions in a high-CO2 world may develop, and suppress low-latitude ecosystems," Irmis says. 
 
 The other authors are Sofie Lindström, Ian Glasspool, Morgan Schaller, Maria Dunlavey, Sterling Nesbitt, Nathan Smith and Alan Turner. They reported the findings in the Proceedings of the National Academy of Sciences. 
 
 Reconstructing the deep past 
 
 The earliest known dinosaur fossils, found in Argentina, date from around 230 million years ago. Within 15 million years, multitudes of species with different diets and body sizes had evolved and were abundant beyond the tropical latitudes. In the tropics, the only dinosaurs present were small carnivores. This pattern persisted for 30 million years after the first dinosaurs appeared. 
 
 In the new study, the authors focused on Chinle Formation rocks, which were deposited by rivers and streams between 205 and 215 million years ago at Ghost Ranch (better known to many outside of paleontology as the place where artist Georgia O'Keeffe lived and painted for much of her career). The multi-colored rocks of the Chinle Formation are a common sight on the Colorado Plateau at places such as the Painted Desert at Petrified Forest National Park in Arizona. During the Late Triassic, North America and other land masses of the world were bound together in the supercontinent Pangea. The Ghost Ranch site stood close to the equator at roughly the same latitude as present-day southern India. 
 
 The researchers reconstructed the deep past by analyzing several kinds of data: fossils, charcoal left by ancient wildfires, and stable isotopes from organic matter and carbonate nodules that formed in ancient soils. "Each dataset complements the others, and they all point towards similar conditions," Whiteside says. "I think this is one of the major strengths of our study." 
 
 Fossilized bones, pollen grains and fern spores revealed the types of animals and plants living at different times, marked by layers of sediment. Dinosaurs remained rare among the fossils, accounting for less than 15 percent of vertebrate animal remains. They were outnumbered in diversity, abundance and body size by the reptiles known as Pseudosuchian archosaurs, the lineage that gave rise to crocodiles and alligators. 
 
 The sparse dinosaurs consisted mostly of small, carnivorous theropods. Big, long-necked dinosaurs, or sauropodomorphs - already the dominant plant-eaters at higher latitudes - did not exist at the study site or any other low-latitude site in Triassic Pangaea, as far as the fossil record shows. 
 
 Abrupt changes in climate left a record in the shifting abundance of different types of pollen and fern spores between sediment layers. Fossilized organic matter from decaying plants provided another window on climate shifts. Changes in the ratio of stable isotopes of carbon in the organic matter bookmarked times when plant productivity declined during extended droughts. 
 
 Drought and fire 
 
 Wildfire burn temperatures varied drastically, the researchers found, consistent with a fluctuating environment in which the amount of combustible plant matter rose and fell over time. The researchers estimated the intensity of wildfires using bits of charcoal recovered in the sediment layers. The amount of light reflected from the fossil charcoal under a light microscope relates directly to the burn temperature of the wood. The overall picture, the authors say, is that of a climate punctuated by extreme shifts in precipitation in which plant die-offs fueled hotter fires, which in turn killed more plants, damaged soils and increased erosion. 
 
 Atmospheric carbon dioxide levels, calculated from stable isotope analyses of soil carbonate and preserved organic matter, rose from about 1,200 parts per million at the base of the section, to about 2,400 parts per million near the top. At these high CO2 concentrations, climate models predict more frequent and more extreme weather fluctuations consistent with the fossil and charcoal evidence. 
 
 Continuing shifts between extremes of dry and wet likely prevented the establishment of dinosaur-dominated communities found in the fossil record at higher-latitudes across South America, Europe and southern Africa, where aridity and temperatures were less extreme and humidity was consistently higher. Resource-limited conditions could not support a diverse community of fast-growing, warm-blooded, large dinosaurs, which require a productive and stable environment to thrive. 
 
 "The conditions would have been something similar to the arid western United States today, although there would have been trees and smaller plants near streams and rivers and forests during humid times," says Whiteside. "The fluctuating and harsh climate with widespread wild fires meant that only small two-legged carnivorous dinosaurs, such as Coelophysis, could survive." 
 
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 The research was funded by grants from the National Science Foundation (EAR 0801138, 1349650, 1349554, 1349667, and 1349654). 
 
 Other funding was provided by Richard Salomon Foundation, National Geographic Society Committee for Research & Exploration, University of California Museum of Paleontology, University of Utah, Grainger Foundation, Dyson Foundation (MFS), and Field Museum Women's Board - Geocenter Denmark (grant nr 6-2013). 
 
 Fieldwork was conducted with the permission and support of the Ghost Ranch Conference Center. ||||| One of the missing links in our understanding of the Triassic Period – between 252 and 201m years ago – is why there were so few dinosaurs in the tropics. Our research suggests that volatile, hot dry weather and high carbon dioxide levels are to blame. The research can even tell us something about the challenges we humans face from climate change. 
 
 The first dinosaurs emerged just over 230m years ago, during the Late Triassic Period. This was one of the most dynamic intervals in the Earth’s history, with large-scale climatic changes. The planet was also coping with the recovery from one mass extinction and the onset of another. At the same time, many of the animal groups that dominate today’s terrestrial ecosystems – including frogs, salamanders, turtles, lizards, and mammals – were emerging. 
 
 One of the major unresolved questions of dinosaurs’ rise to dominance is why large-bodied herbivorous dinosaurs were missing from the tropics, despite the fact that they lived in higher latitudes. Small, carnivorous dinosaurs, however, populated the entire planet – including in the tropics. 
 
 Of crushing importance 
 
 To tackle the issue, our international team investigated sedimentary rocks from a number of places around the Upper Triassic Chinle Formation in New Mexico, including the fabled “Ghost Ranch”, whose multicoloured cliffs inspired artist Georgia O'Keeffe’s landscapes. However, they also preserved North America’s most extensive fossil evidence of the rise of dinosaurs and their competitors. 
 
 At the time that these sediments were deposited by rivers and streams, the areas were very close to the equator at about 12°N latitude (northern New Mexico is at 36°N today). This is the same as the current latitude of the southernmost tip of India. 
 
 By excavating unweathered rock in the field and then crushing samples in the lab we could separate the isotopes of carbon from fossilised organic matter in rocks using mass spectrometry. The isotopic ratios suggest that major rapid changes in ecosystem productivity and atmospheric CO 2 levels took place during the Triassic Period. 
 
 These rocks also preserve abundant fossil charcoal. Based on the amount of light reflected from fossil charcoal under a microscope, we could see that wildfires must have swept the landscape at the time. These would have continually changed the vegetation available for large plant-eating dinosaurs. 
 
 By extracting fossil pollen and spores from the sediments and by excavating and identifying vertebrate body fossils, we could also identify the plants and animals living in the area. Our data show that plant groups varied in abundance in connection with climate swings, and that the only dinosaurs present were rare, meat-eating theropods. As such, we conclude that large plant-eating dinosaurs were absent because there were not enough predictable food and water resources for them to thrive. 
 
 Our study suggests that the climatic effects of elevated CO 2 , which were four to six times that of modern levels, drastically reshaped the environment and had profound consequences on the composition of ecosystems on land. 
 
 The discovery is not only important for understanding our past. Rapid climate swings and extremes of drought and intense heat driven by increasing atmospheric CO 2 levels have as much ability to alter the vegetation supporting modern human populations as they did for the large plant-eating dinosaurs in the Triassic. ||||| Early carnivorous dinosaurs (background) were small and rare, while other reptiles like long-snouted phytosaurs and armored aetosaurs (foreground) were common, 212 million years ago in what is now northern New Mexico. 
 
 Giant dinosaurs steered clear of the tropics for tens of millions of years because wild climate swings there were too much for them to handle, researchers say. 
 
 This finding could shed light on troubles that climate change might bring in the next few centuries, scientists added. 
 
 Dinosaurs emerged about 230 million years ago in the late Triassic period. They came to dominate life on land for 135 million years during the subsequent Jurassic and Cretaceous periods, until a cosmic impact brought a cataclysmic end to the Age of Reptiles about 65 million years ago. 
 
 Within 15 million years after dinosaurs first appeared, multitudes of dinosaur species had evolved. Inexplicably, the giant long-necked, long-tailed, vegetarian dinosaurs known as sauropods — the largest creatures to ever walk the Earth — were rare in the low latitudes around the equator for up to 30 million years after their origin, even though they dominated high latitudes before then. [Images: One of the World's Biggest Dinosaurs Discovered] 
 
 "For several decades, researchers have noticed a curious case — large plant-eating dinosaurs seemed to be much more common at high latitudes during the Triassic," study lead author Jessica Whiteside, a geochemist at the University of Southampton in England, told Live Science. "However, it has only been in the past decade that we've realized they're completely missing from the tropics, where only a few small carnivorous dinosaurs dwelled." 
 
 Reconstructing dino-scapes 
 
 To help solve this mystery, Whiteside and her colleagues analyzed rocks from a location known as Ghost Ranch in New Mexico (which inspired famed artist Georgia O'Keeffe's landscape paintings). The researchers focused on the multicolored cliffs of the Chinle Formation, which are a common sight at places such as the Painted Desert at Petrified Forest National Park in Arizona. 
 
 For nine years, the investigators studied the rocks deposited by rivers and streams between 205 million and 215 million years ago, during the late Triassic, when the Americas and other land masses of the world were bound together in the supercontinent Pangea. Back then, the Ghost Ranch site resided near the equator at about the same latitude as the southernmost tip of India does today. The site is rich with fossils from the late Triassic. 
 
 The scientists reconstructed the first detailed look at the climate and ecology during the emergence of the dinosaurs by looking at a variety of types of data from the rocks. Fossil charcoal helped the scientists deduce wildfire temperatures; fossil bones, pollen and spores helped them figure out the kinds of animals and plants living in the region; isotopes of carbon and oxygen from fossil organic matter helped researchers estimate levels of atmospheric carbon dioxide and how much vegetation existed there at the time. 
 
 "Each dataset complements the others, and they all point towards similar conditions," Whiteside said in a statement. "I think this is one of the major strengths of our study." 
 
 Dinosaurs were rare among the fossils at Ghost Ranch, accounting for less than 15 percent of vertebrates, or animals with backbones. The dinosaurs were outnumbered in diversity, abundance and body size by the reptiles known as pseudosuchians, the lineage that gave rise to crocodiles and alligators. The few dinosaurs at the site were mostly small carnivores. [In Images: Ancient Monsters of the Sea] 
 
 Plant fossils helped fill in the picture. Different groups of plants at Ghost Ranch often alternated from common to rare, as suggested by shifting abundances of different types of pollen and spores. This hinted at repeated sudden changes in climate. In addition, the way that levels of carbon isotopes went up and down over time suggested that levels of vegetation could rise and fall depending on strong fluctuations in rainfall. 
 
 Fossil charcoal suggested that raging wildfires every few dozen years could reach temperatures of up to about 1,100 degrees Fahrenheit (600 degrees Celsius). These may have been due to abrupt shifts in climate that drove massive plant die-offs and fueled hotter fires. 
 
 Climate swings 
 
 The new findings suggest that the tropics in the late Triassic possessed a highly unpredictable hot climate that could swing between wet seasons in some years and extreme droughts in others. "The conditions would have been something similar to the arid Western United States today, although there would have been trees and smaller plants near streams and rivers and forests during humid times," Whiteside said in the statement. 
 
 This harsh, fluctuating climate and its repeated wildfires would have made it difficult for abundant vegetation to grow and survive, preventing giant herbivores from invading the region. "Only small two-legged carnivorous dinosaurs such as Coelophysis could survive," Whiteside said in the statement. 
 
 This highly unpredictable hot and dry climate was linked with high atmospheric levels of carbon dioxide that were "four to six times that of modern levels, but similar to levels predicted for 100 to 200 years in the future," Whiteside said. "These data therefore suggest there are potentially profound challenges to human sustainability in the future if we experience the high carbon dioxide conditions predicted to develop in the coming 100 to 200 years." 
 
 In the future, scientists could look at other tropical, late Triassic sites, Whiteside said. 
 
 She and her colleagues detailed their findings online June 15 in the journal Proceedings of the National Academy of Sciences. 
 
 Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.
– Scientists have long been baffled by a lack of Triassic period fossils from large, herbivorous dinosaurs known as sauropods near the equator. A new study offers some illumination: It suggests a hot, unpredictable climate and high carbon dioxide levels kept some of the world's first dinosaurs away—and may shed light on our own issues with climate change. Researchers first analyzed ancient sedimentary rocks in New Mexico, which would have been much closer to the equator as part of the supercontinent Pangea some 215 million years ago, reports LiveScience. In separating carbon isotopes from fossilized organic matter, they identified significant and rapid changes to the ecosystem and atmospheric CO2 levels—which were four to six times those of today. Pollen and spores suggested available plants varied in quantity based on the frequent changes, while fossil charcoal showed evidence of wildfires every few dozen years that wreaked havoc on vegetation. The combined factors suggest an environment too unstable for sauropods until about 30 million years later, though small, carnivorous dinosaurs did populate the area. "The conditions would have been something similar to the arid Western United States today, although there would have been trees and smaller plants near streams and rivers and forests during humid times," study author Jessica Whiteside explains in a press release. Eerily, she writes at the Conversation that "rapid climate swings and extremes of drought and intense heat driven by increasing atmospheric CO2 levels have as much ability to alter the vegetation supporting modern human populations as they did for the large plant-eating dinosaurs in the Triassic." Whiteside adds we can expect "profound challenges to human sustainability in the future if we experience the high CO2 conditions predicted to develop in the coming 100 to 200 years." (Scientists made an incredible discovery inside "crap" dino fossils.)