Climate change brought tropical forest to Wyoming
Rhett A. Butler, mongabay.com
November 11, 2005
Climate change 55 million years ago caused significant changes in forest composition and the distribution of mammals according to a new study in Science. The Paleocene-Eocene Thermal Maximum, in which temperatures rose by as much as 10 degrees in a relatively short period of time, helped bolster the "Age of Mammals," which included the first appearance of modern primates. After an initial period of increasing aridity in northern latitudes like the study site of Bighorn Basin in northwestern Wyoming, it appears that forests transitioned towards warm tropical ecosystems with closely spaced trees, ideal for the evolution of primates.
News releases from institutions involved in the research can be found below.
UF researcher: Global warming dramatically changed ancient forests
By Cathy Keen
University of Florida news release
November 10, 2005
The findings, which appear in this week's issue of the journal Science, provide the first evidence that land plants changed drastically during a period of sudden global warming 55 million years ago, said Jonathan Bloch, a University of Florida vertebrate paleontologist and member of the research team.
"It indicates that should we have a period of rapid global warming on that scale today, we might expect very dramatic changes to the biota of the planet, not just the mammals and other vertebrates, but forests also completely changing," said Bloch, who is a curator at the Florida Museum of Natural History on the UF campus.
Scientists have known there was significant turnover in mammals during this rapid period of global warming called the Paleocene-Eocene Thermal Maximum, in which temperatures rose by perhaps as much as 10 degrees in the relatively short time span of 10,000 years, then lasting for another 80,000 to 100,000 years, Bloch said.
Global warming allowed mammals to emigrate across northern land bridges, marking the first appearance of perissodactlys in the form of the earliest known horse; artiodactyls, a group of even-toed ungulates that includes pigs, camels and hippos; as well as modern primates, he said.
But until now, no clues were available as to what happened to plants during this shift, considered one of the most extreme global warming events during the Cenozoic, the "Age of Mammals," Bloch said. "It was very puzzling because it looked like there was nothing going on with plants, which was rather strange and disconcerting."
Excavations by team leader Scott Wing, a paleontologist at the Smithsonian Institution, in the Bighorn Basin of northwestern Wyoming uncovered fossil leaves and pollen alongside fossilized mammals in rocks that were deposited during this turbulent geologic interval.
"Up until this point we have not had a place in which we have mammal and plant remains preserved in the same rocks spanning what we call the Paleocene-Eocene boundary," Bloch said. "Amazingly, these plants came from what would have been more tropical environments."
Some of the plant remains resembled those found in rock deposits of similar age unearthed in Mississippi, Louisiana and Texas, including relatives of poinsettia and sumac, Bloch said.
However, plant fossils found in the same area dating immediately before and after this period of rising temperatures reflected typical mid-latitude forests of the time and included relatives of dawn redwood, alder, sycamore and walnut, Bloch said. As temperatures cooled, floral newcomers appeared from Europe, including species of linden and wing nut. These plants probably emigrated along the same land bridges that animals traveled, he said.
Because his research specialty is mammals, Bloch said he is particularly interested in understanding how the movement of plants affected the earliest evolution of modern primates, which first appeared throughout the world during this period.
"I would very much like to know what these forests were like when these first modern primates were coming in because it has implications for how these animals lived and behaved right from the beginning," he said.
If the landscape evolved from an initially drier habitat, with patchy open spaces, into a more lush tropical forest with densely packed trees, it might have played a role in the evolution of primates' climbing skills, Bloch said. The ancestors of living primates would have been leaping through the tree canopy, foraging for fruit and insects, he said.
Partly because of the dramatic change in mammals, including the first appearance of modern primates, and also because of the interval's rapid temperature change, there has been a wide range of scientific interest in the Paleocene-Eocene boundary, Bloch said.
The warming was caused by a gigantic release of carbon dioxide into the atmosphere that was comparable to the atmospheric effects expected from human burning of fossil fuels, he said.
"You can't predict the future, but there has been a time in the past where we had similar type of conditions, and we might look to that experience," Bloch said.
Original press release: UF researcher: Global warming dramatically changed ancient forests
From Mississippi to Wyoming, Plants Once Danced to Fast-Changing Climate Tune
National Science Foundation News Release
November 10, 2005
Scientists have discovered the first fossil leaves from a period of rapid global warming 55 million years ago. The leaves tell a story about plants alive during that time: a fast-changing climate allowed southern-dwelling trees and shrubs to move north in a hurry. In fact, plants spread from the Gulf Coast to Wyo.--a distance of some 1,000 miles--in 10,000 years or less.
A sudden global warming, called the Paleocene-Eocene Thermal Maximum, or PETM, raised global temperatures as much as 18 degrees Fahrenheit (10 degrees Celsius). Previous research linked the PETM with mass extinctions of bottom-dwelling marine organisms and the migration of mammals across Arctic land bridges. Now, research results appearing in the Nov. 11 issue of the journal Science provide the first evidence the warming also affected land plants.
"This study shows that vegetation responded rapidly to a major change in climate during the PETM. Plants that previously were common much farther south migrated northward," said Enriqueta Barrera, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the project.
Scott Wing, a paleobiologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., led the research team. He said plant ranges changed as quickly during the PETM as they did when glaciers retreated from the northern continents in the past 20,000 years.
Similar rapid changes in plant life might be expected in the future as a result of human-induced global warming, Wing said, if habitat destruction doesn't block the paths by which plants disperse to their preferred climate zone. "No two events are ever exactly the same," he said, "but the history of life on this planet has a lot to tell us about our possible future."
According to Wing, the PETM was caused by a massive release of carbon into the atmosphere and ocean, making it an analog for the global warming that is expected as humans add carbon dioxide to the atmosphere, primarily by burning fossil fuels.
The new results were taken from fossil leaves and pollen found in the Bighorn Basin of northwestern Wyo. "The Bighorn Basin is a well-known treasure trove for fossils because enormous amounts of sediment were deposited there as the Rocky Mountains rose," said Wing. "Those sediments and the fossils they contain are now exposed in spectacularly eroded badlands."
Fossil mammals and chemical analysis of rocks were key to determining the age of the leaf fossils, which are the first discovered from the PETM interval.
Plant fossils from before and after the PETM document the typical northern forests of the time, including relatives of dawn redwood, alder, sycamore, walnut and sassafras. Fossils from the PETM itself show that--for a short time--the area supported an entirely different type of vegetation, one dominated by members of the bean family and including warmth-loving relatives of poinsettia, sumac and paw-paw.
Some of the plant fossils found in the PETM in Wyo. were known from rocks of similar ages in Miss., La., and Texas. The southern plants occurred throughout the PETM in Wyo., then disappeared, presumably unable to survive there as the global climate cooled at the end of the event, said Wing.
The return to a cooler climate brought a different set of plants to Wyo. Relatives of linden and wingnut emigrated from Europe to North America across Arctic land bridges during the peak warmth, then established themselves in Wyo. forests after the global heat wave passed. Scientists see a similar pattern of migration in animals that lived during the PETM, suggesting that they, too, moved in concert with rapid climate change.
The National Science Foundation
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering, with an annual budget of nearly $5.47 billion. NSF funds reach all 50 states through grants to nearly 2,000 universities and institutions. Each year, NSF receives about 40,000 competitive requests for funding, and makes about 11,000 new funding awards. The NSF also awards over $200 million in professional and service contracts yearly.
Original press release: From Mississippi to Wyoming, Plants Once Danced to Fast-Changing Climate Tune
Rapid Warming Caused Vegetation Changes
Penn State News Release
November 10, 2005
"There has been an absence of fossil leaf sites dating to the Paleocene-Eocene Thermal Maximum (PETM)," says Dr. Francesca A. Smith, postdoctoral researcher in geosciences, Penn State.
Scientists have long known that during the PETM, mammalian communities changed, but without plant fossil samples, they could not say the same for plants. The PETM is unusual because the warming of 9 to 18 degrees Fahrenheit occurred in only 10,000 years, a geologically short time span. Researchers believe that increased carbon dioxide caused the warming, but underlying causes of the increase are still being debated.
"The PETM provides an important analog to present-day anthropogenic global warming, because the two episodes are inferred to have similar rates and magnitudes of carbon release and climate change," the researchers report in today's (Nov. 11) issue of Science.
Dr. Scott Wing, Department of Paleobiology, Smithsonian Museum of Natural History, led the expedition to the southeastern Bighorn Basin, Wyoming, that found new boundary sequences of fossils that covered the change from the Paleocene to the Eocene. These sequences, unlike those found in the past, contained both leaf and pollen fossils.
"Finding fossil leaves from this period is difficult," says Smith. "Leaves are only rarely preserved and the fossil beds for this time period are only 130 to 160 feet thick."
To ensure that the new areas were actually in the proper time period, the researchers used two dating methods. Smith and Dr. Katherine H. Freeman, professor of geosciences, Penn State, looked at the chemical signature of the carbon in the fossils. From marine sediment studies, researchers know that during this time period, the heavier form of carbon, carbon 13, occurred less frequently in the atmosphere. Smith and Freeman identified these fossil beds as having the proper carbon composition for the PETM. Coupling carbon with the mammalian fossils found in the beds, including the oldest known horses that were the size of a cat and the ancestors of modern primates, the researchers identified the beds as coming from the PETM.
Analysis of the plant fossils showed that the plants from before and after the PETM were from typical forests for the time, containing relatives of dawn redwood, alder, sycamore, walnut and sassafras. However, the bean family, including relatives of poinsettia, sumac and paw-paw, dominate the fossils during the PETM. These are plants more commonly found during that time period, 1,000 miles to the south in Mississippi, Louisiana and Texas. These plants migrated north in 10,000 years or less.
The leaf fossils also allowed researchers to look at the PETM climate. By comparing the numbers of smooth edged leaves to toothed leaves, they found that the temperature change in the Bighorn basin was about 9 degrees Fahrenheit warmer during the PETM. By looking at the leaves' surface areas, researchers could estimate precipitation.
"Using these methods, we can infer the temperature changes and determine that the area was dry at the beginning of this period and wet toward the end," says Smith. "Rainfall declined about 40 percent and later recovered."
At the end of the PETM, forests returned to their original composition with the addition of plants like relatives of the wingnut and linden that migrated into the area from Europe across Arctic land bridges.
"So much of the information that we have about ancient terrestrial climate during the PETM comes from the Bighorn basin area because it is one of a handful of terrestrial sequences for that time period," says Smith "To interpret the record, we need to have as much information as we can get."
According to Wing, similarly rapid changes in flora might be expected in the future as a result of human-induced global warming.
Other members of the research team include Guy J. Harrington, University of Birmingham, UK; Jonathan I. Bloch, Florida Museum of Natural History, Gainesville, and Douglas M. Boyer, Stony Brook University. The National Science Foundation, Roland Brown Fund and Florida Museum of Natural History supported this research.
Original press release: Rapid Warming Caused Vegetation Changes