CO2, BIG DINOSAURS AND THE EQUATOR

FROM:  NATIONAL SCIENCE FOUNDATION
Big dinosaurs steered clear of the tropics
Climate swings lasting millions of years too much for dinos

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 made a living.

The long absence at low latitudes has been one of the great, unanswered questions about the rise of the dinosaurs.

Now the mystery has a solution, according to scientists who pieced together a 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.

The findings, reported today in the journal Proceedings of the National Academy of Sciences (PNAS), show that the tropical climate swung wildly with extremes of drought and intense heat.

Wildfires swept the landscape during arid regimes and reshaped the vegetation available for plant-eating animals.

"Our data suggest it was not a fun place," says scientist Randall Irmis of the University of Utah.

"It was a time of climate extremes that went back and forth unpredictably. Large, warm-blooded dinosaurian herbivores weren't able to exist close to the equator--there was not enough dependable plant food."

The study, led by geochemist Jessica Whiteside, now of the University of Southampton, is the first to provide a detailed look at climate and ecology during the emergence of the dinosaurs.

Atmospheric carbon dioxide levels then 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.

"These scientists have developed a new explanation for the perplexing near-absence of dinosaurs in late Triassic [the Triassic was between 252 million and 201 million years ago] equatorial settings," says Rich Lane, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research.

"That includes rapid vegetation changes related to climate fluctuations between arid and moist climates and the resulting extensive wildfires of the time."

Reconstructing the deep past

The earliest known dinosaur fossils, found in Argentina, date from around 230 million years ago.

Within 15 million years, species with different diets and body sizes had evolved and were abundant except in tropical latitudes. There the only dinosaurs were small carnivores. The pattern persisted for 30 million years after the first dinosaurs appeared.

The scientists focused on Chinle Formation rocks, which were deposited by rivers and streams between 205 and 215 million years ago at Ghost Ranch (perhaps better known 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.

In ancient times, North America and other land masses 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: from fossils, charcoal left by ancient wildfires, stable isotopes from organic matter, and carbonate nodules that formed in ancient soils.

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 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 nor any other low-latitude site in the Pangaea of that time, as far as the fossil record shows.

Abrupt changes in climate left a record in the 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 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 sediment layers.

The overall picture is that of a climate punctuated by extreme shifts in precipitation and in which plant die-offs fueled hotter fires. That 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 (ppm) at the base of the section, to about 2,400 ppm 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 the 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 wildfires meant that only small two-legged carnivorous dinosaurs could survive."

-NSF-
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Cheryl Dybas, NSF

NEWLY FOUND GROUNDHOG-LIKE SKULL MAY CHANGE VIEWS ON EARLY MAMMAL EVOLUTION

FROM:  NATIONAL SCIENCE FOUNDATION 

Scientists discover fossil of bizarre groundhog-like mammal on Madagascar
Newly discovered fossil alters thinking on evolution of early mammals
Paleontologists have discovered an almost complete skull of a previously unknown mammal that likely resembled a large modern-day groundhog and lived alongside dinosaurs.

The species, found on Madagascar, is shaking up theories of early mammal evolution and diversity.

Stony Brook University paleontologist David Krause led the research team, which reports its findings in today's issue of the journal Nature.

The new fossil mammal is named Vintana sertichi.

Vintana belongs to a group of early mammals called gondwanatherians, which had been known only from a few teeth and jaw fragments.

Because of this fragmentary understanding, the mammals' evolutionary placement hadn't been clear. The well-preserved skull of Vintana sertichi is giving researchers their first clear insights into the life habits and relationships of gondwanatherians.

"We know next to nothing about early mammalian evolution on the southern continents," says Krause. "This discovery underscores how little we really know. No paleontologist could have come close to predicting the odd mix of features this cranium exhibits."

The skull measures almost five inches long, twice the size of the largest known mammal skull from the Age of Dinosaurs in the Southern Hemisphere.

At a time when the majority of mammals were shrew- or mouse-sized--mere shadows of dinosaurs--Vintana was a super heavyweight, estimated to have had a body mass of about 20 pounds, two or three times the size of an adult groundhog today.

Vintana's skull has an unusual shape, with deep, huge eye sockets, and long, scimitar-shaped flanges for attachment of massive chewing muscles.

"This is the first discovery of a cranial fossil from the extinct group of mammals called Gondwanatheria in the Southern Hemisphere," says Yusheng (Chris) Liu, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research along with the National Geographic Society.

"The finding will help us better understand the early evolution of this mammal group," says Liu.

The initial discovery came about by chance, says Krause.

Vintana means luck and refers to the good fortune its discoverer, researcher Joe Sertich, then of Stony Brook University, had in finding the fossil.

Sertich collected a 150-block rock matrix filled with fish fossils. When the block was CT-scanned at Stony Brook, the images revealed something rare inside--a nearly complete skull of a previously unknown ancient mammal.

"When we realized what was staring back at us on the computer screen, we were stunned," says scientist Joe Groenke of Stony Brook, the first to view the CT images.

Groenke spent the next six months extracting the skull from the surrounding rock matrix, one sand grain at a time.

Krause and colleagues conducted a comprehensive analysis of the skull, much of it using micro-computed tomography and scanning electron microscopy to reveal minute aspects of its anatomy.

They compared the skull to those of hundreds of other fossil and extant mammals.

Its teeth, eye sockets, braincase, and inner ear revealed that Vintana was likely a large-eyed herbivore that was agile, with keen senses of hearing and smell.

These and other features were also used to analyze its relationships to other early mammals.

Vintana and other gondwanatherians were probably close relatives of multituberculates, the most successful mammalian contemporaries of dinosaurs on Northern Hemisphere continents.

Krause says that a major question remains for scientists: How did such an unusual creature evolve?

Madagascar was an island for more than 20 million years before the time in which the rock strata containing Vintana were deposited.

Krause theorizes that the primitive features of the skull are holdovers from a time when an ancient lineage that ultimately produced Vintana was marooned on the island.

It was this isolation, he believes, first from Africa, then Antarctica/Australia, and finally the Indian subcontinent that allowed the evolution of Vintana's unique and bizarre features.

-NSF-

Media Contacts
Cheryl Dybas,

NSF VIDEO: RESEARCHERS DISCOVER NEW SPECIES OF DINOSAUR IN TANZMANIA

THE EXTINCTION BEFORE THE AGE OF DINOSAURS



Edaphosaurus. Exhibit Museum of Natural History, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan, USA.
　

FROM: NATIONAL SCIENCE FOUNDATION

What Happened to Dinosaurs' Predecessors After Earth's Largest Extinction 252 Million Years Ago?
Predecessors to dinosaurs missed the race to fill habitats emptied when nine out of 10 species disappeared during Earth's largest mass extinction 252 million years ago.

Or did they?

That thinking was based on fossil records from sites in South Africa and southwest Russia.

It turns out, however, that scientists may have been looking in the wrong places.

Newly discovered fossils from 10 million years after the mass extinction reveal a lineage of animals thought to have led to dinosaurs in Tanzania and Zambia.

That's still millions of years before dinosaur relatives were seen in the fossil record elsewhere on Earth.

"The fossil record from the Karoo of South Africa, for example, is a good representation of four-legged land animals across southern Pangea before the extinction," says Christian Sidor, a paleontologist at the University of Washington.

Pangea was a landmass in which all the world's continents were once joined together. Southern Pangea was made up of what is today Africa, South America, Antarctica, Australia and India.

"After the extinction," says Sidor, "animals weren't as uniformly and widely distributed as before. We had to go looking in some fairly unorthodox places."

Sidor is the lead author of a paper reporting the findings; it appears in this week's issue of the journal Proceedings of the National Academy of Sciences.

The insights come from seven fossil-hunting expeditions in Tanzania, Zambia and Antarctica funded by the National Science Foundation (NSF). Additional work involved combing through existing fossil collections.

"These scientists have identified an outcome of mass extinctions--that species ecologically marginalized before the extinction may be 'freed up' to experience evolutionary bursts then dominate after the extinction," says H. Richard Lane, program director in NSF's Division of Earth Sciences.

The researchers created two "snapshots" of four-legged animals about five million years before, and again about 10 million years after, the extinction 252 million years ago.

Prior to the extinction, for example, the pig-sized Dicynodon--said to resemble a fat lizard with a short tail and turtle's head--was a dominant plant-eating species across southern Pangea.

After the mass extinction, Dicynodon disappeared. Related species were so greatly decreased in number that newly emerging herbivores could then compete with them.

"Groups that did well before the extinction didn't necessarily do well afterward," Sidor says.

The snapshot of life 10 million years after the extinction reveals that, among other things, archosaurs roamed in Tanzanian and Zambian basins, but weren't distributed across southern Pangea as had been the pattern for four-legged animals before the extinction.

Archosaurs, whose living relatives are birds and crocodilians, are of interest to scientists because it's thought that they led to animals like Asilisaurus, a dinosaur-like animal, and Nyasasaurus parringtoni, a dog-sized creature with a five-foot-long tail that could be the earliest dinosaur.

"Early archosaurs being found mainly in Tanzania is an example of how fragmented animal communities became after the extinction," Sidor says.

A new framework for analyzing biogeographic patterns from species distributions, developed by paper co-author Daril Vilhena of University of Washington, provided a way to discern the complex recovery.

It revealed that before the extinction, 35 percent of four-legged species were found in two or more of the five areas studied.

Some species' ranges stretched 1,600 miles (2,600 kilometers), encompassing the Tanzanian and South African basins.

Ten million years after the extinction, there was clear geographic clustering. Just seven percent of species were found in two or more regions.

The technique--a new way to statistically consider how connected or isolated species are from each other--could be useful to other paleontologists and to modern-day biogeographers, Sidor says.

Beginning in the early 2000s, he and his co-authors conducted expeditions to collect fossils from sites in Tanzania that hadn't been visited since the 1960s, and in Zambia where there had been little work since the 1980s.

Two expeditions to Antarctica provided additional finds, as did efforts to look at museum fossils that had not been fully documented or named.

The fossils turned out to hold a treasure trove of information, the scientists say, on life some 250 million years ago.

Other co-authors of the paper are Adam Huttenlocker, Brandon Peecook, Sterling Nesbitt and Linda Tsuji from University of Washington; Kenneth Angielczyk of the Field Museum of Natural History in Chicago; Roger Smith of the Iziko South African Museum in Cape Town; and Sébastien Steyer from the National Museum of Natural History in Paris.

The project was also funded by the National Geographic Society, Evolving Earth Foundation, the Grainger Foundation, the Field Museum/IDP Inc. African Partners Program, and the National Research Council of South Africa.

-NSF-