The demise of the dinosaurs 65 million years ago opened the door of opportunity for mammals to take over the Earth—that much is clear. What’s coming into focus, thanks to a study out in Science, is just how fast mammals maxed out their size once the terrible lizards were out of the way.
“For the first 140 million years of our evolutionary history we really did nothing—we were really kind of boring,” Felisa Smith, an associate professor of biology at the University of New Mexico and coauthor of the new study. … But across all of the major continents, during the first 25 million years after the dinosaurs were wiped out, mammals underwent an explosive growth spurt. By 42 million years ago, however, the researchers found, the intense growth had leveled off. [Scientific American]
Smith’s team surveyed fossils from around the world, including 32 different mammalian orders. No matter where they looked, she says, they saw the same pattern. Mammals that survived the extinction event were small, mostly rodent-sized. Then all over the planet they exploded in size during that period of 20 to 25 million years.
When it comes to explaining why the woolly mammoths died out, “death from above” could be down for the count.
Nearly 13,000 years ago, North American megafauna like the mammoths and giant sloths—and even human groups like the people of the Clovis culture—disappeared as the climate entered a cold snap. As DISCOVER has noted before, there’s been a controversial hypothesis bubbling up saying that a comet impact caused it all, but other scientists have been shooting holes in that idea of the last couple years. In a study in this week’s Proceedings of the National Academy of Sciences, a team led by Tyrone Daulton pooh-poohs what may be the last major evidence that supports the impact idea.
That evidence takes the shape of nano-diamonds in ancient sediment layers, a material said to form during impacts only.
During the Pleistocene epoch animals thought big: It was the age of the megafauna, when creatures like the mammoth, an 8-foot-long beaver, and a hippopotamus-sized wombat walked the Earth. But these giants vanished one by one, and scientists have long wondered why.
Debate over what caused the megafauna to die out has raged for 150 years, since Darwin first spotted the remains of giant ground sloths in Chile. Possible causes have ranged from human influence to climate change in the past, even to a cataclysmic meteor strike. [BBC]
Now, a discovery on the South Pacific island nation of Vanuatu seems to have answered the question for at least one species. Researchers have turned up the bones of a giant land turtle in a dump used by the people who settled on the islands 3,000 years ago, and lead researcher Trevor Worthy says the evidence strongly suggests that the turtles were hunted into extinction.
A fungus found within ancient mammoth dung is providing scientists with clues about how the large ancient mammals collectively known as megafauna went extinct. The fungus, Sporormiella, produces spores in the dung of large herbivores. These are then preserved in the layers of mud and can provide an index of the number of these animals, or megafauna, that roamed the environment at a particular time [BBC News]. For a new study, researcher Jacquelyn Gill collected and analyzed spores in sediment samples from an Indiana lake and several sites in New York.
From Gill’s analysis, published in the journal Science, she concluded that North American megafauna began a slow decline around 15,000 years ago and vanished about 1,000 years later. The data suggests megafauna started going extinct much earlier than previously though, which basically wipes out two theories of their extinction.
The giant, prehistoric kangaroo that once hopped over the Australian landscape may have been wiped out by the first human settlers on that continent, a new study argues. In making this claim, the researchers are entering into a long-running debate over whether Australia’s “megafauna,” which also included marsupial lions and hippo-sized wombats, were driven extinct by the changing climate or by overzealous hunting. And while the new study, which will be published in the Proceedings of the National Academy of Sciences, makes an interesting case for the latter hypothesis, some researchers are not convinced.
Researchers analyzed the teeth of the nearly seven-foot-tall kangaroo, known as Procoptodon goliah, to determine what it ate and drank. Different sources of water and food leave trace amounts of particular types, or isotopes, of hydrogen and carbon atoms, which are deposited in the teeth like a recorded diet. Additionally, tiny patterns of wear give clues about the type of food a given creature chewed. The team concluded that the giant kangaroos fed mainly on saltbush shrubs [BBC News]. These hardy bushes thrive in arid conditions, which makes it less likely that the kangaroos ran out of food as the continent’s climate got hotter and drier.
A cooling climate, not human hunters, were at fault for the extinction of the prehistoric cave bear (Ursus spelaeus), according to a new study. Researchers examining cave bear remains now say the giant vegetarians died from starvation and much earlier than previously thought. “The disappearance of the cave bear around 27,500 years ago was probably due to the significant decline in quantity and quality of plant food, which in turn was the result of marked climatic cooling,” [Telegraph] said researcher Anthony J. Stuart.
Previous radiocarbon dating of cave bear remains incorrectly placed their apocalypse at 14,000 years ago because some of the remains were actually those of brown bears, still alive today, that were mistakenly identified. The new study excludes previous errors and includes new data taken from remains found in ancient hibernation sites in the Alps. The new extinction date, 27,800 years ago, coincides with a period of significant climate change, known as the Last Glacial Maximum [or Ice Age], when a marked cooling in temperature resulted in a reduction or total loss of the vegetation that the cave bears ate (today’s brown bears are omnivores) [LiveScience.com].
Woolly mammoths may all look the same in your average natural history museum display — the extinct animals are always depicted with the same curly tusks, shaggy hair, and lumbering feet. But researchers have just discovered that they were not all the same, that two genetically distinct groups of mammoths roamed the Siberian plains many millennia ago, and that one group avoided extinction for an extra 30,000 years.
Researchers first went in search of tufts of mammoth hair that had been frozen in the permafrost. They then used a new technique that allowed them to read the complete DNA sequence of an animal’s mitochondria (an energy-producing organelle within a cell) from a single hair. The DNA in mitochondria is passed only through the mother’s line, and doesn’t give information about changes in gene function, as nuclear DNA can. But it is useful because it doesn’t change from parent to offspring, making it easy to show when different animal groups are present [Nature News].