Posts Tagged ‘Paleontology’

15,000-year-old campsite in Texas challenges conventional story of American settlement [Scientific Breakthrough]

24 Mar
15,000 years ago, humans camped in a lush Texas valley, leaving thousands of artifacts behind, from tools to face paint. This could be definitive proof that ancient people arrived in America by boat, not by walking the Bering Strait. More »

A piece of 50 million-year-old preserved lizard skin reveals how ancient animals looked [Paleontology]

23 Mar
Using new infrared light techniques, scientists have at last been able to analyze the chemical composition of a piece of lizard skin, preserved for millions of years in dry rock. So what did these reptiles look like in pre-human times? More »

Mass Extinctions Change the Rules of Evolution

02 Sep

A reinterpretation of the fossil record suggests a new answer to one of evolution’s existential questions: whether global mass extinctions are just short-term diversions in life’s preordained course, or send life careening down wholly new paths.

Some scientists have suggested the former. Rates of species diversification — the speed at which groups adapt and fill open ecological niches — seemed to predict what’s flourished in the aftermath of past planetary cataclysms. But according to the calculations of Macquarie University paleobiologist John Alroy, that’s just not the case.

“Mass extinction fundamentally changes the dynamics. It changes the composition of the biosphere forever. You can’t simply predict the winners and losers from what groups have done before,” he said.

Alroy was once a student of paleontologist Jack Sepkoski, who in the 1980s formalized the notion that Earth has experienced five mass extinctions in the 550 million years since life became durable enough to leave a fossil record. Graphs of taxonomic abundance depict lines rising steadily as life diversifies, plunging precipitously during each extinction, and rising again as life proliferates anew.

As the fossil record is patchy and long-term evolutionary principles still debated, paleobiologists have historically disagreed about what these extinctions mean. Some held that, in the absence of extinctions, species would diversify endlessly. The Tree of Life could sprout new branches forever. Others argued that each taxonomic group had limits; once it reached a certain size, each branch would stop growing.

Sepkoski’s calculations put him on the limits side of this argument. He also proposed that, by looking at the rate at which each group produced new species, one could predict the winners and losers of each mass extinction’s aftermath. Groups that diversified rapidly would flourish. Their destiny was already established.

“It’s a clockmaker vision of evolution. Each group has fixed dynamics, and if there’s an extinction, it just messes it up a bit,” said Alroy. “That’s what I’m challenging in this paper. There are limits, and that’s why we don’t have a trillion species. But those limits can change.”

Alroy crunched marine fossil data in the Paleobiology Database, which gathers specimen records from nearly 100,000 fossil collections around the world. He used a statistical adjustment method designed to reduce the skewing influences of paleontological circumstance — the greater chances of finding young fossils rather than old, the ease of studying some types of rock rather than others.

Historical species diversity among marine animals of Cambrian, Paleozoic and Modern origin.

The analysis, published September 2 in Science, produced what Alroy considers to be the most accurate reflection of extinction dynamics to date. And while his data supported the notion that each group’s diversity eventually hits a limit, he didn’t find Sepkoski’s correlation between pre-mass-extinction diversity rates and post-extinction success. Each mass extinction event seemed to change the rules. Past didn’t indicate future.

In an accompanying commentary, paleontologist Charles Marshall of the University of California, Berkeley noted that Alroy’s statistical methods still need review by the paleobiology community. The Paleobiological Database, for all its thoroughness, might also be incomplete in as-yet-unappreciated ways. “There will be no immediate consensus on the details of the pattern of diversity,” he wrote. But “the pieces are falling into place.”

Enough pieces have come together for Alroy to speculate on his findings’ implication for the future, given that Earth is now experiencing another mass extinction. Starting with extinctions of large land animals more than 50,000 years ago that continued as modern humans proliferated around the globe, and picking up pace in the Agricultural and Industrial ages, current extinction rates are far beyond levels capable of unraveling entire food webs in coming centuries. Ecologists estimate that between 50 and 90 percent of all species are doomed without profound changes in human resource use.

In the past, many evolutionary biologists thought life would eventually recover its present composition, said Alroy. In 100 million years or so, the same general creatures would again roam the Earth. “But that isn’t in the data,” he said.

Instead Alroy’s analysis suggests that the future is inherently unpredictable, that what comes next can’t be extrapolated from what is measured now, no more than a mid-Cretaceous observer could have guessed that a few tiny rodents would someday occupy every ecological niche then ruled by reptiles.

“The current mass extinction is not going to simply put things out of whack for a while, and then things will go back to where we started, or would have gone anyway,” said Alroy. Mass extinction “changes the rules of evolution.”

Images: 1) A fossil skull of Dunkleosteus, an apex predator fish that lived between 380 million and 360 million years ago, and had what is believed to be history’s most powerful bite./Michael LaBarbera, courtesy of The Field Museum. 2) Graph of species diversity among marine animals of Cambrian, Paleozoic and Modern origin./Science.

See Also:

Citations: “The Shifting Balance of Diversity Among Major Marine Animal Groups.” By J. Alroy. Science, Vol. 329 No. 5996, September 3, 2010.

“Marine Biodiversity Dynamics over Deep Time.” By Charles R. Marshall. Science, Vol. 329 No. 5996, September 3, 2010.

Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.


Valley of the Whales

08 Aug

Paleontologist Philip Gingerich looks for sea monsters in the Egyptian desert. He assembles fossils of ancient whales that died there when it was covered by an ocean. One such whale is the Basilosaurus, which had small hind legs.

“Complete specimens like that Basilosaurus are Rosetta stones,” Gingerich told me as we drove back to his field camp. “They tell us vastly more about how the animal lived than fragmentary remains.”

Wadi Hitan—literally “valley of whales”—has proved phenomenally rich in such Rosetta stones. Over the past 27 years Gingerich and his colleagues have located the remains of more than a thousand whales here, and countless more are left to be discovered.

Researchers hope that whale fossils can help them understand how a land mammal evolved into an aquatic form that became our modern whales. Link

(Image credit: Richard Barnes/National Geographic)


Triceratops controversy shakes paleontology to its bones [Mad Paleontology]

06 Aug
Paleontologists have discovered a shocking fact about the relationship between the celebrated Triceratops dinosaur (left) and its less-glamorous, holey-headed counterpart, Torosaurus (right). Turns out they're not evolutionary cousins. In fact, Triceratops is just a younger version of Torosaurus. More »

‘Lucy’s Grandfather’ Fossil Makes Humanity’s Ancestor Seem More Like Us

22 Jun

A 3.6 million-year-old fossil from one of humanity’s earliest ancestors is more human-like than expected — and much taller.

The discovery makes Lucy, the best-known fossil of all, appear to be exceptionally short by comparison. Lucy and the new skeleton are both Australopithecus afarensis, the first fully bipedal primate and a direct ancestor of humanity. Unlike Lucy and every other A. afarensis fossil, the new skeleton has complete forelimb and hindlimb bones, allowing researchers to estimate its size more accurately.

The new A. afarensis specimen stood between 5 and 5 1/2 feet tall, towering over Lucy’s 3-foot height. Other fossil fragments suggested that Lucy was an unreliable measuring stick for A. afarensis, but the new fossil is the most conclusive evidence yet. Dubbed “Kadanuumuu,” or Big Man, it is described June 21 in the Proceedings of the National Academy of Sciences.

Big Man’s limbs also appear well-suited for running, in contrast to the shortened gait implied by Lucy’s skeleton. The proportions compare to those found two million years later in Homo erectus, and would not be out of place in a modern human, said study co-author Owen Lovejoy, a Kent State University paleoanthropologist.

“The difference between Australopithecus and humans is much less than everyone expected,” said Lovejoy. “Upright walking and running were pretty advanced at 3.6 million years ago, and they didn’t change much over the next two million years. Most of the changes in that period of time took place elsewhere.”

Lovejoy was also part of the team that discovered Ardipithecus ramidus, a 4.4 million-year-old possible human ancestor that was officially described last October. Ardipithecus was far less chimp-like than expected.

That raises the possibility that it’s the other Great Apes, rather than humans, whose bodies have evolved the most over the last few million years.

Big Man, with a rib cage shaped more like our own than that of a chimpanzee or gorilla, reinforces that notion.

“Chimps and gorillas are again the unusual form. Hominids and ourselves bear many primitive traits that haven’t been specialized like they have in gorillas,” said Lovejoy.

“The classic cartoon of the ape turning into the human doesn’t work at all.”

Image: Yohannes Haile-Selassie/PNAS.

See Also:

Citation: “An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia.” By
Yohannes Haile-Selassie, Bruce M. Latimer, Mulugeta Alene, Alan L. Deino, Luis Gibert, Stephanie M. Melillo, Beverly Z. Saylor, Gary R. Scott, C. Owen Lovejoy.

Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.