Paleontology news

Large size and a fast bite spelled doom for bony fishes during the last mass extinction 65 million years ago, according to a new study to be published March 31, 2009, in the Proceedings of the National Academy of Sciences.

Today, those same features characterize large predatory bony fishes, such as tuna and billfishes, that are currently in decline and at risk of extinction themselves, said Matt Friedman, author of the study and a graduate student in evolutionary biology at the University of Chicago.

"The same thing is happening today to ecologically similar fishes," he said. "The hardest hit species are consistently big predators."

Studies of modern fishes demonstrate that large body size is linked to large prey size and low rates of population growth, while fast-closing jaws appear to be adaptations for capturing agile, evasive prey—in other words, other fishes. The fossil record provides some remarkable evidence supporting these estimates of function: fossil fishes with preserved stomach contents that record their last meals.

When an asteroid struck the earth at the end of the Cretaceous about 65 million years ago, the resultant impact clouded the earth in soot and smoke. This blocked photosynthesis on land and in the sea, undermined food chains at a rudimentary level, and led to the extinction of thousands of species of flora and fauna, including dinosaurs.

The end of an era Some 65 million years ago, the earth's most recent 'mass extinction' took place. One or more catastrophic events - such as a comet strike or increased volcanic activity - produced widespread fires and clouds of dust and smoke that obstructed sunlight for a long period of time. These adverse conditions killed off about 60% of the plant species and numerous animals, including the dinosaurs. Only the most well-adapted plants and animals were able to survive this mass extinction - but what is 'most well-adapted'?

A role for DNA duplication?

Jeffrey Fawcett, Steven Maere and Yves Van de Peer (VIB-UGent) have been working as bioinformatics specialists to decode various plant genomes - the complete content of a plant's DNA - ranging from small weeds to tomatoes and rice to trees. Time and again, they have been confronted with the fact that, over the course of the history of these plants, their entire DNA was duplicated one or more times. By means of sophisticated research techniques, they have dated these duplications as closely as possible.

Yves Van de Peer's group then noticed that the most recent duplications occurred at approximately the same time in all of the plants. But, in terms of evolution, 'the same time' is relative: the DNA duplications occurred between 40 and 80 million years ago. So, the bioinformaticians worked to refine the dating. Thanks to their expertise in comparative genome studies and their extensive database, they were able to make a very precise dating of the duplications on the basis of standard evolution trees. This indicated that, in all of the plants under study, the most recent genome duplication occurred some 65 million years ago - thus, at the time of the last mass extinction.

A universal mechanism

From these results, the VIB researchers concluded that plants with a duplicated genome were apparently the 'most well-adapted' for survival in the dramatically changed environment. Normally, in unaltered circumstances, duplications of DNA are disadvantageous. In fact, they cause very pronounced properties that are not desired in an unaltered environment. However, in radically changed circumstances, these very properties can make the organism better adapted to the new climate.

In previous research, Yves Van de Peer had discovered very old genome duplications in early ancestors of vertebrates and fish. At that time, he showed that these duplications were probably crucial for the development of vertebrates and thus of human beings as well. So, genome duplication is probably a universal mechanism that has ensured that the role of our planet's vertebrates and flowering plants has become much greater over time.

credited to vib.be

Among the hundreds of plants that have been domesticated in the New World, none has received as much attention or been subject to as much debate as corn, or maize (Zea mays L.), arguably the most important crop of the Americas. Controversies have existed for years over what the wild ancestor of maize is and where and when it was domesticated. An international team of scientists led by Dolores Piperno, archaeobotanist at the Smithsonian's National Museum of Natural History, and Anthony Ranere, professor of anthropology at Temple University in Philadelphia, have discovered the first direct evidence that indicates maize was domesticated by 8,700 years ago, the earliest date recorded for the crop. The research findings will be published March 23 in the journal, Proceedings of the National Academy of Sciences.

It is certain that maize was originally domesticated in Mexico from a wild plant called "teosinte," and genetic studies of modern populations of teosinte and maize suggested this event occurred somewhere in the Central Balsas Valley region of tropical southwest Mexico. However, no research on early prehistoric human settlement and agriculture had been carried out there. Piperno and the team searched this region of Mexico for locations that showed human occupancy for the time period they thought to be critical to maize domestication, from approximately 8,000 to 9,000 years ago. They discovered sites dating to this age, excavated them and analyzed the stone tools and plant remains they retrieved. Microfossil (starch grain and phytolith) analysis from a rock shelter called Xihuatoxtla, conducted in part with Irene Holst at the Smithsonian Tropical Research provide direct evidence for the domestication of maize and a species of squash.

"Our findings confirm an early Holocene age for maize domestication and indicate that it is another important New World crop that had its origins in the tropical forest," said Piperno. "Much more work needs to be done in the Central Balsas region to investigate even earlier periods when teosinte must have been exploited by early human populations and then initially cultivated."

The evidence corroborates a large quantity of previous research carried out in the lowland tropical forest south of Mexico by Piperno and other investigators that indicated maize spread to Panama approximately 7,600 years ago and was well established in northern South America about 6,000 years ago.

The archaeological record establishes tropical southwest Mexico as an important region where early agriculture occurred in the New World and adds maize to the roster of important cereals (others are wheat and barley from the Middle East) that were cultivated and domesticated by 9,000 years ago. The team's findings also contribute to the growing body of evidence that seasonally dry tropical forests were important centers of early human settlement and farming in the Neotropics. Early agriculture in this region of Mexico appears to have involved small groups of cultivators who were shifting their settlements seasonally and engaging in a variety of subsistence pursuits.

credited to si.edu

Feathered dinosaurs may have been the rule, not the exception. A stunning new fossil from China reveals primitive filamentary feathers on a dinosaur only distantly related to birds, indicating that all dinosaurs share a feathery ancestry.

All of the feathered dinosaurs found since Sinosauropteryx startled the world in 1996 come from a group of two-legged predators called theropods, which gave rise to birds. Now Hai-Lu You of the Institute of Geology in Beijing, China, along with three colleagues, has found feather-like filaments on a fossil named Tianyulong confuciusi (Nature, vol 458, p 333).

About 70 centimetres long, the plant-eating Tianyulong lived from about 140 to 100 million years ago. The fossil is a member of the ornithischian group of dinosaurs that diverged about 220 million years ago from the other main branch of the dinosaurs, which contained the theropods. The presence of feathers on both branches of the evolutionary tree suggests they were present in the ancestor of all the dinosaurs.

If the ancestral form had such filaments, then they might be present in many or most dinosaurs - although skin impressions left by large dinosaurs lack feathers, suggesting that the trait died out in larger species.

Feathers might even stretch back to the pterosaurs, which split from the ancestors of dinosaurs shortly before the dinosaur groups emerged. A few pterosaur fossils possess hair-like stubble.

While modern flight feathers are elaborately branched, the new fossil's feathers are hollow single filaments - "the most primitive basic feather structure", says ornithologist Alan Brush at the University of Connecticut at Storrs. Similar feathers still exist on the tail of the 12-wired bird of paradise and in the "beards" of wild turkeys.

credited to newscientist.com

A giant head and gill-covered body make this newly reconstructed creature (pictured) "one of most bizarre fossil creatures that there is," one scientist said.

The 505-million-year-old critter was first identified in 1912 from fossil pieces. Over the years, bits of it showed up in museum collections mislabeled as jellyfish, sea cucumbers, and various other creatures.

But expeditions in the 1990s began to uncover more complete specimens, which suggested the animal, dubbed Hurdia Victoria, was much more unique than previously thought.

Now, a well-preserved specimen found in the collections of the Smithsonian National Museum of Natural History in Washington, D.C., and fossil fragments from the Burgess Shale in British Columbia, Canada, have helped scientists to finally piece together the animal's appearance.

At about 12 to 16 inches (30 to 40 centimeters) long, Hurdia was one of the largest hunters prowling the seas during the Cambrian period.

As a free swimmer—a trait rare at that time—the invertebrate likely caught "whatever it could get its claws onto," such as mollusks and sponges, said lead study author Allison Daley, a Ph.D. student at Sweden's Uppsala University.

The shield protruding from Hurdia's head—which did not offer protection to its body—has particularly stumped Daley and colleagues, whose research appears tomorrow in the journal Science.

Daley speculates that the shield acted as a feeding aid, funneling prey toward the animal's appendages.

It's hard enough to find fossils of hard things like dinosaur bones. Now scientists have found evidence of 95 million-year-old octopuses, among the rarest and unlikeliest of fossils, complete with ink and suckers.

The body of an octopus is composed almost entirely of muscle and skin. When an octopus dies, it quickly decays and liquefies into a slimy blob. After just a few days there will be nothing left at all. And that assumes that the fresh carcass is not consumed almost immediately by scavengers.

The result is that preservation of an octopus as a fossil is about as unlikely as finding a fossil sneeze, and none of the 200 to 300 species of octopus known today had ever been found in fossilized form, said Dirk Fuchs of the Freie University Berlin, lead author of the report.

Before my visit to Argentina, I had no real grasp of how large the very biggest dinosaurs could be. In the end, all it took was a glance at a single bone.

I was in the Argentine Museum of Natural Sciences in Buenos Aires when I came across a vertebra from a dinosaur's back. What to compare it with? A human vertebra would fit comfortably in the palm of your hand. An elephant's would take two hands. At 1.6 metres tall, the vertebra in front of me was on another scale entirely - it would need a forklift truck to shift it.

The vertebra belonged to argentinosaurus, a 100-million-year-old dinosaur that, as far as we know, was the biggest land animal that ever lived. In life it was 35 metres long and weighed around 80 tonnes.

Argentinosaurus is a member of the sauropods, an instantly recognisable group that includes diplodocus, brachiosaurus and apatosaurus. Sauropods had long necks, long tails, barrel-shaped torsos and trunk-like legs. They weren't all enormous, but the big ones were extraordinary.

No land animal has come close to the size of argentinosaurus and its ilk (marine animals are a different story - see "The whales' tale"). The biggest land animal today is the African elephant, with a large male weighing in at around 6 tonnes. The largest land mammal ever was a 6-metre-tall hornless rhino known as Paraceratherium, which lived 30 million years ago and would have tipped the scales at 15 tonnes. Even among the dinosaurs, sauropods were in a class of their own. A mature Tyrannosaurus rex would have weighed just 7 tonnes, while the largest non-sauropod was a duck-billed dinosaur from China called shantungosaurus, which weighed in at 16 tonnes.

Sauropods' unprecedented bulk has long posed a thorny problem for biologists. How did they get to be so big? Why have no other land animals reached such massive proportions before or since? There have not been convincing answers to these questions. Until now.

"We now have a coherent theory on how dinosaur gigantism evolved," says Martin Sander, a palaeontologist at the University of Bonn in Germany. For six years, Sander has headed an international team of scientists put together to tackle the gigantism conundrum. It turns out that sauropods had a unique set of biological features that combined to propel them to unrivalled sizes.

Bigger is better

Getting bigger has evolutionary advantages, explains David Hone, an expert on Cope's rule at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China. "You are harder to predate and it is easier for you to fight off competitors for food or for mates." But eventually it catches up with you. "We also know that big animals are generally more vulnerable to extinction," he says. Larger animals eat more and breed more slowly than smaller ones, so their problems are greater when times are tough and food is scarce. "Many of the very large mammals, such as Paraceratherium, had a short tenure in the fossil record, while smaller species often tend to be more persistent," says mammal palaeobiologist Christine Janis of Brown University in Providence, Rhode Island. So on one hand natural selection encourages animals to grow larger, but on the other it eventually punishes them for doing so. This equilibrium between opposing forces has prevented most land animals from exceeding about 10 tonnes.

Large size poses other problems too. How do you support your massive bulk? How do you cram enough food and oxygen into your body? How do you prevent yourself from overheating? Somehow the sauropods overcame all of these challenges.

Sauropod-like dinosaurs first appeared about 220 million years ago and quickly grew very large. The earliest known true sauropod is the 210-million-year-old, 15-tonne isanosaurus (Comptes Rendus Palevol, vol 1, p 103). From there, they just kept on getting bigger. Massive sauropods evolved time and time again, in different lineages all over the world.

How did this come about? In the 1990s, Janis suggested that one important factor was the sauropods' method of reproduction. Like all dinosaurs they laid eggs, while nearly all mammals give birth to live young.

"The larger a mammal is, the fewer offspring it has, and the further apart they are born," explains Janis. "Yet big dinosaurs could carry on having large clutches of eggs and lots of young. As dinosaurs increase in size you don't see any reduction in the number of young." Elephants only give birth every four years. In the same period, a big dinosaur could have laid hundreds of eggs.

This would have allowed sauropods to sidestep one of the hazards that large size usually brings. Faced with a crisis, the population would have had the potential to rebound much more quickly than large mammals can (Annales Zoologici Fennici, vol 28, p 201). Support for Janis's hypothesis has come from studies of fossilised eggs. Sauropods left behind an astonishingly detailed record of eggs and nests, sometimes with well-preserved embryos inside. The eggs were the size of ostrich eggs or smaller and the clutches contained up to eight eggs, although larger clutches have been found in Argentina.

Small fry

Egg laying and a lack of parental care, however, cannot be the whole story as all dinosaurs laid eggs and few cared for their young. So Sander looked elsewhere in search of further pieces of the puzzle.

It seems obvious, but in order to get very big, it helps to grow fast. To understand dinosaur growth rates, thin sections of their bones are examined under microscopes. Most dinosaurs have growth lines - akin to tree rings - in their bones, indicating the fitful growth typical of animals with a sluggish metabolism. Sauropod bones, in contrast, have a pattern of continuous growth similar to that seen in mammals and birds. Sander concludes that sauropods had a fast metabolism, which enabled them to attain immense sizes relatively quickly. "No other dinosaur has such high growth rates as sauropods," he says.

Research by his team on a 30-tonne Asian sauropod called mamenchisaurus shows how this rapid growth translated into astonishing weight gains. At its peak, it grew up to 2 tonnes a year. In comparison, an African elephant gains at most 200 kilograms in a year.

Fast growth is all well and good, but once an animal reaches an immense size, how does it deal with the demands of its body and its lifestyle? Sauropods all conformed to the same basic body plan: a long neck terminating with a small head, a huge barrel-like body and, inevitably, thick sturdy legs. Sander and others now argue that the creatures' unique anatomical combination - inside and out - was key to its sizeable success.

In the 1980s, Jyrki Hokkanen of the University of Helsinki in Finland tackled one part of this problem - how to support and move a massive body. By analysing bone and muscle strength in large animals, he concluded that even the largest sauropods were nowhere near the theoretical upper limit for body size. "Brachiosaurus could have been at least a couple of times bigger and still have walked on land," he concluded (Journal of Theoretical Biology, vol 118, p 491). So, while a large sauropod would have been cumbersome, that in itself did not inhibit its size.

A related problem is how to get enough oxygen. In 2003, Mathew Wedel of the Sam Noble Oklahoma Museum of Natural History solved this by showing that sauropods had bird-like lungs.

Birds breathe in a far more efficient way than mammals. When they inhale, air fills their lungs and also air sacs further inside their body. Upon exhaling, fresh air from the air sacs flows out and replaces the air that was in the lungs. This means that the lungs contain a constant stream of fresh air and can extract up to two-and-a-half times as much oxygen per breath as a mammal. "Sauropods had an air sac system that was, as far as we can tell, just as complex as that of birds," says Wedel (Paleobiology, vol 29, p 243).

Bird-like breathing would have helped to support a large size in a variety of ways. First, it solves the problem of getting enough oxygen. Secondly, the air sacs were located in and around the vertebrae, greatly reducing their weight. Giant vertebrae, such as the one I saw in Argentina, would have been full of air sac cavities, like a Swiss cheese, keeping the overall body weight down.

Finally, breathing like a bird would solve another problem: how the sauropods stopped themselves from overheating. A high metabolism coupled with a huge body, with its low surface area-to-volume ratio, would normally spell trouble. "Big sauropods could probably pant to cool themselves off, like ostriches," says Wedel.

Anatomy also explains how an 80-tonne animal could obtain enough to eat. The largest land animals today are all vegetarians that survive by eating huge amounts of plant material of poor nutritional quality. This is because there is not enough higher-quality food such as fruits and seeds to sustain a large animal, but grasses, leaves and branches are much more abundant. It is assumed that this is true for the extinct giants too.

But subsisting on poor quality forage means eating a lot. An elephant spends as much as 18 hours a day feeding, eating up to 200 kilograms of vegetation a day, and the ability to eat enough in the time available is one limiting factor on their size.

Large sauropods probably needed to eat a tonne of vegetation a day, so how did they manage it? Sander sees the crane-like neck and small head as being the key.

The lightweight vertebrae allowed their necks to grow longer, which would have increased their feeding range, both side to side and up and down. This would have allowed them to stand still while their necks did all the work, helping to conserve energy.

What is more, instead of chewing their food, sauropods used their simple peg-like teeth to pluck leaves and branches from plants before swallowing them whole. This allowed them to cram in much more food per day than if they had spent time chewing. It also meant they had no need of heavy grinding teeth and the elaborate musculature that goes with them, reducing the mass of their heads and allowing their necks to grow even longer.

The nutrients from this huge unchewed meal would have been extracted by lengthy microbial fermentation inside their huge torsos. That, however, posed yet another problem. As flowering plants did not evolve until late in the sauropods' reign, their diet was limited to plants such as monkey puzzles, ginkgos and horsetails. According to animal nutritionist Jürgen Hummel at the University of Bonn, it is commonly believed that such fodder is of exceptionally low nutritional quality. How did the sauropods manage to survive on this restricted diet?

Hummel set about trying to find out. In 2008, he simulated dinosaur digestion by placing samples of these primitive plants among the gut microbes of sheep. It turns out that many of the plants were more nutritious than they had been given credit for. "When you give the ancient plants enough time, they are digested quite reasonably. A long retention time in the digestive tract of a sauropod would have been the solution," he says (Proceedings of the Royal Society B, vol 275, p 1015).

With their unique combination of reproduction, growth and anatomy, sauropods were able to overcome the limits on body size that have constrained all other land animals, and it was a hugely successful design. The giant sauropods were a fixture of the dinosaur age, persisting for 145 million years. Yet it is 65 million years since they became extinct. Could Earth ever see their like again?

Sander believes there is no reason why not - but you would need another extraordinary set of biological attributes to come together. "Sauropods did a number of things right, but I don't think they are the only way to reach gigantic sizes," he says. "However, you would need a mass extinction to reset the whole system to zero, plus evolutionary runs of 30 to 40 million years to give a different design a chance to see how far it can take body size." Argentinosaurus, it seems, will hold the crown for a long time to come.