Dinosaur origins pushed further back in time
The footprints date to the Early Triassic, some 250 million years ago The first dinosaur-like creatures emerged up to nine million years earlier than previously thought.
That is the conclusion of a study on footprints found in 250 million-year-old rocks from Poland.
Writing in a Royal Society journal, a team has named the creature that made them Prorotodactylus.
The prints are small - measuring a few centimetres in length - which suggests the earliest dinosaur-like animals were about the size of domestic cats.
They would have weighed at most a kilogram or two, they walked on four legs and they were very rare animals.
Their footprints comprised only two or three per cent of the total footprints on this site.
The footprints date to just two million years after the end-Permian mass extinction - the worst mass extinction in the history of the planet.
According to Stephen Brusatte, from the American Museum of Natural History in New York, who led the research: "In geological terms this is just the blink of an eye."
He told BBC News: "We can basically say that the dinosaur lineage originated in the immediate aftermath of this extinction which is a completely new idea and a very radical re-interpretation of the early history of dinosaurs".
In the end-Permian extinction event, more than 90% of all life on Earth was wiped out due to massive volcanic eruptions, sudden global warming and the stagnation of the oceans.
Up until recently, scientists had thought that dinosaurs emerged 15 to 20 million years after the mass extinction, when the planet had become more habitable.
But the new footprints suggest that the rise of dinosaurs was intimately related to the devastating extinction event.
Prorotodactylus was about the size of a domestic cat, say the researchers "Without this mass extinction there would never have been dinosaurs," said Mr Brusatte.
"There's a degree of symmetry about that because when dinosaurs went extinct 65 million years ago, that opened space for mammals," he added.
Although the footprints are characteristic of dinosaur-like creatures, they do not provide the absolute proof that a fossilised skeleton would.
"We'd rather have a skeleton because footprints are a little open to interpretation," Professor Mike Benton, from Bristol University, told BBC News.
He believes that the discovery is important - but he says it would have been published in one of the top two scientific journals in the world if Mr Brusatte had been able to provide further evidence for his claim.
"I bet you if (he had found) a skeleton which was unequivocal it would have been a front page."
The findings are published in Proceedings of the Royal Society B: Biological Sciences.
Source : BBC| By Helen Briggs BBC News science reporter |
A computer simulation of the Earth's climate 250 million years ago suggests that global warming triggered the so-called "great dying". 
A dramatic rise in carbon dioxide caused temperatures to soar to 10 to 30 degrees Celsius higher than today, say US researchers.
The warming had a profound impact on the oceans, cutting off oxygen to the lower depths and extinguishing most lifeforms, they write in the latest issue of Geology.
The research adds to the growing body of evidence that higher temperatures, rather than a giant space rock hitting the planet, led to the greatest mass extinction in history.
Prehistoric extinction
The extinction, at the end of the Permian Period and the beginning of the Triassic, has puzzled scientists for many years.
Some 95% of lifeforms in the oceans became extinct, along with about three-quarters of land species. 
Many possible reasons for this catastrophic event have been proposed - including impacts, volcanism, climate change and glaciation. Hard evidence, however, has been difficult to find.
The latest data from scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, supports the view that extensive volcanic activity over the course of hundreds of thousands of years released large amounts of carbon dioxide and sulphur dioxide into the air, gradually warming up the planet.
Deep impact
The NCAR team used a research tool known as the Community Climate System Model (CSSM) which looks at the combined effects of atmospheric temperatures, ocean temperatures and currents.
Their work indicates that temperatures in higher latitudes rose so much that the oceans warmed to a depth of about 3,000m (10,000ft). 
This interfered with the circulation process that takes colder water, carrying oxygen and nutrients, into lower levels. The water became depleted of oxygen and was unable to support marine life.
"The implication of our study is that elevated CO2 is sufficient to lead to inhospitable conditions for marine life and excessively high temperatures over land would contribute to the demise of terrestrial life," Jeffrey Kiehl and colleagues write in Geology.
Until recently, computer models of past climate have been hampered by the difficulty of accounting for complex interactions between the various components of the Earth's climate system
Professor Paul Wignall, of the University of Leeds, UK, who studies the Permian-Triassic boundary, says the models have not been sophisticated enough to recreate such "lethal super-greenhouse climates".
"I suspect many in the modelling community have been sceptical about just how bad conditions were 250 million years ago, even though the evidence is in the rocks; but now the latest climate system modelling is able to replicate climatic conditions that came close to destroying life on Earth," he told the BBC News website.
Scientists have described a new primitive dinosaur species, Eocursor parvus, which lived in the Late Triassic - about 210 million years ago.
Unearthed in South Africa's Free State, the creature appears to have been a small, agile plant-eater.
The team tells a Royal Society journal that Eocursor sheds light on the early evolution of the Ornithischia.
This important group included the well known herbivororous dinosaurs Triceratops and Stegosaurus.
The fossil specimen was first identified in 1993 but only recently appraised.
It is by far the most complete example of a Triassic ornithischian known, comprising skull and skeletal material, including bones of the backbone, arms, pelvis and legs.
Gripping hands
In its day, Eocursor would have been little bigger than a fox. Its bone structure and light form suggest it moved swiftly.
The scientists say the creature provides the earliest evidence for the origins of many skeletal characteristics seen in the ornithischian group, including the backward-pointing pelvis. 
A comparison has been done across a wide range of specimens and this indicates that Late Triassic ornithischians were really quite rare. The group then diversified in the subsequent early Jurassic, filling empty herbivorous niches following mass extinctions of other creatures.
"We know ornithischians were a very successful and important group of plant-eating dinosaurs that first appeared 220 million years ago, in the late part of the Triassic Period," explained Dr Richard Butler, a palaeontologist at the Natural History Museum, London, UK.
"Eocursor is a very small and primitive dinosaur that would have eaten plants with its leaf-shaped teeth and had an unusually large, grasping hand. The lower leg bones are very long, suggesting it would have been able to run fast on its hindlegs to escape from predators."
The name Eocursor comes from the Greek eos, meaning "dawn" or "early", the Latin cursor meaning "runner" and parvus meaning "little"
Gap filler
"The earliest dinosaurs we know are about 228 million years old, so this one is only just a bit younger than that," commented Dr Paul Barrett, a NHM researcher unconnected with the new study.
"The fossil record for early meat-eating dinosaurs is slightly better; and for some of the other plant-eaters, we also have not-too-bad a record. But for the ornithischians, we have almost nothing; so in that sense, this is a major find," he told BBC News.
The assessment is reported in Proceedings of the Royal Society B: Biological Sciences.
The research team included co-workers at the Iziko South African Museum in Cape Town and the University of Cambridge, UK. |  The rise of the dinosaurs was prolonged, not sudden  |
It shows that dinosaurs co-existed with a more primitive group of reptiles for millions of years before becoming the most common land animals on Earth.
Experts had thought that once dinosaurs emerged, they swiftly replaced their relatives the dinosauromorphs.
But the latest study in Science journal questions this idea.
Dinosaurs first appeared around 230-220 million years ago, towards the end of the Triassic Period.
By the beginning of the Jurassic Period, about 200 million years ago, they had become the dominant creatures on land - and would remain so for another 135 million years.
But the reasons for their success - and why the dinosauromorphs faded away - are poorly understood. 
This is because the fossil record leading up to the Jurassic is relatively sparse.
Some researchers had assumed that dinosaurs were quick to supplant their more primitive relatives, the dinosauromorphs.
In other words, they got a "lucky break".
Pace of change
Dinosaurs may have either outcompeted their reptilian relatives for resources, or taken advantage of some catastrophe that devastated the Dinosauromorpha.
But fossils described in the latest issue of Science suggest that if competition occurred, it was over a prolonged period, according to the team that unearthed them in the south-western US.
The Late Triassic cache from Hayden Quarry, New Mexico, contains primitive dinosaurs and several species of dinosauromorph - including the newly identified species Dromomeron romeri. 
The researchers also found a diverse range of other animals, including amphibians, fish and crocodile-like reptiles.
These, along with other contemporary fossil "assemblages", imply the rise of the dinosaurs throughout the Triassic was a more gradual process.
Randall Irmis, from the University of California, Berkeley, US, and colleagues suggest the dinosaurs may have co-existed with the dinosauromorphs for some 15-20 million years.
"Finding dinosaur precursors - or basal dinosauromorphs - together with dinosaurs tells us something about the pace of changeover," said Mr Irmis.
"If there was any competition between the precursors and dinosaurs, then it was a very prolonged competition."
Important findings
Dr Richard Butler, a dinosaur specialist from London's Natural History Museum, UK, called the study and the discoveries "very important".
"The authors believe that their discovery demonstrates that the dinosaur takeover occurred gradually rather than rapidly. We certainly know now that dinosaurs didn't take over immediately after they evolved," he told the BBC News website.
But Dr Butler said there were still signs of rapid change at the conclusion of the Triassic.
"The big question is what happened right at the end of the Triassic period. At this point we see one or more major extinction events, with all of the primitive dinosaur-like and crocodile-like reptiles becoming extinct, and only dinosaurs, crocodiles and pterosaurs (flying reptiles) surviving."
Exactly when and how these extinction events occurred is poorly understood; but asteroid strikes and climate change have been implicated.
"These extinctions may have opened up ecological space for dinosaurs to expand into, and might have occurred in a relatively short period of time," Dr Butler explained.
"So in this sense I think it is still possible that early dinosaurs could have benefited from a 'lucky break'."| By Victoria Gill Science reporter, BBC News |
 Asilisaurus kongwe was a very close relative of the dinosaurs |
Scientists have discovered a dinosaur-like creature 10 million years older than the earliest known dinosaurs.
Asilisaurus kongwe is a newly discovered herbivore that lived during the middle Triassic period - about 245 million years ago.
The scientists say that its age suggests that dinosaurs were also on the Earth earlier than previously thought.
They described their findings in the journal Nature.
The study was led by Dr Sterling Nesbitt from the University of Texas at Austin in the US.
He said: "This new evidence suggests that [dinosaurs] were really only one of several large and distinct groups of animals that exploded in diversity in the Triassic period, including silesaurs [like this one], pterosaurs, and several groups of crocodilian relatives."
Dr Randall Irmis from the Utah Museum of Natural History in the US was also involved in the study. He said that this group of creatures - the silesaurs - were the "closest relative of the dinosaurs".
"It was to dinosaurs much like chimps are to humans - kind of cousins," he told BBC News.
 Asilisaurus stood up to 1m tall and walked on all fours |
"Since we have one line of the family tree, the other branch must have existed at the same time. So this suggests there are other very early dinosaurs that we haven't found yet."
He also said that the creature was not what the researchers expected an early dinosaur cousin to look like.
"It was a weird little creature," he said. "We always thought the earliest relatives were small, bipedal, carnivorous animals.
"These walked on four legs and had beaks and herbivore-like teeth."
'Failed experiment'
Dr Paul Barrett, a palaeontologist from the Natural History Museum in London said that the finding provided scientists with important information about how dinosaurs evolved.
"The creatures share a lot of features with dinosaurs," he said. "They show us an intermediate step between more primitive reptiles and the more specialised dinosaurs."
The fossil record indicates that this group of primitive creatures went extinct approximately 45 million years after they emerged.
The dinosaurs, on the other hand, were far more successful and walked the Earth for about 165 million years.
Dr Barrett said: "[Silesaurids] were like a failed experiment in how to build a dinosaur."
| By Paul Rincon Science reporter, BBC News |
 Early dinosaurs tended to be small in size |
Immense volcanic activity helped the dinosaurs rise to prominence some 200 million years ago, a study suggests.
Dinosaurs were the dominant vertebrates on land for some 135 million years.
While it is widely accepted that an asteroid or comet wiped them out, there has been less agreement on the factors which led to their ascendancy.
Research in PNAS journal suggests volcanic eruptions changed the climate, causing a mass extinction that wiped out the dinosaurs' main competitors.
The scientific paper, by researchers from the US and Taiwan, looked at several lines of evidence such as the remains of plant wax and wood from sedimentary rocks interbedded with lava flows. From these, they were able to extract vital data about the climate at this time.
The lava flows are dated to the end-Triassic extinction, 201.4 million years ago, which wiped out 50% of tetrapods (four-limbed animals) on land, 50% of terrestrial plants and 20% of marine families.
The scientists examined how two different isotopes (or forms) of carbon fluctuated during these volcanic eruptions. They found that the "heavy" form of carbon was depleted relative to the "light" form.
Super greenhouse
They say this reflects disturbances in the carbon cycle at this time, including a spike in atmospheric carbon dioxide (CO2) and aerosols (fine solid particles).
This would have resulted in "super" greenhouse warming, according to lead author Jessica Whiteside, a geologist at Brown University in Providence, Rhode Island.
"We are showing that these events are synchronous with the extinction and that the events all occur within a few tens of thousands of years of the eruption of these huge lava flows," Dr Whiteside told BBC News.
The scientists have not yet determined the killing mechanism behind the mass extinction.
Neither can they say for sure why the dinosaurs survived it, although Dr Whiteside suggests it could have been "blind luck".
Nevertheless, they propose that the climatic catastrophe caused by the mass eruptions led to the extinction of the dinosaurs' main competitors, the crurotarsans.
These ancient crocodile-like creatures had competed vigorously with early dinosaurs during the Triassic Period.
The study is not the first to posit a link between volcanic activity and the end-Triassic mass extinction.
But the relationship between volcanism, carbon isotope anomalies and extinctions had never been tested in rocks preserving records of all three phenomena. The scientists say this is the first study to do so.
Big break-up
The so-called volcanic "flood basalts" form a giant geological entity known as the Central Atlantic Magmatic Province (Camp).
This was formed during the break up of the "supercontinent" known as Pangaea, causing lava to pour out on to the Earth's surface for some 700,000 years.
"This is actually the largest flood basalt province known in the Solar System. It covers something like 9-11 million sq kilometres. To give you an indication of how large that is, it's about one-third the size of the Moon," said Dr Whiteside.
"We're talking about a serious amount of the Earth being covered in lava."
It dwarfs the Deccan traps, a large igneous province in west-central India. The volcanism which created the traps had been implicated by some in the extinction of the dinosaurs 65 million years ago.
Earlier this month, a panel of experts strongly endorsed evidence that a space impact was instead responsible for this extinction.
Writing in Science journal, they ascribed the cause to a 10-15km space rock striking the Yucatan Peninsula. This caused a global winter that played havoc with marine and land ecosystems.
No comments:
Post a Comment