Walking on two legs million of years before dinosaurs
Earliest Known Ancestor of Placental Mammals Discovered April 2002 - National Geographic
Mammals that give birth to live young
Fossil sheds light on early mammals BBC - April 24, 2002
A mouse-like fossil found in north-eastern China has been
identified as the earliest known member of the family of
mammals whose descendents include humans.
Walking on two legs million of years before dinosaurs
November 2, 2000 - BBC
A newly discovered fossil of a reptile that walked on two legs shows that bipedal locomotion evolved long before the dinosaurs.
This discovery has shown interesting and exciting things happening in the evolutionary history of reptiles well before the advent of dinosaurs.
The exquisitely preserved, 290-million-year-old skeleton of Eudibamus cursoris was dug up in a German quarry by an international team of scientists.
It is the oldest known member of the Parareptilia, a major group of primitive reptiles. Eudibamus does not appear to be a direct ancestor to later reptiles, including some dinosaurs, that adopted a bipedal posture and gait.
This may indicate that the ability to walk upright on two legs arose several times independently during reptile evolution.
Built for speed
Although only 26.1 cm (10.3 inches) long, the Eudibamus fossil contains a wealth of clues about how the reptile moved.
The skeleton shows all the signs of bipedalism
Scientists say the creature's upper limbs were relatively short for its overall size, while its lower limbs were relatively long. The reptile also had an unusually long foot and tail, proportions usually indicative of bipedal locomotion.
They think the long tail could have served as a sort of rudder, compensating for changes in the animal's centre of gravity as it moved along in an upright position.
Other evidence of bipedalism comes from the arrangement of the hip, knee, and ankle joints in the reptile's lower limb. The surfaces of these joints are arranged so that the bones in the legs formed a straight line when the hind limbs were fully extended.
Dinosaurs and mammals
This means that the creature's ankles and knees were able to flex and extend in only one plane in a similar way to how human knees and ankles move mostly back and forth, but not side to side.
Eudibamus cursoris appears to be the earliest known tetrapod, or four-legged vertebrate, to adopt this distinctive posture and gait.
"This find is fascinating because it confirms that bipedalism is an innovation that has happened several times," said Professor Robert Reisz, of the University of Toronto at Mississauga.
"It happened in some dinosaurs, and their bird descendants, and it happened in mammals, so it must be a good idea in terms of evolution."
Evolved several times
"There are only a couple of times in evolutionary history when animals have gone from a sprawled posture like that of a four-legged lizard to an upright posture when they tuck their limbs under the body.
The fossil was uncovered in a German quarry
"It happened once in dinosaurs and again with mammals. So to find an example of an animal that did this before dinosaurs or mammals is particularly exciting."
According to the researchers, who report their work in the journal Science, even on four legs, the creature's distinct posture would have distinguished its movement from the sprawling gait used by the other tetrapods of the time.
Eudibamus belongs to an extinct family of early reptiles with an unusually large geographic range, compared to its contemporaries in the early Permian (about 290 to 268 million years ago).
Unique locality
"It was thought that the ability to run on two legs and stand upright first emerged in dinosaurs and their relatives. But this discovery has shown interesting and exciting things happening in the evolutionary history of reptiles well before the advent of dinosaurs," said professor Reisz.
The teeth of Eudibamus indicate that it was a plant eater, so it was not using its speed to chase food. Instead, it probably used its sprinting speed to escape predators.
Professor Reisz and colleagues plan to continue excavations at the German quarry, which has already yielded a number of other well-preserved fossils. "It's a super site, a unique locality," said the palaeontologist,
"And it gives us a chance to show that some neat things were happening with reptiles in the Palaeozoic, long before the appearance of dinosaurs."
February 4, 1998 - AP
Scientists have found fossil embryos that might be the oldest known remains of creatures with definite left and right sides -- a group that includes people and the vast majority of modern-day animals.
The embryos are part of spectacular trove of small but highly detailed fossils found in China. The fossils are some 570 million years old, give or take 20 million years, and come from an early and poorly understood stage in animal evolution.
The discoveries don't reveal any major surprises about evolution, but experts say they're important because they show that exquisitely preserved fossils of soft-bodied animals can still be recovered from that crucial era.
The embryos are about the size of sand grains. They might be the earliest known remains of "bilaterians," which are animals that, unlike sponges or jellyfish, have definite left and right sides. That's everything from worms to us.
The fossils come from a time before animals developed skeletons, shells or even limbs. Basic body differences were just appearing. Creatures of this era lived in water and included sponges and animals resembling jellyfish and sea anemones.
By some 565 million to 560 million year ago, animals had gotten complex enough to crawl through mud, leaving worm-like tracks. But it wasn't until about 535 million years ago that animals started diversifying rapidly into the basic body plans seen today, like those of mollusks, starfish, snails, and animals with a spinal cord.
Just what set off this "Cambrian explosion" is a major mystery that the new findings might help illuminate.
The embryos described in Knoll's paper were balls of cells, like early embryos of animals today, and scientists don't know what kind of animal they would have become.
The Science paper describes some embryos and the oldest known fossils of sponges. The sponge finding is significant because it confirms evidence from genetic studies and analysis of their simple anatomy that sponges would be that old.
The fossils were found in Guizhou Province of southern China. The animals probably lived in water a few yards deep, and soon after they died their tissues were rapidly replaced with calcium phosphate, which has preserved their structure in such exquisite detail.
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