These are harsh conditions in which to work

The fossils were found within a week of each other by researchers backed by the National Science Foundation.

The first dinosaur is a new type of theropod - a two-legged forerunner of birds - and is thought to have lived about 70m years ago.

The second - a 200m-year-old sauropod similar to a diplodocus - was found on a 3,900-metre-high mountaintop.

The carnivorous dinosaur was found by Judd Case, James Martin and colleagues on James Ross Island, off the coast of the Antarctic Peninsula.

They say the creature is related to the famous T. rex and the smaller, but swifter, velociraptors that terrified movie-goers in the film Jurassic Park.

Water burial

The remains include fragments of an upper jaw with teeth, isolated individual teeth and most of the bones from the animal's lower legs and feet.

The carnivorous dinosaur was recovered from ground that was once under water

The creature was roughly 1.8 to 2.4 meters (6 to 8 feet) tall. It would have inhabited the Antarctic when the climate was very much more benign than it is today.

To have been preserved at all, the animal probably floated from the shore out to sea after it died and settled to the bottom of what was then a very shallow area of the Weddell Sea.

The ground is now above sea level and accessible to scientists.

The other dinosaur was found inland by a different group of researchers thousands of kilometres away near the Beardmore Glacier.

They found embedded in solid rock what they believe to be the pelvis of a primitive sauropod, a four-legged, plant-eating dinosaur that would have had a long neck and tail.

Early form

Now known as Mt Kirkpatrick, the area was once a soft riverbed before millions of years of tectonic activity pushed it skyward.

The sauropod pelvis was taken out of solid rock

Based on field analysis of the bones, the team led by William Hammer of Augustana College in Rock Island, Illinois, believes the pelvis - roughly one metre across - is from a primitive sauropod.

The team says it probably represents one of the earliest forms of the emerging dinosaur lineage that eventually produced animals more than 30 metres (100 feet) long.

Basing his estimates on the bones excavated at the site, Hammer suggests the new, and as-yet-unnamed, creature was between 1.8 and 2.1 metres (six and seven feet) tall and up to nine metres (30 feet) long.

Hammer says the rocks in which the find was made helped to establish that the creature lived roughly 200 million years ago, millions of years before the creature Case and Martin discovered on the Antarctic Peninsula.