Palaeontologist Pablo Puerta lies beside the femur of the newly discovered dinosaur. Photo: AP
The bones of what is thought to have been the largest creature to walk the Earth have been discovered in Argentina.
Measuring 40 metres from its nose to the tip of its tail, standing 20 metres tall and weighing 70 tons - the equivalent of 14 African elephants - the animal is believed to be a new species of titanosaur, a huge herbivore of the long-necked sauropod group that lived in the Late Cretaceous period.
The calculation of its size is based on a thigh bone that stands taller than an average man. It beats by some six tonnes the previous record holder, Argentinosaurus.
The bones were initially discovered by a local farm worker a year ago in the desert near La Flecha, about 200 kilometres west of the Patagonian town of Trelew.
They are now being excavated by a team of palaeontologists from Argentina's Museum of Palaeontology Egidio Feruglio, headed by Dr Jose Luis Carballido and Dr Diego Pol. They have retrieved some 150 bones said to come from seven individuals, all in "remarkable condition".
"Given the size of these bones, which surpass any of the previously known giant animals, the new dinosaur is the largest animal known to have walked on Earth," a spokesman for the researchers told BBC News.
"Its length, from its head to the tip of its tail, was 40 metres. Standing with its neck up, it was about 20 metres high - equal to a seven-storey building."
The dinosaur - which is yet to be named - is said to have lived in the forests of Patagonia between 95 and 100 million years ago, based on the age of the rocks in which the bones were embedded. "It will be given a name describing its magnificence and in honour to both the region and the farm owners who alerted us about the discovery," the spoksman said.
There have been many previous contenders for the mantle of the world's largest dinosaur and some scientists say it is difficult to determine with any certainty which is the winner.
The Argentine researchers say the number of bones discovered give them enough material to be confident they have found "the big one".
Dr Paul Barrett, a dinosaur expert from the Natural History Museum, agreed that it was "a genuinely big critter", but he cautioned that further research was needed before declaring the find the world's biggest dinosaur.
Paleontologists also had differing methods for calculating size and weight based on incomplete skeletons, he added.
Argentinosaurus - also from Patagonia and discovered in 1987 - was originally estimated at 100 tons but its weight was later revised down to about 70.
"Without knowing more about this current find it's difficult to be sure," Dr Barrett said. "One problem with assessing the weight of both Argentinosaurus and this new discovery is that they're both based on very fragmentary specimens - no complete skeleton is known, which means the animal's proportions and overall shape are conjectural."
The find came in the same week that Argentine palaeontologists announced the discovery of the fossilised remains of a unique member of the sauropods - but one at the other end of the size spectrum.
The fossils, also found in Patagonia, provided the first evidence that whip-tailed diplodocid sauropods survived well beyond the Jurassic period, when they were thought to have been made extinct, the paleontologists said. Named Leinkupal laticauda - a combination of native Mapuche words for "vanishing" and "family," and Latin words for "wide" and "tail" - the dinosaur is thought to have been just 30 feet long.
It may be the smallest of the sauropod family called diplodocids.
Sebastian Apesteguia, the palaeontology director at Maimonides University, described Leinkupal laticauda as "a very small guy in a lineage of giants".
"We don't know the weight but considering that many of its bones were very delicate and light and most of its body was formed by neck and tail, the weight could not be impressive, actually no more than an elephant," he said.
The Leinkupal laticauda remains were found in rocky outcrops of the "Bajada Colorada", a Cretaceous-era formation south of the town of Picun Leufu in Neuquen province. The researchers said the discovery was also the first proof that diplodocid sauropods reached South America.