By Paul Rincon
BBC News science reporter
Fossil hunters on the Isle of Wight have unearthed bones from the biggest dinosaur so far discovered in the UK.
The neck bone belonged to a dinosaur that was more than 20m long
One fossil - a single neck bone from the 125-130-million-year-old sauropod dinosaur - measures an astonishing three-quarters of a metre in length.
Based on this, a team of UK and US researchers believes the huge reptile was probably over 20m long and could have weighed as much as 40-50 tonnes.
Details of the discovery appear in the scientific journal Cretaceous Research.
"It is impressively big," team leader Darren Naish, of the University of Portsmouth, told the BBC News website.
The long-necked sauropods were the biggest and heaviest group of dinosaurs in existence.
Physical features of the fossil suggest the British creature had similarities to two other known sauropods: Brachiosaurus and Sauroposeidon.
The well-preserved cervical vertebra was found in 1992 along a stretch of beach between Chilton Chine and Sudmoor Point. It was enclosed in a rock matrix called siderite.
"Siderite is very tough - it's an iron-impregnated clay. After 125 million years or so, it sets like concrete. This enclosed and protected the very fragile bone," explained Steve Hutt, of the Dinosaur Isle museum, where the specimen is on display.
Mr Naish realised the fossil's importance in 2000 and decided to describe it for publication in a scientific journal.
"The bone contains a wealth of information that allowed us to work out with confidence exactly what sauropod it belonged to. This, coupled with the giant size, was what attracted me to take a further look," Mr Naish explained.
Fossil hunters have also discovered a second neck bone that probably comes from the same animal. But this is less well preserved and had been lying on the beach for some time, say researchers.
Scientists say the sauropod's skeleton had been eroding out of nearby cliffs and there may be more remains still to be found.
The fossils originate in the best known dinosaur-bearing rock unit in the Isle of Wight - the so-called Wessex Formation.
This allowed the researchers to easily date the plant-eater to Lower Cretaceous times. It lived alongside other dinosaurs such as the bulky, beaked Iguanodon and the fleet-footed, two-legged Hypsilophodon.
The bone is certainly amongst the biggest ever found in Europe. But Mr Naish said as yet unpublished sauropod fossils from Portugal and Spain were even larger.
In February this year, researchers announced the discovery of fossilised bones from what would have been a 35m-long (about 115ft) creature weighing 50 tonnes near Riodeva in eastern Spain.
"But given that until recently people didn't think there were any big sauropods in the Lower Cretaceous, I think this is part of a bigger story," said Mr Naish.
The world's biggest and heaviest dinosaur is commonly said to be Argentinasaurus, a 37m-long (120ft), 80-100-tonne creature known from South America.
However, a 2.4m-long (8ft) fossil vertebra from a creature called Amphicoelias fragillimus was pulled out of the Morrison Formation of North America in 1877.
Based on the description of the bone made by its discoverer Edward Drinker Cope, the animal it belonged to would have been some 52m (170ft) in length.
However, the huge specimen has since disappeared, which makes this impossible to verify.
The vertebral bone described in the latest research paper was found by fossil hunter Gavin Leng. It was cleaned up by David Cooper, a volunteer at the Dinosaur Isle museum in Sandown, Isle of Wight.