Which dinosaurs were the biggest?

The biggest dinosaurs were all herbivores, or plant eating, dinosaurs, many of whom had long necks to reach leaves on the highest trees.  By contrast, the largest carnivorous dinosaurs were relatively smaller.

The largest dinosaur for which there is a complete fossil record is Diplodocus; the specimen, discovered in 1907 and now on display in Pittsburgh’s Carnegie Museum of Natural History (link), is 89 feet long and weighed between 33 and 66 tons.  However, most scientists believe that fossils discovered in more recent times point to the existence of much larger dinosaurs.

The tallest dinosaur is believed to have been the massive Sauroposeidon (http://en.wikipedia.org/wiki/Sauroposeidon), which stood some 60 feet high, thanks to its long neck.  However, that does not make it the largest dinosaur ever:  that title is thought to go to Argentinosaurus, which as its name suggests, was discovered in Argentina in 1993 – or at least small fragments of its fossil skeleton were.  Argentinosaurus is estimated to have been some 115 feet long and weighed up to 100 tons.  You can get some idea of its size here.  (http://www.hcc.hawaii.edu/~pine/Phil100/argentinosaurus.html).  All these massive dinosaurs were plant eaters and relatively docile.


What was the largest carnivorous dinosaur?

Contrary to popular belief, Tyrannosaurus Rex was not the largest meat-eating dinosaur, as huge and fearsome as it was.  40 feet long, and up to seven and a half tons in weight, it is the best-known dinosaur, due largely to its reputation as one of the most terrifying land-based predators in Earth’s history.  http://en.wikipedia.org/wiki/Tyrannosaurus_rex).  The largest carnivorous dinosaur was probably Spinosaurus, at up to 57 feet long and up to 9 tons in weight.  This dinosaur’s name means “spine lizard.”  It had a spiny sail on its back, the purpose of which is hotly debated, but which may have been used to warm and cool itself, like a big radiator, or for courtship displays, like a peacock’s tail.  Spinosaurus even has his own web site!  (http://www.spinosaurus.com/)
If you compare them to modern day items like a car or a bus, how big were they?
The largest dinosaurs ever to exist were simply massive.  The tallest dinosaur of all was Sauroposeidon; its long neck could reach up to 60 feet high, which is roughly the height of a six-story building.  The immense Argentinosaurus did not reach quite so tall, but was far larger overall – about the length of three school buses end to end, and 100 tons in weight – about as heavy as three F-15 fighter planes!
The world’s largest meat-eating dinosaurs were not quite as massive as this, but nonetheless were much larger than most modern-day equivalents.  The feared T. Rex weighed in at about 7.5 tons in weight, making it about as heavy as four 1959 Cadillac Eldorados!


What did they eat?

Different species of dinosaurs had a wide and varied diet.  The world’s largest dinosaurs were plant eaters: many evolved long necks to reach leaves on the highest branches of trees, while others gathered in herds like modern elephants or antelopes.  The most famous dinosaurs are probably the great predators like Tyrannosaurus Rex.  Most scientists agree that this and the other largest meat-eating dinosaurs were both hunters and also scavengers, helping themselves to the meat of already-dead animals, just as modern lions and hyenas do.

Where did they live?

Dinosaur fossils have been found on every continent on Earth, indicating that they spread throughout the planet during the millions of years they walked the planet. Moreover, dinosaurs were not restricted to the land!  Many of the largest dinosaurs were sea dinosaurs or “ichthyosaurs,” which shared many of the characteristics of dolphins and whales, and some of which may have been carnivorous, as well.  There were also a large group of winged “dinosaurs” called pterosaurs, which were able to fly just like birds.  Technically, these two types of reptile are not dinosaurs at all, but are popularly thought of as such.

Why did they die out?

The dinosaurs first emerged in the period known as the late Triassic about 230 million years ago, and were finally wiped out by a catastrophic event some 65 million years ago, an event which allowed mammals to become the dominant land animals, which in turn allowed humans to evolve.  This means that dinosaurs were the dominant life form on the planet for some 150 million years.  By contrast, humans have walked the Earth in their present form for only around 250,000 years.

The cause of this massive extinction is still hotly debated (http://www.ucmp.berkeley.edu/diapsids/extinction.html).  Most scientists now believe that the available evidence points towards an asteroid, some six miles in diameter, hit the Earth with a force some two million times that of the largest hydrogen bomb ever detonated, sending up a huge plume of dust, blocking the sun’s rays, and killing plant life all over the planet.