How did the sometimes massive dinosaurs haul their bulk around? First on two legs and later on four legs, whatever suited their lifestyles best.

It wasn't until the recovery of complete dinosaur skeletons that dinosaurs were reccognized as having been largely bipedal - a most unusual stance for a reptile, and one that led to much speculation about their locomotion, behavior, and physiology.

	Sprawling Stance Thighs and upper arms project straight out from the body, so that the knees and elbows are bent at right angles, like the common iguana (iguana iguana)
	Semi-Sprawling Stance Thighs and upper arms project downward and outward, so that the knees and elbows are slightly bent, like the dwarf crocodile (osteolaemus tetrapsis) and primitive archosaurs.
	Erect Stance The thighs and upper arms project straight down from the body, so that the knees and elbows are straight, in the fashion of birds and mammals. All dinosaurs had this stance.

Two Feet

Most carnivores walked around on their hind legs and used their hands to catch and hold on to thier prey.

Walking upright on two legs was an efficient means of getting around that, curiously, most modern animals (besides birds, humans and possibly kangaroos) have overlooked.

They share this characteristic with pterosaurs, their closest relatives, as well as with their descendants, the birds. Thier footsteps show that the bipedal dinosaurs walked as birds do, putting one foot in front of the other, toed slightly inward.

Four Feet

Others walked on all fours mainly because their enormous size and weight needed support.

If you're an average 10-year old, each of your feet support about 33 pounds. Each of a Diplodocus's feet carried 200 times as much weight. Yet the dinosaur was rock steady on them, since its head and neck counterbalanced its tail.

Four-legged animals like dinosaurs have two girdles, or sets of bones and muscles. The pectoral girdle, better known as the shoulders, connects the upper spine and rib cage to the front limbs. The pelvic girdle, or hips, links the lower spine to the rear limbs.

So, as dinosaurs grew in number and size, many of the biggest plant-eaters plopped down on all fours like elephants and developed extra-long necks so they could chow down without budging their massive bodies.

These dinosaurs, such as Apatosaurus, were more like prehistoric moving trucks that labored to cart their big bulk around.

The early plant-eating Sceliosaurus's hind foot was heavily armored with bony, jaw-breaking studs which ran the length of its body. Sceliosaurus always walked on four legs. Its hind heet was strong and broad and had four powerful toes to support the heavy body.

Two And Four Feet?

Some dinosaurs had the option walking either on two or four legs, depending on what they were doing at the tine. They could move around slowly on all fours, feeding on lower vegetation, but when alarmed, could rear up and charge off on hind legs alone. These dinosaurs needed special "hands" that allowed for weight support, as well as grasping.

Iguanodon's hand is remarkable because it shows clearly how the different ways a hand can be used. The large thumb spike was a fearsome defensive wepaon. The middle three fingers, which ended in hoof-like bones (typical of toes used for walking on). The fifth finger was flexible, and used for holding food.

Corythosaurus often adopted this pose, resting or walking on its hind legs. It left its small hands free to hold on to plants. It probable ran on its hind legs to escape predators. Their hands, however, revealed that several of the fingers ended in broad, flat hooves, so Corythosaurus must have also walked on all four legs from time to time.

A Plateosaurus's hand had sharp, narrow claw used for holding things or for tearing leaves off branches. It fed at ground level (on all fours), and then reared up on its hind legs to reach treetops. The joints between the bones enabled the hand to be bent back to allow Plateosaurus to walk on all fours.

Some believe that Apatosaurus, using its long, heavy tail as a counterbalance, actually reared up on its hind legs and, with its otherwise hard-to-explain short forelimbs resting on the tree trunk, reached up to heights of 35 feet to browse on tasty treetop vegetation.

Fast Or Strong

You can be either fast or strong, but not both. Dinosaurs were usually one or the other, and they pretty well perfected it. Their designs clearly were a good solution to the problem.

Dinosaurs on two legs could have turned on a dime and kept their arms free for other purposes -- like grabbing unfortunate prey and, perhaps, taking flight as they evolved into birds.

T. rex seems to have had a wide range of mobility in its joints, which would lead you to the preliminary conclusion that this was a very maneuverable creature.

Fossil footprints in Greenland suggests that predatory dinosaurs maneuvered their legs at the hips, not at the knees like birds, giving them broader reach.

How fast were dinosaurs?

Several different methods are used to calculate speed. The two basic approaches for estimating dinosaur speed are comparing to recorded speeds of modern animals of similar body size and build, and measuring distances between fossil footprints in a trackway and using these distances to calculate estimated speed.

Walking-speed estimates for medium-sized bipedal (two-legged) dinosaurs vary from 4 kph to 6 kph, and peak running-speed estimates vary from 37 kph to 88 kph. The highest figure (88.6 kph) is the same as the peak speed of the currently fastest land animals, such as the North American pronghorn "antelope" (Antilocapra americana), and very probably is too high.

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