Amazingly enough, dinosaurs are divided into two orders:  Saurischia and Ornithischia.  Saurischia (lizard-hipped) are characterized as such because of their forward jutting pubic hipbones and their elongated neck bones.  They are divided into two infraorders:  carnivorous (meat-eating) bipedal (walking on two legs) theropods and herbivorous (plant-eating) quadrupedal (walking on four legs) sauropodomorphs.  Ornithischia (bird-hipped) are characterized as such because their pubis (hipbone) is slanted back parallel to another hipbone and they have a predentary bone at the tip of their toothless lower jaw.  They are plant eaters.  There are three infraorders:  the birdlike ornithpods, the armored thyreophorans, and the horned or thick skulled marginocephalians. 

Sauropodomorphs belong to the Saurischia order.  Sauropodomorphs (lizard feet forms) are characterized as having small heads and long necks and tails.  They are believed to have traveled in herds and range in size from small to very large.  They were plant eaters and could be either bipedal or quadrupedal.  Sauropodomorpha are divided into two infraorders:  Sauropoda and Prosauropoda.

Prosauropoda is one infraorder.  They are distinguished by their big curved thumb claws.  They ranged in size from small to large.  There are seven families:

Thecodontosauridae (socket-toothed lizard)- were bipedal.  They grew to approximately eight feet long. 

Anchisauridae- was small and lightweight.  They grew to be no more than eight feet long and weighed only sixty pounds.  Fossils were found in North America.

Massospondylidae-were medium sized creatures.  They had a long neck and tail.  They grew to be approximately seventeen feet in length.  Fossils were found in North America and Africa. 

Yunnanosauridae- had self-sharpening spoon shaped teeth.  They grew to be twenty-three feet in length.  Fossils were found in China.

Plateosauridae- had a bulky body, a long neck and a small head.  They grew to length of twenty-six feet.  Fossils were located in Europe.

Melanorosauridae (black mountain lizard)- was a quadrupedal that grew to be twenty-four feet in length.  Fossils were found in South Africa.

Blikanasaurisae- was a quadrupedal.  They had stocky hinds legs.  They grew up to seventeen feet in length.

Sauropoda is another second infraorder.  They had hollow vertebrae.  They were quadrupedal plant eaters that ranged in size from large to humungous.  Many relationships are unclear.  These are nine family groups:

Vulcanodontidae- was a quadrupedal herbivore that grew to be twenty-one feet long.

Barapasauridae- their exact classification is uncertain.  They were massively built creatures that grew up to sixty feet in length.  They had spoon shaped teeth with edges for tearing off leaves.  Fossils were found in Asia.

Cetiosauridae (whale lizard)- they were huge animals weighing up to twenty-seven tons.  They had short necks and tails but their legs were nearly seven feet long.  They grew to be sixty feet in length.   Fossils were found in Europe.

Brachiosauridae- was one of the heaviest known dinosaurs weighing up to eighty tons.  Their front legs were much longer than their back legs.  They had a neck that could be as long as fifty-three feet.  They grew to be eighty-five feet in length.  Fossils were found in North America, Europe, and Africa.

Titanosaurisae- were the most widespread of member.  Fossils were found in South America, Europe, Asia and Africa.  They grew up to sixty feet in length.

Camarasauridae- is believed to have lived in herds for protection.  They had a boxlike head and large nostrils.  They grew up to sixty feet and weighed up to twenty tons.  Fossils were located in North America and Europe.

Euhelopodidae- had long necks believed to consist of nineteen neck vertebras.  They grew to be fifty feet in length.  Fossils were found in Asia.

Dicraeosauridae-were smaller than other members of the group.  They had short necks and tails with a large head.  Their vertebrae had Y-shaped spikes running along the back and neck.  They were forty-six feet in length.  Fossils were located in Africa.

Diplodocidae- is known as the longest dinosaurs measuring up to eighty-nine feet long.  They were built with pillar like legs, extremely long necks and long narrowed tipped tails.  They also had elongated heads with nostrils on top of their heads near their eyes and small teeth.  Fossils were found in North America.