This lifeform has been extinct for over 20,000 years.

Four Legged Walking Dinosaurs (Sub-Order Sauropoda) contain the large plant eating dinosaurs such as Brontosaurus. The flat topped teeth would be suitable for eating plants. Although these species walked on four legs, many scientists now believe that they sat on their hind legs and tail to reach high into the trees.  

Following are some length and weight estimates* of the various giants that occurred in this group. (The elephant is included for comparison purposes.)
  
   Elephant                       25 feet     6 tons
   Apatosaurus (Brontosaurus)     75 feet    20 tons
   Brachiosaurus                  85 feet    80 tons
   Supersaurus                   100 feet    90 tons
   Ultrasaurus                   110 feet    80 tons
   Seismosaurus                  120 feet    95 tons

Several almost complete skeletons of Apatosaurus have been found in various places in western North America.

A complete skeleton of Brachiosaurus was found in Tanzania, and the skeleton is now in Berlin. The skeleton is eight-five feet long.

Supersaurus is known only from a few bones found in Colorado.  Size estimates of this species are speculative because of lack of information on the tail. If the tail were long and narrow, Supersaurus could have been up to one hundred and forty feet long.

The name Ultrasaurus is confusing taxonomically because this name has been applied to both a Korean and a Colorado species. The Colorado example is known from only a few bones. Although the Korean species has turned out to be smaller, the Colorado species could have been one hundred feet long.

Seismosaurus was found in New Mexico in 1986. An almost complete skeleton has been found. This skeleton would indicate that Seismosaurus was about one hundred and twenty feet long.

*Some of the above species are known only from a few excavated bones. Therefore, the sizes are merely estimates.

Reptile Hipped Dinosaurs (Order Saurischia) contain many of the dinosaurs with which the general public is familiar. These are usually divided into two different sub-orders. Theropoda (T. Rex) were dinosaurs that walked on two hind legs. The Sauropoda (Brontosaurus) walked on all four legs. All members of this order are extinct.

Reptiles (Class Reptilia) are an ancient group of scaled  chordates. These scales may be permanently joined, as in the  turtles, or flexible, as in the snakes. Reptiles are land-based. Their eggs are laid on land and the young are air breathing.

Backboned Animals (Phylum Chordata) are the most advanced group of animals on earth. These animals are characterized by having a spinal cord or backbone. Most members have a clearly defined brain that controls the organism through a spinal cord. Fish, amphibians, reptiles, birds, and mammals are in this phylum.

Currently, some taxonomists believe that the fish should be divided into two groups (sharks and regular fishes) and that there are some other primitive groups in the phylum such as hagfish or lampreys.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.