The fossil record of the dinosaurs suggests that they either walked with
4 legs or 2 legs. There were no true flying dinosaurs or swimming dinosaurs.
There were flying and swimming reptiles in the Mesozoic, but these are not
The flying reptiles, closely related to the dinosaurs, are called
pterosaurs. The swimmers belonged to several groups, including mosasaurs,
ichthyosaurs and plesiosaurs, none of which were dinosaurs. Moreover,
although the largest dinosaurs approached the size of the modern blue whale,
the smallest known dinosaur was no larger than a chicken. Presently, the
fossil record shows that the largest and smallest known dinosaurs roamed the
Earth at the same time. Seismosaurus (the longest dinosaur) and Compsognathus
(the smallest dinosaur) both lived during the Late Jurassic period of
the Mesozoic, though in different parts of the world.
- Before lab, cut pieces of string or tape about 3 meters (approximately
10 feet) long. Tape them to the floor of your classroom in a place where
the whole class can observe them.
- Read My Visit to the Dinosaurs. Make sure you use the pictures
to compare sizes of dinosaurs.
- Using the dinosaur models, have the students guess, or state, the
lengths of the smallest and the largest known dinosaurs. Tell them that
the longest dinosaur known was a plant-eating sauropod (long-necked,
long-tailed, walked on all four feet) dinosaur called Seismosaurus.
Hold up the Brachiosaurus model as an example of a sauropod
dinosaur. Seismosaurus was between 120 and 150 feet long, weighed
about 80 tons, and is known from fossils found in New Mexico. There were
a number of other long sauropod dinosaurs too, including Diplodocus,
Ultrasaurus, and Mamenchiasaurus that were between 90 and 100
or more feet long. These big sauropods are sometimes referred to as
The smallest dinosaur, Compsognathus, was a bipedal (walked on
its hind legs only), meat-eater that was about two feet long. Compsognathus
was no larger than a chicken.
- Tell the class that the dinosaur models are made to
scale (if you have the Carnegie Dinosaur Models), with the
exception of the Velociraptor. So the models are as big as they were in real life.
Have the class line up the dinosaur models from smallest to largest.
Fit the Velociraptor into its real position using the summary of
body lengths for each type of dinosaur model listed below. Children can
imagine what these sizes mean by comparing them to your ten-foot tape on
the floor, or by measuring themselves and figuring out how many of their
own bodies it would take to make the lengths of the different dinosaurs.
- Hand out the "What is a dinosaur" worksheet and have the
students color in animals they think are dinosaurs. Review responses
when everyone is finished. The answers are:
(1) a crocodile, which is a reptile; it has a sprawled posture, so
cannot be a dinosaur; (2) a dinosaur;(3) not a dinosaur; it is a
pterosaur, a reptile; dinosaurs did not fly (4) and (5) are dinosaurs.