Apatosaurus is easy to draw, we just need 2 colors.
Draw a big oval in the middle of your page.
Now draw a tall rectangle on the left side of the oval.
Draw a smaller rectangle next to the first.
Draw another tall rectangle on the other side of the oval.
And one more smaller rectangle right next to it!
Draw a small dot some on the right side of the page.
Draw a line on the inside of the oval, on the right side.
Now connect the each end of that line to the dot, you just made a long triangle! 📐
Now draw a very tall rectangle on the left of the oval, going near the top of the page.
Draw a circle to create a head for your dinosaur. 
Color in your dinosaur, but leave the 2 smaller rectangles for last.
Fill in the empty rectangles now, and color them in extra hard so they are darker than the rest.
Last but not least, let's make our dinosaur happy and draw a smiley face in the circle.
Your apatosaurus is complete! 🎉