NOVA Education
NOVA Evolution Lab Interactive Lesson Mission 2

MISSION 2 — One Small Step 

There have been a number of dramatic transitions over the history of life. After a few billion years of nothing but single-celled organisms, multicellular life developed. Organisms evolved tissues and organs. Plants developed spores, flowers, and seeds. Animals developed complex neurological systems and external and internal skeletons. And, of course, bacteria evolved novel methods to live just about everywhere on Earth.

One of these great transitions is the subject of this level. Have you ever heard of an animal called Tiktaalik? How about Acanthostega? They are but two of the many remarkable fossils we have that document the transition of animal life from water to land.

Play "One small step" and answer questions 6–9 after you've completed that level. 

  1. For an animal that lives in shallow water, what is the advantage of having eyes on the top of its head? 

7. Ichthyostega is a 370-million-year-old fossil from Greenland. Ichthyostega had digits, eyes on the top of its head, and strong, armlike bones. It also had no gills and a reduced tail—traits it had in common with Tulerpeton. Acanthostega, Eusthenopteron, and Tiktaalik all had gills and full tails.

Use the abbreviations provided to draw a phylogenetic tree that includes Ichthyostega with the "Visualize It" button below. Refer back to your completed tree for this level in the game.

A = Acanthostega

E = Eusthenopteron

I = Ichthyostega

Tu = Tulerpeton

Ti = Tiktaalik

D = digits

E = eyes on top of a flat head

G/T = loss of gills and a reduced tail

S = strong, armlike bones

8-9. Click the button below to answer questions 8-9. Remember to refer to your completed tree and the species comparison tab if you are not sure of your answers.