Berkeley site for fossil research

 Home> Lines of Evidence

top navigation bar

bottom navigation bar
grey bar

Transitional Forms (1 of 2)

Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms. There are numerous examples of transitional forms in the fossil record, providing an abundance of evidence for change over time.

Pakicetus (below left), is described as an early ancestor to modern whales. Although pakicetids were land mammals, it is clear that they are related to whales and dolphins based on a number of specializations of the ear, relating to hearing. The skull shown here displays nostrils at the front of the skull.

A skull of the gray whale that roams the seas today (below right) has its nostrils placed at the top of its skull. It would appear from these two specimens that the position of the nostril has changed over time and thus we would expect to see intermediate forms.


Read more about specific examples of transitional vertebrate fossils at the Talk.Origins Archive Transitional Vertebrate Fossils FAQ.

  Note that the nostril placement in Aetiocetus is intermediate between the ancestral form Pakicetus and the modern gray whale — an excellent example of a transitional form in the fossil record!



• Aetiocetus skull image courtesy of Tom Deméré, San Diego Natural History Museum.
• Gray whale skull image provided by Pearson College and Race Rocks

next page

Search · Site Index · Navigation · Copyright · Credits · Contact 
Understanding Evolution For Teachers Home · Understanding Evolution Home

Read how others have recognized the Understanding Evolution website

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s