Skip to Content

It’s a Crocodile! No, a Fish! No, a Dolphin!

Interpreting Evolutionary History from Fossil Evidence


Andrea Bixler
Biology Department
Clarke University


It is not uncommon to hear creationists argue that evolution is not science because no one saw it happen, or for students to wonder how we can know anything about the physiology or behavior of organisms that went extinct hundreds of millions of years ago.  This case study, designed to complement the typical teaching of the scientific method that focuses on experimentation, emphasizes how much we can learn from observations. Starting from a mystery fossil that was collected by historical figure Mary Anning, students are presented with an array of comparative evidence to help them determine whether the organism was a crocodile, a fish, a dolphin, or something else. This case would be appropriate for an introductory majors biology course, particularly one in which evolution is covered.  It is taught in the flipped format, with videos on the scientific method and fossil evidence to provide students with background prior to starting the in-class work.  Students then work in groups to evaluate the evidence presented.


  • Become more familiar with the scientific method, particularly instances in which experimentation is not possible.
  • Practice analyzing various lines of evidence, forming a hypothesis based on what they know, and evaluating their hypothesis based on additional data.
  • Be able to clearly distinguish hypothesis and theory.
  • Learn about the various types of information that can be gained from examination of a fossil, including transitional fossils.


Comparative vertebrate anatomy, fossils, forensics, scientific evidence, transitional fossil, missing link, ichthyosaurs, Cartorhynchus, Mary Anning

Topical Areas

N/A, Scientific method, Scientific argumentation, Women in science

Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

Flipped, Interrupted



Subject Headings

Anatomy  |   Biology (General)  |   Evolutionary Biology  |   Science (General)  |   Zoology  |   Paleontology  |  

Date Posted


Teaching Notes

Case teaching notes are password-protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, begin the process by registering.

Teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience, details about how the case may be taught, and a list of references and resources.

Answer Key

Answer keys for the cases in our collection are password-protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, begin the process by registering.


The following video(s) are recommended for use in association with this case study.

  • The Scientific Method Made Easy
    This video is a good refresher on the scientific method and is particularly valuable in its comparisons to how a criminal case is discussed in a courtroom, its discussion of the self-correcting nature of the scientific method, and its description of what happens after a hypothesis is supported (peer reviewed publication, development of a theory). Running time: 9:16 min.
  • Scientific Method
    An alternative to the above, this video also provides a recommended overview of the scientific method. Running time: 4:15 min. Produced by BrainPOP.
  • What Can We Learn from a Fossil?
    Using the example of a fish and a hominin, this video describes in simple terms what types of evidence can be learned about long-extinct species based only on fossils. It also goes into more depth on one example of scientists learning about the physiology of an extinct animal. Running time: 5:55 min. Created by Andrea Bixler for the National Center for Case Study Teaching in Science, 2016.


Andrea Bixler
Clarke University
New, relevant research: or see description from New Scientist, "Ancient reptile looked like a cross between a dolphin and a shark,"