For excellent summary discussion of Tiktaalik, with updates,
Click Here for the Understanding Evolution site. Included are:
+ Discussion of the inappropriateness of using term "Missing Links"
+ Map showing site of discovery - very good for use in classroom
+ Photo of reconstruction and original fossil
+ Cladogram showing position of Tiktaalik relative to the rest of the tetrapod clade
+ Relative position to other fish-to-tetrapod transitional fossils in detailed cladogram

Updates (2009 and 2010) to the original posting (May 2006):
* Details of cranium reveal a mosaic mix of fish-like and tetrapod-like features, as expected in a transitional form.
* Hyomandibula (large in fish - helps gill breathing, becomes stapes in ears of mammals).
* New fossil footprints put origin of first tetrapod back before 400 mya -
considerably earlier than the Tiktalik and other known vertebrate transitional fossils of that period - suggesting that Tiktaalik and "relatives" lived on as such for many millions of years beyond the actual transition, [perhaps like the platypus may be a living vestige of an early stage of the emergence of mammals from egg-laying pre-mammals, or the Anhinga bird (with claws on wings) suggests the much earlier transition of birds from their theropod ancestry.] Consequently, vertebrate paleontologists may well want to search in earlier strata (pre-400 mya) for those earliest remains of that transition.

Classroom discussion question, to which you could add:
Given the latest info about 400 my old tetrapod footprints, what age of sedimentary rocks might a paleontologist want to search for more fossils showing the transition from fish to tetrapods?

# You may already know that the genes for making our limbs are nearly identical to those for making fish fins.
# But why are the genes for the formation of our limbs so similar to those for making wings in flies?
# How are breasts, sweat glands, scales and feathers connected?
# How do the generations in a human family tree relate to the hierarchy of the major groups of animals?
# Why does our history (and pre-history) make us sick? Look at obesity, heart disease, and hemorrhoids.
# Why do so many of us have sleep apnea, choke more easily as we age, and get hiccups?
# What do sharks have to do with the fact that male humans are prone to hernias?
# How can the study of certain bacteria shed light on a variety of metabolic diseases linked to mitochondria?

These many practical questions about how our ancestral past connects to our modern human condition make it so obvious how useful a knowledge of evolution can be. Paleontologist and anatomist Neil Shubin brings a fascinating account of how we came to be the way we are, tying together and making sense out of many seemingly unrelated observations.

Early in this little book, Shubin describes how he applied his fascination with fossils to predict a likely region in Northern Canada, in rocks of a particular age, where he would most likely find fossil evidence of a transition between fishes and land vertebrates, from the fins of fish to the limbs of tetrapods. In 2006, he announced his discovery of a fish fossil with a pair of fins in the rear, and typical leg bones in its forelimbs - Tiktaalik - a fish with wrists! It fills a short but important evolutionary gap for a time when that transition must have happened, from all the fossil evidence previously found. This was an example of a "Fair Test" - where results could have weakened the previous understanding that such a transition must have happened, but they didn't, so the understanding becomes even stronger. Be sure to check the discussion (with updates and teaching ideas) of Tiktaalik at the Understanding Evolution site (outlined at top of this page).

Weaving his experience with anatomy and fossils, he adds the growing wealth of knowledge about evo-devo, how genes control the development of limbs and other structures. In the process, Shubin sprinkles brief accounts of how scientists gradually discovered the process and began to explain its mechanism. In like manner, he extends our understanding of genetic tools that control the development of tissues and organs, taking what seems to be a very complex process, and showing how the modifications and timing for just a few basic types of tissue can produce the great diversity that we find.

In the process, Shubin reveals how body plans unfold, how organs of vision, hearing and other senses can be traced to their places and functions in other animals. Again and again, he points to the clear evidence where current anatomical structures can be seen as old structures (found in other creatures) that have been "repurposed," clear examples of "descent with modification."

Great summer reading for all biology teachers. Be prepared to take a few notes. I know you will want to include a number of Shubin's illuminating examples throughout your course, as well as in your unit on evolution. If you develop any clever interactive activities built around those examples, please share with us at ENSIweb. At the very least, be sure to encourage your students to read the book. Many eyes will be opened.
Larry Flammer
ENSI Webmaster