One of the major underpinnings of biology is that all life shares a common ancestor. If the scientific theory of evolution is true, we should be able to make predictions about what forms led to the variety of forms we see today.
As an example, we can predict that between fish fossils and early land tetrapods, that there should be a transitional species that shares characteristics that are common between fish and land tetrapods. This transition eluded us until relatively recently.
If you look at all land animals today, they have a common theme for forelimbs. One bone, two bones, lots of small bones, and finger-like bones.
We see this same pattern in amphibians, reptiles, mammals, dinosaurs, birds etc. They all have variations on the same theme. In order to confirm that they all had a common ancestor, in the fossil record, we should find a layer of rock that existed somewhere between fish but before land animals. This should be somewhere in the Devonian, approximately 375 million years ago.
In 2004, a paleontological team lead by Dr. Neil Shubin found an exposed area of Devonian rock in Ellesmere Island in Northern Canada. After five years of digging, and on the final trip, they finally hit pay dirt. They found an exposed snout of a fish-like animal and sent it home to be slowly extracted from the rock. It was a perfect example of a transitional species. It had fish-like bones, but it also had arm-like structures instead of fins. It had a wrist, a neck and several other features that fish do not have. It could maneuver on land, but spent most of its time in the water. This organism became known as Tiktaalik, the fishapod.
Tiktaalik roseae is a classic example of the power of predictive evolution. Scientists knew that if evolution were true, this sort of animal SHOULD exist, and if it does exist, its remains should be present at a particular time and within a particular layer of rock. They set out to find it, and they actually found it!
Watch Professor Neil Shubin talk about the discovery of Tiktaalik.
PBS Media Lesson Plan about Fishapod: https://gpb.pbslearningmedia.org/resource/evol07.sci.life.evo.lptiktaalik/tiktaalik-evolution-of-a-fishapod
Thank you for reading! :-)
“Nothing in Biology Makes Sense Except in the Light of Evolution” – Theodosius Dobzhansky