Well… definitely the dinosaurs.
In recent decades, the link between birds and dinosaurs have been strengthened through research into avian and dinosaur anatomy, together with the discovery of new feathered dinosaur fossils in China. It is now well established that many theoropods such as velociraptor and tyrannosaurus indeed had feathers. And it is thought that at least one species of theoropod were ancestors of modern day birds, so that most scientists now even classify birds under the dinosaur family tree.
Controversy is brewing though, as some scientists are disputing the claim that certain theropod dinosaurs evolved into birds. They believe that it could have been the other way around – that it was the birds that evolved into a few species of theropod dinosaurs. They conclude from their research that the small dromaeosaurids like velociraptor and microraptor could instead be flightless birds. It’s definitely not a forgone conclusion yet. Even if some of these dinosaurs descended from birds, there’s still the question of the ancestry of birds – were birds descended from earlier theoropods then?
No doubt the Creationists are going to have a field day with this news. But that’s how science is – it corrects itself, and our knowledge is never final. If observations arise that prove a long held theory to be wrong, we discard it and search for a better theory. Sometimes it’s difficult, as during the quantum mechanical revolution of the 1930s, but we have to move on. As John Polkinghorne says, “Radical revision is no more easy for scientists than it is for theologians“.
The occasional occurrence of radical revision in scientific theory-making means that one cannot claim the achievement of science to be that of the attainment of absolute truth. However, we have seen that there is sufficient continuity of understanding across the boundaries of paradigm shifts to be able to interpret science’s development as resulting in a tightening grasp of physical reality. ~ John Polkinghorne
Scientific knowledge, in the absolute sense, is always tentative. Science is founded on the proposition that everything we think we know about the natural world can, in principle, be rejected if it does not meet the test of observation and experiment. The very practice of science, at its core, is a constant exercise of extending what we do know about the world, and then correcting what we thought we knew for sure. It simply means that evolution is a scientific idea, and scientific ideas rise or fall on the weight of the evidence. ~ Kenneth Miller, Finding Darwin’s God
There are times when one must cling to the strangeness of experience, resisting the temptation to deny part of that experience in order to achieve a facile, but unsatisfactory, relief from perplexity. ~ Sir John Polkinghorne, Science and Theology
We can never prove beyond doubt that a thing is true, only that it is false, and science is lost without those bold enough to interrogate its scientifically correct beliefs. ~ Edward Harrison, Cosmology: The Science of the Universe