An IDolator's clarification

IDolator David Tyler wants to make something clear about a new fossil, Yanoconodon:

The first point to make is that this is not an example of a transitional fossil. …

Rather, the new fossil has been hailed as illustrating an important evolutionary transition: detachment of the middle ear bones from the mandible. It is therefore better described as a fossil claimed to have a transitional structure associated with ear bones.

You get that? It's a fossil of a transitional form, not a transitional fossil.

Here's the thing. Practically every fossil is transitional in some sense. Every fossil had ancestors and most represents a population which left descendants. Fossils like Tiktaalik or Yanoconodon are important not because the are located at some transition between a specific, known ancestor and a specific, known descendant, but because they possess structures which are transitional between a form characteristic of one major group of organisms and another. They show how an evolutionary pathway happened by retaining major anatomical features from that transition.

i-e293ecc1228ef0493221d8a7fa54fc23-yanoear.jpg
I don't know whether Yanoconodon has any living modern descendants. Odds are against that. Most species go extinct, which means that most descendants of an ancient species are probably extinct. But Yanoconodon is a recent descendant of one of the first individuals to possess a particular arrangement of its jaw bones, and retains that arrangement.

Modern mammals have a single bone in their lower jaw, while reptiles have 4. In one of our reptilian ancestors, the bones had gotten re-arranged, the actual hinge of the jaw moved to the bone with all the teeth, and freed up the other bones. In time, the other three got attached to the ear canal, but were still attached to the main jaw bone, making them both ear bones and jaw bones.

In Yanoconodon and species like it, those three bones are somewhat separated from the main bone of the jaw, and are becoming exclusively ear bones. By successive modifications after the time of Yanoconodon, those bones became the smallest in the human body, the malleus, incus and stapes – the three bones of the ear.

When we look at this 5 inch-long fossil, We don't know if we are looking at our direct ancestor. Chances are it is a close relative of our ancestors, a different branch off of the tree of life. What makes it transitional is the unique arrangement of its ear bones. What makes it fascinating is that it is a peek into a part of life's great history. It stands on its own four legs as a sign of what life can do.

Tags

More like this

The latest Nature reveals a new primitive mammal fossil collected in the Mesozoic strata of the Yan mountains of China. It's small and unprepossessing, but it has at least two noteworthy novelties, and first among them is that it represents another step in the transition from the reptilian to the…
Rusty Lopez of the New Covenant blog has stated that his latest response to me regarding the "testable creation model" that he advocates will be his last. I thank him for an engaging dialogue on these issues, and regret that he chooses not to continue the conversation. He says he does not have the…
Cast your mind back to June, when a stunning fossil animal called Darwinius (alternatively Ida or "The Link") was unveiled to the world to tremendous pomp and circumstance. Hyperbolic ads declared the day of Ida's discovery as the most important for 47 million years. A press release promised that…
The hit parade of creationist responses to Tiktaalik roseae continues with this article about the response of Ken Ham, founder of the American wing of Answers in Genesis. Like the rest, it's amusing for the almost total lack of any substantive response to the facts. "If you look at a platypus, a…

You get that? It's a fossil of a transitional form, not a transitional fossil.

Crystal clear. It's a comment that's stupid, not a stupid comment. Couldn't be more different. Important distinction, that.