How does one find a transitional fossil? It’s a lot harder than I ever imagined.
I just started reading a book that looks quite promising: Your Inner Fish: a Journey into the 3.5 Billion Year History of the Human Body (2008), by Neil Shubin. The author is a professor of anatomy at the University of Chicago. Shubin is also the provost of the Field Museum in Chicago.
The first thirty pages of the book have been delightful. Shubin is a paleontologist who ended up teaching human anatomy. He discovered that this was a good combination, because “the best roadmaps to human bodies lie in the bodies of other animals.” By looking at other animals, we can often better understand the complex structure of the human body. “The reason is that the bodies of these creatures are often simpler versions of ours.”
Shubin was part of the expedition that discovered Tiktaalik, a 375 million-year-old fish fossil that represents an intermediate life form. In fact, Tiktaalik represents one of the greatest transitions in the history of life: the invasion of land by fish.
Like a fish, it has scales on its back and fans with thin webbing. But, like early land-living animals, it has a flat head and neck. And, when we look inside the fan, we see bones that correspond to the upper arm, the forearm, even parts of the wrist. The joints are there to: this is a fish with shoulder, elbow and wrist joints. All inside a fin with webbing.
[This photo is from Wikipedia]. Shubin details the extensive planning that was necessary to find this world-class fossil. You don’t just randomly pick a spot to start digging for rare transitional life forms. “We look for places that have rocks of the right age, rocks of the right type to preserve fossils, and rocks that are exposed at the surface. There is another factor: serendipity.”
It takes a lot of work to know where to dig and how to dig out a fossil of the sort. It took Shubin six summertime trips to a remote area in the Arctic. And you don’t just drive out there in a car. There are no roads anywhere to be seen. It takes a lot of money and therefore a lot of persuading in order to get the necessary grants to allow a highly trained team to go out to such remote spots.
Speaking of remote, Shubin mentions that ancient sea floors show up in the darndest places. For instance, if you go to the North face of Mount Everest, almost within sight of the mountain peak, you can find fossilized sea shells (you can also find lots of ancient sea creature fossils at the top of the Grand Canyon). The place where Shubin found Tiktaalik would seem equally unlikely to those of us who are not familiar with paleontology. The area where Tiktaalik was discovered (Ellesmere Island, Canada, only 1000 miles from the North Pole) was formerly an ancient tropical delta, much like the current Amazon, where fish would have thrived and fossilized. This area was chosen because geologists had previously discovered that exposed rock dated roughly 375 million to 380 million years old existed at Ellesmere. After discovering Tiktaalik Shubin named it. Tiktaalik is an Inuit word meaning “large freshwater fish.”
Shubin writes with a personal yet precise style. The journey he is discussing in his book doesn’t only have to do with finding the ancient fish he discovered near the North Pole. That is just the beginning. Most of the book has to do with the relationship between ancient fish and modern human anatomy:
How can I be so sure that this fossil says something about my own body? Consider the neck of Tiktaalik . All fish prior to Tiktaalik have a set of bones attached to the skull to the shoulder, so that every time the animal band its body, it also bent his head. Tiktaalik is different. The head is completely free of the shoulder. This whole arrangement is shared with amphibians, reptiles, birds, and mammals, including us. The entire shift can be traced to the loss of a few small bones in a fish like Tiktaalik. I can do a similar analysis for the wrists, ribs, errors, and other parts of our skeleton-all these features can be traced back to a fish like this. This fossil is just as much a part of our history as the African hominids, such as australopithecus afarensis, the famous “Lucy.” Seeing Lucy, we can understand our history is highly advanced primates. Seeing Tiktaalik is seeing our history as fish.
As a make my way through Shubin’s book further, I’ll will be writing more about it at this site. I’m really looking forward to this.
I’m tempted to send copies of this book to a few creationist acquaintances, so that they can read Shubin’s fascinating account about the existence and discovery of an undeniable transitional life form. Then again, those creationists would probably deny that the fish with a neck and a wrist ever lived, arguing that God put that fossil there to test their faith . . .