News From The Tiktaalik Front

Unless you are evolutionarily predisposed to living under a rock, you know the story behind Tiktaalik. For the rock dwellers out there I will elaborate. Back in 2004 Neil Shubin PHD made the Tiktaalik discovery. He reasoned, and rightly so, that if the theory of evolution was correct, (and it is) then a transitional fossil between fish and four legged land walkers would fall in the time period of roughly 380 million years ago. He decided that if this transitional creature was out there to be found, it would be found in rock layers dating back to that time. Mr. Shubin managed to get funding for an expedition, and went about finding this fossil. Found it he did. This predictable power of evolution is perhaps THE most important aspect of evoulutionary theory. An amazing discovery. Mr. Shubin later authored the book “Your Inner Fish” (which sadly I have yet to read) and apparently has been back to his Tiktaalik honey hole, fishing for more fossils.

Found them he did. The first Tiktaalik discovery was the front end of the animal with the head and front “feet.” This time they found the back half, completing the picture of this incredible animal. I am going to crib in part much of the story, which was realeased from here: http://www.uchospitals.edu/news/2014/20140113-tiktaalik.html   

“The discovery of well-preserved pelves and a partial pelvic fin fromTiktaalik roseae, a 375 million-year-old transitional species between fish and the first legged animals, reveals that the evolution of hind legs actually began as enhanced hind fins. This challenges existing theory that large, mobile hind appendages were developed only after vertebrates transitioned to land. The fossils are described by scientists in theProceedings of the National Academy of Sciences, online on Jan. 13.

“Previous theories, based on the best available data, propose that a shift occurred from ‘front-wheel drive’ locomotion in fish to more of a ‘four-wheel drive’ in tetrapods,” said Neil Shubin, PhD, Robert R. Bensley Distinguished Service Professor of Anatomy at the University of Chicago and corresponding author of the study, which marks his inaugural article as a member of the National Academy of Sciences. “But it looks like this shift actually began to happen in fish, not in limbed animals.”

Discovered in 2004 by Shubin and co-authors Edward Daeschler, PhD, Associate Curator of Vertebrate Zoology at the Academy of Natural Sciences of Drexel University, and the late Farish A. Jenkins, Jr., PhD, of Harvard University, Tiktaalik roseae represents the best-known transitional species between fish and land-dwelling tetrapods.

A lobe-finned fish with a broad flat head and sharp teeth, Tiktaaliklooked like a cross between a fish and a crocodile, growing up to a length of 9 feet as it hunted in shallow freshwater environments. It had gills, scales and fins, but also had tetrapod-like features such as a mobile neck, robust ribcage and primitive lungs. In particular, its large forefins had shoulders, elbows and partial wrists, which allowed it to support itself on ground.

However, only specimen blocks containing the front portion of Tiktaalikhave been described thus far. As the researchers investigated additional blocks recovered from their original and subsequent expeditions to the dig site in northern Canada, they discovered the rear portion of Tiktaalik, which contained the pelves as well as partial pelvic fin material. The fossils included the complete pelvis of the original ‘type’ specimen, making a direct comparison of the front and rear appendages of a single animal possible.

The scientists were immediately struck by the pelvis, which was comparable to those of some early tetrapods. The Tiktaalik pelvic girdle was nearly identical in size to its shoulder girdle, a tetrapod-like characteristic. It possessed a prominent ball and socket hip joint, which connected to a highly mobile femur that could extend beneath the body. Crests on the hip for muscle attachment indicated strength and advanced fin function. And although no femur bone was found, pelvic fin material, including long fin rays, indicated the hind fin was at least as long and as complex as its forefin.

“This is an amazing pelvis, particularly the hip socket, which is very different from anything that we knew of in the lineage leading up to limbed vertebrates,” Daeschler said. “Tiktaalik was a combination of primitive and advanced features. Here, not only were the features distinct, but they suggest an advanced function. They appear to have used the fin in a way that’s more suggestive of the way a limb gets used.”

Tiktaalik pelves were still clearly fish-like, with primitive features such as an undivided skeletal configuration, as opposed to the three-part pelvic girdle of early tetrapods. However, the expanded size, mobility and robusticity of the pelvic girdle, hip joint and fin of Tiktaalik made a wide range of motor behaviors possible.

“It’s reasonable to suppose with those big fin rays that Tiktaalik used its hind fins to swim like a paddle,” Shubin said. “But it’s possible it could walk with them as well. African lungfish living today have similarly large pelves, and we showed in 2011 that they walk underwater on the bottom.” End Quote.

So to sum it up, Tiktaalik had developed “walking feet” well before it made its move to land. As well as rudimentary lungs and a ribcage. All of these traits made it (I would suspect) much easier for this creature to invade land, and go on to provide the evolutionary foundation for all vertebrates today. Absolutely amazing!  Even more awseome is this (also cribbed from the link above)  “Shubin will be hosting a three-part TV series based on his book “Your Inner Fish,” on PBS in April 2014, tracing the origins of the human body through the DNA of living animals and the legacies of now-extinct, but biologically important species such as Tiktaalik roseae.” It is safe to say I am really looking forward to this. Is it April yet?

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s