How We Got On Land, Bone by Bone

Before about 370 million years ago, our ancestors were scaly creatures that lived in the sea, swimming with fins and using gills to get oxygen from the water. And then, over the course of millions of years, they began moving ashore, adapting to the terrestrial realm. They became tetrapods, a lineage that would eventually produce today’s amphibians, reptiles, birds, and mammals. As scientists have unearthed fossils from those early days, one lesson has come through ever more loud and clear: the transition was not a single leap. Instead, it was drawn out and piecemeal.

One of the most important of these fossils came to the world’s attention in 2006. Digging in the Arctic, a team of scientists found a 370-million-year-old creature they dubbed Tiktaalik. As I wrote at the time on the Loom, Tiktaalik belonged to a lineage of aquatic vertebrates called lobefins–a group that today includes lungfish and coelacanths. A number of anatomical features set lobefins apart from other fish, and show them to be more closely related to us and other tetrapods. They generally have stout fins that contain bones corresponding to the upper bones of our arms and legs. Some fossils of lobe fins don’t just have a bone corresponding to the humerus–the long bone attached to the shoulder–but the radius and ulna, too.

Tiktaalikcast400.jpg
The front half of Tiktaalik. Photo © Ted Daeschler
But even among lobefins, Tiktaalik was remarkably tetrapod-like. It had a distinct neck, for example, and its fins had additional limb-like bones. Along with bones corresponding to a humerus, radius, and ulna, it even had wrist-like bones that functioned as a joint, as they do in our hands. Without digits, Tiktaalik couldn’t grasp a branch with its fins. But it could do a decent push-up in the muddy shallows that it called home in the Devonian Period. (Neil Shubin, one of the discoverers of Tiktaalik, told the creature’s story in his 2009 book Your Inner Fish.)

The bones that Shubin and his colleagues described in 2006 came from the front half of Tiktaalik. Only now, eight years later, have Shubin and his colleagues unveiled the other half of this remarkable beast. And they’ve now stretched out the transition from fish to tetrapod even more.

It was not what Shubin and his colleagues were expecting. The closest lobe-fin relatives of tetrapods had tiny pelvises, which only served to attach muscles that controlled the pelvic fin during swimming. Tiktaalik had a massive pelvis–as big as those of the earliest true tetrapods with legs and digits. And like us, it also had a massive scoop carved out of the side, where the ball of the femur could fit.

tiktaalik-diagram-550
Image courtesy of John Westlund, University of Chicago.
The discovery prompted Shubin and his colleagues to look back at the thousands of other fossil fragments they had found at the Tiktaalik site over the years, many of which remained puzzling to them. They compared the new Tiktaalik bone to those unclassified fossils and found that they had unwittingly found five other Tiktaalik pelvises. Until they knew what a Tiktaalik pelvis actually looked like, they didn’t know what they had.

All those hip bones have brought Tiktaalik into sharper focus. For one thing, they show that the creature could get big. The largest pelvis bones they’ve found suggest that Tiktaalik could grow up to nine feet long. Our ancient relatives, in other words, were the size of alligators.

nationalgeographic


I remember reading about the initial discovery a while back but at the time it was incomplete. The article tells the story of why it took so long to get a complete picture of the fossil. I didn't quote that part, but it explains when they excavated the fossil they had to break it in half to transport because it was s big. To preserve the fossil for transport they cover them in plaster which makes them even bigger. Basically, it was to big to move in one piece the exact words were"it was a giant boulder".

Well this is another step in filling in the evolutionary tree. The pelvic bones of Tiktaalik show a species in mid evolution to becoming one of our first ancestors to walk on land. I look forward to the next big discovery.

reply to post by Grimpachi

Come on, man ... do you really believe 'the story'?

I've become convinced we evolved from bananas. After all, we share 50% of their DNA. LINKY

reply to post by Snarl


You wouldn't be entirely wrong in the sense that both ourselves and bananas as well as every other organic life form on Earth evolved from the same single called organisms a few hundred millennia ago.

reply to post by Grimpachi


I wonder if it all points to every form of species eventually gets to where we are given enough time.

Or if the other species are already in there higher form....

It's a weird question that science hasn't proven yet..

reply to post by Treespeaker


It is all about survival of the species. Each species has found its niche and if it is successful in that niche there isn't much else to drive them to evolve further. Their are some species which have hardly evolved at all over millions of years because their current form has been adept to its surroundings basically there was no need to change further.

This is an interesting case of exactly such a species.

The Human-Sized Salamander That Smells Like Pepper

reply to post by Snarl


In DNA terms, 50% is a huge gap. We're missing half of what makes a banana a banana, and the banana is missing half of what would make it human.

They say pigs share 98% of our DNA. This doesn't mean our ancestors are pigs.

Saying that we're descended from bananas is like saying you are descended from your 3rd cousin twice removed who is a year younger than you.

reply to post by Glass

Ahhhh ... thread revival? I LOVE Grimpachi's threads. They always leave huge gaps for breadth of discussion ... and that takes a God-given talent he wouldn't want to admit to. My forte is bashing around like a bull in a china shop, but the noise (sometimes) hurts even my ears. I also like to fish, and it is rare I drop a line I don't hope to reel something in on. What I liked about this particular thread was its title "How We Got On Land, Bone by Bone" ... (soft science) approach.

You see, I've got some ideas on the subject of evolution as well. Mine have not received main-stream soft science consideration as of yet. Would you like to meet me in the debate forum, carry on a conversation here ... or were you simply trying to poke me in the eye with that there sharp stick of your'n?

-Cheers

ETA: Some food for thought

reply to post by Grimpachi


Is it just me, or does this seem a little too subjective and speculative

Scientist 1- "Hey look at that, it's got a pelvis with what looks like a scoop where the ball of a femur could fit"
Scientist 2- "Hey yea, it does kind of look like that. Let's look at those other fragments of bones from previous fossils that we couldn't identify.
Scientist 1- "Imagine that, more pelvises, just like ours!"

reply to post by PhotonEffect


To me they did things the correct way. They had incomplete fossils and instead of making a hypothesis from incomplete data they shelved them. Once they discovered a fairly complete fossil then the fragments could be identified. It was a lengthy process of gathering and uncovering evidence. I think it was done by the book, and now their findings can be added to the books.

reply to post by Grimpachi


I don't doubt they did it the "right" way, but still, it seems (to me) they're relying on some guess work here, if not leaps of logic.

Kind of like seeing a rabbit in the clouds...

Only my opinion of course.

So I guess the retard alligator gar didn't evolve with the rest of us? They stayed stupid unsophisticated alligator gar?

You think they would have developed vocal cords at the very least right?

Evolution is ridiculous, it's just so dumb I can't fathom how anyone can look at this crap with a straight face and teach it.

reply to post by xstealth


Your entitled to your opinion, and you seem to speak as if you know better than all those scientists so what would be your explanation for the diversity of life on earth as we know it?

Grimpachi
reply to post by xstealth

 

Your entitled to your opinion, and you seem to speak as if you know better than all those scientists so what would be your explanation for the diversity of life on earth as we know it?

Yes I know, and it makes more sense than the evolved from anything.

20 And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven.

21 And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good.

22 And God blessed them, saying, Be fruitful, and multiply, and fill the waters in the seas, and let fowl multiply in the earth.

reply to post by xstealth


OK I see you are good with the God did it claim.

Thanks for the enlightened evidence based opinion.

xstealth
So I guess the retard alligator gar didn't evolve with the rest of us? They stayed stupid unsophisticated alligator gar?

What exactly makes them stupid or unsophisticated? Viewing the world through an anthropomorphic lens will never allow you to see the big picture let alone what's outside of the box you've build for yourself to hide in.

You think they would have developed vocal cords at the very least right?

Why would you expect that? There are plenty of living creatures that haven't needed that as an adaptive advantage.

Evolution is ridiculous, it's just so dumb I can't fathom how anyone can look at this crap with a straight face and teach it.

Of course, well researched science is just ridiculous when we can get all the I for action we need out of a several millennia old book about supernatural fairy tales. Who in their right mind would ever trust in the scientific method when we have an infallible anachronistic bronze age manuscript to tell us how to live in the silicon age.

peter vlar

xstealth
So I guess the retard alligator gar didn't evolve with the rest of us? They stayed stupid unsophisticated alligator gar?

What exactly makes them stupid or unsophisticated? Viewing the world through an anthropomorphic lens will never allow you to see the big picture let alone what's outside of the box you've build for yourself to hide in.

You think they would have developed vocal cords at the very least right?

Why would you expect that? There are plenty of living creatures that haven't needed that as an adaptive advantage.

Evolution is ridiculous, it's just so dumb I can't fathom how anyone can look at this crap with a straight face and teach it.

Of course, well researched science is just ridiculous when we can get all the I for action we need out of a several millennia old book about supernatural fairy tales. Who in their right mind would ever trust in the scientific method when we have an infallible anachronistic bronze age manuscript to tell us how to live in the silicon age.

big bang, evolution, even down to black holes.

These are theories, because all the scientists in the world together can't prove either one.

I believe in black holes for the record, but now Hawkins says they don't exist and they are 'gray holes' and the light is like running on a thread mill trying to escape, it gets nowhere.

reply to post by xstealth


After years of him telling people that they existed. I tire of people passing their ideas, and theorem off as fact of the matter. I understand that ideas evolve, but it seems like most scientists don't. With the rigidity that they hold to their beliefs, it boggles the mind. One can definitely see the comparison to religious ideology. I would just like a scientist to be intellectually honest, and say; "We don't know. We think we do. But we don't. We wish we did. We have ideas, but that's all they really are right now. In a hundred years, they will most likely look back on this time and laugh. The way 'modern' scientists do about middle age teachings."

reply to post by Chronogoblin

In a hundred years, they will most likely look back on this time and laugh.

You just might be right about that we may look back at the theory of evolution and laugh about how much was wrong, but I am absolutely certain the theory itself will be realized as fact more so than today. It will never be looked back on and realized to be as absurd as a two thousand year old collection of stories written by goat herders trying to explain how the universe came into being.

Star for that post.

Grimpachi
reply to post by Chronogoblin

 

It will never be looked back on and realized to be as absurd as a two thousand year old collection of stories written by goat herders trying to explain how the universe came into being.

The 'story' is far far older than that. Wait'll that cat gets out of the bag.

reply to post by Chronogoblin

I don't get it. On the one hand you say that they rigidly hold on to their beliefs and on the other you say that in a hundred years their beliefs will have advanced to the point that the current beliefs will seem comical.