Thursday, November 27, 2008

Hey Creationists!

Have you ever made the claim that there are no transitional fossils? Well you can stop it right now because I'm about to give you a picture-filled post of just a few of the transitional fossils that exist. Real pictures of fossils where you can see the features that are emerging. I won't include ones that actually require an understanding of vertebrate anatomy to appreciate, because all those long words are a lot less persuasive than clear pictures (click on them to see a larger version for more detailed examination). Rest assured, however, that if you so desire I can provide a detailed description, complete with literature citations, of exactly how things like eyes and ears and wings evolved. But that's a task for another day.

Oh, and by the way? Transitional animals are not chimeras. You aren't going to find something that has a head just like a modern bird, a body just like a modern lizard, and a tail just like a modern amphibian. That's not how it works. If that doesn't make sense to you, go learn something before you try to "disprove" evolution with your old book.

Exhibit One: Archaeopteryx

This is probably the most famous transitional fossil ever found. I have a photograph of the real thing (not a cast) to start with, and then I'll point out the details.

See those feathers? That's what makes this reptile so special. It has all the structures necessary for powered flight, and the feathers we associate with modern birds, but it still has a reptilian skull (including teeth, if you look closely), and claws on the end of the forelimbs. It also still has a full bony tail, something modern birds have since mostly lost. The other evidence supporting this transition is overwhelming, from flightless dinosaurs with feathers for display to the close similarity between the protein that forms reptile scales and the one that forms bird feathers in modern times.

This is Epidexipteryx, and it's a dinosaur, not a bird. It could not fly. However, there are clearly feathers visible in the fossil, possibly for display purposes. This is not the only fossil of its kind (China seems to have all kinds of feathered dinosaurs in its rocks), but it is a particularly good one, where the feathers are very easy to pick out. It's fossils like this that make it clear that the question, "What good would feathers do for a reptile that couldn't fly?" is a silly one. Yes, feathers are lightweight and useful for flying, but most likely they were first an advantage for body temperature regulation, then for attracting the opposite sex, then finally as an asset for gliding (and later still, powered flight). In modern birds, all three uses exist (after all, why else do penguins, emus, and ostriches have feathers even though they can't fly? Temperature regulation and looking good for the ladies, that's why). Now with fossils like Epidexipteryx, we see that flight may have been a sideline for only one part of a group full of temperature-regulating, good-looking dinosaurs with feathers.

Oh, and in case you wanted an example of a dinosaur which probably only had feathers for warmth?
Here you go. This is called a "fuzzy raptor", and it's another fairly new discovery from China. Those orange areas, if examined closely, are not mineral elements from the fossilization process. They are proto-feathers - strands of keratin that create fluffy, soft feather-like projections. Good for warmth, but not all that pretty, and useless for flight because they are not aerodynamic. Like Epidexipteryx, the fuzzy raptor was flightless and its skeleton is reptilian, but feathers would have still been very useful as insulation.

So, which came first, the feathers or the wings? The feathers did. And as for the teeth, well, modern birds can still grow reptilian teeth in their beaks. The gene is just off, not gone. Believe it or not, but genetics is a powerful tool for providing evidence for relationships between species.

Exhibit Two: Tiktaalik

This fossil was actually found in Nunavut, Canada, which I think is great. Not that I would want to try excavating fossils in permafrost way up on Ellesmere Island, but it's a fantastic discovery that was made in my home country, so I'm doubly impressed.

Tiktaalik is a transitional species between fish and tetrapods (meaning four-limbed animals, which includes all amphibians, reptiles, birds, and mammals). It is part of a group that is the ancestors of amphibians, reptiles, birds, and mammals, and seems to most resemble crocodilians, with eyes on the top of its head and sharp carnivorous teeth. Leg bones are visible in this photo, but they are fin-shaped. Other aspects of the physiology indicate that these limbs could not have carried Tiktaalik around on land much, if at all, because they most likely could not support the animal's entire weight easily. However, they had movable joints within the fin structure like the bones in our shoulders, elbows, and wrists and a more flexible neck without the bony gill plates of fish, features that today only exist in tetrapods and not in fish species.

As for transitioning from gills to lungs...

The close-up at the bottom-right of the image shows rib bones similar to modern tetrapods', with the ability to encase lungs. However, it still had gills for use underwater. Those are harder to see in fossil photos, but the bones where gills would be attached are labelled on the above diagram as "cbr", meaning "ceratobranchial", a bone structure associated with gills in modern fish.

Exhibit Three: Ambulocetus

Whales are always a point of contention for creationists. How could land-living mammals become so well-adapted to the water that they look just like fish? (Well, except for their bone structure and the fact that they breathe air and so on.) In fact, we know a considerable amount about whale evolution now. Here is a series of three photos that lead up to modern whales, and there is a fairly smooth transition between them:

This is Pakicetus. It was a land-bound carnivore (see those huge teeth?), but it had long webbed toes for swimming. Because of this, it is possible that it did a considerable amount of hunting in the water.

This is the aforementioned Ambulocetus, the main (but not sole) transitional fossil in the whale lineage. Somewhat similar to Pakicetus, it has long toes, most likely with webbing, but its joints are set up primarily for swimming and not for running or walking. It would have been able to swim easily, but walking would have been awkward, so it most likely spent the majority of its time hunting (teeth!) in the water. Also, its longer and better-reinforced tail would have been more useful for water propulsion than Pakicetus' thinner, shorter tail.

This is Dorudon. Its front limbs are much smaller than those of Ambulocetus and shaped like flippers, as is seen in modern whales, except that the finger bones are more elongated than in a modern whale. It also has a long, strong tail that would have made it a very powerful swimmer. What is most important, however, is the hind limbs. In modern whales they are teeny tiny hip bones with no outer musculature associated with them, but in Dorudon they are small but noticeable protrusions. Dorudon, who is in so many ways like a whale, still has legs.

One other aspect of the three photos worth looking at is the skulls. All three are very similar in shape, with the only differences being in nostril position (closer to the top of the skull for Dorudon compared to its earlier relatives) and minor shifts, such as the loss of the plate at the back of the skull seen in Pakicetus (not aerodynamic), and the rounder jawbone seen in Dorudon (again, more aerodynamic).

Exhibit Four: Odontochelys

Turtles seem like an unusual group of reptiles. Since the Cretaceous–Tertiary extinction, they are the only marine reptiles left in existence, and their morphology (having a shell, for example), makes them seem very different from all other modern reptile groups, even if they belong to a land-living species. However, now we have a fossil of a proto-turtle with only the bottom part of a shell, pictured below:

This is a top-down view of Odontochelys. It looks a bit like a turtle, with the wide torso and the small skull, but the more interesting photo is below:

This is what that same creature looks like from the bottom. Does that bony underside look familiar? It's almost identical to the underside of modern turtles, but these reptiles hadn't developed a full shell yet. Oddly enough, scientists predicted that early ancestors of turtles might look like this because when turtle embryos develop, they grow their underside armor first and their shell afterwards, suggesting that shell development might have come at a later point in the turtle lineage than the development of an armored underside. Embryonic morphology has long been an indicator of an animal's evolutionary past, and this is just one of many instances where evolutionary history and modern animal development both support the same conclusion.

Exhibit Five: Australopithecus and the other Homo species

It seems to terrify a lot of people to think that humans aren't a special exception to the laws of nature. We evolved, just like everything else. Humans are animals, vertebrates, mammals, and primates, as well as hominids, so we evolved from other species just like everything else has. If we were created to be special, why do we share between 95% and 98% of our genes with chimpanzees? Why do human embryos grow gills, webs between their digits, and tails during development? Why do we function biologically like every other placental mammal on the planet? The most obvious, while possibly not the most meaningful, answer is that we are just another animal who, due to a series of natural events and fortuitous mutations, happened to get smarter and smarter until we were capable of creativity, innovation, and imagination. Sentience may be a rare trait that is not easy to evolve naturally, but it certainly makes more sense that increased intelligence was a beneficial adaptation to an otherwise ordinary animal species rather than we were created separately from all the other animals and "chosen" to be extra-important... even though in most ways we are no different from any other creature on the planet.

These are example skulls from the eight best-studied Australopithecus and Homo species, including us. The upper left skull is very similar to modern chimpanzees, with a relatively small braincase and a simian facial structure. As the skulls progress from left to right, there is a gradual increase in brain size, and in the Homo species particularly in the front of the skull, where the frontal lobe is located. More human facial structures are also seen gradually emerging, with the face becoming less sunken and more even with the jaw.

What, that's not enough transitional fossils for something as important as humans? Fine then!
This gives both front and side views of humanoid skulls, again from Australopithecus afarensis in the top left to Homo sapiens in the bottom right, but with even more gaps filled in. With this series, the skull changes look even more gradual and sequential, with the first looking very much like an ape and the last few looking very similar to us. This is very compelling evidence for human evolution. Where is the evidence that we appeared out of nowhere? How can creationism explain the existence of all these fossils?

Need I say more? Human evolution is not "speculation". This is one of the most complete sets of fossil transitions we have for any animal on Earth, and it shows where we, the human animal, came from. We came from apes. Before that we looked a little like lemurs, and long before that we looked like shrews. It's not embarrassing or horrifying to be connected to the rest of nature. It shouldn't be frightening either. We are merely equally important as everything else, not more important - that should give us some humility and some perspective on our place on this planet.

Sure, it'd be nice to be specially chosen to be smart enough to reflect on our own existence, but we weren't. We got it through nature, just like whales got their flippers from nature, turtles got their shells from nature, and birds got their feathers from nature. If anything, this should tell us that being aware of our impact on other species like no other creature can be comes with the responsibility to act sustainably within the world's ecosystems. Destroying nature hardly seems like a way to show we're grateful for being this smart, and we need to stop justifying lording over everything by saying we have some "divine" right to do whatever we want with the Earth. We don't. We are not special. We will die along with millions of other species if we continue to harm the balance of nature like we are doing today. Being sentient will not save us from starvation if we breed our plants into genetic uniformity and destroy the ecosystems that protect our food species from disease and allow them to reproduce successfully. Believing in some higher power bestowing leadership on our species will not save anyone from being killed by a new disease that could have been cured by a plant that we burned and deforested into extinction.

Any questions?

3 comments:

  1. I thought you might like this site I made, it's kinda of a tl;dr version of your post. ;-)

    http://www.transitional-fossil.com

    ReplyDelete
  2. I love it, Transitional Fossil!

    If you don't mind, I will be directing creationists there in my future internet debates when they make silly statements like "there are no transitional fossils".

    ~PD

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  3. ooohhhh.... when I come back I wanna be a Fuzzy Raptor! yeah, that's what I'll be cuz I'm a fuzzy cute and cuddly kind of guy! hehehehehehe

    Thank heathens I don't have to really worry about coming back.

    ReplyDelete