Apr 24 2009

Pinniped Evolution

The joke is getting so overused now it is becoming a cliche in skeptical circles – what happens when a paleontologist fills in a gap in the fossil record? They create two gaps, one on each side. But it is often used because it pithily exposes the intellectual buffoonery of those evolution deniers (aka creationists) who deny common descent. What is a “gap;” how big does it have to be to call into question common decent; or rather how small do the gaps have to shrink before creationists will accept common descent?

Perhaps the biggest outright lie in the creationist camp, still frequently parroted, is that there is a lack of transitional fossils in the fossil record. That is why it is important to showcase to the public the steady stream of beautiful transitional fossils that are being added to our already copious fossil record.

In the most recent issue of Nature, scientist present yet another pesky gap filled in with a transitional fossil, this one an early pinniped – which includes seals, sealions, and walruses.

The fossil is between 20-24 million years old and is dubbed Puijila darwini. Here is the technical description from the Nature article.

The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing.

What this means is that the creature was able to walk on land, was likely a carnivore, but had some early adaptations to the water, such as webbed feat. Think of an otter (it was 110 cm long) with a long tale and the teeth of a dog.  The earliest pinniped fossils come from 20-28 million years ago, about the same time as this fossil, and already have fully developed flippers.

This fossil suggests answers to several unknowns – what evolutionary path did pinnipeds take, what are their closest relatives, and where greographically did their evolution take place? This fossil suggests they evolved in the fresh waters of the arctic, as opposed to the the northwestern US, where the earliest pinniped fossils were found. This one fossil does not settle this last question, but does suggest the arctic as a viable alternative.

I can anticipate the standard creationist denial. They will argue that this fossil cannot be a direct ancestor to pinnipeds because it is as old, and not older, than the earliest pinniped fossils with fully formed flippers.  This is true, as the authors of the Nature article readily state. Most fossils will not be direct ancestors to living descendants. This is because evolutionary relationships are bushy – they are not a ladder of linear progression. A randomly discovered fossil is therefore likely to be on a side branch, not one that lead directly to species that happen to be extant.

The same is true of Archaeopteryx – the transitional species between small theropod dinosaurs and modern birds. Archaeopteryx is almost certainly not on the main line that led to birds. But it does show that in the right time and place there were feathered dinosaurs that had half reptilian and half bird-like morphology. Evolutionary theory also predicted that we would find more – and we have, in spades. There is now a fairly full assortment of feathered dinosaurs at different stages of evolution from dinosaurs to birds, filling in the gaps on either side of archaeopteryx.

The same was true of Ambulocetus, the walking whale. This one species is clearly transitional from terrestrial mammals to whales, but was also adapted to it current niche. It didn’t “know” that its clade was evolving toward whalenss, it was just adapted to its current lifestyle. We can only put it into perspective today – as a transitional species, because we know what some of its ancestors became. And, as with Archaeopteryx, we have since found numerous other fossils filling in the gaps on either side.

We could also look at Australopithecus robustus. This was not the first extinct hominid discovered, but let us say this was the only fossil homonid we had. It is clearly transitional between humans and modern apes, suggesting that we share a common ancestor. But it is also clearly not a direct ancestor of modern humans. It sits on an evolutionary branch that exists in the morphological space between humans and chimpanzees, but is not on the branch that leads directly to modern humans.

But in reality we have many homonid fossil species, and we have a pretty good idea of those whose direct ancestors are modern humans.

Creationists rhetoric is often clueless about the nature of speciation. They argue as if they think that one species turns into another, but ignore the fact that one species can turn into two or more through speciation – separated populations taking different paths. They are therefore puzzled that (taking this new fossil for example) a slightly older fossil can look more like modern pinnipeds than this new fossil. They ignore the fact that the definition of “modern” or “advanced” is relative – in this case relative to modern pinnipeds. When one common ancestor species splits into two, one of which leads to modern pinnipeds and the other does not, the ones on their way to becomming modern pinnipeds will look more like their modern descendants than those on the branch that did not evolve in that direction. So species on the side branch (again, “side” relative to the line that lead to extant species), may retain features that are “primitive” in the extant line.

To further clarify this point (because it is so often confused by creationists), evolution predicts that we will find fossils that are morphologically roughly transitional between extant species with a common ancestor and at a time and place in the past where this evolution was taking place. But it does not predict a strict linear sequence because speciation creates a complex and bushy picture of evolutoinary relationships.

But what has happened, and is happening, in each of the examples I gave and many others, is that as more and more fossil are found they fit nicely into a reasonable tree of relatedness, temporally and morphologically. Evolution predicts that something like Puijila darwini had to exist, and at about the age that it is. Creationism does not. It further predicts that we will find more fossils that flesh out pinniped evolution even further.

Creation “scientist” Duane Gish famously quipped in his many debates with scientists that the notion of terrestrial mammals evolving into whales was like a cow taking to the water, a strategy he characterized as an “utter” failure. Nice pun, but intellectually vacuous. He should have been thinking of otters, not utters. There are already known many living species with various degrees of adaptation to aquatic life. Otters and beavers are comfortable on land, but are good swimmers.  Seals and sealions are able to awkwardly shuffle about on land, but are even more adpated to the sea, with flippers instead of feet. Manatees are similar to walruses, but are one more notch further adapted to the sea and lost their ability to amble out onto land. And whales are fully adapated to aquatic life.

These creatures do not represent and evolutionary sequence, but they do show a plausible sequence of variable degrees of adaptation to the water. And we have been finding fossil species that show a similar sequence, with walking whales and now walking seals.

The fossil evidence for common descent is so stunning in its confirmation of evolutionary theory, that I cannot help wonder about the cognitive dissonance it creates in any creationist even modestly familiar with the evidence.

Share

24 responses so far

24 Responses to “Pinniped Evolution”

  1. Iason Ouabacheon 24 Apr 2009 at 1:25 pm

    Great post. Ironically I was just talking about this subject with my wife yesterday since my daughter is now obsessed with walruses. Nice to know I got most of the details right.

  2. _Arthuron 25 Apr 2009 at 10:16 am

    What good is a half-flipper ?

  3. HHCon 25 Apr 2009 at 11:56 am

    This lake fossil illustrates that we have had salt-water and fresh water seals in North America. The sister species otters liked the rivers,streams, and lakes.

  4. HHCon 25 Apr 2009 at 12:01 pm

    There are also sea otters worldwide.

  5. Brendanon 25 Apr 2009 at 1:38 pm

    Arthur: Just as a “half wing” is great for gliding from tree to tree, a “half flipper” could conceivably retain function in water while making mobility on land less cumbersome than a long flipper.

  6. rc_mooreon 25 Apr 2009 at 2:24 pm


    The fossil evidence for common descent is so stunning in its confirmation of evolutionary theory, that I cannot help wonder about the cognitive dissonance it creates in any creationist even modestly familiar with the evidence.

    Creationist have mastered the art of “doublethink”:

    The power of holding two contradictory beliefs in one’s mind simultaneously, and accepting both of them….To tell deliberate lies while genuinely believing in them, to forget any fact that has become inconvenient, and then, when it becomes necessary again, to draw it back from oblivion for just so long as it is needed, to deny the existence of objective reality and all the while to take account of the reality which one denies…

    George Orwell — 1984

  7. Steven Novellaon 26 Apr 2009 at 7:47 am

    Arthur – if you are serious (I wasn’t sure if you were being sarcastic, that is such a creationist cliche), there are two basic answers.

    The first is called exaptation – the use of a feature for a different purpose than the one for which it evolved. So, as suggested, a “half-wing” may have evolved as a full gliding appendage. Half-feathers my be full insulation.

    The other process is incremental, and I think that is the one that applies to the “half-flipper”. With flight there is a certain threshold you have to get to before you can take to the air. This does not apply to swimming. Each slight change can provide a slight advantage (just look at what olympic swimmers do). Even the tinniest webbing between the fingers will allow for slightly faster swimming than no webbing. Therefore there is a continuous Darwinian advantage for swimmers every step of the way from leg to flipper.

  8. Doctor Evidenceon 26 Apr 2009 at 10:32 am

    http://www.bidstrup.com/virus.htm

  9. [...] recently wrote a post for NeuroLogica in which I discuss the latest transitional fossil find – a pinniped (seal, sealion, walrus) [...]

  10. dreamking00on 26 Apr 2009 at 11:46 am

    It drives me crazy, but not even the “creates two new gaps on either side” gag fully accounts for the claim that the fossil record doesn’t show transitions. If you can believe, it’s even DUMBER than that. Take these droppings of wisdom, from http://www.newgeology.us/presentation32.html: (the url alone indicates that it’s a ludicrous YEC website)

    “All fossils are of complete animals and plants, not works in progress “under construction”. That is why we can give each distinct plant or animal a name. If evolution’s continuous morphing were really going on, every fossil would show change underway throughout the creature, with parts in various stages of completion…So every plant and animal, living or fossil, should be covered inside and out with useless growths and have parts under construction. It is a grotesque image, and just what the theory of evolution really predicts.”

    So, they’d expect to see an otter with the hind flippers of a seal, or a coyote-like artiodactyl with useless flukes on the end of its tail. Is there a logical fallacy of “completely full of hogwash?”

  11. HHCon 26 Apr 2009 at 12:03 pm

    Dear Doctor Evidence, I read your posting of the Mind Virus by Scott Bidstrup. He comes up with facts that are not correct, for example Christianity is accepted by 1 out of 3 persons in the world. No, Christianity is not the dominant religion numerically across the world. He wishes to trace bigotry to Judaism. Let’s clear a few things up historically. Theologians have traced the beginning of the New Testament to a sect which believed in Light of the World, a euphemism for wisdom. The sect existed before “Jesus”. They created a story about a crucifixion. At least 500 Jews were crucified during Roman times. So they were concerned with this type of torture and death, but which “Jesus” are they creating? They write about a archetypal “Jesus”.
    By the way, religious Jews do not believe in hell or orginal sin. You are judged by your words and actions. Jews accept the Bible which is the only Testament. The New Testament is a work which is not accepted. So you can proceed with your diatribe against the Christian faith, but that does not help explain an evolutionary concept in biology.

  12. HHCon 26 Apr 2009 at 1:12 pm

    Christianity focuses on the importance of human sacrifice as evidenced by religious paintings in museums across the world. Judaism does not believe in human sacrifice such as the pagan rituals in the” Rites of Spring”. In fact, the faith attempted to substitute animal sacrifice for human sacrifice at the onset. This type of sacrifice was not an effective practice for the faith and was discarded. Instead, every year when the High Holy Days are observed, Jews seek redemption through prayer, repentance, and charity. No higher sacrifice is required.

  13. Doctor Evidenceon 26 Apr 2009 at 5:02 pm

    Hi HHC, thanks for your comments.

    I tend to be terse myself, so I didn’t describe my intention
    for that link, which was to relate a portion of its content to
    Dr N’s “cognitive dissonance” comment.

    Some of us in recent entries in this blog have been
    attempting to (speculatively) understand not just
    *that* (for example) evolution-deniers continuously make
    use of bad logic and crank claims (the “design inference”),
    but *why* they do. what’s going on in their minds?

    The Bidstrup essay has related ideas, , and proposed mechanisms of cause (how do we test his claims?)

    If he’s making wrong historical claims, or misrepresenting aspects of some religions, well there’s no excuse for that.

    your friend, DE

  14. Doctor Evidenceon 26 Apr 2009 at 5:06 pm

    resending, as text placed between two angle-brackets
    was filtered. I’ll instead enclose the text in double-quotes.

    Hi HHC, thanks for your comments.

    I tend to be terse myself, so I didn’t describe my intention
    for that link, which was to relate a portion of its content to
    Dr N’s “cognitive dissonance” comment.

    Some of us in recent entries in this blog have been
    attempting to (speculatively) understand not just
    *that* (for example) evolution-deniers continuously make
    use of bad logic and crank claims (the “design inference”),
    but *why* they do. what’s going on in their minds?

    The Bidstrup essay has related ideas,

    “…the rejection of scientific facts one knows to be true, the denial of the conflicts of fact and doctrine that exist throughout the believer’s belief system as they relate to his understanding of the world around him.”,

    and proposed mechanisms of cause (how do we test his claims?)

    If he’s making wrong historical claims, or misrepresenting aspects of some religions, well there’s no excuse for that.

    your friend, DE

  15. HHCon 26 Apr 2009 at 5:47 pm

    The use of the term “cognitive dissonance” is a marketing strategy for social psychology research. Its very smooth sounding and its easy to remember. But the actual research to support it is weak. Please steal another concept from psychology to explain your frustrations with creationists.

  16. DevilsAdvocateon 26 Apr 2009 at 7:23 pm

    HHC?

    Cognitive dissonance is just a term to describe when a person simultaneously holds contradictory beliefs. Obviously it’s a real thing and is very common. For psychology to have a term for it is hardly just a marketing strategy. The research on it is weak? ‘Research’ need go no further than the nearest church to confirm it.

    Where did you get that idea?

  17. artfulDon 26 Apr 2009 at 9:56 pm

    http://skepdic.com/cognitivedissonance.html

  18. rc_mooreon 27 Apr 2009 at 12:45 am

    “Cognitive dissonance is just a term to describe when a person simultaneously holds contradictory beliefs.”

    See my comment on “doublethink” above. Cognitive dissonance is the feeling of discomfort about the contradictory beliefs. My point was that creationist do not have cognitive dissonance, they have mastered “doublethink”.

  19. SteveAon 27 Apr 2009 at 7:22 am

    Hi Steve,

    Couple of typos:

    ‘webbed feat’

    ‘utter failure’ (is that ‘udder failure’? In the context of the pun).

  20. RickKon 27 Apr 2009 at 8:15 am

    @dreamking00

    Yes, Harun Yahya, Kirk Cameron & Ray Comfort, and many others use this argument all the time. And many of them just add more fuel to the cognitive dissonance by agreeing that “adaptation” is possible – that a lizard can “adapt” webbed feet or new organs, little by little, but can’t transform into another “kind” without going through this impossible state of being where they are “covered inside and out with useless growths and have parts under construction.”

    It’s like suggesting that when a baby grows into an adult, first the right arm grows to full size, then the left foot, then the nose, and so on. Of course, that’s nonsense. In fact, the transformation is gradual and happens over the entire person. The intermediate forms are all perfectly viable, and we can even name them: “toddler”, “child”, “teenager”, etc.

    In the evolution-denialist world, there are two types of people: those that openly lie and spend their time finding soundbites to make their lies sound better, and those who repeat the lies out of ignorance. If you educate the second group, eventually the first group gets marginalized like the Flat Earthers. But sadly, they never go extinct.

  21. DevilsAdvocateon 27 Apr 2009 at 9:15 am

    “My point was that creationist do not have cognitive dissonance, they have mastered “doublethink”.”

    Ah, I see.

    In my opinion, many of them do have cognitive dissonance in the sense that many know full well the problem evolution poses for their religion, but they bluster on anyway under the rubric of ends justifying means. They only pretend at an intellectual exercise in debating evolution vs. creationism, but in actuality, theirs is a political battle.

    Just as many people continue to attend church through cultural inertia, without much genuine belief in the Bible as written, I suspect many of the creationist leaders accept evolution to a far greater degree than they’d ever admit publicly.

  22. TheBlackCaton 27 Apr 2009 at 2:32 pm

    Great post. Ironically I was just talking about this subject with my wife yesterday since my daughter is now obsessed with walruses.

    NOOOO!!!!! Stop her, stop here before it’s too late. I had a friend in high school was obsessed with walruses. Believe me, you have no idea what you are getting yourself into. Get her off that track now or you are DOOOOOMED!!!

  23. Bill J.on 02 May 2009 at 9:14 pm

    Here is what a friend of mine wrote when I talked to him about transitional fossils. He graduated from the same Evangelical University I did. I am no longer a religious believer.

    “What transitional fossils? I’ve not seen any – and one cannot attempt to link one group of animals to another group on the other side of the world.

    Where are the transitional animals from rats to horses? In my estimation, whether the horse has three toes or a hoof, it is still a horse based on appearances only. So far, how many animals can we … Read Moreactually link with DNA tests? I dont think there are too many, if any, that that can be done with – thus, again in my estimation we have a lot of conjecture here and no hard science like DNA comparisons to cinch the deal.”

    What should I say to a guy like this, if anything?

  24. Bill J.on 03 May 2009 at 5:20 pm

    He also said, “My contention is, scientific method cannot be applied to morphology and proving evolution from a common pool of life.”

    What do you think Dr. Novella?

    Thanks,

    Bill

Trackback URI | Comments RSS

Leave a Reply

You must be logged in to post a comment.