Bebej: A Maiacetus Fossil

Science
#6

Yes, please invite him.

Here is a point from the article that I find amazing:

The preservation of a fetus positioned for headfirst delivery suggests that Maiacetus was still coming back onto land to give birth, even though it was spending most of its time in the water.

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(S. Joshua Swamidass) split this topic #7

3 posts were split to a new topic: Why We Invite Scholars

(Ryan Bebej) #8

Well, it didn’t take too much arm-twisting. Just an email from Josh. What would you like to chat about?

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(S. Joshua Swamidass) #9

@rmbebej, thanks for joining us! It is a pleasure to have you with us.

My first question concerns this. Can you help me understand why this is a valid inference?

It seems that the chances of seeing a pregnant Maiacetus are very, very low. I wonder if the only reason we see this fossil is because there was something wrong with the pregnancy, say, that the little one was oriented in correctly. This would explain why we even see this fossil. I am filling some details here, assuming that pregnant Maiacetus fossils are rare. I also do not know nearly enough to speak confidently here. This is really an opportunity for us to probe how paleontologists think through questions like. How do you know that this is really the normal orientation of delivery for Maiacetus?

Before you answer, it might be worth explaining to everyone why this is consider an important step in the evolution of mammals. This has to do with fully aquatic births right? Breech birth means that the newborn’s nostrils and lungs are not exposed to the sea till the very last second, when the mother can help the little one to the air. Note, of course, that whales are not mouth breathers, because their esophagus is not connected to their windpipe. Do we even know this is the case for Maiacetus too? I digress. Did I get that explanation right?

Finally, once we get a bit into this, I’m curious to go a bit deeper on other questions about whales with you too, that have come up on other threads. For example, we’ve been in an exchange with the Discovery Institute about this thread: Molecular Genetics of Whale Evolution. You might also be uniquely qualified to answer this question too: Is Evolution a Great White Whale?

Thanks for joining us. Looking forward to learning from you.

(John Harshman) #10

Several questions come to mind.

  1. How weird is it that Thewissen and Gingerich published the first whale astragali nearly simultaneously? And both soon after the first SINE data were published?

  2. Do you have any opinion on the phylogenetic position of mesonychids? Of Andrewsarchus?

  3. Do you think the evolutionary story of whales would convince a creationist? Have you ever discussed that with a creationist?

  4. What do you think of Kurt Wise’s notion that artiodactyls might be a “kind” and that whales evolved over a hundred years or so after 2000 BC?

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(S. Joshua Swamidass) #11

@John_Harshman is referring to this:

(S. Joshua Swamidass) #12

Can you post some images @John_Harshman, so the rest of us can follow what you are asking? Perhaps a couple reconstructions/fossils and some proposed trees?

(Blogging Graduate Student) #13

I don’t see how this follows. An implicit assumption would seem to be that it’s rare for pregnant females to die for reasons other than complications in the pregnancy. I don’t think finding a pregnant female would be all that rare. For example, if 1% of the population is pregnant at any one time, it seems reasonable to expect that on the order of 1% of fossils we find would be pregnant. That’s not rare at all, all things considered.

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(John Harshman) #14

Given that whales of modern aspect were known long before the time of Christ, The short gap between the claimed flood date and the beginning of recorded history is all the time allowed. That’s why it’s 100 years or so.

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(S. Joshua Swamidass) #15

How many Maiacetus fossils do we have? As I understand it, not that many full specimens. Though please correct me. Yes, I am assuming that intact, pregnant females dying is rare, except in childbirth or another abnormality. This seems to match what we know of many species.

Maybe I am totally wrong, maybe obviously so. I just want to know how a paleontologist thinks through objections like this.

(@T.j_Runyon)

(Blogging Graduate Student) #16

That’s my impression too, but how many is enough to not be surprised to find a 1 in 100 specimen? 10? 50? 100?

More rare than the “background” level of death in a population? Surely that would imply that pregnancy has some kind of protective effect, no?

I too am interested in how a palaeontologist thinks about these things, since I only dabble (and even then rarely in taphonomy).

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(Curtis Henderson) #17

I’m completely unqualified to answer the rest of the questions, but I have experience with this one! The short answer is “no”. As Josh has posted, Kurt Wise is probably the one scientist/creationist that most-actively engages with the evidence, and he still sticks with the hypothesis that modern whales may have undergone evolution at astounding rates over the last few thousand years.

Most creationists I have discussed whale evolution with simply insist that the whale “ancestors” were simply different “kinds” that were all present at creation, and only appear to be a chronological progression.

Dr. Georgia Purdom (PhD in Molecular Genetics from Ohio State University in 2000) has admitted that there is no evidence that would convince her of anything other than a 6 literal-day creation. I think very few creationists would blink an eye at the evidence of whale ancestry.

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(S. Joshua Swamidass) #18

I’m not sure that is really the definitive answer. I’ve seen a different sort of response. When we draw people into the wonder of it all, there are ways around the simple dismissals.

I have a nearly 3 year old son. He is fascinated by all things animal, especially dinosaurs. Though he does to seem to like trucks and trains more, for the moment. He is curious about hippos and elephants and cows, and all sorts of things. That childlike curiosity is our natural state. As we grow older, it matures to include a cognitive dimension too. We are wired to ask the “why” questions everywhere. Tapping into this side of our nature is very difficult to resist, even by creationists. We all wan to cognitively enter into the beauty of nature with the great “why?”

The story of whales, brings to the surface so many why questions. It is absurdified with the cartoon of cow to whale. Though, if we were to discuss hippo to whale, or seal to whale, now there are interesting conversations to be had. For example. why would creationists speak of cows here? More curiously, what would a walking whale look like? What is different about a whale’s ears and ours? Do they have a different body plan than ours or not? If they do, at what point is that plan different?

All these questions are nearly irresistible to the un-injured mind. They beckon us to wonder in the mystery and beauty of it all. Perhaps we are not certain the answer in the end, but we usually beginning to reject the simplistic answers of polemicists (on both sides) as absurd. This is potent material with which we are working. Just watch my son roaring like a T-rex and you’ll see it too.

Rather than just making “arguments,” the trick is to bring people in the beautiful complexity of it all, focused more on questions than answers. Of course, our answers begin to change, but now from a place of trust and knowledge, and much less from polemics. So, I am happy to report I’ve seen many a creationist change their mind when we talk about the beauty of whales. Why not? Some are bigger than dinosaurs, and they are one of only a few species on earth we know have a concept of grandmother.

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(S. Joshua Swamidass) #19

The protective effective of being young, and not senescent. Most dead animals are not pregnant or in labor, far less than one would expect from chance alone. Exceptions I am sure can be found (spawning grounds?), but I’m talking about the general pattern.

(Blogging Graduate Student) #20

I’m not so sure. I think most dead animals didn’t die of old age, they died as a result of disease, predation, etc - factors uncoupled from senescence. Not entirely though, which is why in my example where 1% of individuals in a population are pregnant, I used fairly wide error margins (on the order of) to describe how often they should be found as fossils (i.e. died). Certainly there will be a trend towards older individuals dying, including past reproductive age, but I don’t think this bias is enough to make it particularly unlikely for pregnant individuals to die for reasons unrelated to the pregnancy itself.

(S. Joshua Swamidass) #21

@rmbebej, help us out?

(Ryan Bebej) #22

First, I’ll note that, at this rate, there is absolutely no way I’ll be able to keep up with all these posts! Too much time spent in class, lab, meetings with students, commuting, etc. But I’ll do my best to answer questions as I have time.

Second, I’ll note that the Maiacetus paper is open access and available here. Many of the specific questions you might have about this particular fossil can probably be answered there.

Now to @swamidass’s questions first…

Before you answer, it might be worth explaining to everyone why this is consider an important step in the evolution of mammals. This has to do with fully aquatic births right? Breech birth means that the newborn’s nostrils and lungs are not exposed to the sea till the very last second, when the mother can help the little one to the air. Note, of course, that whales are not mouth breathers, because their esophagus is not connected to their windpipe. Do we even know this is the case for Maiacetus too? I digress. Did I get that explanation right?

There are multiple possible explanations for why tail-first presentation is ubiquitous in cetaceans, but reducing the possibility of drowning during birth is among the most plausible reasons. (Gingerich et al. discuss some of these possibilities briefly on p. 15 of the paper.) Head-first presentation is pretty much universal in land mammals, so this implies that at some point, early cetaceans made the switch to tail-first delivery.

My first question concerns this. Can you help me understand why this is a valid inference? It seems that the chances of seeing a pregnant Maiacetus are very, very low. I wonder if the only reason we see this fossil is because there was something wrong with the pregnancy, say, that the little one was oriented in correctly. This would explain why we even see this fossil. I am filling some details here, assuming that pregnant Maiacetus fossils are rare. I also do not know nearly enough to speak confidently here. This is really an opportunity for us to probe how paleontologists think through questions like. How do you know that this is really the normal orientation of delivery for Maiacetus ?

The inference that this is a near-term fetus positioned for headfirst delivery is certainly something that one could contest. In fact, Hans Thewissen (another whale paleontologist) posted a comment on the PLoS ONE article shortly after publication, arguing that this was in fact the whale’s last meal rather than its fetus. I know that Gingerich et al. considered this, but as they describe in the article (p. 10), they think it is more likely to be a fetus based on the preservation of the skull. I think you’re fine in assuming that finding pregnant fossils is not very common, but it’s not super rare either. I could cite many examples of fossils that are clearly pregnant (including live-bearing marine reptiles from the time of dinosaurs and also fossil horses). Given that there are only two fossil specimens known for Maiacetus, only one of which was possibly pregnant, it is difficult to infer whether or not this would have been typical or atypical presentation. But given its overall anatomy, its presumed terrestrial competence, and the universality cephalic presentation in land mammals, headfirst delivery seems like a reasonable interpretation.

Ok, I’ve gotta hit the road for my commute. I’ll resume writing when I can!

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(T J Runyon) #23

Ryan has pretty much said everything i would say and more. For what it’s worth, Hans is very good about answering emails with any questions you’d like answered. So you might want to email him @swamidass. I won’t be too much help here. I worked on Basilosaurids. Not too familiar with Maiacetus. And to be honest today is the first time I’ve read the paper. I know a little about its feet and the evidence for webbed feet. That’s about all I could contribute.

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(Ryan Bebej) #24

Responding to @John_Harshman now:

How weird is it that Thewissen and Gingerich published the first whale astragali nearly simultaneously? And both soon after the first SINE data were published?

I’m not going to divulge anything specific here because it’s not really my place to share secondhand accounts in a forum like this, but the timing of those two papers was not really all that coincidental. If you want to get in the weeds on this, just look at the submission/acceptance/publication dates of the papers, along with the acknowledgments for who provided feedback on the manuscripts…

Do you have any opinion on the phylogenetic position of mesonychids? Of Andrewsarchus ?

I haven’t kept up much on where exactly folks place mesonychids relative to all other ungulates, but I do consider them outside of Cetartiodactyla and not closely related to Cetacea.

Do you think the evolutionary story of whales would convince a creationist? Have you ever discussed that with a creationist?

I guess it depends on how open-minded the creationist was. I’ve certainly had many conversations with creationists over the years, but I tend not to participate in debates. I almost always talk about my work and why I find the evidence for whale evolution to be so compelling, but I recognize the variety of reasons why some well-meaning Christians can have trouble with that. My goal is generally to try and have thoughtful and respectful conversations with people, trying to help them to see that even folks with an evolutionary perspective on the world can still be brothers and sisters in Christ.

What do you think of Kurt Wise’s notion that artiodactyls might be a “kind” and that whales evolved over a hundred years or so after 2000 BC?

This is crazy to me. In supporting a position like this, they’re suggesting that evolution can render profound changes far more quickly than even the most ardent evolutionary biologists would imagine. Joel Duff has written about the evolution of this hyper-speciation model in YEC circles at his blog, and it is absolutely fascinating. I also know that they have a Pakicetus on the Ark Encounter, but I don’t know whether they’re suggesting that it was a now extinct creature unrelated to any modern forms, or if it was the ancestor of all modern cetaceans, which have evolved since the flood.

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(Ryan Bebej) #25

Replying to @evograd and @swamidass re: pregnant specimens:

As for Maiacetus, there are two known specimens. While many species are known by many partial specimens, there are also many species that are just known from a few – or even one!

I would say that pregnant specimens are rare – usually so exceptional that they warrant a detailed description, even if the species is already well known to paleontologists. For instance, this stunning specimen of a well-known fossil horse species made headlines a few years ago. But we do see these published frequently enough that they are on our radar when interpreting new fossil assemblages.

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