Pharyngula

Maiacetus

My teaching schedule this semester is a major time-suck; I’m teaching genetics and all of its associated labs (you really don’t want to know how much prep time goes into setting up fly labs), I’m doing some major revision of the content this year, and I’ve got this asymmetric schedule that packs everything into the first half of each week. So I simply have to protest when those evil (Stein was right!) scientists announce a major discovery on a Tuesday, which just happens to be the very worst day of the week for me. They’ve gone and found another important whale transitional fossil, Maiacetus, and I’m just going to have to tell you to go read a bunch of other fine blogs that already have it covered.

i-bd63fdc1acedcd8fb4bd46a00b992235-maiacetus.jpeg
(Click for larger image)

Skeletons of the Eocene archaeocete whales Dorudon atrox and Maiacetus inuus in swimming pose.

(A, B)- Dorudon atrox (5.0 m; 36.5 Ma) based on UM 101222 and 101215 [11] in lateral and dorsal views, respectively. (C, D)- Maiacetus inuus (2.6 m; 47.5 Ma) based on male specimen GSP-UM 3551 in lateral and dorsal views, respectively.

It’s beautiful. It’s clearly adapted for aquatic life, but it has another revealing feature: this specimen was pregnant at death, and the fetus is oriented for a head-first birth, which is not good for birth at sea (the head would pop out, baby would take its first breath, and drown before the tail emerged), so this animal would have had to give birth on land.

But like I said, you’ll have to read Carl Zimmer, Ed Yong, Brian Switek, or Greg Laden this time around for all the details. Or read the paper yourself! It’s freely accessible.

Comments

  1. #1 Tualha
    February 4, 2009

    Damn, one more gap.

  2. #2 James F
    February 4, 2009

    I’m surprised this wasn’t in Science (like Gingerich’s 2001 paper) or Nature. On the other hand, what a coup for PLoS ONE, which continues to succeed far beyond what I ever would have imagined – bravo!

  3. #3 Valis
    February 4, 2009

    I read this over at Greg Laden’s. Absolutely fascinating. So what was that about the xtians moaning there’s no evidence of transitional forms? In your face!

  4. #4 Nerd of Redhead
    February 4, 2009

    Interesting looking paper. I printed it out and will peruse it later, when my caffeine levels are higher than now. Just thumbing through the printout it looks like it will be a good read. Thanks for the link PZ.

  5. #5 DaveX
    February 4, 2009

    I keep a bookmark folder titled “LOOK AT THIS!” with things to show my daughter when she gets home from school. This is going right in it. Amazing!

  6. #6 raven
    February 4, 2009

    To put a little perspective on this: One of the creos Icons of Lies and Evil was, “What about the whales? There are no land whales or transitional fossils. They just sort of appeared in the ocean.” Besides whales are irreducably complex and no one has seen a cowawhale.

    This was decades ago. Then, wait for it. Scientists found walking whales, swimming and walking whales, land forerunners of whales and so on. A series of transitional fossils nicely illustrating the evolution of an artiodactyl to an adaptive radiation of marine forms.

    Of course, the creos just moved the goal posts. The brighter among them have been driven back 13.7 billion years to before the Big Bang happened. The dullwits are still babbling on about how no one has seen a cow turn into a whale.

  7. #7 KillerChihuahua
    February 4, 2009
  8. #8 LisaJ
    February 4, 2009

    Wow. That is awesome. Look at those limbs!

    DaveX, that’s fantastic. It makes me feel great when I hear that people are educating their children about the excitement and coolness of science.

  9. #9 FishNChimps
    February 4, 2009

    The transition is truly beautiful. It’s the one that I’ve used to wow my kids – the thought that a 4-legged land creature evolved into the whale. I think it’s more awe-inspiring than the primate > human evolution, but then I’m just a layman numpty.

  10. #10 Philipp
    February 4, 2009

    How jealous I am of your students (apart from the obvious reasons). We had to breed the friggin’ flies ourselves. The first few sessions of genetics lab were backed with Fly-breeding How tos and mixing the goo that these critters eat.
    …btw, I really like the smell of the ether

  11. #11 LisaJ
    February 4, 2009

    #10: oh yeah, that fly food is some nasty smelling stuff. I believe my lab mate is mixing some up this morning… mmmm, can’t wait. Good luck with the fly prep. PZ, I imagine that it can’t be much fun.

  12. #12 bobxxxx
    February 4, 2009

    I look forward to the Christian Discovery Institute’s explanation.

  13. #13 RationalFuture
    February 4, 2009

    BUT IT’S STILL A COW !!!!!1111 :)

  14. #14 Stephen Wells
    February 4, 2009

    No, hang on, if it died in late pregnancy that means it didn’t leave any descendants so it’s not a transitional form so…

    (kidding!)

  15. #15 Steven Dunlap
    February 4, 2009

    Wow. Free education on the web. It’s there if you know where to look.

    I regret that I can think of no more witty a contribution than a simple thank you to PZ for taking time from his insanely busy schedule to post this.

  16. #16 Monado
    February 4, 2009

    Stephen, you can’t tell from a fossil how many previous whalish calves it had. :-)

  17. #17 Monado
    February 4, 2009

    Beautiful fossils. I sure hope that the shaded bits are the bits we don’t have and not the bits we have.

    Actually, if you just look at ways of life, e.g. black bear, polar bear, otter, sea lion, seal, whale, you can kind of get the picture of how evolution might happen with each stage surviving quite nicely, thank you.

  18. #18 Charles Wade
    February 4, 2009

    Simply put, thank you for this post and the links. Now please excuse me as I thank the other blogmasters for their excellent writing.

  19. #19 Rev Matt
    February 4, 2009

    Genetics was one of the few college level science classes I took (I majored first in Psychiatry, then History) and it was a truly fascinating class. Had I taken it earlier in my college career I might have majored in biology instead.

    I recall at one point the professor explaining how one discovery can change everything, illustrated with a story about one of the genetics courses he took in college where at the end of the semester the professor said “Well the good news is you’re all going to get A’s. The bad news is that new research just released demonstrates that most of what you learned this year is wrong.”

  20. #20 Bodach
    February 4, 2009

    Thanks, PZ, that is seriously cool.

    Tualha, it’s two gaps now, not one.

  21. #21 SS
    February 4, 2009

    I work in the University of Michigan paleontology museum and we’ve been working on casting a 40 million year old basilosaurus for months now. I wonder if this will be the next casting project when we finish the basilosaurus this summer. This is a seriously awesome find and I feel even luckier that I get to hang out with these guys on an almost daily basis. Phil (first author) is a really good guy, and Bill (4th author) is perhaps my favorite person ever. Just high quality people.

    The fetus in the birth position is a one in a million find. I work on developmental stuff quite a bit (mostly on hominins, not whales) and this find is a dream come true for people who do that sort of thing.

    The “suck it, creationists!” gets emphasized a lot on this blog (and for good reason), but it can’t be underestimated what this find will allow us to learn about a very, very cool evolutionary process that we didn’t know much about only a few years ago.

  22. #22 SteveM
    February 4, 2009

    “Tualha, it’s two gaps now, not one.”

    She said “one more gap”, one gap has become two gaps; therefore, one more.

  23. #23 Matt Heath
    February 4, 2009

    Bodach: There was a gap before. Now there are 2. The increase in the total number of gaps is one.

  24. #24 Janine, Queen of Assholes
    February 4, 2009

    Yet again, this is so much more interesting and fascinating than any religious story that states that god created it.

  25. #25 Neil B ?
    February 4, 2009

    Interesting critter. I gather already I’m right to presume, fossils of pregnant animals with fetus included are very rare. I wonder, have transitionals popped up often enough by now that the scientific case “punctuated equilibrium” (as per folks like legit paleontologist Stephen Gould and not interventionistic creationism) is weaker and weaker? But didn’t they find enough to at least support the idea of markedly uneven rates of change as a rule? I have a theory to explain part of that: people tend to group things together in their minds, in categories – so maybe a tendency to see a collection as being “the same entity” for awhile. Or, did they strictly use very objective markers of comparison to avoid just that subjective effect?

    Also, how efficient is the loss of “unneeded” vestigial arms etc., since not working on the same pressure of need as a trait selected “for” per some need? tx

  26. #26 Eric
    February 4, 2009

    Wow! The beauty of this find actually gave me chills.

  27. #27 JCollum
    February 4, 2009

    One more gap, one less gap. The fossil record is full of gaps; don’t defend the gap. The alternate “theory” is just one big gap: “God did it, I dunno how.” Like those underwear gnomes on South Park: “Step 1: There was God. Step 2: uhhh ??? Step 3: Profit! (and people and animals and so on)”

  28. #28 Feynmaniac
    February 4, 2009

    But Geoffery Simmons said there were no transitional fossils of whales. He even read an article in Scientific American during his research and everything!

  29. #29 Paul
    February 4, 2009

    It’s great to see PLoS ONE get a paper of this importance, having research available for anyone to read in open access journals is one of the best things to happen in science communication in recent years. I look forward to the day when the anti-science movements will no longer be able to hide in the “gaps” in the easily accessible published record.

    If the open access movement succeeds it will hopefully also make misrepresentation and quote-mining just that little bit harder to get away with.

    And what a cool fossil!

  30. #30 Andrea M
    February 4, 2009

    It’s indeed a very interesting and nice finding…

    but are we sure that the orientation of the foetus is the ‘right’ one? What if the foetus had an abnormal presentation (e.g. headfirst instead of tail-first) in this specimen and the mother died due to complications arising from this?
    And also, is the connection between ‘head first’birth and partus on firm land really so strong? At some point, the transitional species must have either been a head-first-birth animal living in water or a leg-first-birth animal living on land…

    Other than this nitpicking, it’s yet another nail in the Creationism-ID coffin.

  31. #31 Jesse
    February 4, 2009

    Neil,

    There is no reason to assume that both gradualism and punctuated equilibrium can’t valid models of evolutionary tempo. There is evidence in the fossil record of stasis followed by rapid change from allopatric speciation, and there is evidence of gradual change with transitional forms. Both processes are valid hypotheses supported by data, the real question is: is on of them more dominant in the fossil record than the other?

  32. #32 Brett McCoy
    February 4, 2009

    Geez, I just can’t keep up with all of these transitional forms anymore. Looks like the book that came out last year on the fossil record that I am currently reading is already obsolete.

  33. #33 BJ
    February 4, 2009

    Don’t these silly people know there’s no such thing as transitional forms? I still recall being in grad school when a local Christer group invited a Creationist to speak. We had to go. Not expecting to change any minds but, like having a Holocaust denier on campus, you just can’t let them get away with it. Unfortunately, he wasn’t a particularly good Creationist and we had no trouble completely ripping him apart. Very politely, of course, we are Canadians. I knew he hadn’t been keeping up at all when he trotted out the old whale canard. I remember raising my hand and introducing him to Ambulocetus and kin. Good times.
    Oh well, got to get back to my flies. Not only are we doing simple crosses in the Intro Biology, the Genetics students are doing mapping and polytene chromosomes (D. virilis!). Of course, we know who has to set up all those files. Muggins, here, that’s who.

  34. #34 Epinephrine
    February 4, 2009

    Beautiful fossils. I sure hope that the shaded bits are the bits we don’t have and not the bits we have.

    They are. The article has some nice images attached to it, I think you can see them directly here

  35. #35 Dave Godfrey
    February 4, 2009

    Monado #17

    Yes the shaded bit is what we don’t have.

    There are two specimens, one of which is male. The male is 12% bigger, and has significantly larger canines giving an idea about the animal’s behavioural ecology- i.e. there was probably some competition for mates, but nothing like what we see with Elephant Seals.

    Andrea M

    A head-first animal giving birth in water would drown the newborn. The next stage could be an animal that would be even more awkward on land than this is (perhaps behaving like a turtle, where only females ever return to land after hatching). When tail-first delivery appears that would allow the animal to completely sever its links with the land, and allow animals like Basilosaurus to do away with functional legs altogether.

  36. #36 APC
    February 4, 2009

    Um, isn’t it possible that the backward whale is what killed the mother?

    I should point out that I am an atheist.

  37. #37 GCUGreyArea
    February 4, 2009

    Umm, maybe it died because the fetus was the wrong way around? The orientation of the fetus is only an indicator that it gave birth on land if it can be established that this was the norm for the species.

  38. #38 Ancient Brit
    February 4, 2009

    Excellent bit of news. One thing, though – and here I’m putting my head on the chopping block :) – is it truly the case that a head-first delivery orientation implies birth out of water?

    I’m thinking of two things: one, if the fetus is within an amniotic sac then it’s been “breathing” liquid for some time, so the transition from the womb to the outside world could still be undertaken in water (maybe water just as salty as amniotic fluid) without drowning, as long as the process didn’t take too long (umbilical cord presumably still attached and providing some oxygen), and two, don’t we humans occasionally undertake water-based birthing without drowning?

    Just a thought…

  39. #39 Jim
    February 4, 2009

    Pardon the inquiry from a non-scientist, but this history of whale evolution got me thinking. Could the whale’s long-gone ability to saunter up onto the shore have left a vestige of instinct that leads them to occasionally beach themselves today?

  40. #40 David Marjanovi?, OM
    February 4, 2009

    I wonder, have transitionals popped up often enough by now that the scientific case “punctuated equilibrium” (as per folks like legit paleontologist Stephen Gould and not interventionistic creationism) is weaker and weaker?

    Nope. To even see the difference in the fossil record, you need an incredibly rich record. This does happen sometimes, but I’m talking about diatoms forming the equatorial Pacific ocean floor here, not about one or two whale fossils every couple of million years.

    Punk eek is supposed to work on a very small scale; it’s not even close to Goldschmidt’s “hopeful monsters”. It’s Gould’s biggest failure that he didn’t manage to explain this to the general public.

    Also, how efficient is the loss of “unneeded” vestigial arms etc., since not working on the same pressure of need as a trait selected “for” per some need?

    I think what you mean is that it’s always an advantage if you don’t need to build and maintain a body part.

  41. #41 Greg F.
    February 4, 2009

    Oddly enough, VW has embraced the idea of using transitional fossils to help them sell new sports wagons. Well, erm… sort of.

    http://worldofweirdthings.com/2009/02/04/tiktaalik-is-that-you/

  42. #42 Kevin Schreck
    February 4, 2009

    Very exciting! A very important find, and this one so clearly looks like an intermediate, there’s really no rational denying it.

  43. #43 Jeanette
    February 4, 2009

    Such a busy schedule, and yet you still find time to provide us with all of these posts. Thank you, PZ.

  44. #44 Thomas R. Holtz, Jr.
    February 4, 2009

    @#25 Neil B:

    Gould’s operational definition of PuncEq (in Structure of Evolutionary Theory) runs something like “morphological transitions between species occupy the first 10% or less of a species duration; during the remainder of the species’ duration there is no net trend”. As such, a species like Maiacetus (known only from a couple of skeletons from the same bedding plane) are useless in judging PuncEq vs. Phyletic Gradualism.

    But a common misunderstanding is that PuncEq is the same thing as major saltationism: big transformations all at once. Gould and Eldredge were promoting nothing of the sort! Their initial examples were cases like the transformation of one trilobite species into another as noted by the appearance of an extra lens in the eye, or one species of the snail Cerion into another.

    The argument was over whether the transformations we call speciation represented a relatively rapid (thousands to few hundreds of thousands of years) events vs. the continuous sum of transformations over the whole species duration. It did not state that the morphological differences between species was any greater in one model than the other (although as Eldrege & Gould, and others, pointed out, species boundaries under phyletic gradualism would be entirely arbitrary, whereas under punctuated equilibrium the punctuation even would serve as an actual historical marker of a new species).

  45. #45 Thomas R. Holtz, Jr.
    February 4, 2009

    By the way, does it make anyone else here sad to see the science posts like this thread having on a few dozen comments, but “The Stupid, It Burns” have 350 at the time of this writing?

    I hope that we have a lot of pharyngulites reading and enjoying both the science posts and the creationism ones, but not posting on the science ones because they don’t feel they have anything special to add.

  46. #46 Nerd of Redhead
    February 4, 2009

    TRH, you do have a point. I read the full paper, but didn’t understand every little nuance since I’m a chemist, not a paleontologist. I recognized that it was a fine paper, that described the findings in detail. I recognized the importance of the find, but since it isn’t my field, not the true importance. So there really isn’t much to talk about unless a paleontologist posts here and walks us through the importance. So only a limited few post. A godbot is somebody to mock, which draws a lot of interest, since you don’t have to be a specialist to have an opinion on godbots.

  47. #47 Alec
    February 4, 2009

    And notice this from the paper:

    we would predict that a near-term basilosaurid fetal skeleton, if found intact, would be positioned to be born tail-first as is seen in living whales

    A nice reminder that real science makes testable predictions. I hope they’re out still out there digging for more fossils – it would be great to see this one confirmed.

  48. #48 Kel
    February 4, 2009

    Why is it that boneheads still say “There are no transitional forms.” Have they even asked a scientist?!?

    Transitional fossils: ignored by boneheads since 1861

  49. #49 RamziD
    February 4, 2009

    Thomas R. Holtz,

    I think that may be the case. Nothing excites me more than a great scientific find and I really enjoy reading and learning more about all the wonderful scientific achievements.

    I’m jealous of all Ph.Ds because science is so beautiful in it’s fundamental form and I can imagine how fulfilling it would be to immerse yourself in that (I did neurobiology research in college but chose not to try for a graduate science degree). I have an MD training which allowed me to get a pretty broad scientific education, but nothing too detailed in any particular field. My interest in something like evolutionary biology is immense, but my knowledge somewhat superficial and therefore I enjoy just reading all the articles/comments and learning as much as I can.

  50. #50 Turdus
    February 4, 2009

    I am in no way convinced that being born head first implies that the animal gave birth on land. There is no reason to automatically assume that being born head first would result in drowning. The fact that modern cetaceans are born head first to prevent drowning is an unproven assumption. I seem to remember seeing a film of a captive whale (sorry, can’t remeber which species)being born head first and it did just fine. Maybe being born head first has something to do with the shape of modern cetaceans and uterine contractions (easier to push against a firm rounded large head than a thin soft set of flukes at the end of a narrow soft tail than it does with taking the first breath). Either way, the calf doesn’t breathe until it reaches the surface and does not need to breath as long as the umbilical chord is not compressed and/or the placenta is still attached. All that is needed is a behavioral mechanism to prevent inspiration until the surface of the water is broken. Either way the fetus’s head is bathed in fluid until it reaches the surface. Furthermore, who knows how close this animal was to parturition? Mammalian fetuses often change their orientation in utero prior to birth. For many mammals, either an anterior or posterior position at birth can be normal, and it is not that critical. I am in no way convinced that the fetal head position in this species proves it gave birth on land and am quite frankly surprised this is being accepted so readily by so many who should otherwise know better. Just my two cents as a Veterinarian who does a lot of reproductive work and seen a lot of dystocias. If someone can point me to some solid evidence offering proof that an anterior presentation of cetacean calves results in drowning death due to inappropriate inspiration while still submerged I will happily admit that I am wrong!

  51. #51 gabriel
    February 5, 2009

    you really don’t want to know how much prep time goes into setting up fly labs .

    PZ – you owe it to yourself to read this paper. Seriously.

    Enhancing Undergraduate Teaching and Research with a Drosophila Virginizing System

  52. #52 Ancient Brit
    February 5, 2009

    A follow-up to my earlier post about birth at sea: apparently sea otters mostly give birth at sea and the young don’t drown during the birth.

    Different species, I know, but the principle’s the same: air-breather giving birth in water. I haven’t been able to ascertain orientation prior to birth or even online video of a sample birth, yet.

    Refs:

    1. http://www.seaworld.org/animal-info/info-books/otters/birth-&-care.htm (scroll down to section Birth)

    2. http://en.wikipedia.org/wiki/Sea_otter#Reproduction_and_lifecycle

  53. #53 Confused
    February 5, 2009

    (C, D)- Maiacetus inuus … in lateral and dorsal views, respectively.

    Umm. Is this some strange archaeological convention, where “dorsal view” means from the side and “lateral view” means top down? In chick embryology we use those terms the other way around.

    Or do they swim on their sides?
    ;)

  54. #54 Confused
    February 5, 2009

    …of course I meant paleontology, not archaeology. Who me, make a fundamental mistake in a nitpicking post? That’d never happen.

  55. #55 David Marjanovi?, OM
    February 5, 2009

    Does anyone know if hippos give birth tail-first? They give birth underwater, after all.

  56. #56 Peter Ashby
    February 5, 2009

    Well if nobody else will, thanks for the link Greg F. That is a cool ad.

    As for drawing too much from an n=1, sure. But we live in a world of publish or perish. Pushing every ounce of possible meaning from your data is the difference between sinking without trace or getting your next grant application. Nobody without an axe to grind takes that stuff seriously. When I remember some of the stuff on grant applications under the ‘Future Applications of The Research’ section, boy have I written some crap.

  57. #57 Turdus
    February 5, 2009

    Aren’t there fossil Ichthyosaurs with an anterior birth presentation? I know there have been arguments made that those fetuses may have been extruded due to post-mortem build up of gases resulting in expulsion of the fetus, but that fetus was still oriented head first. I have always questioned the orthodoxy that whales are born tail first to prevent the calves from trying to breathe during the birth process. Sometimes that explanation that seems to make the most sense isn’t accurate. Read PZ’s excellent post on why blind cave fish are eyeless.

  58. #58 Alec
    February 5, 2009

    Kel @48:

    Why is it that boneheads still say “There are no transitional forms.” Have they even asked a scientist?!?
    Transitional fossils: ignored by boneheads since 1861

    I think it’s because they are (either ignorantly or deliberately) looking for transitions in all the wrong places. The present tense is key : “There are no transitional forms”. They think that there should be transitional forms between things that exist in the present – so if evolution is true there should be half-way forms between whales and cows walking around (or swimming around) right now. Of course that’s not where evolution says the transitional forms are – the transitional forms are between things that existed longer ago and things that existed more recently.

  59. #59 Owlmirror
    February 5, 2009

    As I keep pointing to as a helpful reference on transitional fossils for the layperson:

    http://www.csicop.org/intelligentdesignwatch/fishibian.html

  60. #60 CG
    February 5, 2009

    Very interesting! Thank you for posting this.

    As for the tail/head first arguments: The article doesn’t say that this proves that this animal gave birth on land, merely that it is evidence of it. It seems like a fairly safe assumption. Seals and sea lions give birth head first and they come on land to give birth. Whales give birth tail first and they give birth in the water. Saying that some land mammals give birth with either orientation is actually proving the case for their being some sort of selective pressure for being born tail first in the water. It doesn’t matter which way land mammals give birth so their reproduction is not impacted by giving birth either way.

    Giving birth tail first is clearly an advantage in the water, which is why whales all do it. It is not necessary to find a case where a whale drown by being born head first to say that is definitely the reason they are born tail first. A reason for their being born tail first isn’t even really required (although the breathing thing seems sensible). They are born tail first, that is a fact. At some point they must have transitioned from head first births to tail first, that is also a fact.

  61. #61 David Marjanovi?, OM
    February 5, 2009

    Yes, ichthyosaurs seem to have been born tail-first.

    By the way, does it make anyone else here sad to see the science posts like this thread having on a few dozen comments, but “The Stupid, It Burns” have 350 at the time of this writing?

    Well, this one is a special case: PZ got to this topic long after many other ScienceBlogs had already posted about it, and had neither time nor inclination to write one of his own (see the top of this post); so I suppose the comments went to the other blogs.

    Do you remember the post on Odontochelys?

  62. #62 Turdus
    February 5, 2009

    CG
    The breathing theory makes no sense. Please explain to me how an emerging fetus can take a breath while it is in the birth canal? If the head has emerged, the fetus is unable to breathe because its chest is still in the birth canal. Mammals breathe by expanding the volume of the pleural cavity through the actions of the diaphragm and intercostal muscles, creating negative pressure in the pleural cavity. This would be impossible while the fetuses chest is still in the birth canal, especially with the muscular contractions of labor pressing on it. Once the chest has been delivered and can expand, the rest of the fetus slips out rapidly (this even applies to quadrupeds born on land, and they have a pelvis that still needs to be delivered – for animals with a cetacean anatomy it would be even easier to deliver the posterior end of the animal once the head and chest are delivered), allowing the newborn to swim to the surface and breathe. It does not matter if the tail is presented first or the head is presented first, it is impossible for the newborn to breathe during the birth process, and it does not breathe until it breaks the surface of the water. To me the idea of the calf being in danger because it might breathe during labor is silly and unproven, and I don’t know why it would be accepted as orthodoxy in scientific circles. It may be one explanation but certainly not the best!
    OF COURSE, there must be some selective pressure on cetaceans to be born tail first, but this may be due to their specialized, non quadrupedal anatomy and the mechanics of pushing out a fetus with the cetacean shape, NOT due to the fact that they are born in water. for example, it may be that it is easier to give birth to a fetus tail first if it has a large head relative to the rest of its body and a short stiff, relatively immobile neck and no pelvis. These features are not shared by seals and other marine mammals that give birth on land. Imagine if you had push a whale or dolphin against some resistant force, but could only do it by pushing its head or its much more narrow, flexible tail. Which would you pick? Maiacetus is a quadruped, just like seals, dogs and sea otters (and I am willing to bet that the quadripedal sea otters are born head first at sea – but I don’t know this for sure). Maiacetus probably gave birth like a quadruped, maybe in the water or maybe on land. It might not need to give birth tail first because its fetus did not have that specialized cetacean anatomy. I think this is a much more convincing argument than can be made for the often repeated (but unproven and unlikely) popular idea that whales are born tail first so they won’t breathe prematurely during birth. Maiacetus may have given birth head first because it was still a quadruped, regardless of whether it gave birth on land or at sea.

  63. #63 Turdus
    February 5, 2009

    David,
    According to Darren Naish, there are Ichthyosaur fossils with young being born (or extruded) tail first.
    http://darrennaish.blogspot.com/2006/06/ichthyosaur-wars-and-marvellous.html

  64. #64 Turdus
    February 5, 2009

    Darn it, I meant to say born HEAD first in comment #63!

  65. #65 CG
    February 5, 2009

    I think we’re in agreement, and arguing about nothing really. I don’t think the breathing thing (or lack of breathing thing) is the big deal here, it just seems to be what everyone grabbed first when they reported on the article. If you read the whole article, they actually talk about a few different reasons that whales could present tail first. Any or all of them could be contributing factors. I don’t think they mention the anatomy point that you brought up, but I think that is also a valid hypothesis. They did talk about potential problems with the newborns swimming away from their mothers accidentally (because they are facing the wrong way) and also that being the first thing out allows the tail to unfurl and therefore improve their swimming ability after birth is complete and a couple of other points I don’t recall. They actually deal with the issue quite thoroughly I think.

    Most likely all of the factors they discuss (and yours too for that matter) have a part to play in the selective pressure to be born tail first. I think the thrust of the article is that this find marks an important transition between a hippo-like animal and a whale-like animal. Even though it displays pseudo-flippers and other aquatic features it is fairly apparent that it still came on land to give birth to it’s young regardless of the “real” reason and that is the important fact.

    The article also mentions a point that you brought up earlier regarding the fetus possibly realigning and we have no way of knowing if the head or tail will present first at the birth seeing that we don’t know how far from birth this animal was. They compare how the fetus would be carried with a whale and a land animal of similar size (I think they used a hippo but I forget) and explain that in both of these creatures while the fetuses can turn around their center line axis they don’t turn in a head to tail manner so it is pretty reasonable to think that this fetus couldn’t reorient from tail to head.

  66. #66 David Ryan
    February 11, 2009

    Sorry all, I’d like to add another comment on the orientation of the fetus in its mother. I’m laboring the point a little longer because there are many, many great things about this fossil and whilst the fetal position is really just one of those, it is worth discussing because its relevance to how long a bow we can reasonably draw in palaeontology from unique specimens.
    My daughter was born last year and we were considering a water birth: we were concerned about the risk of bubs drowning before she was free of the birth canal so we looked into this a bit. Babies don’t drown in water births; what seems to happen is that the umbilical cord continues to supply oxygen until the cord tissue is exposed to air, at which point it constricts and begins to break down. A baby born underwater does not, therefore, have to take a breath of air until it reaches the surface. Another thing we learnt about was the possibility of breech birth, or bubs being born feet first. In human births, this occurs 3% to 4% of the time. That’s a chance of something like 1 in 30. Both of these phenomena, “breathing” underwater and breech birth are probably more likely to be due to us being mammals than being human and whilst I don’t know of any examples off the top of my head, I’ll bet they are out there.
    Based on these observations, one could make a reasonable argument that a)proto whales may have given birth underwater based on what we know about mammalian birth, OR b)this fetus is facing the wrong way around, based on what we know about cetaceans and that position may have contributed to the fact that mother and calf died before a successful birth.
    These are two clearly contradicting theories, but I don’t see how one or the other is better supported by the evidence of a single specimen.
    As with any fossil, there are assumptions based on strong evidence and those that are based on weak evidence. I would suggest that we should be circumspect about assumptions regarding land or sea birth based on this specimen.

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