The Backward Whale

By Carl Zimmer | February 3, 2009 8:00 pm

maiacetus.jpgIf you take a look at a whale or dolphin–any whale or dolphin anywhere on Earth–it will follow certain rules. It will have a blowhole. It will not have legs. It will have horizontal tail flukes it raises and lowers to swim (as opposed to fish that bend from side to side). And it will have been born tail first (as opposed to the head-first position of land mammals). These sorts of rules set whales and dolphins off from other living animals, but only if you look at life as it is today. If you move back in time–especially back between about 50 million and 40 million years ago–the rules collapse.

As I detailed in my book, At the Water’s Edge, paleontologists began to document the transition whales made from land to sea in the late 1970s. University of Michigan paleontologist Phil Gingerich found the skull of a mammal that seemed like it belonged to a land mammal but had some hallmarks known only in whales. Over the past three decades, he and other paleontologists have found a menagerie of magnificently weird whales. They start out able to walk on land and then gradually adapted to living in the water. Their noses crept up their heads, becoming blowholes. They swam at first kicking like otters, then more like seals, and then finally like whales do today.

Of course, the dozens of early whale species paleontologists have discovered are probably only a fraction of the diversity that actually existed. And so whenever new species turn up, paleontologists can use them to test hypotheses about how whales evolved. Gingerich and his colleagues are publishing the details of one today, called Maiacetus, that shines a particularly amazing light on early whale evolution. That’s because they’ve found fossils of both adult males and female Maiacetus–as well as a baby Maiacetus still in her mother.

Gingerich’s team found the 47.5-million-year-old fossils in Pakistan in 2000 and 2004.  They resemble other whales that Gingerich and other paleontologists have found from that same time, with small legs, powerful tails for swimming, and jaws and teeth adapted for catching fish. Like those other early whales, Maicetus had a distinctive “double-pulley” shaped ankle bone that is only found today in even-toed hoofed mammals. (DNA tests show that whales share a common ancestor with even-toed hoofed mammals, their closest living relatives being hippos.)

Gingerich speculated at the time that these early whales were living like seals, spending most of their life in water but still coming back to land to give birth. It was a hypothesis that might be tested should anyone ever find fossil clues to how these early whales gave birth. It turned out Gingerich was the one who found those clues.

fetal-skeleton.jpgAs Gingerich and his colleagues were digging up one female, things got confusing. They started to find bones that seemed to belong to Maiacetus, but were much smaller than the rest of the female’s skeleton. Eventually they realized they were digging up a mother and her unborn calf. (In this drawing, the baby’s skeleton is painted blue.) It was pointing towards the birth canal so that it would be born head first–like land mammals  and seals.

Being born head first is useful on land, because a baby mammal can start breathing air before it is fully delivered. For an aquatic whale, sticking a tail out first means it will be ready to start swimming once labor is over. Judging from the fossil Maiacetus baby, Gingerich concludes that it would have first seen the light of day on a beach, not deep beneath the waves.

In other words, Maiacetus breaks the rules of whales, even as it shows how those rules were made.

Update: For more blog reactions, see Laelaps, Greg Laden, and Not Exactly Rocket Science.

Update: Clarified DNA studies.

Images: Adult reconstruction, John Klausmeyer, University of Michigan Museums of Natural History. Fossil drawing copyright University of Michigan Museum of Paleontology. 

Reference: New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism, PLoS ONE 4(2): e4366. doi:10.1371/journal.pone.0004366


Comments (35)

  1. rickflick

    I just read your book on this subject. Fascinating. Simply fascinating. I remember noting many years ago that while the origin of whales as land mammals was well established, wouldn’t it be neat if we could find a more complete series. Well, my guilty pleasure has arrived. And now the calf in this weird position. OK, now I can die and go to heaven.

  2. Unless this one specimen being pointed head first was just a fluke?

  3. ElGordo

    Edit: “…from land to sea in the late 1970’s.” [and] “…not deep beneath the waves.”

    Great stuff!

  4. TheElkMechanic

    No, it was probably that way on porpoise, since that’s the right way for it to keep from turning blue. Beluga.

  5. Quietman

    Jason R.
    Possibly. The transition stage (whenever it was) must have had many born head first that drowned leaving only those with a predisposition for feet first to propagate. It’s how evolution works.

  6. luca

    Just one curiosity. What if that Maiacetus mum died of child(calf?)birth, because of the little one coming out the wrong way up? Has this possibility been ruled out?

  7. James F


    Might I recommend linking this as a Trackback?

    [Carl: James, your link is bad. I’m not sure how to add a Trackback, so I just added a reference with a link to the paper at the end of the post.]

  8. James F


    Let me drop Bora a line, he would know how to do it – perhaps he can take care of it on the journal’s end.

  9. SW

    “Possibly. The transition stage (whenever it was) must have had many born head first that drowned leaving only those with a predisposition for feet first to propagate. It’s how evolution works”.

    I doubt it would that much be at risk of drowning during birth even if they did come out head first initially, don’t forget the cord would still be attached until severed after birth. I suspect being born feet first was more an adaptation to enable the calf to be in the best position to get a quick lungful of air after the cord was severed and then to keep up with its mother if predators were about. Like other artiodactyls the calves seem precocial and artiodactyl calves are also able to run soon after birth in order to keep up with the protective mother/herd. So the “transition” does not seem too problematic to me.

  10. Jumblepudding

    Of all evolutionary conundrums, whales and bats always blow my mind the most. The thing that sorted it out for me was a comparison of their early ancestors to present-day Mouse Deer, tiny deer that hide underwater when threatened. The fact that the ancestral whales’ ear canals were, through a fluke of Evolutionary developement, already “pre-made” for hearing underwater helped me get my head around it as well.

  11. Charles Wade

    I am a HS physics teacher, and I was amazed by this reporting. Thank you for the good service you provide to me who loves knowledge.

  12. Wiki says sea otters “usually” give birth in the sea, but no info on how the sea otter fetus presents. Any sea otter ob-gyns on this thread? I was trying to think of species that might demonstrate the transition to birth in the sea and whether breech birth precedes or follows the transition. Wild speculation would be welcome too.

  13. As far as I have understood, mammals born head first don’t breathe before the umbilical cord snaps. At what point during birth does that happen in whales? I mean, there isn’t much air to breathe inside the mother either, or…?

  14. Randy Hill

    I hope this is not too dumb of a question to ask on this blog, but what makes the discoverers of this fossil so sure that it is a whale (especially with the physical characteristics described in the drawing)? What makes a whale a whale? What about this fossil places it so easily into the whale “family?”

  15. Jason

    You’re going to have to rewrite Water’s Edge just to reflect all of the recent discoveries.

  16. Randy- the snout and teeth give it away. What taxonomists really care about though are innocuous clues like certain bones in the ear or jaw that are only found in related animals. See the wiki write-up for Pakicetus:

    (Or read Carl’s book)

  17. Modern whales are very embarrassed by this discovery, because they believe that giving birth on land is for sissies… rather the way Navy pilots feel about the Air Force.

  18. Turdus

    I posted this on pharnygula and will also post it here. 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!

  19. Robert Rushing

    Just a fluke. Heh heh.

  20. Lurker #753

    @Brian Schmidt
    I believe otter pups are born… upwards – i.e. mother on her back. Even if they managed to fall overboard on emergence, they’re already furred and >1kg in weight, and the mother would rapidly scoop them back up, so I doubt orientation is critical.

  21. Turdus

    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.

  22. I’ve read that whales give birth tail first, because the calf is born with the head facing the same direction as the mother and instinctively follows her “jetstream drag” (I don’t know the right word) like a remora. If the calf was born head first, it would be facing the wrong direction and they could get separated. Sounds funny, but consider ocean currents and predators attracted to the blood, the calf sticking very close to the mother has a definite advantage. I’d guess Maiacetus gave birth in the warm lagoon shallows, like human ancestors living along tropical shores once did as well, “water babies” hold their breath until they reach the surface, of course.

  23. Excellent article. I’m sure we will find all sorts of dicoveries like this that will continue to amaze and astound us. Thanks for posting this information.

  24. abfabbum

    Turdus, can you not see the other side of this? Perhaps if the head first birth is not because of breathing then it’s due to other factors, like being eaten shortly after birth if it didn’t follow it’s mommy. I believe that’s been mentioned. This evolution has to be the result of something. Else, why would the change have occurred at all? Way to go Gingerich for finding out more about the backwards evolution of the whale from land to sea. Fascinating.

  25. Hobgot

    Since the Hippopotamus gives birth underwater and head first I don’t see how this find establishes one way or the other that M. inuus gave birth on land.

    While the suggestion that tail first birth aids the infant in finding its mother I would not say that this prevents it from drowning.

    Some fish, notably guppies, give birth both head and tail first alternately.


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The Loom

A blog about life, past and future. Written by DISCOVER contributing editor and columnist Carl Zimmer.

About Carl Zimmer

Carl Zimmer writes about science regularly for The New York Times and magazines such as DISCOVER, which also hosts his blog, The LoomHe is the author of 12 books, the most recent of which is Science Ink: Tattoos of the Science Obsessed.


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