To cut right to the conclusion: We now have reason to believe that the proto-whale Maiacetus inuus, a true transitional form, gave birth on land, not in the water.
Artist's conception of male Maiacetus inuus with opaque skeleton overlay. Credit: John Klausmeyer and Bonnie Miljour, University of Michigan Museums of Natural History
Maiacetus inuus is a newly described member of a larger group of proto-cetids (proto-whales) that are believed to be largely aquatic. However, the absolute degree to which these four-legged not quite-whales really was aquatic is subject to further study and analysis. In this paper, an adult female Maiacetus inuus wiht a nearly full term (and rather large) baby Maiacetus inuus still inside it provides a very useful clue that birth was on land. The position of the baby is not whale like (tail first) but rather, land-mammal like (head first).
The fossils are from sediments in Pakistan, and date to about 47.5 million years ago. At that time, the mountainous region of Pakistan was a flat low area, often covered in a sea. This sea was raised up (and thus the fossil bearing sediments exposed) by tectonic forces associated with India shoving into Asia over the last several tens of millions of years.
The stratigraphy of this region is very well worked out. The right side of this diagram shows layers that are tilted and thus exposed over a large area ... these are the layers that the Pakistani mountains are made out of. There are very few anomalies in the stratigraphy here. The left column shows radiometric dates; the next column shows paleomagnetic stratigraphy, the next shows standard chronometric units, and the next shows the biostratigraphy based on comparison of faunal materials. The column with the three color bands ("Sequence stratigraphy") shows various characteristics of the sediments, which are discussed at length in other publications.
The red box shows the layer of limestone, deposited in an ancient sea, in which the fossils of concern here were found. There can be no questions about the date of the fossils.
(Here is the creationist quote mine of the above paragraphs, ready for use on creationist web sites, etc.: According to Harvard trained Palaeoanthropologist, Greg Laden, speaking of Gingerich's find, "The stratigraphy of this region is ... well ... tilted and thus ... There are ... anomalies in the stratigraphy here. The left column shows radiometric dates... which are ... of concern... There can be no ... date of the fossils. ")
U-M paleontologist Philip Gingerich, who led the team that made the discoveries, was at first perplexed by the assortment of adult female and fetal bones found together. "When I first saw the small teeth in the field, I thought we were dealing with a small adult whale, but then we continued to expose the specimen and found ribs that seemed to too large to go with those teeth," he said. "By the end of the day, I realized we had found a female whale with a fetus."
This is the very first case of a fetal skeleton of an Archaeoceti (extinct proto whale). The name of the new species, by the way, derives from "Mother" and Innus, the Roman god of fertility. So it means "Mother of all whales, Apparently Quite Fertile." What will they think of next...
The fetus was positioned head first which probably means delivery on land, though this is somewhat conjectural as it could have been an intermediate system. In addition, the fetus has a full set of teeth, indicating a precocious offspring, ready to fend for itself to at least some degree, was in the offing.
Fossils of female Maiacetus inuus with near-term fetus in utero, as found in the field. The female's skull is shaded white (teeth brown), and other parts of her skeleton are shaded red. The single fetus, in birth position inside the mother whale, is shaded blue (teeth orange). The specimen was collected in three plaster jackets (blue dashed lines), and additional bones were picked up separately. The red dashed line indicates the edge exposed by erosion. Copyright: University of Michigan Museum of Paleontology.
In the same deposits as this female was found a male, somewhat larger in size and also well preserved. The male also has larger canines than the female, scaled to body size. The total degree of dimorphism (size/shape difference) in this species is moderate. This says something about the whale's social system. Almost certainly, the males were not territorial, and there was moderate inter-male competition, possibly indicating mixed sex groups.
Gingerich interprets the large teeth, seemingly adapted for catching and eating fish, as indicative of a life at sea, and he believes that they came to land only for resting and giving birth, and possibly mating. These creatures had four limbs modified partly into flippers for swimming.
Maiacetus is clearly a transitional form between sea-dwelling but possibly near-shore mostly aquatic animals and dedicated sea-dwellers. Also, these particular specimens are very very complete and well preserved. You may recall that some years ago, creationists chided evolutionists because some guy named "Gingerich" had reconstructed all of whale evolution on the basis of a single 'ankle bone' found in a box in some dusty museum. Well, that was never really true. But now, with yet another transitional form and one that is so well preserved to boot, the creationists will be scraping thick egg off their chagrined faces for the rest of the year. According to Gingerich, "Specimens this complete are virtual 'Rosetta stones' ... providing insight into functional capabilities and life history of extinct animals that cannot be gained any other way."
On a final note: This is a major article, published by an internationally recognized dream team of palaeoanthropologists. Since this is published in the Open Access journal PLoS ONE, this publication is a significant marker in the history of Open Access publishing. This is roughly like having a very famous food critic pick your resturant to eat in because she likes it.
The article can be downloaded and enjoyed by anyone with access to the internet here.
Other blog posts on this paper:
Maiacetus at Pharyngula
An Awesome Whale Tale at A Blog Around the Clock
Maiacetus, the good mother whale at Laelaps.
Fossil foetus shows that early whales gave birth on land at Not Exactly Rocket Science
A Fossil Fetus and what it can tell us about the life history of early whales. at The Questionable Authority
Ancient Whales Gave Birth On Land at Palaeoblog
Early whales gave birth on land, fossil find reveals at Science centric
Whale ancestors gave birth on land at ScienceNews
Primitive Proto-Whales May Have Clambered Ashore to Give Birth at Discover 80beats
Gingerich PD, ul-Haq M, von Koenigswald W, Sanders WJ, Smith BH, et al (2009). New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism. PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004366
This is very good...a transitional form. How many gaps does that create?
That's just too frakkin' cool.
I first saw this post on my phone and all I could make out was the title. I turned to my wife and said, sounds like they found a kick-ass transitional form to shove in the creationists collective faces. Of course the creationtards won't acknowledge the significance, but screw them. This is an awesome find! I sooooooo wish I was a scientist sometimes.
Very cool indeed, I wouldn't be surprised if the evolution of the whales will be a key example in school textbooks in years to come.
And it's doubly nice to see it in an open access journal:-)
Awesome! Although I must admit I don't find it entirely obvious why the head-first position of the fetus implies it would be born on land. Do all viviparous sea-living creatures give birth hind-end first? Why?
Think about it...gotta do with..you get it?
Fascinating article. Some really good material here that helps us understand what these creatures were really like.
Felicia, the significance of the orientation is explained in the article as follows: "Cephalic presentation at birth is generally held to be advantageous on land as it enables a newborn to breath during labor. Caudal presentation at birth, in contrast, is generally held to be advantageous at sea as it may reduce the risk of drowning. Caudal presentation may also hold an advantage in water, because it orients the newborn calf to swim parallel to the mother rather than away from her. This might be important for communication, initiation of nursing, and protection from predators. Cephalic presentation does not incur the same risks on a solid substrate."
There is more to it than that, but thats a good summary.
Greg, you say that it's limbs were modifed to flippers. Are you sure? Thats not my reading of the article, and the reconstruction does not seem to show flippers.
Also I'm not at all sure why this is thought to be a problem for creationists. Surely it would have been a more serious challenge for them if it had given birth like a whale? Since it seems many creationists feel that that protocetids and even more so earlier forms like pakicetids are not whales at all, the fact that they didn't give birth in a whale like manner is hardly an issue for them. To put it another way, I assume that as far as many creationists are concerned the fact that an animal they don't believe to be a whale gave birth in an un-whale-like manner is not a problem, indeed I'd guess they would argue it strengthens their case.
As a scientist I find many creationist claims bizarre, but this seems to be creating a straw man to knock down rather than taking issue with an actual creationist claim.
Whatever, it is an amazing fossil from which we can learn a great deal about the life-history of these animals. Also wonderful to see it published in PLOS.
Might I suggest linking this as a trackback?
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.
James: That functionality is either broken at PLoS or broken here at scienceblogs. Historically, the problem has been a PLoS. I have that link in the right box, but all I get is an error when I save the post.
Notice that at the moment there are about a half dozen blog posts out there on this topic, but not one is linked on the trackback page. Not even Bora.
Corax: Right. Flipper like. But actually, I don't think there is necessarily a formal definition here. I suppose one could say a flipper can't have any indication of digits (so, "flipper like" is probably good).
If you tried to send a trackback - don't worry. TOPAZ upgrade saved them elsewhere and will automatically put them on the paper once the process is over.
How did ancestral whales go from headfirst to tailfirst birth? Very cool fossil though. Perhaps the question should be, when did this occur.
As readers of this, and similiar, blogs will know, opponents of evolution have turned their attention in recent years to undermining the credibility of paleontologists. They attempt to exploit instances of poor reasoning, particularly when scientists are making inferences beyond the data.
With that in mind, I offer a few concerns about the interpretation of this fossil. If the fossil were an example of a proto-whale giving birth with cephalic presentation, it would be an important find, for all the reasons given above -but is the fossil really evidence of this?
Obviously the animal did not give birth to the fetus, which means we should be asking the question: rather than assuming the fetus' orientation was normal for the animal, is is possible the fetus' orientation may have actually contributed to the animal's death?
Imagine that the Maiacetus inuus sought out calm waters with few local predators for birthing; this would explain why the carcass has been well preserved, highly intact. Had the animal died within range of the kinds of predators which would normally threaten newborn calves, the carcass would have certainly been dismantled due to scavenging by reasonably large carnivores. We can therefore rule out cause of death by predation.
There are of course many possible causes of death, but the cause of death may have been precisely because of the fetus' cephalic orientation - possibly the inverse of a breach birth trauma for this animal. In any case, we must also consider that the fetus was not preserved in its birthing position, but may have moved during term, or perhaps even after the mother Maiacetus inuus had died.
There are so many unambiguous transitional forms, we don't need to provide grist to anyone's mill by throwing wild interpretations at a clearly inconclusive fossil.
It's unlikely the cephalic presentation resulted in the mother's death. In terms of causing complications to the birth cephalic vs breach presentation is only a significant problem for humans (and possibly some higher apes).
In humans large fetal head size and a narrow birth canal mean that if the body comes out first the neck extends rather than flexes when going through the birth canal. If it flexes the largest cross-section is aprrox forehead to occiput, when extended it is chin to ociput - much larger - this means the head can get stuck.
and possibly some higher apes
Doubtful. Apes have small head, no necks. Probably just humans, as you say.
It is highly unlikely that this whale "died in childbirth" ... death in "childbirth" is very rare except in humans and many domestic critters. Most likely something else went wrong, and there are many possibilities that are not scavengers. Marine mammals die en mass fairly frequently.
Gingerich would certainly be near the top of my list of living "dream-team" paleontologists, but he isn't a paleoanthropologist. In fact, I'm pretty sure that he'd be mildly insulted by the accusation.
And while it would not surprise me if the regular readers of a blog enthusiastically supported the sort of free access provided by PLoS journals, I'm a little surprised that the _author_ of the blog does. Imagine if your provider charged you $2,500 for every blog entry. Check out the cost of publishing with these guys sometime. It's quite something.
James: Funny how the word "Paleoanthropologist" sort of took off like that. My mistake. He's a paleoanthropologist.
The cost of publishing in PLoS varies. The ideal model is that you write the cost into grants and thus it is covered up front. At the opposite extreme would be an independent scholar who had no such funds. That person would have a different price.
I'd also like to add that publishing in "non OpenAccess" journals is not necessarily free. It could cost, say, 1,200 bucks to put a paper with a few graphics in PNAS.
We've put together a quick, informative video about the Joggins Fossil Cliffs in Nova Scotia where you can learn about their significance in Darwin's Theory of Evolution.
It's worth a look!
I am just curious, first creature from the sea crawl out, then later, some distant relative slowly made its way back into the sea? or did the protowhale come out of the sea and birth the collective group of mammals onland???
fossils are coooool!