Scientists find missing link between whale and its closest relative, the hippo

A group of four-footed mammals that flourished worldwide for 40 million years and then died out in the ice ages is the missing link between the whale and its not-so-obvious nearest relative, the hippopotamus.

The conclusion by University of California, Berkeley, post-doctoral fellow Jean-Renaud Boisserie and his French colleagues finally puts to rest the long-standing notion that the hippo is actually related to the pig or to its close relative, the South American peccary. In doing so, the finding reconciles the fossil record with the 20-year-old claim that molecular evidence points to the whale as the closest relative of the hippo.

"The problem with hippos is, if you look at the general shape of the animal it could be related to horses, as the ancient Greeks thought, or pigs, as modern scientists thought, while molecular phylogeny shows a close relationship with whales," said Boisserie. "But cetaceans – whales, porpoises and dolphins – don't look anything like hippos. There is a 40-million-year gap between fossils of early cetaceans and early hippos."

In a paper appearing this week in the Online Early Edition of the Proceedings of the National Academy of Sciences, Boisserie and colleagues Michel Brunet and Fabrice Lihoreau fill in this gap by proposing that whales and hippos had a common water-loving ancestor 50 to 60 million years ago that evolved and split into two groups: the early cetaceans, which eventually spurned land altogether and became totally aquatic; and a large and diverse group of four-legged beasts called anthracotheres. The pig-like anthracotheres, which blossomed over a 40-million-year period into at least 37 distinct genera on all continents except Oceania and South America, died out less than 2 and a half million years ago, leaving only one descendent: the hippopotamus.

This proposal places whales squarely within the large group of cloven-hoofed mammals (even-toed ungulates) known collectively as the Artiodactyla – the group that includes cows, pigs, sheep, antelopes, camels, giraffes and most of the large land animals. Rather than separating whales from the rest of the mammals, the new study supports a 1997 proposal to place the legless whales and dolphins together with the cloven-hoofed mammals in a group named Cetartiodactyla.

"Our study shows that these groups are not as unrelated as thought by morphologists," Boisserie said, referring to scientists who classify organisms based on their physical characteristics or morphology. "Cetaceans are artiodactyls, but very derived artiodactyls."

The origin of hippos has been debated vociferously for nearly 200 years, ever since the animals were rediscovered by pioneering French paleontologist Georges Cuvier and others. Their conclusion that hippos are closely related to pigs and peccaries was based primarily on their interpretation of the ridges on the molars of these species, Boisserie said.

"In this particular case, you can't really rely on the dentition, however," Boisserie said. "Teeth are the best preserved and most numerous fossils, and analysis of teeth is very important in paleontology, but they are subject to lots of environmental processes and can quickly adapt to the outside world. So, most characteristics are not dependable indications of relationships between major groups of mammals. Teeth are not as reliable as people thought."

As scientists found more fossils of early hippos and anthracotheres, a competing hypothesis roiled the waters: that hippos are descendents of the anthracotheres.

All this was thrown into disarray in 1985 when UC Berkeley's Vincent Sarich, a pioneer of the field of molecular evolution and now a professor emeritus of anthropology, analyzed blood proteins and saw a close relationship between hippos and whales. A subsequent analysis of mitochondrial, nuclear and ribosomal DNA only solidified this relationship.

Though most biologists now agree that whales and hippos are first cousins, they continue to clash over how whales and hippos are related, and where they belong within the even-toed ungulates, the artiodactyls. A major roadblock to linking whales with hippos was the lack of any fossils that appeared intermediate between the two. In fact, it was a bit embarrassing for paleontologists because the claimed link between the two would mean that one of the major radiations of mammals – the one that led to cetaceans, which represent the most successful re-adaptation to life in water – had an origin deeply nested within the artiodactyls, and that morphologists had failed to recognize it.

This new analysis finally brings the fossil evidence into accord with the molecular data, showing that whales and hippos indeed are one another's closest relatives.

"This work provides another important step for the reconciliation between molecular- and morphology-based phylogenies, and indicates new tracks for research on emergence of cetaceans," Boisserie said.

Boisserie became a hippo specialist while digging with Brunet for early human ancestors in the African republic of Chad. Most hominid fossils earlier than about 2 million years ago are found in association with hippo fossils, implying that they lived in the same biotopes and that hippos later became a source of food for our distant ancestors. Hippos first developed in Africa 16 million years ago and exploded in number around 8 million years ago, Boisserie said.

Now a post-doctoral fellow in the Human Evolution Research Center run by integrative biology professor Tim White at UC Berkeley, Boisserie decided to attempt a resolution of the conflict between the molecular data and the fossil record. New whale fossils discovered in Pakistan in 2001, some of which have limb characteristics similar to artiodactyls, drew a more certain link between whales and artiodactyls. Boisserie and his colleagues conducted a phylogenetic analysis of new and previous hippo, whale and anthracothere fossils and were able to argue persuasively that anthracotheres are the missing link between hippos and cetaceans.

While the common ancestor of cetaceans and anthracotheres probably wasn't fully aquatic, it likely lived around water, he said. And while many anthracotheres appear to have been adapted to life in water, all of the youngest fossils of anthracotheres, hippos and cetaceans are aquatic or semi-aquatic.

"Our study is the most complete to date, including lots of different taxa and a lot of new characteristics," Boisserie said. "Our results are very robust and a good alternative to our findings is still to be formulated."

Brunet is associated with the Laboratoire de Géobiologie, Biochronologie et Paléontologie Humaine at the Université de Poitiers and with the Collège de France in Paris. Lihoreau is a post-doctoral fellow in the Département de Paléontologie of the Université de N'Djaména in Chad.

The work was supported in part by the Mission Paléoanthropologique Franco-Tchadienne, which is co-directed by Brunet and Patrick Vignaud of the Université de Poitiers, and in part by funds to Boisserie from the Fondation Fyssen, the French Ministère des Affaires Etrangères and the National Science Foundation's Revealing Hominid Origins Initiative, which is co-directed by Tim White and Clark Howell of UC Berkeley.

It's true that as new discoveries are made we need to revise the theory to better match the data we have, but overall the modern synthesis theory is supported by an enormous amount of empirical data. The challenge is not for me to "prove" evolution to you. The challenge is on you to provide data which totally invalidates evolutionary theory. Extraordinary claims require extraordinary evidence.

Hello guys, I've been away for a short time but I have a final thought for us to consider. I still stress the possibility that evolution has been given the special treatment by scientist. That is, in some cases they've been willing to overlook the deliberative processes, or methods, that give science authority and respect:

That the evidence must be evaluated independent of any assumption about the truth of the theory being tested.

That one must be able to prove it false.

That the concept must be formed by empirical demonstration, not by logical deduction.

Confirmations should count only if they are the result of risky predictions.

Though some scientist seem willing to concede that the theory of evolution may be improved, and that our understanding may one day be much greater than it is now, they see any question as to whether evolution itself is true as nonsense. Evolution is the only conceivable explanation for life, and so the fact that life exists proves it to be true.........and the fact that life exists in different forms proves it to be true.........and the fact that those different forms have similar molecular structures proves it to be true.........and we know that ancestors had to exist so we'll group the most likely candidates together - and that proves it to true....and so on.

It's as if the scientific organizations are devoted to protecting evolution rather than testing it, and the rules of scientific investigation have been shaped to help them succeed. The fossil record on the whole testifies that whatever evolution might have been, it was not the process of gradual change in continuous lineages that modern science implies. As an explanation for modifications in populations, evolution is an empirical doctrine. As an explanation for how complex organisms came into existence in the first place, it's pure philosophy. If scientific empiricism were the only value at stake, evolution would long ago have been limited to "micro" evolution, where it would have no important theological or philosophical implications. If evolutionist accepted the primacy of empiricism, they could still hope eventually to find a naturalistic explanation for everything, but for now they would have to admit that they have made a big mistake. To prevent such a "catastrophe", defenders of evolution must enforce rules of procedure for science that preclude opposing points of view.

I only care about this for two reasons:

1. I believe that there is a heaven and a hell and I'd like to see you end up in the former rather than the latter. I can't force that on you. The only thing I can do is tell you what I believe. I have no choice but to move on if you dismiss me as a kook. Big deal.

2. The theory of evolution is an exceptional case which involves religious and philosophical questions distinct from those present in other areas of science. Some may fear the social effects of the "religious fanaticism" that I promote. But whenever science is enlisted in some other cause - religious, political, or racial - the result is always that the scientists themselves become fanatics. This is clear to scientist when they think about the mistakes of their predecessors, but they find it hard to believe that their colleagues could be making the same mistakes today.

There are several post in this thread that denounce creation as fantasy, nonsense, or unreal. Evolution is then called reality, fact, and truth. If science succeeds in this battle it will eventually lead mankind to judge all thinking by scientific criteria, and to that end classify statements as meaningful only to the extent that they can be verified. Science will be considered the only reliable source of knowledge, and the only power capable of of bettering (or even preserving) the human condition. Unverifiable statements such as "adultery is immoral", or "(fill in the blank) is wrong" will either be meaningless noise or an expression of personal taste.

The potential ramifications are so grievous that I selfishly consider my inevitable death a blessing. Science has proclaimed that evolution belongs in the category of knowledge, not belief, and that resistance to it results from ignorance, which they rightly aim to eliminate. They'd better be damned sure about that because the ultimate result isn't our enlightenment - it's our undoing.

Thanks for the long reply.

Evolution is the only conceivable explanation for life, and so the fact that life exists proves it to be true.........and the fact that life exists in different forms proves it to be true.........and the fact that those different forms have similar molecular structures proves it to be true.........and we know that ancestors had to exist so we'll group the most likely candidates together - and that proves it to true....and so on.

It's as if the scientific organizations are devoted to protecting evolution rather than testing it, and the rules of scientific investigation have been shaped to help them succeed. The fossil record on the whole testifies that whatever evolution might have been, it was not the process of gradual change in continuous lineages that modern science implies.

There is considerable debate of the rate of change; whether it is gradual, or has periods of more rapid change due to environmental stressors, and the like.

As an explanation for modifications in populations, evolution is an empirical doctrine. As an explanation for how complex organisms came into existence in the first place, it's pure philosophy.

That all living things have genes and that these genes change over time in populations of animals can be demonstrated empirically. In this sense micro-evolution is an empirical fact. However, macro-evolution is not a philosophy. It is a scientific theory. It is a model of our understanding of how micro-evolution occurs over vastly long time scales. There is considerable evidence for macro-evolution, though it cannot be demonstarted empirically because, obviously, we don't live long enough. I disagree that the theory of evolution is a philosophy such as metaphysics, the study of being, episteology, the study of knowledge, and ethics, the study of human conduct.

. If scientific empiricism were the only value at stake, evolution would long ago have been limited to "micro" evolution, where it would have no important theological or philosophical implications.

Yet we find all these tantalizing bones in the ground which all modern tests show to be incredibly ancient. Why should they be off-limits? Do the existance of these bones themselves threaten?

If evolutionist accepted the primacy of empiricism, they could still hope eventually to find a naturalistic explanation for everything, but for now they would have to admit that they have made a big mistake. To prevent such a "catastrophe", defenders of evolution must enforce rules of procedure for science that preclude opposing points of view.

See, I just can't agree with this. The theory of evolution does not seek to find a naturalistic explanation for everything. I think that's where you go wrong. There are plenty of biologists and molecular chemists who are men of good faith. I don't personally believe that modern evolutionary theory precludes someone from being moral.

"1. I believe that there is a heaven and a hell and I'd like to see you end up in the former rather than the latter. I can't force that on you. The only thing I can do is tell you what I believe. I have no choice but to move on if you dismiss me as a kook. Big deal."

I appreciate you being clear about your beliefs. However I believe just as strongly that your ideas are mislead and your concerns misdirected.

Being labeled a 'kook' is dependent on how you approach and respond to the ideas presented in the debate.

"2. The theory of evolution is an exceptional case which involves religious and philosophical questions distinct from those present in other areas of science. Some may fear the social effects of the "religious fanaticism" that I promote. But whenever science is enlisted in some other cause - religious, political, or racial - the result is always that the scientists themselves become fanatics. This is clear to scientist when they think about the mistakes of their predecessors, but they find it hard to believe that their colleagues could be making the same mistakes today."

All scientists are well aware of the POV they bring to the research they do and are more than willing to expose their ideas to peer criticism to minimize the influence their preconceptions have on their research. This is done in all fields of science including evolution.

It appears that most creationists, being primarily threatened by evolution of all the sciences, focus on that particular discipline as recipient of their machinations. One method of justifying their ire is to bifurcate science into evolution on one side and everything not evolution on the other side so they can freely claim evolution is akin to a religion. This puts evolution on the same level as religion and much easier to attack for being unscientific. If this is the case then all fields of science can be considered works of faith since all use the same procedures in developing theoretical frameworks.

It is interesting that those that class evolutionary theory as a faith seem to ignore the fact that evolution draws from many other disciplines to not only verify evidential findings but to develop and test hypotheses. It is no longer possible to separate evolution from other fields of science.

Another interesting development in creationist circles is the division between what they consider micro-evolution and macro-evolution. They have divided evolution into changes that can be accepted and have been observed and changes that can not be accepted even though they too have been observed. Many have gone so far as to limit evolution to just macro-evolution coupled with abiogenesis in an attempt to co-opt micro-evolution for their own belief system.

Scientists seldom use the terms micro-evolution and macro-evolution, preferring to discuss evolution as the single process it is. If scientists do use those terms they are simply used to differentiate between changes in a population that result in speciation from changes that do not result in speciation. The description applies to variation in degree not to a demarcation point between speciation and not-speciation.

There are many things that can falsify evolution, none of which have occurred and many things which make taking a literal reading of the bible impossible most of which have been verified, yet creationists in their infinite wisdom choose to ignore what the physical world presents them in order to avoid questioning their upbringing.

Evolution was not developed to promote atheism nor to lead people to question their faith. It was and is simply a way of explaining observations and making predictions. It is approached scientifically and meets all the standards of modern science. It makes verifiable predictions and improves our understanding of most areas of biology. It is being used successfully in a wide variety of fields of research and development and is expected to solve what were once considered unsurmountable problems in disparate technologies. It is a modern day success story. It is not evil.

Excuse me while I dismount from my soapbox.

"There is considerable debate of the rate of change; whether it is gradual, or has periods of more rapid change due to environmental stressors, and the like. "

The debate is not either/or it is to what degree do they contribute to the change. The debate is also overblown.

"There is considerable evidence for macro-evolution, though it cannot be demonstarted empirically because, obviously, we don't live long enough."

There have been instances of 'macro-evolution', otherwise known as speciation, that have been observed both in the lab and in nature. The latest that I am familiar with in nature is a case of two isolated populations of the same mosquito, one above ground and one in the catacombs of London that can no longer produce progeny. This is speciation.

"The theory of evolution does not seek to find a naturalistic explanation for everything"

The ToE is not Naturalist Philosophy as creationists portray it but Naturalistic Science, as is all science. Science is limited to physical (natural) observation by it's very nature. But, as you say it does not attempt to explain all things, just the things within it's purview.

"I don't personally believe that modern evolutionary theory precludes someone from being moral."

Evolution simply allows us to explain how morals change over time and apply to a specific culture. Atheists are no less moral than the faithful. Evolution does not, by itself, change people into atheists.

This has most likely already been posted, but it is pertinent to point out the theory of evolution doesn't answer the question of life, the universe, and everything. It doesn't say how or where life came about. It only pertains to the change in the genes of populations of animals that occur over time. To me it sounds like you are setting up a circular argument, for the purpose of knocking it down.

I was trying to address some earlier post that I'd received which basically said that evolution has been proven. Therefore, "creationist" are loons.

There is considerable debate of the rate of change; whether it is gradual, or has periods of more rapid change due to environmental stressors, and the like.

The rate of change may explain the gap in fossil evidence and that's fine. However, the question remains unanswered and I wish that everyone would acknowledge that.

However, macro-evolution is not a philosophy. It is a scientific theory. It is a model of our understanding of how micro-evolution occurs over vastly long time scales. There is considerable evidence for macro-evolution, though it cannot be demonstarted empirically because, obviously, we don't live long enough. I disagree that the theory of evolution is a philosophy such as metaphysics, the study of being, episteology, the study of knowledge, and ethics, the study of human conduct.

That's fine. I didn't mention macro-evolution, but questioned the idea that evolution can explain how complex organisms came into existence in the first place. On the other hand, I would say that macro-evolution is on thin ice (in my opinion). If common ancestors and chains of linking intermediates once existed, fossil studies should be able to identify them. If it is possible for a single ancestral species to change by natural processes into such different forms as a shark, a frog, a snake, a penguin, and a monkey, then laboratory science should be able to discover the mechanism of change. If laboratory science cannot establish a mechanism, and if fossil studies cannot find the common ancestors and traditional links, then I submit to you that macro-evolution fails as an empirical theory.

Yet we find all these tantalizing bones in the ground which all modern tests show to be incredibly ancient. Why should they be off-limits? Do the existance of these bones themselves threaten?

I don't see a conflict here. Sure, many people claim to be able to date creation with the Bible, but I think they're way off the mark. It isn't a journal or diary, so we have no idea how much time passed between this or that. If I resent the "leaps" made by some that support evolution, I resent the "leaps" made in the name of scripture even more. We're always incorrect when we claim that the Bible supports this or that scientific fact (the earth is the center of the universe, the earth is 6,000 years old, etc.)

The theory of evolution does not seek to find a naturalistic explanation for everything. I think that's where you go wrong. There are plenty of biologists and molecular chemists who are men of good faith. I don't personally believe that modern evolutionary theory precludes someone from being moral.

I meant the future - evolution as an explanation for creation carried to it's logical conclusion. I'm sure that many good people work in chemistry and biology and I don't mean to say that scientist = reprobate. But there are a lot of people that have already taken the position that scientific evidence is the only truth, and the greatest number of those people can be found defending evolution as fact. Implicit in their argument is the idea that religion, or anything else that can't be proven with evidence, is nonsense.

I think that evolution, as generally taught, has an unnecessary anti-religious aspect to it. Aside from that generality, I'd point to the prominent scientist such as Gould, Crick, Dobzhansky(? spelling), Hexley and others that teach evolution as fact and creation (God) as lunacy. I think there's a guy coming on CSPAN tonight to argue the validity of science over religion. He'll be arguing in favor of science, it'll be interesting to see what he has to say.

b_sharp,
I would argue that science picked the fight with religion, not the other way around. Consider the 'Scopes Trial' for example.

Another interesting development in creationist circles is the division between what they consider micro-evolution and macro-evolution. They have divided evolution into changes that can be accepted and have been observed and changes that can not be accepted even though they too have been observed.

I think that Darwin and T.H. Huxley are responsible for that distinction.

I disagree in general with your assertions that evolution has been approached scientifically, meets all the standards of modern science, and makes verifiable predictions (at least not significant predictions). You imply that evolution is almost indisputable, but I've not found anything to substantiate such a claim.

The very word "evolution" has been made so ambiguous that it can be used to justify almost any pro-evolution stance. To be clear, I'm refuting the notion that creatures that share almost no similarities came from a common ancestor at some point and the notion that the common ancestor came from (what is the leading theory on that now anyway? Aliens?).

Anywho, you made your beliefs clear, and although I think your wrong, I'll respect your position.

If common ancestors and chains of linking intermediates once existed, fossil studies should be able to identify them.

There are lots of good examples of fossil evidence of common ancestry. Of course, the farther back you go, typically the fewer good fossils you find and there is always margin for error. I have a nice fossil trilobite I use as a paperweight. It's clearly an arthropod, and a distant relative of today's horseshoe crabs. The trilobite is not believed to be a direct ancestor of the horseshoe crab, but it doesn't seem unreasonable that these two creatures shared a common ancestor. All insects are arthropods. Why are there no fossils of honeybees found in the same layers of rock with the trilobites? More to the point, how does searching for this answer lead people away from morality?

Though there is very little we can definitively say about the origin of life on earth, one thing is clear and that is all life (viruses being somewhat an exception here, but even they are not incompatible) uses the same DNA molecule, and some proteins made from these molecules are common in nearly all lifeforms. This infers commonality and relation. Whether this inference necessarily implies a divine creation at work is a matter for personal introspection, but there is certainly a strong connection between all life on earth.

I meant the future - evolution as an explanation for creation carried to it's logical conclusion.

I still think you're making this extrapolation that the more someone learns about evolution, the more atheistic that person becomes. It is well known that science deals with the observable and reproducable. However, in and of itself does not speak on "metaphysical" issues such as ethics and morality. Like any tool, it has the capacity for misuse. I think most scientists are aware of this limitation. Sure there are some people for whom science is their religion, but picking out a few noted athiest scientists and holding them up as a standard is a pretty hasty generalization. I tend to think if someone is arguing science versus religion, that person is asking the wrong questions. That's just my opinion. Personally, I don't see any conflict between faith in the Creator and accepting that the genes of populations of plants and animals change over time.

All insects are arthropods. Why are there no fossils of honeybees found in the same layers of rock with the trilobites? More to the point, how does searching for this answer lead people away from morality?

Because the trilobites were extinct before the bees came along. Besides, the idea that all anthropoids had a single ancestor has yet to be demonstrated. As to the other question, you're twisting my point. Searching for bees in rocks doesn't lead people away from morality. Claiming that science is the only real way to truth, and that which cannot be validated by science must not be true is. That's the prevalent idea among evolutionist (not just a handful of atheist scientist) - and it's regularly pointed out by them as an indication that their theory is superior to creation. That is where they take a turn towards ultimate immorality.

There are lots of good examples of fossil evidence of common ancestry. Of course, the farther back you go, typically the fewer good fossils you find and there is always margin for error.

Like what? If everything evolved there should be an abundance of intermediary fossils. This is why I say that scientist have broken away from core scientific principals and methods in defense of evolution. Let's look at the fossil evidence:

The honeybees that you mentioned earlier supposedly originated on earth about 180 million years ago. They have remained unchanged ever since. 180 million years and they don't even show the slightest beginning of mysterious transformation. What gives?

The marsupials are a favorite of evolutionist. Consider the kangaroo and wallaby. They apparently arrived on earth so recently that they haven't had time to make an evolutionary history via the fossil record. Some point to a few other marsupials as being "related". This is exciting news. They had to of morphed at such a fantastic rate that we should be able to find a freakish wombat-garoo or something of that sort of we look hard enough.

What about birds? They just kind of "appeared" with feathers about 100 million years ago. They looked a hell of a lot like the birds of today. We're missing a lot of the part bird / part whatever creatures to still support the gradual change idea.

We can trace hippos and / or elephants back about 60 million years ago to Moeritherium. Where in the world did he come from? Whatever animal you point to, I'm sure it almost had a heart attack when it sired him because the fossil record is blank before that and in between that (as always).

Tigers, lions, jaguars......we're still out to lunch on that one. There isn't a clear fossil record on them either.

One of my favorites is the shark. We found one that swam the oceans 350 million years ago. I think it's safe to say that Cladoselache and the modern day shark are essentially indistinguishable. That's disappointing because if their fins haven't started to shrink away by now, we'll never live to see a shark with legs. Please take note of the fact that Cladoselache apparently didn't have parents either. 349 million years ago - nothing...........350 million years ago - POOF a damned shark. Wow.

We could go on and on. All of these things seem to have just "showed up" one day where nothing closely resembling them had been.

Where's your fossil evidence? You can't look at fossils and think "evolution" is reasonable. Why do you keep saying that, "there are lots of good examples of fossil evidence of common ancestry"???? Scientific study of evolution doesn't appear to be objective.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.