Posted on 02/08/2005 3:50:43 AM PST by PatrickHenry
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.
And you're convinced that applies to me yet you fail to see that I'm convinced it applies to you.
I am just trading Bible verses with you. Since you don't have any science to debate, I thought I would go down to your level trading insults with the Bible.
What a good use you creationists have for the Bible. ;-)
No, Behe thinks mousetraps were designed.
Well gene sequencing is a means science uses to determine descent. . .You can't determine what occurred first in gene according to the position of it in a gene.
That's not how gene sequencing is used in determining descent. (not saying it's definitive, of course, and nobody is claiming so as per the flagellum merely indicative) Are you saying it's not used for such a purpose??? Careful in how you answer.
Because "I don't know" has the same level of explanation as "God did it".
It most certainly does not. Saying "God did it" is a stopping point. Saying "I don't know" is a starting point. If are unwilling to honestly say "I don't know" you will never find the answer.
Saying "I don't know" to problems that are well explained through a theory is what most people in this thread upset.
Most people? I'd say the sides are pretty even and what has my side upset is the unwillingness to say "I don't know" when that is the honest answer.
Take this quiz: What is the defninitive common ancestor between man and chimp? Now why are you sure there is one?
And I say the same thing about you there too :-)
You are arguing from faith.
The fact of Jesus Christ Resurrection is necessary to be a Christian. Faith comes in where the person chooses to believe in it or not.
Without Christ risen, Christianity is the same as Muslim or any other false religion.
No, you don't know enough science to know whether it is factual or not. You have already refused to read the facts several times, but continue to try to debate based on, well, nothing but your uninformed opinion.
You would be a much more effective Christian if some reality penetrated your world view.
I have Faith that Christ's rising is a fact, I wasn't there though.
But it is actually taught that that E=MC2applies only to nuclear reactions and not to chemical reactions.
You don't believe the Bible? You only have faith that Christ rose without believing what the Bible says is a fact?
Hmmmmmm...
It seems you chose to believe as fact that Noah put millions of animals on an Ark and mucked out all their stalls with 8 people, but you only have "faith" that Christ rose without accepting the literal Bible as fact.
I think you need to go back and rethink your whole set of principles for living.
In all practicality E=mc2 does only apply to nuclear reactions.
I would teach kids about the energy transformation in beginning chemistry, so they begin to understand the big picture.
You can worry about if you want, I don't know why you would.
What is a "SHUBI"? Is that an acronym? Looks like one, like SCUBA, or PETA.
shubi, I don't have time to go through the next 1000 posts from this line, but it is really annoying and it is clear to all on this thread that Jayson has a strong point and all you can do is boast about your credentials.
If you really were a biologist, you would understand that Jayson's logic is 100% accurate regarding "what" evolution is defined as. Whether you agree with the theory or not is a different argument which apparnetly you are incapable of matching wits with (biologist or not).
From my perspective I don't have a problem with evolution as a theory or when enough facts exists as a fact. The real problem is that so many people have agendas its all propaganda. Fundamentalist Christians who think the earth is still flat versus evolutionists who think they are actually scientists. Its actually pretty funny to watch if your paying attention to the facts, not the propaganda.
Cheers!
"Take this quiz: What is the defninitive common ancestor between man and chimp? Now why are you sure there is one?"
There are many reasons to know there was a common ancestor. One indicator is the vitamin C gene deficiency.
Another is the greater similarity of our DNA to chimp DNA than any other animal.
We don't have to find the common ancestor, which might have only existed for a very short period of time probably in Africa, before it split into several different populations that would speciate according to the environment of the ecological niche they inhabited.
Thanks for the complete Bravo Sierra. Try to look for a clue. Jaysun has no science at all on his side, no facts-nothing but misinterpretation of the Bible.
That you think nonsense has merit is your problem.
I should add, that if you had read Jaysun's posts, you would see he does not know what the definition of evolution is. Apparently, you may not know either.
Like a typical propaganda-based evolutionist (without a mind for science), you refused to take on an important, and still unanswered question. Are you willing to approach this topic or are you still going to hide behind your "credentials"?
Like a typical propaganda-based evolutionist (without a mind for science), you refused to take on an important, and still unanswered question. Are you willing to approach this topic or are you still going to hide behind your "credentials"?
"You can worry about if you want, I don't know why you would. "
If you want to represent yourself as a Christian, quote reams of Bible verses and attempt to evangelize; the least you could do is have some understanding of the basis of Christianity.
As to my screen name, it is a nickname some friends gave me long ago. I like it because it reminds me of the Sinatra song.
It could be the acronym for shut Hank up before idiocy.;-)
There are hundreds of observed speciations.
Go learn some biology.
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