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.
Right. There is NO way creationists will ever accept true science.
Uh huh, but individuals don't count in evolution, only populations.
Do you think that chimp/human mating has produced creationists? ;-)
Are you saying you never visit the creationists' websites?
I have never ridiculed God. And your calling my religion perverted is very Christian of you.
If you fail to stand up to the conventional wisdom of your peers you will never be a great scientist.
But you call mine perverted. Please tell me that you recognize religious faith and scientific fact as two different things.
That's true when the changes are just allele changes. It's also true when genes are inserted or copied within existing chromosomes. But somewhere along the line, chromosomes are duplicated or fused or whatever, changing the count. Otherwise, common descent is invalid.
There are (at least) two possible scenerios when this happens: one is that it happens frequently enough within a population that the "new" types find mates; the second possibility is that sometimes this just isn't an absolute barrier to reproduction.
I haven't found a good one yet but this might be a start (fairly technical, depending on your bio background).
It's just plants. I'll try to do more later today but I'm off to work now.
http://www.ucmp.berkeley.edu/glossary/gloss6/index.html
I don't get your point.
What you said is true, but it tends to support my point that blind faith will come back to bite you.
For instance, one reason the creationists can never come up with a peer reviewed paper on evolution is they have preconceived notions that there is no such thing.
So, in terms of the authenticity of its "tradition," creationism has as much credibility as Kwanzaa.
It's hard to take someone seriously when their first post on the thread is:
I bet the first whale that jumped on the beach and suddenly started breathing air only did so to get away from all of his pals and their cruel jokes about his freakish half hippo appearance.
Quite to the contrary, I fervently want to believe in God but since there is no evidence whatsoever of his existence and much to suggest otherwise, I don't. Sorry that I don't conform to your silly stereotype.
My statement was conditional, and included both alternatives. If I were making a definitive statement I would've began: In fact, I personally think that since abiogenesis is the ultimate origin of life on earth...
Well, it would actually since the modern thesis demands a common ancestor.
Well, no, it really, actually wouldn't. The "modern thesis" is not a religious dogma fantasized irrationally out of the ether. It is a compiled scientific paradigm established by the overwhelming evidence of common descent. The reason that the "modern thesis" is the modern thesis is simply because every form of life we've discovered clearly evidences a descent common with every other known form of life. If we uncovered some terrestrial life form that evidenced an origin apart from this common lineage, it would not even remotely undermine the scientific evidence of common descent for every other known form of life.
The modern thesis "demands" nothing aside that it account for all the scientific evidence. If the evidence changes, the thesis will change accordingly. Religion has its own separate rules so try not to confuse the two.
What evidence would it take for you to believe in God?
Evidence of his existence, as opposed to conjecture about the unexplained.
Blind faith works both ways. Abiogenesis -- to put it mildly -- is not established. What if it weren't true despite the expectations of many? Many believe it possible that everything can come into existence by undirected means. What if they are wrong? Shouldn't someone try to point that out to them?
For instance, one reason the creationists can never come up with a peer reviewed paper on evolution is they have preconceived notions that there is no such thing.
I don't know how narrowly you are defining "creationist". Since you believe in a "creator" to me you would be a "creationist".
Now the IDers aren't arguing "young earth" or even rejecting evolution -- Behe, IIRCl, has said he accepts common descent.
And of course the IDers are getting published. Why one was just published in the "Proceedings of the Biological Society of Washington". Of course the editor was then promptly fired , which may explain why they aren't published a lot.
There is far more evidence of God than of accident.
of to work.
I don't believe in accident. I believe that if every factor were known the entire universe and its entire history past, present, and future could be plotted out on a graph.
The myth that a human baby popped out of a chimp is a myth, not part of evolution.
Perhaps we should be careful not to conflate God with what men say about God.
Actually there are some ICR folks who get published. I've looked up some of their articles. Of course their published articles are mainstream science with mainstream conclusions (usually as one of several co-authors).
So my question has been and remains, what is the ID research program?
What if you are wrong?
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