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.
If you have to go back to 1625 to find someone who you think is an authority on young earth, it really boggles the mind that you think this is pertinent. Darwin didn't discover evolution until about 200 years later.
Do you not see the problem with your thinking?
Give it up. Give us any fact that refutes evolution, instead of the fallacy of appeal to authority.
Just because some pastor tells you that the Bible means something other than it does and you must follow it or go to the nether world, doesn't mean it is true.
The Meyer article is not science. You are using the fallacy of authority again. ID will be using this one irrelevant article to scream that they are published from now on. It is pathetic.
The only conclusion one can draw from Hague's paper is Genesis is not authoritative.
I don't agree with that conclusion, but that is what his premises require.
excuse me?
They are really doing some amazing things in genetics.
I wonder why ID hasn't taken this up. They could take their vocal genes out and give us some peace from their nonsense.
"If I drink to much beer today I'll have to swallow some Aspirin tomorrow."
I recommend washing it down with Scotch.
"I do not believe my sainted mother is just as much an animal as the beetle scurrying in my garden."
What about your mother-in-law? Beetle? Cockroach? Snake?
I note that it has now been 9 hours since I answered a specific fallacy, and though the one to whom I replied has been activer on the thread since that time he has not seen fit to attempt rebuttal OR admit his error.
I am beginning to detest these people.
They give religiosity a very bad name, and through the promulgation of their charicature of an understanding of science they tarnish the reputation of science itself among the general population.
They also, as noted by others, stain the public perception of the GOP and conservatism.
"I do notice people on here do really get their beards' in a knot defending evolution, must mean a lot to them."
Actually, we can't defend evolution from your kind of attacks. The attacks have no merit. It is only by repetition of stuff like 24 hr day and the global flood caused all the dino bones to stratify in chronological order that creationist nonsense gets accepted. Along with the peer pressure to believe nonsense under threat of damnation, it would be laughable if it were not such a serious threat to the survival of Christianity.
You refuse to believe what the Bible means.
Face it.
Is it really necessary to threaten everyone with hellfire if they don't believe your silly take on the Bible?
C14 dating only is accurate to at most 50,000 years.
Other dating methods are used to date fossils.
hrmn.
news to me.
I do not dispute, but seek citation of source w/ table of halflife etc...
thanks.
"evil" is a word I am loath to use without pressing need and ample evidence.
however, I do see evidence of a great deal of sinfulness in their modes of conduct.
Now we are disputing the facts concerning Noah's ark. What is about all this you feel threatened by? Do you have very much invested in your desire that there is no God?
Sometimes the scientist may come to the conclusion that the supernatural exists, but he does so by means other than the practice of science.
So many people here think way too much! Being able to distinguish between right and wrong, a liar and an honest man, corruption and honor does not require agreeing with reams of paper from scientists full of 9 syllable words that have been compliled after a theory has been announced in order to support the said theory. Those of you who WANT evolution to be a proven fact all have something that must bother you about the theory. Honestly, in your mind, what is the flaw in evolution? I'm not asking the creationist, anti-evolution, complete and intact species people. I mean, you must have a problem with evolution some where, something doesn't seem right in your minds.
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