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.
Echidna?
Once you bring God into it, anything is possible -- even evolution. I just don't think it's likely much less beyond criticism.
And God made fossils to help us find oil deposits.
No, God didn't design the human eye. It evolved. No Almighty God would have been so stupid as to come up with this design.
Why are you so compelled to be blindly ignorant of the fact of evolution?
Thank you for your reply. It was well said and I appreciate you taking the time to explain it to me. I just find that both sides of the argument have supporters that can be a bit overzealous in their defense of their positions. Whenever I find someone who gets so emotional about an issue, I wonder what exactly their motivation is.
It is also "God created man in His own image and man returns the favor."
When did I ever say I disagreed with evolution?
militant? What have I ever said in this thread to earn the militant status? Just because I'm not falling for the evoultion hoax does not mean I am ignorant. Darwin came up with a theory and the scientific community has spent the last 150 years gleaning information in a bias attempt to support it. Maybe those who fall for hoaxes are merely open-minded and not dupes.
Well if you agree, why are you nitpicking about links?
Anyway, I can't stand people who don't make their position clear and then debate anyway.
But since you seem to be a Navy vet, I forgive you.
I know. Your point is wrong. Bishop Ussher's estimate was only accepted by certain sects and then became really popular about 100 years ago when the fundamentalists dreamed up this nonsense against evolution.
It's not a matter of me refuting it, it's a matter of you supporting it.
Now do you believe that all life came from a single cell?
Probably. It might have come from two cells or more. I don't know.
It IS a matter of you refuting it. Science accepts evolution as fact (as close as science comes, since science is always ready to drop something if refuted).
Creationists have no evidence to support their positions. All they do is create strawman arguments and baffle rubes with Bravo Sierra.
"Darwin came up with a theory and the scientific community has spent the last 150 years gleaning information in a bias attempt to support it. "
LOL Yeah, it is much better to go a 150 years and develop no evidence to support creationism in a biased attempt to support silly nonsense and Bible misinterpretation.
Separate cells or a multi-celled creature?
I repeatedly asked because I never recieved an answer. Since your answer is that the wolf and dog are 2 seperate species, are you implying that mankind created a new species of animal? Oh, I'm 49 going on 12.
You also. Are you saying that mankind created a new species of animal?
This is a real hoot! I can't believe y'all spent all day on this.
I never said I agree with evolution either. I'm nitpicking about links because I thought the guy should get off his high horse. Too bad you can't stand me. I am a ten year Submarine Vet. I haven't sought your forgiveness, nor do I think I need it. It is the overzealousness on both sides that I question, including your own.
Yeah I mispelled monkeys. Does that bother you enough call me illiterate? Did I spell that right, teacher? I wouldn't call you a name unless we were face to face so you could demand satisfaction, doubt that would though.
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