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.
Ah, now we are moving from the Special Theory of Relativity to the General Theory of Relativity ...
Let there be light occurs before the days of creation. The first few sentences are more important than the rest, IMHO.
no. no. no. no. no.
"we" are doing no such thing.
I shall retire from this segment of the discussion for the purposes of the conservation of my sanity, which CAN be converted to something else
:)
ekshooley, that chem101 class existed for one purpose alone: to weed out premeds who couldn't cut it.
I'll tell ya about it sometime.
ICR has no science. Talk origins is ALL science.
You have twisted into a false equivocation for some reason.
I can tell you are closed to any rational discussion. So, I won't be attempting to teach you anything further.
yes, but that PHRASE came into being long after man grew accustomed to associating sunrise with beginnings. I ain't impressed by it nohow.
But. but. but. but the GT of Relativity says that the "person" cannot distinguish whether he is accelerating or rather stationary in a gravitational field.
For example, the "classical" case of the person in the elevator that is accelerating upwards. He doesn't know he is accelerating, just that "gravity has increased".
Or, close your eyes and jump off a building. You will be accelerating but have NO sensation of accelerating, just a floating feeling (ingnoring wind noise), till you hit the ground.
LOL Could you put a different caption on that?
Not Chem 101. You are thinking of Organic Chemistry.
There is a lot written about the influence of Sun God worship got into the Bible.
oh, no - I am not going to get into that one, either
I have no desire to deliberately goad the religious participants on this thread.
NOT AT TULANE
I said evidence, not proof. You have given no evidence. You haven't given any proof either. All you have given is opinion, feeling or hunch.
I was simply trying to point out the difference between scientific evidence and the Bravo Sierra most creationists expound.
I have several evidences for God. One is the phrase "let there be light" in Genesis. This is an indication that Genesis is divinely inspired, as simple bronze age people would not know about E=mc2 or the Big Bang. This type of "predictive" passage is similar to what scientific theories allow us to do.
To me, science is confirmation of God's existence. To try to convince creationists that the Big Bang or conversion of mass and energy is evidence for God is like pulling teeth.
The biggest evidence for God is Christ's Resurrection. Any Christian that does not put that on the list, is not much of a Christian.
s-The bacterial flagellum is not even irreducible. Some bacterial flagella function without the L- and P-rings.
t-Now, this did not come up in my previous post addressing this subject but for a flagellum to function it needs the pump and motor, not the rings.
It is pathetic you don't even understand what the definition of irreducible complexity means, it is your side's own made up term.
LOL
Talkorigins.org holds the view that since evolution has occurred only fools believe otherwise -- which is fine. I do think they feign an objectivity they don't have, which is a little dishonest.
I am not enough of a math guy to understand that stuff.
When some one is in an accident they say they were thrown into the windshield. That is actually the GT inertial frame of reference view (The car is slowing down but and accelerating (non-inertial) frame of reference). From the persons view (inertial frame of reference) it would be more appropriate to say that the windshield flew against the person.
Seems that the layman is way ahead on this one as Eienstien had to introduce non-inertial frames of reference to explain the GT of relativity, acceleration and gravity.
this is the first time I have heard of chemical and kinetic reactions having anything to do with conversion of energy to mass and vice-versa.
Note to creationists: The above is called learning (also humility, a character feature of Christ that creationists don't display very often)
It is pathetic you don't even understand what the definition of irreducible complexity means, it is your side's own made up term.
OK. Define irreducible complexity.
Rakia, the word for firmament is literally the beating of metal into a thin foil. In the context of Genesis, which is the only place I can find the word used like this, I am convinced it is a description of the bounds of the universe.
It was translated firmament, because no one really knows what that is. Until recently, no one would dream to translate it the way I do.
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