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.
"Good. We're rejecting the direct Darwinian path. "
Pretty much demonstrates YOUR bias. LOL
(The only difference is that Evolution uses public funding and a captive audience to be promoted--other religions are pretty much on their own to promote what they believe).
Uh, right, no evidence against evolution in your arsenal either?
No matter how much you attack evolution for being as void of data as creationism, until you actually come up with data for your position, you have NOTHING.
There are mountains of data supporting evolution. One of the pieces of data evolution doesn't consider is creation of original life. It's not in the Theory.
"bemused that there are folk that actually believe fish can grow arms!"
Bemused that anyone would be so ignorant of what science actually says...
When you explain evolution to your kids or other people in your church, do you lie to them like the above?
In common parlance, entropy has been associated with disorder, but that's not really the definition of entropy. The change of entropy in going from state A to state B is defined to be the heat absorbed by the system in a reversible process connecting the two states divided by the temperature at which the heat is absorbed. An increase in entropy is accompanied by an absorption of heat, a decrease is accompanied by a release of heat. Consider the sun and the surrounding space. The sun continually releases a large amount of heat, call it q, into the surrounding space. The sun's entropy decreases as a result by an amount equal to Q/6000K, since the surface temperature of the sun is 6000K. The surrounding space, at the same time, increases in entropy by an amount Q/3K. Therefore the overall entropy change as a result of this heat release is Q/3-Q/6000, which after some algebra is equal to 1999q/6000. Since Q is very large, this is an enormous increase in entropy. A similar analysis shows that the earth's absorption of solar energy from the surrounding space is accompanied by an entropy decrease equal to 93q/282, where q is the amount of heat that the earth absorbs from the surrounding space, a value typically much smaller than Q, the heat output of the sun. (I have assumed an average temperature for earth of ~50 F) Even in a worst case scenario, which would be assuming that the earth absorbs all the energy output of the sun (ie. Q=q), the overall process would result in an entropy increase of ~0.003Q, which would be a very large increase since Q is very large. In reality, the entropy increase is 1999Q/6000 - 320q/969, which is larger than the case where Q=q, since q is usually several orders of magnitude smaller than Q.
The practical upshot is that the absorption of solar radiation is a process that increases the entropy of the solar system to such a degree that it can be used to drive processes that would result in a decrease in entropy, such as evolution. That's why shubi is correct in saying that the sun makes entropy irrelevant on earth. To a good approximation, the solar system is an isolated system. Therefore, the total entropy of the solar system must increase, but the second law makes no requirement that all parts of the solar system must increase in entropy.
Another excellent explanation. It is refreshing to see so many science geeks on the side of rationality here.
There is also no need for the functions in biological organisms to be restricted to the specific function found in the putative IC organism.
At one time Behe proposed that the eye was an example of IC until it was shown that it could very easily have evolved. He has now chosen flagellum because he believes it will be too difficult for 'evolutionists' to show possible paths for evolution. He is wrong of course.
http://www.newswise.com/p/articles/view/503362/ http://www.talkdesign.org/faqs/flagellum.html
What evidence do you have that evolution is a religion, other than your faith that it is?
you are kidding, I hope
I'd be interested in where you get your dates for TTSS.
Dates on soft parts that don't fossilize are difficult to establish or verify.
Another TTSS paper.
http://www.millerandlevine.com/km/evol/design2/article.html
"you are kidding, I hope"
Ask your average person what would fall faster, a 10lb weight or a 2lb weight. Then ask them which would hit the ground first between a dropped bullet and a bullet fired horizontally.
Now, what do you think the answer to your question might be?
well, that 10lb-2lb question is a trick question.
insufficient data.
assuming air resistance is not a factor, the 10"lb" weight would hit the ground sooner than the 2"lb" weight by an immeasurably infinitessimal amount of time, as the gravity constant is actually a sum of those of the masses in question (earth's and that of the object)
but, yes, I see your point.
sickening.
Unless "there" is the top of the hill.
Take the tyres away and you'll have something you can make heat.
You're not going to start arguing that wheel could have evolved and been put to use by random mutation?
The function is introduced by an observer. The theory of evolution works with no aim.
I'll concede that the theory of evolution -- unlike ID -- is not an empirical science.
How can we be sure about the function or aim of a flagellum? We just observe the results.
Then, five, two-pound weights tied together would fall faster than one two-pound weight .... hmmmm
very, very slightly.
not enough to measure by any method available to science at this time.
it is, like the chemistry error you corrected for me, a matter of convenient shorthand: the Earth's mass (and, thus, gravity, is so disproportionately huge that the difference between the gravitic acceleration of a 1kg mass vs. a 5kg mass is so small it cannot be measured directly.
Actually, it depends on the order. If you drop them at the same time, true. If you pick up the 10# and drop it and then pick up the 2# and drop it, they will fall in the same time.
ok, you lost me.
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