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.
So... you're an atheist baiting us with ridiculous assertions that only a creationist with a grammar school science background could think of? haha, big joke.
You're not an atheist too?
I didn't realize you were an atheist.
I like this one:
"Most people, sometime in their lives, stumble across truth. Most jump up, brush themselves off, and hurry on about their business as if nothing had happened." - Sir Winston Churchill
"When a man who is honestly mistaken hears the truth, he will either quit being mistaken or cease to be honest.
Cool! Thanks for the link, I hadn't heard of that one.
You dissed yourself. Your logic remains faulty. (and I agree, you are hilarious)
Well, then, a problem could arise there because there are a number of organized religions whose organization itself derived from certain interpretations that they all adhere to. However, it has been my experience that those Christians I meet are generally pretty tame and not fanatical in-your-face types that show up here. Most in my church believe in Noah's Ark, the flood, and a young earth...but they are not radical about it. It is not like it is a requirement to worship there. Most of our evangelical work is done through matters of the heart and spirit. Noah's Ark, the flood, and a young earth are not matters that are even discussed much. Yet because we have young earth believers in our congregation, we would be labled as nutcases and whackos by many who have posted on this board. Even though our Doctrine about Christ is acceptable and widely held as correct.
In Arabic this is sometimes referred to nunation. An N jumps from the end of one word to the first of another or vice versa, but that's a whole nother story.
Richard Rhodes is pretty good as a writer; he wrote "The Big Red Bomb."
Bamford's "Body of Secrets" isn't bad either.
Sometimes, trying is just not good enough ...
A simple man believes anything,
but a prudent man gives thought to his steps.
(Pr 14:15).
Of course everyone knows that springs couldn't have been designed without being designed as a part of a mousetrap, since there's no other purpose that springs can be used for. Same applies to metal rods, pieces of wood, etc. That's the downfall of many of these irreducible complexity arguments. It is possible that all the parts evolved for some other function and only later became incorporated into the system that is claimed to be irreducibly complex.
If you have facts, Faith is not necessary.
Sorry if I make your headache worse, but... Special relativity actually implies that the mass of an object is not an absolute quantity. That is the mass of an object depends on its reference frame and the reference frame of the observer who measures its mass. The mass of the object in a reference frame in which that object is at rest is called its proper mass, or more commonly (and surprisingly enough) its rest mass. In a reference frame in which that object is moving its mass will be measured to have a larger value than the rest mass. This is a consequence of the fact that, at least in ordinary circumstances, there doesn't seem to be any such thing as negative energy. So the answer to your question, based on relativity theory is that both the object and its environment are moving. If you are moving with respect to the environment in the same direction as the object and at the same speed, you will measure the rest mass of the object. If you are in any other reference frame you will measure a higher mass.
That's probably because, as an approximation, the law of conservation of mass holds pretty well in chemical reactions. You wouldn't be able to actually measure the mass loss in any reaction. This law is a simpler one to teach chemistry students than the law which actually holds. The law of conservation of mass (as well as the law of conservation of energy) has been superseeded by the law of conservation of mass-energy, but there's really no reason to introduce that distinction into an introductory chemistry course.
You mean that whole series of fossils that some creationist claim are "just apes" and other creationists claim are "fully human." I would think that disagreement among creationists as to whether these are apes or men would be sufficient evidence that we have something in between.
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