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.
Malthus agreed with you in theory and developed the whole "we are going to overpopulate" idea.
actually, as a deceleration is in kinetics considered an acceleration, the winshield is changing vector faster than the passenger, so the winshield IS being thrown at the passenger.
Note also that 99% of the websites discussing combustion and nuclear energy will not say that either. If fact, probably 90% of them will say that combustion conserves mass unlike nuclear energy which converts mass to energy.
But once again, think of what we have. We have mathematical models of "fictitious" particles, atoms, molecules and how they are held together.
In combustion, we are changing the "binding energy" of the atoms in the molecules resulting in an energy release.
In fission, we are changing the "binding energy" of the nuclei of the atoms resluting in an energy release.
In fusion, we are changing the "binding energy" of the nuclei of the atoms resulting in an energy release.
That "binding energy" is what holds the particles together. We talk of Nuclear energy, we talk of chemical energy. Only because the chemists have beat it into our heads, do we find it hard to say that combustion converts mass to energy.
(Examples above all considered to be exothermic reactions)
"I"ve always had the personal belief that, if you step outside a literal interpretation, the parable of genesis sounds very similar to the big bang theory and a brief history of time."
That is my conclusion after 15 years of study of the Hebrew in Genesis 1.
I think that is what I said. That would be the statement in classical physics but people, unknowingly, use Einstiens non-inertial reference to say "the person was thrown into the windshield.
If it stood alone, I might agree with you. But combined with all the other things in Genesis that make modern scientific sense, I can't agree.
I agree that pagan beliefs are in the Bible in some places.
In fact, much of the Old Testament is about God trying to keep the Israelites from worshipping some other god/gods. The first two Commandments deal with this problem.
aside from the aforementioned 120 year lifespan, what else?
(remember: no dodgy interpretations - you can interpret things the way you want, but I can do so as well)
"you will have no other gods before me"
that has always been a matter of fascination: why not simply "there are no other gods"?
He allowed for the married man who must always worship his wife or forever be doomed to hell on earth.
hehhehheh
"Both the man-made world and the biological world are full of examples of "Irreducible Complexity." That is, systems or machines which were designed with a number of specific parts "wherein the removal of any one of the parts causes the system to effectively cease functioning."
Here is your definition. It was falsified before Behe published.
"Intelligent design proponents are now gaining a strong foothold in one of the last remaining towers of evolution theory, biology."
I really thought the above passage was a hoot. The ONLY tower of evolutionary theory is biology, and IDers don't know what that says, either.
Are you actually so ignorant of evolution to suggest that it proposes that the first life form had the "instructions" for creating all divergent species existing today in it?
Are you so ignorant of genetic coding as to suggest that simple life forms can develop into complex life forms without any sort of "instructions"? If it were possible, I'd like for you to explain how that happens.
so even if evolution required what you claim (and it does not), it still wouldn't matter how that first life form came into existence, so long as it did.
It only doesn't matter to people who can't grasp the fact that how life came into existance is the very heart of the debate. For the creationist, the knowledge that God created all life as we see it today settles the issue. But for evolutionists, they have to deal with the lack of transitional forms in the fossil record, the lack of evidence for 'ape-men,'. The failure to answer the question regarding if we evolved from apes, then why are the apes still here? So by dispensing with the "where did life begin?" question, evolutionists are free to invent any sort evolutionary tree.
Are you really so ignorant of evolutionary theory to believe that we evolved from apes or are you just a troll injecting the rediculous into the argument for disruption's sake?
I do not need scientific evidence to know there is a God, all that is required is Faith. Humans are able to have this, animals and plants are not.
Even today it is difficult to confirm the age of people who claim to be more than 100 years old.
yes - it is hard to find someone who was around when they were born for a corroboration :)
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