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.
You believe that bacteria spread because they evolve resistance to antibiotics and become more fit to survive?
The evolution arguement is such that time explains everything. Yes a man and a maple tree are 2 completely types of organisms, why is this? Because 2 billion years passed by! Isn't it obvious when you notice you are not sprouting leaves and the tree is! Billions and billions I tell you , man!
But they're no longer *WOLVES*.
Is that clue phone ringing yet?
What nonsense. By this "logic", anyone who observed a modern hunter would conclude that humans have always had guns -- it would be ridiculous to imaging generation after starveling generation waiting for them to be invented.
If this change goes on for long enough, you get an animal significatly different than its ancestor.
Developing tolerance is a far cry from speciating. I love that word. Would one who speciates be known as a speciator?
Let me ask you, and I'm serious about this question because I don't know.
Did God simply snap his fingers to create a physical earth, or did he make it in layers?
And did He simply think an adult Adam into existance? Or did he create Adam as an infant, and then nurture him into adulthood by teaching him how to hunt and survive?
What about Eve?
Did God instruct her on how to procreate?
Did He help Eve physically deliver Cane and Abel, and even cut the umbilicle cord, since there were no doctors around to help?
And where did Cane and Abel find wives to marry?
How was it that a city East of Eden was already formed when Adam and Eve were the only ones God created?
I'm serious about some of these questions, and when I read these comments on FR claiming some inside knowledge as to how this amazing universe came into being, my curiosity is peaked and I want to know more.
No, it isn't, but thank you so much for repeating that creationist canard.
Yes a man and a maple tree are 2 completely types of organisms, why is this?
Why are they "2 completely types"? Could we have that in English?
Because 2 billion years passed by!
No, because of the action of evolutionary processes. Time alone doesn't do a lot.
Isn't it obvious when you notice you are not sprouting leaves and the tree is! Billions and billions I tell you , man!
The astute reader will note what goofy "arguments" the anti-evolutionists make, and how they fail to even attempt to address the mountains of scientific evidence on the subject...
Here, Hank, have a cookie. Now run and play with your friends.
I get ya! And the animals that were being hunted developed defenses to protect them from the technological advancements of the hunter.
We'll just call you Mr. Specious.
They are all canines and can still mate. Wolves for all practical purposes are just a wild dog.
I'll say it again, wolves and dogs are the same species, they have exactly the same DNA structure.
I don't see any conflict between science and religion. The Lord created the heavens and the earth and life. But the law as written down by Moses doesn't go into great detail in explaining the mechanisms. The Creator gave us a brain, I believe with the intention that we use it.
Technically speaking, neither. See my post #37, starting at the sentence, "Humans have 23 pairs of chromosomes"...
Chromosomes tend to undergo fission and fusion, but the genetic material doesn't magically "appear" or get "lost", it just gets repackaged.
A wise man once said, "never argue with a fool, bet him money". How much money would you like to wager on your claim?
OK, there's one person who believes that if nobody reports seeing it, then it didn't happen.
For Johnny Cochran & Co, finding you would be "one down, eleven to go".
Two animals with exactly the same DNA structure are identical twins.
They are all canines and can still mate.
So can lions and tigers -- are you going to claim that they're the same species? Warning, this is a trick question for anyone who doesn't know a lot about the relevant biology. Yes, that would be you.
Wolves for all practical purposes are just a wild dog.
What exactly are these "practical purposes" of which you speak?
And no, wolves are not "just wild dogs". Nor are dogs "just tamed wolves".
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