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.
There is no religious fanatic so obnoxious as the doctrinaire PhD crank longing for tenure and relevance.
No it couldn't, because your Mustang doesn't replicate itself, which is one of the three necessary conditions for evolutionary processes to occur. (The other two are heritable variation, and selection.)
Duh. Ridiculing a distorted cartoon-version of an opposing position is known as a "straw man fallacy", because it's equivalent to knocking around a scarecrow dressed up to look like Mike Tyson, then beating your chest about how you've defeated the champ...
That also explains why Hoyle's moronic "tornado in a junkyard" analogy (so beloved by creationists) is bogus as well. It's a completely invalid model of evolutionary processes. Hoyle was famous as an astronomer, but as a biologist he was way out of his field and pretty much a complete idiot (he also believed that insects might be as smart as humans, but just hiding it from us...)
Creationists don't deny that animals are related. What we dispute is how they got there.
Your thread falsely implies that a simple copying error accounts for the change between animals. But what your thread doesn't show is ALL of the differences in genetics between those different animals. It's a lot more than just one change.
The differences are better explained by "Common Design". Humans share 50% of their genes with Bananas. That doesn't mean that humans came from bananas or shared a common ancestor with bananas.
I do believe that eventually my dog will evolve into road kill.
Okay, I now believe that humans and human lice have a common ancestor. Talk about a leap of Faith!
If Pope said that, would that make a difference to you?
Just stating the facts, son.
If that bothers you, then *you're* also invited to tackle the part of my post you're trying to pretend you didn't see:
If you disagree, feel free to provide alternative explanations accounting for ALL the mountains of available evidence which explains *all* of the evidence (not just some small corner of it, *ALL* of it) in a way that a) makes actual sense, and b) somehow explains why all the evidence "just happens" to point strongly towards evolutionary processes if in fact they never actually happened. Go for it.We all await the elucidation which is sure to come from your great intellect and massive knowledge on this subject.
Really, the world of science is just dying for further helpful insights from you on these active research topics. Please review the papers in my post and get back to us with your dissertations on them. Since you take exception to my assessment, then surely something *must* be wrong with all of these findings -- please identify the errors for us. Have your mommy explain the bigger words if you need assistance.
And that goes for the rest of the anti-evolution know-it-alls on these thread as well. Come on, folks, show us what ya got. Since you're such self-proclaimed experts on evolutionary biology, this should be a piece of cake for y'all. Now's your chance, go for it. If evolution is the nonsense you claim it is, feel free to point out what's wrong with each of these papers, and what theory you've got that better explains the results and observations (*ALL* of them, not just one or two isolated observations).
Once you've finished with those, I'll post a few thousand more for you, but hey, that should be no problem for you "experts", you've got it all figured out already, right?
There is no religious fanatic so obnoxious as the doctrinaire PhD crank longing for tenure and relevance.
Are you under the mistaken impression that having nothing more substantive to add this petulant whining is going to help make you appear less of a "religious fanatic", less "obnoxious", or less of a "doctrinaire crank" than those whom you accuse who do actual research and support their positions with evidence?
Because if so, it's not working.
WOW! That maple tree is my cousin a trillion times removed!
No faith involved, just ability to analyze evidence.
When any creationist, AIG, ICR or DI actually provides some evidence for their arguments from personal incredulity, I might take the attacks on science seriously.
Until then, it just makes me sad that so many people in this country believe misinterpretations of the Bible that falsely make them think they are superior spiritually.
Because they have. See post #37. Read the links, as well as the primary literature referenced in the links.
I bet it was a really intersting world when birds just "kinda" flew. They just really didn't have it down yet. Maybe birds just kinda sang. That's it! A hummingbird hums because he hasn't evolved enough to know the words yet!
What makes you think you are better than a maple tree?
Maple trees are pretty. They give us various useful items, including maple syrup and they provide homes for various other living things that you are also related to.
Indeed it is. So did you have some sort of point?
So bristling with anticipation of heresy! So righteous! Righteous me a Grant! Of course the hippo is the missing link, it just makes so much sense.
And anyone who'd dispute that the close ties of all earthly life, found in the genetic programming, means that one species popped out of another is evidence of the reader's refusal to wear shoes in winter...
I think that pretty little artist's rendering (which has the horse in the wrong "swoop" of evolution, btw) ought to be recreated in stained glass and mounted on an altar to Hopeless Tenure Track and Our Lady of Perpetual Unemployability.
All very amusing...
"Humans share 50% of their genes with Bananas. That doesn't mean that humans came from bananas or shared a common ancestor with bananas."
Your keen analysis makes it more likely we are related to bananas.
I did not even imply that I might be better than a maple tree. I am just delighted to have discovered we are related!
(he also believed that insects might be as smart as humans, but just hiding it from us...)
Did he believe that creationists are almost as smart as humans, but just hiding it from us?
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