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.
I think the definition of species works pretty well, but you'll always be able to find exceptions.
You actually believe mammals, such as whales, breathe underwater?
The original sets of animals that God made. The representatives of which Noah carried on the Ark.
Now I know you'd like me to answer whether Noah carried both lions and tigers on the Ark or just representative cats. I don't know that. I wasn't there, and the only record we have doesn't say. But we do tend to think of "cats" as all one kind, as opposed to hippos and whales, which are so dissimilar in appearance, and functionality that we don't.
Haven't had time. I WILL SOON!!! :-)
No.
If man is a product of evolution, he is evolved from what came before him.
The forth verse of Genesis chapter two tells us that the 7 days of creation are the "generations" of the creation of the heavens and earth. (not 7 nights and days but generations for the seas, heavens and land to populate. In that order.)
The first three chapters of the same book make it abundantly clear how separate man was from the rest of creation.
Well then hell, son, go ahead and "easily prove" it false. There's a Nobel Prize in it for you if you can.
"If...."
Just look at the statements of IT COULD IT MIGHT WE THINK It only proves there is NO EVIDENCE
Okay, let me see if I have this straight -- according to you, actual facts gathered from the real world don't count as evidence of *anything*, BUT, the mere fact that some scientists use words indicating their humility actually "proves" (in your mind) that "there is NO EVIDENCE" whatsoever for evolution, period.
Have I got that right? Because if I do -- you don't.
Just a bunch of dead things buried in rock layers laid down by water...just what you would expect if Noah's Flood was real.
I regret to inform you that there are a huge number of discrepancies between what is actually found "buried in rock layers", versus what one would find "if Noah's Flood was real".
But hey, you're not interested in that "evidence" stuff, so I won't trouble you with it.
And THAT mans Genesis is accurate, and evolution is a lie.
Ooooookay... Then why is God telling lies in the genome? Please explain.
...albeit with varying levels of success.
Don't think so. Science cannot shore up weak faith.
sshhh!
What "kind" is this animal?:
The problem with your definition of "kind" is that it tends to fall apart rather easily around the edges.
I think they are just more militantly desperate as they watch their relevence to society and political influence wane.
Insisting on proper spelling and grammar is repressive!
To uneducated morons, I suppose.
my favorite part is when they say "in the beginning there was nothing....and then it exploded!"
Wouldn't the next Republican Convention be interesting if a few of these militant whacko nutjobs attended? It'd be wall-to-wall coverage on CNN and the MSM.
That was because it was written by man.
Doesn't look like it to me.
But, hey, I thought this was a thread about Scuba Teddy K.
Then man was not created in the beginning.
The timing of this new "proof" of macroevolution is very suspect. Funny, just when they need it the most, POOF it appears.
...and then along comes evolutionary science to back up the Genesis story on the order of creation. Man musta been real good at guessin' way back then.
Scary ain't it?
Thought you might like further help with your difficulties over the notion of "Surface Appeal" and the pitfalls that it often has for scientists (those guys who are accountable and have to give demonstrable value for their theories)
Below is a link to a study that explores the connection between poor dental hygiene (something you might associate with the Stubborn Superstitious) and coronary artery disease.. There is a line here that speaks directly to the "surface appeal" pitfall..."Desvarieux stressed that evaluation of the two conditions occurred at the same point in the lives of those studied making it impossible to ascertain at this point "which comes first, the periodontal disease or thickening of the carotid artery."...
You see, it would be an easy assumption to make--that if you take care of your teeth, your heart will be better off. But it may well be a corresponding condition, or a connecting genetic predisposition--not a cause-and-effect situation. The doc has to be careful about making a big noise over this possible discovery, since we'll shortly know whether she's right or wrong (accountability).
Just thought you might like to see what science looks like, when it's really working.
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