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.
No joke. Few Christians had any problem with Darwin until certain populist politicians, and later Internet shysters, decided they needed something new to grandstand about.
So, you are claiming that acting haughtily and cutting people down with disparaging remarks is something that you were prompted to do by the Holy Spirit?
Or penecillin and anti-biotics, the greatest achievements of the 20th century. Do we know the names of those who get credit for this? I don't, but I know the name of Darwin, the founder of the Religion of Evolution.
HEY! No pictures of Tikrit Teddy here!
Skeletons have been unearthed which are clearly those of some variety of whale, yet they have a vestigial pelvis that contemporary whales do not. Animals change over time. We can directly observe this in drug-resistant bacteria.
Bring it down from the mountain, prophet! Sprinkle some of that holy water!
If you can't produce a new fruit fly under ideal conditions after hundreds of years of geographical isolation, laboratory selection out for type, tens of thousands of opportunities for mutation...and then this last attempt by the U of Chicago scientist to delve into the dna with super-microsurgery...if you can't manage one little fly, who's ignorant?
Right! A crocodile adapts to live in salt water, but it is still a crocodile, it does not "speciate".
Eh, ya got a little self righteousness in my eye there, buddy. :P
*wipe wipe*
The idea that animals change over time doesn't invalidate the fact that we have dominion over the earth. Non sequitur?
Your point is very damning. Such as life just happened, man with all is arrogance and intelligence cannot make life "just happen" in the laboratory on purpose. Man cannot make evolution just happen. okay, there's that whole dairy cow thing, and that wolf and dog thing but they did not "speciate" when the were designer bred, wolves and dogs are the same species.
No, that's my point. It's impossible to speculate without more information. To give an example, if the earth in a million years has giant pools of mercury rather than oceans of water, life, if any survives, would look different than it does now. It would be reasonable under this scenario, for example, to speculate that organisms that don't require water would be found. (What the physical form of these organisms would be is difficult to determine.) It would be reasonable to speculate that any organisms that would live in the mercury oceans would have body shapes that are more streamlined than fish and aquatic mammal are currently. Prediction is a tricky thing, however. We currently can't predict the weather with any degree of accuracy more than a day or two ahead of time. That doesn't mean we don't understand the mechanisms of weather, however. You could be expected to reasonably speculate about your great, great, great, great grandchildrens' hair color, but you would probably be wrong.
You are fast, got it in on the 4th post.
If animals, or rather the genes of families of animals did not change over time, there would be no drug resistant strains of disease. Do you deny that drug resistant strains of bacteria exist?
Sheep were breed in ancient times for twinning, and now most sheep twin if the shepherd knows what he's doing. Domestic sheep must be shorn regularly, because they have been bred to the point that they cannot naturally shed their fleeces--and will die from suffocation after years of being unshorn. All still--the sheep.
We see the chihuahua, and the Great Dane. All dogs.
Speciation is the question here--not that animals change.
Argument by name calling
"The mind *boggles* at the ability of the anti-creationists to MISS THE POINT so badly. "-Ichneumon
Finally, We anti-evolutionists agree with you 100%!!!!
We can prove you wrong quite easily, actually.
But don't let the facts get in the way of your smugness, since you seem so pleased with it.
But, wouldn't you think, since we've been playing with fruit flies for about three hundred years...
Okay, I'll bite -- exactly who do you hallucinate has been "playing with fruit flies for about three hundred years?
in Beijing, Detroit, Florence, Terra Fuego...and generations could well be in the hundreds of thousands.
Fruit flies don't have a life cycle *that* fast, m'dear... One day in the egg, seven days as a larva, six days pupating. Minimum generation time is thus about two weeks. And although people first dabbled in fruit fly experiments in the early 1900's, Drosophila didn't really take off as a test subject until after the discovery of DNA in the 1950's.
Nor was "creating a new species" the goal of these experiments, but even if it had been, that means that there have only been around 1000 fruit fly generations, total, under experimental conditions. That's a considerable amount, but hardly enough to allow the evolution of fruit flies into, say, non-flies, as you so ridiculously demand to be shown.
Do you likewise foolishly insist that geologists show you a brand new mountain range developed from flat land via plate tectonics in the past 100 years?
Wouldn't you think we'd at least get a New Fly, if the theory has anything to it at all?
Oh, you mean like this?
Hint: Ordinarily, fruit flies have only *two* wings...
It'd sure bolster your religion and its dogma--
And "it'd sure bolster" your credibility if you learned why science is not a "religion" and does not rely upon "dogma", it relies upon evidence and experimental results.
which may be why so many scientists claim to have Given Life when they clearly have not.
What *are* you babbling about here?
I know you think any anti-evolution argument is bearing false witness, but it is not.
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