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.
Then, examine why it is so important for you to think that you are right, and that you find it necessary to belittle others. Perhaps you just haven't evolved as much as other decent folk. Maybe you should consult a Therapist. I have to go now, hopefully you get the help you need to overcome your personlity disorders. Good luck on becoming a fossil someday.
No.
Sure sounds familiar to my digital ears, and the Great Speciator has been strangely quiet...Surely you're not hiding under a new name after forbidding me to post to you?
Then that's yet *another* thing you're wrong about.
Why would anyone want to choose a nomdeplume of such a depressing insect?
Because it's a fascinating one.
We can.
When Darwin discovered evolution, did evolution get upset and decide to stop in it's tracks?
No, but a lot of folks decided to start asking some really lame questions...
Yes! I laugh at your pomposity! HAHAHAHAHAHAHAHA
</creationism mode>
"Senatus Bloatus"
What I see here is a post completely devoid of substance. "I know people(anonymous) who laugh at (unspecified) stuff (for no reason given)." Cool.
Relatedness of life is an easy thing for even a Superstitious mind to manage--it's the insistence of "See? I'M RIGHT. IT ALL HAPPENED THIS WAY." Well, that's not acceptable and it is not scientific. You not only do not know how it happened, but you'll likely never know. You'll only see bits and pieces of that whole picture, some of which is illuminating, and some that is just a veil.
I read a good bit of lit in the pharm industry, in which I invest. Evo scientists would do well to learn to qualify their language with a little humility as the writers of new medicines do. Certainly, people who invent life-saving meds do not boast extravagantly of "Creating New Species" when they cannot and have not. Those pharm scientists also run the risk of killing people with their errors--they are accountable--they are not Voodoo Speculators. When you compare the cautious language of those who have to account for their assertions with real lives, you quickly see the difference between a Scientist and a fabricator of fairy tales.
Buy a clue. Evolution does not cover the origin of life. It only details how life changes over time. One need not know the origin of the atmosphere to study the weather.
Depends on the environmental pressures in the future. Also, humans are likely to engage in genetic engineering on our own species in the future to adapt humans to low-gravity environments and the like. We'll be responsible for our own evolution in the future, most likely.
Well here you go then. Photosynthetic bacteria.
I think maybe you need to fix your computer, or rethink what the internet is.
I tested 20 links and two came up blank. There are all kinds of possible reasons for a link being down other than its being invalid. It is impossible to give a list of links and be certain that all of them will work all the time.
An awful shame--all those fascinating creatures, now extinct.
I am. :-)
because from what I can see, your chances of convincing your chief interlocutor and his smirking friends of the soundness of any results of evolution studies are about the same as convincing them that they need remedial thinking lessons.
True, but every once in a long while one does surprise me. But I'm not writing for their benefit, I'm writing for the benefit of the lurkers who might be "on the fence". Plus, I'm always fascinated by seeing the many ways in which "certain folks" can find to dodge.
Willful blindness is almost always an incurable malady.
Or as the old saying goes, "you can't reason a man out of a position he didn't reason himself into in the first place."
There's also usually a strong measure of this involved:
"I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives."
- Leo Nikolaevich Tolstoy (1828-1910)
Dogs are an interesting example. We've been messing with their characteristics for only a few thousand years and we already have breeds, such as the chihuauhua and Great Dane, that cannot breed with one another naturally. Continue this trend for hundreds of thousands or millions of years and the descendants of chihuahuas and Great Danes will most certainly be considered separate species of animal.
That would probably raise the level of conversation in your house.
This happens to be unnecessary because "creation scientists" have (if implicitly) conceded the point that DNA can be repackaged and chromosome numbers change within a single "created kind".
Although creationists frequently cannot decide the boundaries of kinds, even in the case of the "clearly separate" categories of humans and apes (see the chart I posted above), there is at least one case where there seems to be universal agreement. Horses, the living members of the Family Equidae, are commonly cited as the paradigmatic example of a "created kind". Yet look at the chromosome numbers:
Ah, well I can't find a simple chart, but suffice to say that there are (IIRC, and not counting those of hybrids) at least ten distinct karyotypes among the Equids, with 2n chromosome numbers ranging from 32 to 66.
ROFL! Sorry, but that doesn't even *begin* to address the actual challenge. If that's the "best" you can do, don't bother.
Simple.
Simple things for simple minds.
Life was created, and life forms were created intact and complete.
You still haven't attempted to tackle the challenge. You'll need to explain how/why, for example, your scenario would cause the specific pattern of shared endogenous retroviruses which is found in comparative DNA studies. (Hint: It wouldn't, unless the "creator" was INTENTIONALLY BEING MISLEADING and trying to "fake us out" into falsely *believing* that evolution had occurred when it hadn't. Are you sure you want to go there?)
And that's just one of literally MILLIONS of evidenciary observations your "alternative" scenario to evolution will have to account for. You've got your work cut out for you.
Changes that occur within species is nothing more then genetic variation, not evolution.
Not real clear on the definition of the word "evolution", are you?
And that is good science.
How can your simplistic "explanation" be "good science" when it doesn't explain the evidence, makes no testable predictions, and is not falsifiable?
Come back when you have more of a clue.
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