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.
Are you seriously suggesting that, on a purely physical level, there's a fundamental difference between a tree and a human other than a difference in the DNA of each? Both start their development as single cells and proceed according to the instructions in their DNA codes. Are you seriously suggesting that if one of your cells were removed from your body and its DNA replaced with DNA from a maple tree and a new organism cloned from that modified cell, that the new organism would not be a maple tree? (I'm not saying that such a thing is practically possible, BTW, but it's easy to consider it as a thought experiment, although I wouldn't be surprised if such a thing were possible in the very near future.)It has been demonstrated that the DNA of an organism does change over time. It has also been demonstrated that humans and maple trees have over 50% of their DNA in common. Now, if DNA changes over time and differences in DNA are what fundamentally separates one species from another, what would prevent the DNA of a maple tree from changing sufficiently to produce the DNA of a human, given enough time for a sufficiently large change in the DNA to occur.
The astute reader will note that several arguments made by Ichneumon are invalid because so many of his purpoted supporting documents that are listed as links on the WWW in Ichneumon's posts do not exist. His documents supporting missing links are missing links!
That is not the realm of the scientist. A scientist can demonstrate what is plausible and reasonable--but what you want in the province of the shaman. The article was perfectly interesting until the scientist wanted to claim something he could not possibly claim--that not only are the hippo and whale related (we already knew that, btw) but that means--positively--that they were produced by some common ancestor. Kabang, popped out of the same cabbage patch.
That requires huge assumptions and leaps of faith--all kinds of surprising surmising.
The flies have indeed been the material of genetic experiments before we knew what genetics are. If ideal lab conditions, over considerable time and insolation, cannot produce your new Pet, it's not likely that nature can magically produce millions of fortuitous accidents in perfect fortuitous order!.
I don't know how it came about--and I'll admit that. You claim to know, and that is obvious arrogance. Who's the scientist?
Shhh... Don't confuse him with facts until he accepts my bet...
You are fast, got it in on the 4th post.
what can I say, he was the first qualifier I could think of
Yes. A shih zhu is a dog that you could argue is barely a dog. But...a dog still. Embarassing, but your Golden Retriever still have to claim it as kin. When that fluffy thing springs into a new species, let me know. Everyone is waiting to watch.
But this just creates 2 more missing links!!
;)
Your post says " even a bit of lost overlap." When you can repackage the chromosomes in a lab and create a new species, or prove this by showing the world a current day mutation creating a permanent species, then I'll believe it.
Until then, you are just speculating.
I've been reading much on the subject lately. I have required a puppy that is a wolf/dog hybrid, he heeds special care and containment considerations. I don't know the exact wording but I'm sure you'll correct me becaue i know I'll be wrong. Canis lupis is the wolf? Canis canis is the dog? I have read recently that the scientific community have done away with different classifications between these animals because they are all the same species. There was no speciating. Wolves being designer bred by man for certain specific functions did not speciate the wolf into a new species.
My labrador will never be anything other than a spoiled fat pooch who sleeps on the couch when I'm not home. However, consider for the sake of argument her children's children thousands of generations distant, bred by us for intelligence, loyalty, and other desirable physical traits. That superior descendant of the current dog may be sigificantly distinct from the dogs that exist today as to be considered a different species. It might not even be able to breed with contemporary dogs, if any were to still exist that far in the future. Or if so, the children of such a union might be mules, unable themselves to procreate.
I am also interested in another question that literal six day creation brings up. If the earth, the universe and all life on it could not possibly have been created over an extended period of time, but rather all at once, why does the Bible say that it actually did occur over an extended time, rather than all at once? After all, six days and 15 billion years are both extended times, only differing in degree. Why didn't God just create everything without ANY time passing? Why did He create everything in six days and in stages when He could obviously have just spoken the word and everything would have immediately been created? Through an understanding of relativity and big bang cosmology, it's possible to give at least one answer to this question. Relativity tells us that in a reference frame with a large gravitational field, time passes more slowly. That is if two observers measure the duration of an event, observer A who is in a high gravitational field will measure a shorter time than observer B who is in a low gravitational field. Big bang cosmology (combined with conservation of mass-energy) tells us that the entire mass/energy content of the universe was initially present in a very tiny volume of space. This would lead to enormous gravitational fields. Perhaps God, as an observer in this high gravitational field reference frame of the early universe, measured a duration of six days for creation whereas we in our low gravitational field reference frame measure this duration as 10-15 billion years.
Okay, I misworded what I meant to say. No need to talk down to someone becuase they do not go for the evolution fairy tale, "Once upon a time, millions and millions of years ago....."
Thanks for the ping!
True enough.
But the Bible does not tell us HOW the earth was created, or HOW man was created, does it.
Many creationists simply presume that the word "created" means that God snapped his fingers, and everthing was thus.
In the absense of a clearer explanation in the Bible, why is it so hard to believe that God created some creatures over a long period of time.
If God knows the number of hairs on a given man's head, then why does it not make sense that God also guides and forms the biological process in which DNA and genetics change and evolve.
And given that God uses many allegorical type stories in the Bible to get across his point, why is it so hard to fathom that some passages which you consider to be literal are also allegorical.
Are horses and asses the same species? They are close enough to produce viable offspring, yet those offspring themselves cannot procreate. We call them mules.
Bearing false witness AGAIN! Do y'all learn that in Sunday School?
But they haven't quite managed it yet. Still, they send out press releases that It Has Happened, even though...it hasn't happened. Given all the ideal lab conditions, all these perfect opportunities, all these Brilliant Minds--I believe it draws attention to the fact that speciation was supposed to have happened by accident, fortuitously, in perfect fortuitous accidental order. link
Not only that, but you can mix zebras up and get striped "mules."
A coyote can breed with a wolf, a wolf can breed with a dog, a dog can breed with a coyote. This is one species of animal with different variations.
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