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, I am the spoon that stirs the contents of what is inside the pot and the kettle. :-)
It is unfortunate the your blind agenda and the fundamentalist agenda have turned a very intersting field of science into a political issue.
Oops! Sorry, that's redundant (poor proofreading). I should've deleted "the contents of" and just left "what is inside" or vice versa.
The first equation shows an increase in mass as calculated by the energy converted.
The second equation shows an increase calculated from the change in velocity of the particles.
This link definitely gives a whole new meaning to my favorite nickname for him...."Teddy, the Whale".
This equation serves as a way to calculate how much mass is converted to energy or energy to mass in a reaction.
However, to answer one of your specific questions, we can directly observe the evolution of bacteria. Since the use of antibiotics has become widespread, bacteria have steadily and routinely developed resistance. Drug-resistant strains of bacteria is a fact. The theory of evolution explains this fact. Creationism does not. The emergence of drug-resistant strains of infectuous organisms can now be scrutinized in great detail with modern DNA sequencing technology. We can now record an entire bacteria genome in computerized format and compare it with those of other bacteria in a short amount of time. Comparitive genomics is a relatively new field, only recently made practical due to advances in computing technology. In bacteria, due to their extremely rapid life cycles, we can objectively see their evolution taking place. We can quantifiably measure how fast they pass their traits down to their descendants. We know they have the same building blocks of life as larger animals like us.
Thanks for the links and info. I've seen many examples of "proof" that end up being inconclusive - perhaps this will be different. See you around.
AAAAAIIIIGH!!!
You keep saying this about me and I'm thinking this about you. You never did answer my question about peer review and you missed the whole point of irreducible complexity.
You have already refused to read the facts several times,
You haven't presented any facts.
The one Behe was referring to was.
I carry several mild mutations of which I am aware.
- one causes broad spectrum photosensitivity
- one causes my connective tissue to be a bit more elastic than is normal. a more severe penetration of this allele would cause true hyperflexibility in the skin and joints.
- one causes early development of mild arthritis
- one prolongs post-pubescent physical maturation. I stopped getting taller three years ago, at 33 years of age. I am still getting broader across the shoulders, and will probably not reach my peak muscle mass until my early forties.
- one causes male pattern baldness
- one very peculiar and seemingly quite rare and utterly pointless one causes immediate, involuntary, and violent aversion to exposure to carraway seeds. This is not a histological reaction (not an allergy) but an immediate neurological reaction set, including violent nausea. I have not yet met or heard of anyone outside of my bloodline having this trait.
It is very likely that I carry several others of which I am unaware.
it is almost 100% likely that you do as well.
Why should we assume they evolved this way and were not created? Now, your answer is going to be able to be distilled into something along the lines of "you're stupid" or "you're a religious fanatic incapable of imagination" which I suspose is the same thing as "you're stupid"
For the record, I don't reject the idea of man and ape having common descent but there is nothing wrong skepticism about it either..
We don't have to find the common ancestor,
Nor do we have have to duplicate the process in which this common ancestor could evolve into chimp and man -- which is convenient.
are you sure you aren't Lazamataz's evil twin?
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