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.
Your post #664 is nothing but picking at nits and imagined "holes", and you want me to refute it? Wow! You want me to refute that which you will not post! Sorry, unlike some of the creationists here, I cannot read your mind.
Apparently you can't read or comprehend the written word either. Since you referred to post #664, I think that ought to be the post to refute, don't you?
thanks, see ya 'round.
I think the French Christians were into beheading but more common was burning the non-believers. OTOH, in Vietname they just shot you if you didn't convert.
There are several places in the first four chapters in the Bible that have two versions of the same story, each slightly different. The creation stories are one of those with the first story at Gen 1:1 and the second at Gen 2:4.
The theory is that at one point the tribes of Israel were split politically into two sides. And that both sides gradually developed different versions of parts of the early Bible.
The undeniable truth that the Bible has been altered over time is found in the Dead Sea Scrolls, where ancient versions of current books of the Bible were found that were significantly different than versions of 1000 years later. And, there were multiple copies of some of these, some of them different from each other.
Just as family members in this country 200 years ago didn't all spell their last names the same (example: Neighbors, Nabors, and Neighber might be used by brothers) early versions of the Bible that were hand transcribed may have accumulated errors.
I know this won't sit well with litteralists. But the earliest litteral copies of some of the books of the Bible do not match what you can purchase at the Christian book store.
To those litteralists out there, which Hebrew version was "correct"?
Pretend this is "Hannity and Colmbes" and just answer the question, don't avoid it like Barbara Boxer would.
Not to mention that some passages in the KJV got into it via "notes in the margins" of earlier texts.
ah. thanks.
well, again: I said my piece on that in #813
These are not the result of proofs. These are observed regularities; (which is what "law" means in most scientific contexts). Not all of them are even correct. Bode's Law is false, for example. Newton's laws of gravitation are false.
Are you serious? That was the major issue for the creationists in 2004!
What I said was for the creationists to keep their FALSE SCIENCE out of the public arena.
Maybe you don't realize the consequences of the words you type here, so I'll keep it simple for you. If you keep Creationism out of the public arena, then there is only evolution to discuss.
Other posters have doubted your veracity and integrity. Please consider this when calling others "false witnesses".
Maybe you don't realize the consequences of the words you type here, so I'll keep it simple for you. If you keep Creationism out of the public arena, then there is only evolution to discuss.
I say "FALSE SCIENCE" and you equate it to "CREATIONISM". Are you saying that creationism is false science?
Be careful; you're clearly dealing with a Road Scholar.
;-)
My veracity and integrity are intact. I always post the actual words when I refer to bearing false witness.
There is a good song about Michael the Slob in the new parody CD -- YOU'VE BEEN FREEPED, Vol. 1.
"Other posters" - You mean the ones bearing false witness on me ...
Okay, fill me in. Have you really cut an album?
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