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.
Read it?
Why? What did they change this time??
Darwin said his fossils were there but we didn't find them yet. Stephen Jay Gould says the fossils aren't there, that's why there are gaps in the fossil record. If I told you I did my homework, but the dog ate it, would you believe me? Once again, the proof, is that there is no proof. Evolution is such a fun theory, you can think up any zany idea from microbes on meteors to aliens with a mission to populate the universe and 'science' will back you up; but what happens if you say, " In the beginning, God......
Correct. We still do not know how gravity causes bodies to attract, how electrical charges repel, how mass is converted into energy as the candle burns ...
Now, show me the baby.
Interesting, but you still haven't explained the origins of Ted Kennedy. He's just not natural.
Boy, is he ever missing!!
I would not be surprised if you hadn't even clicked the link I provided. That site does not address the theory of evolution. It addresses cosmology.
The order of creation was told in the Bible thousands of years before science confirmed it.
Thought you would never ask.
The problems with interbreeding are well documented except in Genesis.
...and dogs are still man's best friend.
Weird ain't it?
Are you endowed by your Creator will certain unalienable rights?
You never met my dog. lol
The Kennedy clan is originally from West Virginia???
Nor can we explain why the moon does not spin with relation to the Earth. That one always gets me.
Gravity. Actually it does spin in relation to the earth. It's spin rate exactly matches it's rate of revolution around the earth.
A closed mind gathers no thought.
You sought to persuade through overkill?
No, I was showing a pattern in the evidence.
I know that species are related--but your underlying assertion--"they arose from them"--is just not borne out as "proof" by any such list.
Not all by itself, no. In interlocking relation to dozens of other lines of evidence, yes.
Interesting, indicative, but hardly doctrine.
See above.
I then pointed out what many people do to evo-shamans--
Oh boy, more petulant, pointless namecalling. How typical.
that life dwindles rather than proliferates.
That's not what the evidence clearly indicates, but if you want to cling to your fantasies, go for it.
Species decrease rather than increase.
Please do not present your fantasies as if they were fact, or were supported by the evidence. They are not.
That there were more "then" and less "now" points to a speciation theory that lacks generative potency.
It would if that were the case, but since you're just MAKING IT UP, I'd say that it actually rather indicates the paucity of your own position.
Hint: How many, say, bird species were there ~200 million years ago? Zero. How many are there now? Over 10,000.
Bigger hints:
Extinction, diversity and survivorship of taxa in the fossil recordBiodiversity *increases* over time.
Each new day brings a story of a new "Eve" of our genetic ancestry, and the evos go into High Ritual Mode to worship their new goddess. A few months later, a new Eve and, with no spraining of cognitive dissonance, seems to be as welcome as the previous, abandoned, Eve was.
What are you babbling about here? Give a *specific* example, with links or citations, of an alleged "new story" which you feel should require "spraining of cognitive dissonance", and/or similar documentation for what you mumble is a "previous, abandoned, Eve". In other words, please demonstrate that you even know what in the hell you're talking about.
That the programming of life swaps around could be some very useful information for applied science--
Huh? Again, *try* to be coherent, and give *specific* examples for a change, don't just ramble in a vague fashion and then spew empty platitudes like:
I'd just prefer that the scientists keep their religion to themselves.
Well in that regard, you have nothing to worry about. Evolutionary biology is not a religion. If it *seems* like it to you, then you quite simply don't actually understand it.
I meant nervous in the same way as a sheep is nervous around a drunk Scotsman.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.