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.
We have had at least two YEC'ers say that they hold these views inspite of differing views by their pastors and Churches.
Please provide us a link to a science website that says anything remotely backing your ridiculous assertion.
Ah, another bad tempered evolutionist heard from....for your information, you're referencing the wrong post...so follow the thread from the top and then you'll be informed. Besides all that, I wasn't talking to you so take your vitrol elsewhere.
Please provide us a link to a science website that says anything remotely backing your ridiculous assertion.
I asked whether you were ignorant or a disruptive troll. Only one or the other would paste such cr@p.
The vitriol and nastyness has been exclusively coming from you.You are completely unable to maintain a civil discourse with people you disagree with. That being the case, you need to go elsewhere since you are unable to handle conversations where others do not share your viewpoint.
Please provide us a link to a science website that says anything remotely backing your ridiculous assertion.
Hard to do since I've made no ridiculous assertions, only replying to them.
We keep hearing that man-from-ape stuff 10 times a day. It is false and you are either ignorant or disruptive to post it.
I will refer you back to the two rediculous statements:
But for evolutionists, they have to deal with the lack of transitional forms in the fossil record, the lack of evidence for 'ape-men,'. The failure to answer the question regarding if we evolved from apes, then why are the apes still here? Typical statement made by those that oppose evolution but are ignorant of evolutionary theory.
So by dispensing with the "where did life begin?" question, evolutionists are free to invent any sort evolutionary tree. Typical derogatory statement made by anti-evolutionist that has no basis but is just meant to inflame and distort the science and the people that practice science.
It is false and you are either ignorant or disruptive to post it.
It's not, so get used to it. If by disagreeing with you is considered disruption, so be it. You'll get banned for name calling long before I get banned for disruption.
Are you serious?
When you used the phrase earlier about
"What were the pillars made of that the fellows that cooked up the Bible thought the earth was supported by ..."
That phrase and other such little jabs at the Bible during this thread led me to believe that you were one of those who might summarily dismiss the Bible as a source of anything worth learning. I apologize if I was wrong, but that was my perception.
Not a literal meaning? What would you call the device that takes the flow of acid from outside the bacterium to the inside or an agent that imparts motion?
As a creationist, I am sure you have trouble separating the two . . .
As someone who takes the Bible seriously, I've tried to be gentle in pointing out the silliness of your posts. Perhaps I've failed. So, being as how you are a minister, I will leave with this bit of scripture.
Either you make it up, or you get it from creationist websites.
Of course I made it up, VI. And the responses that you and Wild Turkey gave are priceless and got a lot of laughs here.
So sue me.
My problem is not with the Bible, but the fanatics that insist that they only know how to interpret it.
I've been told that there are disrupters here that post nonsense just to try to get the science folks banned. You have "warned me" that I would get banned. 2+2=4.
He warned me a few posts ago that I would get banned. Maybe that is his game.
Wow, the B is not even close to the W on the keyboard, but I still called you BT, sorry. I type too fast, but that's weird...
It's too late. I was still trying to figure out what BT was an acronym for ...
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