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.
My little book? I have thousands of books. I know, you mean the Bible. Do you believe there is a God? If not YOU must be the most Supreme being, being a man, right? It only takes some mere decades of being on this earth, two of which are spent in childhood and adolescence ( I have to stop and look words up, mis-spell just one word and everything you say is discounted, "He's illiterate!" "She's a witch!" talk about your Dark Ages), to discover they are so intelligent they can discount thousands of years of history and knowledge acquired by others.
I don't know, Hindu-Arabic numerals were a great advance in mathematics as was algebra. Where do you think that these were developed? (Hint: Al gebra was the original name in the language of the people who developed it) Who do you suppose developed the science of astronomy to the point where really accurate calendars were possible? (Hint: they did so before Columbus and didn't live in Europe, Asia, or Africa) Who developed geometry, trigonometry, and many of the philosophical foundations of modern education, not to mention the form of governement that we consider to be the most desirable today? (Hint: Zeus might be pretty mad at you if you can't figure this one out.) Last time I checked, the Arabs, the Mayans and the Ancient Greeks were not Christians. This doesn't even mention the Chinese who made some pretty big advances in material science (paper, gunpowder) or early civilizations who developed written languages and agriculture.
Mathematics may be very useful while considering evolution or any other theory regarding the past.
For example: The number of ancestors required for me to have exist doubles every generation into the past, this must happen. 2 parents, one generation back, 25 years. Eight great-grandparents, 3 generations back 75 years.
20 generations back I must have had 1,048,576 grandparents, this is all in one generation of time,500 years ago.
30 generations back, 1,073,741,824 grandparents, of course evenly half men, half women. 750 years ago.
35 generations back it required 17,179,869,184 grandparents for me to exist as I am today. At my 25 year per generation average this would have been 875 years ago.
Now, every generation requires my grandparents to double, a generation can only be so long. Of course there were not 17 billion people on earth, let alone all of European descent 875 years ago. I have thoughts on this, what are yours?
at some point, your (and my, and those of everyone else) ancestors start to appear in the family tree at multiple loci, as the divergent branches cross each other.
this is not a problem.
Still I need 8 great grandparents discounting everyone else. 20 generations ago I, myself had to of had 1,048,576 grandparents whether they were shared by many others or not. A biological fact, right?
no, fellah. read again.
your family tree crosses itself many times.
meaning that some of your ancestors are represented as "20th-great grandfather" through multiple lines, essentially creating "virtual" duplication where no real duplication has occured.
shall I generate a chart to graphically explain this process?
No, I understand, like 2 and 3rd cousins marrying they have the same gg-ggg-grandfather. But still.
It seems to me that your argument would rule out the possibility that we all are decendants of Adam and Eve. After all, to go back that many generations, there must have been an astronomical number of people, not two.
but, still, what?
beyond second-cousin, the genetic issues are nil.
this doesn't even get into the level of distal-family "inbreeding" concommitant to populations isolated by geography, tribalism, or other factors.
Okay, I said I had my thoughts on it. The world is not as rigid as my set scale, as you help point out. But could it be such a change as to drop my 20 generation ancestors from over a million to mere thousands? Must've been.
I did not put it forth as an arguement. And as you see, the answer to my speculation rules nothing out.
It is believed that the "zero" originated in India but how much influence was Hindu and the details are lost.
What is your main problem with the theory of evolution? I just cannot believe you accept it whole hog.
Now we are disputing the facts concerning evolutionary science. What is about all this you feel threatened by? Do you have very much invested in your desire that there is evolution?
yes.
if you are truly interested in the topic, I'm sure you can find a reputable geneologist who can show you how often the crossings occur, and at what point they become essentially inevitable, using documented lineages of families rather than logical speculation.
I think you need another roll of aluminum foil ...
You need to go talk to your minister. The tin-foil is not working.
.......This PROPOSAL places whales squarely within the large group of cloven-hoofed mammals....."
(Emphasis MINE)
Either it's fact or it's a proposal. Why are science writers so ignorant?
I have no "main problem" with the theory.
I have some complaints about some of the details, the persistence of reliance on morphologic similarity, an institutional bias in favor of graduation rather than paradigm shifts, etc... but these stem from human impatience: in time, the amount ofd data available, andour understanding of those data, will correct these minor flaws.
Your math is way off. You forgot the extensive in-breeding ...
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