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.
So based on your response in #37 should we mark you down as "Undecided" or "Ambivalent"?
.
;-P
I'd give my right arm to be ambidextrous.
Festival of creationoid hysteria placemarker.
I don't doubt that there is debate on the topic among biologists. This sort of wrestling is what science is all about.
However, I am intrigued by the idea that the existance of the domesticated dog is somehow evidence for the fixity of species and a disproval of evolutionary theory. Here we have an animal which, though similar to wolves, has obvious physical and tempermental differences from wolves. Pretty much everyone acknowledges that contemporary dogs were bred from wolves. Pretty much everyone acknowledges that over several thousand years time men molded wolves into what we wanted them to be. Since these traits are determined genetically, it stands to reason that we have changed their genes over time. In my opinion the existance of domesticated animals supports the ideas that the forms animals take are *not* fixed, but instead can and do change over time. Were this not the case, wolves would have remained wolves and not have been bred into dogs, aurochs would not have been bred into cows, grass would not have been bred into wheat, and strains of streptococcus and gonorrhea bacteria would not have been bred (unintentionally) into penicillin-resistant varieties.
Yes -- which part were you having trouble understanding?
When you can repackage the chromosomes in a lab and create a new species,
Define "new species" as you are using it in this sentence.
or prove this by showing the world a current day mutation creating a permanent species, then I'll believe it.
Why "current day"? And define "a permanent species" -- as opposed to what, the temporary kind?
Are you sure you know what you're talking about?
Until then, you are just speculating.
No, actually, I'm not. But I wouldn't expect someone like you to understand that.
You, however *are* merely speculating, since you are forming your opinion without even a superficial knowledge of the vast amount of evidence which is available on this subject.
Come on, son, take me up on my challenge in the earlier post -- if the vast amounts of evidence accumulated on this topic of biology (a tiny fraction of which is presented in that post, but it'll take you *months* to read just that tip of the iceberg) *isn't* actually the overwhelming support for evolutionary common descent that it certainly appears to be, then *where* exactly have all those myriads of biologists been mistaken, *what* actually explains the full body of evidence better, and *why* would your non-evolutionary alternative explanation end up "accidentally" causing all that evidence to only *look* like ironclad evidence for evolution?
Answer the question. Now.
Or admit that you're "just speculating" and don't really have any idea what in the hell you're talking about.
What I don't understand is, after the dinosaurs were wiped out, why didn't evolution make some more of them. Or is that in the works and we just have not waited long enough. Or, did evolution 'decide' to make some different stuff this time around.
Are wolves and dogs the same species? Yes or no?
Yeah right! And if life began in the primordial soup billions of years ago has it happened again since? was this just a one time thing?
One of the key events seems to have been a point mutation in the FOXP2 gene.
You guys get funnier the more you speak!
Are you dodging giving an answer MR educated intellect? It's a very easy thing to give an answer of yes or no. Is the wolf and the dog the same species?
So much of this debate is a Show Trial for Smartypants, which makes the "evidence" suspect from the start.
They are mistaken right from the start because evolution never happened across phylum boundries.
Simple.
Life was created, and life forms were created intact and complete.
Changes that occur within species is nothing more then genetic variation, not evolution.
And that is good science.
I'm sheepish to provide examples here, but hey....look at the platypus. ;^)
Really? Which ones?
His documents supporting missing links are missing links!
That joke was just barely funny the first time. And now you've used it, what, three times now? You're going to feel pretty silly once you sober up.
Willful blindness is almost always an incurable malady.
Naaa...just looking for evidence of something that is classified as both plant and animal.
And monkies are likely to fly out of my butt! What an evolutionary masterpiece of an event!
Wow, so much digital ink--so much ego! You have a lot at stake, here.
I don't have time to click all those links but,I'm certainly impressed!
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