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.
oh, well thank you then. I need to got to learn to utilize all the things you all know how to do on here that I don't. I think there's a Free Republic tutorial some where, right?
Nevermind, I found the tutorial under the "help" section.
ok.
this is the first time I have heard of chemical and kinetic reactions having anything to do with conversion of energy to mass and vice-versa.
That has never changed, even though medicine has raised the mean and median age limits. Once you survive infancy, plague, war, pestilence and bad genes, technology doesn't contribute much.
My father is 96. He survived a hip fracture two years ago and is still healthy. He hasn't required any high-tech medical help, other than the pin in his hip.
I once heard that the "firmament" was a layer of water above the earth that contributed to humans, animals, and plants living longer and being larger.
I don't disagree. Let me go back and check my post. I think I did qualify that was the formula for ideal exponential growth, and that the actual rate will reach some limit due to environmental conditions. I didn't mean to imply populations necessarily grow exponentially, and it is entirely possible of course for growth rates to be zero or negative.
it's a puzzlement.
there are three basic options
1. wild-assed guess, that turned out to be accurate
2. there were enough people to make it to about that age to be observable, and a general paradigm was deduced
3. "somehow, they knew"
I don't buy #1
I lack data by which to decide between #s 2 and 3
Understood. Most HS's and even a lot of college courses teach otherwise.
http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0003691.html
E = mc2 This conversion of mass into energy is the basis of atomic power. Einstein’s special theory of relativity (1905) correlates any gain, E, in energy with a gain, m, in mass, by the equation, E = mc2, in which c is the speed of light. The conversion of mass into energy in accordance with this equation applies universally, although it is only in nuclear reactions that the percentage change in mass is large enough to detect.
You might find this interesting.
http://galileo.phys.virginia.edu/classes/252/mass_and_energy.html
again, thanks. either they didn't teach this in chem 101 at Tulane in '89... or I didn't learn it ;)
I"ve always had the personal belief that, if you step outside a literal interpretation, the parable of genesis sounds very similar to the big bang theory and a brief history of time.
cute.
I loathe relativity - it makes my head hurt.
"an object in motion has more mass than it does at rest"
ok, but which object is actually in motion: the object, or its environment?
Here is a simplifies presentation of physics which shed some light.
ubi est lincum ad hoc?
ah.
hehhehheh
It's all relative. If your twin brother is coming at you at a very high speed, he will weigh more and hit you harder. OTOH, from his reference, you are the big bully heading to him at a high rate of speed.
I'm not kidding, dammit!
:)
seriously, this kinda stuff confuses me.
if an object accelerates away from Earth, to us it sure looks like it is going faster... but from the appropriate outside reference it would appear to be slowing down.
from its own reference, it would notice the acceleration, but once the thrust ceased it would appear to be motonless while the rest of creation staggers past.
this kinda stuff nuts me out.
I would wager they didn't teach it. Chemistry courses are focused on the old law of conservation of mass and that is drummed into the students heads so often even the teachers start to believe it.
That is no mass is lost in combustion because the "lost mass" went up in smoke.
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