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.
I already handed him one of his heads. LOL
Pay you for the effort? I thought you guys did this for fun. If you want to get paid for it - get on TO's payroll. :)
FR seems to be having server problems.
I have received multiple "an error has occured. the error has been logged" messages in the last few minutes of forumsurfing.
I am signing off for now.
Me too.
You handed me a cut and paste job from talkorigins and didn't bother to cite the reference, Professor.
I wasn't dodging you. I am just not familiar with your hypothesis.
Its a list of transitionals from reptiles to mammals which you said doesn't exist.
I'd say your claims have been totally disgraced.
Well there you have it--the proverbial "purple cow" that noone ever saw! Evolution "scientists" continue taking themselves seriously just for our amusement. :p
Entropy is a catalyst for chemical reactions and that most assuredly could result in change. The question is: "how did such a complex and ordered system arise from goop?"
Maybe there is a good, clear answer, but the simple fact that a sun created heat resulting in chemical reactions does not explain much.
Listen fool, you are not an atheist
I'm well aware that I'm not an atheist, but I never claimed to be either. That's just you doing your usual jumping to conclusions. I don't think you really know what you are talking about because you tend to use hysterical hyperbole and flaming invective in your posts. I think you post that way because you think it makes you a bigger man or something.
Let's face it: you're just an unpleasant person to be around. You are too quick to give offense when none has been offered to you.
My question should not be so threatening to you, a scientific mind would want to know.
Mud, Mud glorious mud
Nothing quite like it for cooling the blood
So follow me, follow
Down to the hollow
And there let us wallow in glorious mud!
I just posted evidence of speciation of reptiles to mammals.
I posted several other links or papers on the same subject on this thread.
Whoa, that's a pretty bold assertion. Care to elaborate? BTW, I do know a little about entropy, so don't hold back in your explanation.
Of course you would! Your interpretation of the data is based on Darwinian assumptions.
Reptile to Mammal Transition: The Reptile-Mammal transition is also claimed to be a complete fossil transition--so complete and convincing that Stephen J. Gould even termed it the "Crown Jewel" of the fossil record. The thinking goes that a major group of reptiles called the Synapsids had a subgroup called the Therapsids which turned into what are called the "mammal-like" reptiles, the Cynodonts, which eventually became true mammals. It is claimed that changing skull bones and locomotio-related morphology show the transition from a reptilian to a mammalian form. Let's take a look at this transition to see just how convincing it really is. Fortunately, some experts have had a few things to say about this transition. The proposed reptile --> mammal transition: Anapsidia (most primitive reptiles) --> Synapsida (Pelycosaurs (Sphenacodonts)) --> Synapsids (Therapsids) --> Synapsids (Therapsids (Cynodontia)) --> early Mammalia --> modern major Mammal groups:
Anapsidia (the most primitive reptiles) --> Synapsidia:
“The ancestors of mammals [synapsids as a group] are identified from the same horizon and locality as the earliest conventional reptile, Hylonomus”.34
Synapsida (Pelycosaurs (Sphenacodonts)) --> Synapsids (Therapsids):
“The transition between pelycosaurs and therapsids has not been documented.”34
Synapsids (Therapsids) --> Synapsids (Therapsids (Cynodontia)):
"Two much more advanced groups of carnivorous therapsids, the therocephalians and cynodonts, appear in the Upper Permian of Russia and southern Africa. We have not established the specific origin and interrelationships of these groups. They may have evolved separately from primitive carnivorous therapsids." 34
Synapsids (Therapsids (Cynodontia)) --> Mammalia
“The transition to the first mammal, which probably happened in just one or, at most, two lineages, is still an enigma.”35
“[we] cannot yet recognize the specific [cynodont] lineage that led to mammals.”34
(34)Carroll, Robert L. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman. New York, Pg. 361, 397, 377, 398, 395.
That list is overly confident and quite open to interpretation The first definite marsupial. Known only from teeth. is not definitive
Another creationist joins the fray. LOL
Do you have any evidence that actually refutes evolution or are you just another misinterpreter of the Bible who ridicules science that he doesn't understand?
LOL OK mister expert on marsupial dentition. How do you know this?
And is there only one objection to that whole list of transitionals?
And if you are not a creationist, why do you care if they have been debunked?
You call that evidence? you truly are a "scientist" in the mold of Al Gore. I bet you think global warming "science" is pretty cool too.
shubi, i haven't read a single thing from you that might indicate you know anything in the scientific realm. You are truly a liability to the real world of science.
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