Research team claims fossil-only study of placental mammalian evolution time frame is wrong

Jan 15, 2014 by Bob Yirka report
An artist’s rendering of the hypothetical placental ancestor, a small insect-eating animal. Credit: Carl Buell

(Phys.org) —A team of researchers from the U.K. (led by Mario dos Reis) is directly challenging the results of a study conducted by another team (led by Maureen O'Leary) that concluded last year that placental mammals came to exist after the demise of the dinosaurs, not before. dos Reis et al maintain that their study using what's known as the molecular clock, proves that placental mammals came before the demise of the dinosaurs. They have published a paper in the journal Biology Letters describing how they came to their conclusions and why the other team is wrong.

Placental mammals are a kind of mammal, they deliver babies rather than eggs, and include all mammals except marsupials—that much biologists can agree on. When the first such mammals first evolved is still subject to fierce debate. The problem comes down to how those seeking to find the definitive answer go about it. O'Leary et al claim the only proven method of dating timelines for organisms is by studying the fossil evidence—no fossils of placental mammals have been found that predate the time when the dinosaurs died out. dos Reis and others on his side shoot holes in that line of reasoning by noting that it's eminently possible that some organisms, such as placental mammals, existed for which there is no . Those that agree with him believe that using what's known as the molecular clock is a much more accurate way to construct timelines. It's based on scientific studies that have shown that mutations in the cells of organisms mutate at a constant rate. Thus, to determine when a type of organism first originated, researchers study its genes, discern its mutation rate, and then count backwards to calculate its likely origination date. In the case of placental mammals, dos Reis and his team say using this method (they studied 36 mammalian genomes and included fossil evidence) shows that existed at least as far back as 108 million to 72 million years ago—which of course means they were there when the dinosaurs roamed the Earth.

In their paper last year, O'Leary and her team acknowledged the work of those that rely on the , but noted that calculating mutation rates is still somewhat of an art, rather than a pure science, and thus, conclusions based on them cannot be taken as fact.

Neither side can prove they are right of course, the only way both sides will ever agree, it appears, is if a fossil can be found that belonged to a placental mammal that lived before the demise of the —until then, the battle will likely rage on.

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More information: Neither phylogenomic nor palaeontological data support a Palaeogene origin of placental mammals, Biology Letters, Published 15 January 2014 DOI: 10.1098/rsbl.2013.1003

Abstract
O'Leary et al. (O'Leary et al. 2013 Science 339, 662–667. (DOI: 10.1126/science.1229237)) performed a fossil-only dating analysis of mammals, concluding that the ancestor of placentals post-dated the Cretaceous–Palaeogene boundary, contradicting previous palaeontological and molecular studies that placed the ancestor in the Cretaceous. They incorrectly used fossil ages as species divergence times for crown groups, while in fact the former should merely form minimum-age bounds for the latter. Statistical analyses of the fossil record have shown that crown groups are significantly older than the oldest ingroup fossil, so that fossils do not directly reflect the true ages of clades. Here, we analyse a 20 million nucleotide genome-scale alignment in conjunction with a probabilistic interpretation of the fossil ages from O'Leary et al. Our combined analysis of fossils and molecules demonstrates that Placentalia originated in the Cretaceous.

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julianpenrod
1 / 5 (8) Jan 15, 2014
Again, a demonstration of the patent fraud in "science". It is declared that there are no fossils of placental mammals that predate the dinosaurs. This leads to the conclusion that there were no placental mammals before the end of the Age of Dinosaurs. dos Reis is described in the article as "shooting holes in that line of reasoning", by stating that "it's eminently possible that some organisms" left no fossil record. In other words, saying that it's reasonable to accept that something exists, even though there's no proof! And yet they still demand the presence of God claiming no evidence and saying no evidence is proof!
Incidentally, marsupials are not mentioned, indicating fossils for them remain. Is a mouse so different from a marsupial shrew that one leaves fossils and the other doesn't?
FainAvis
5 / 5 (3) Jan 15, 2014
Julian you get a 1 for prevarication.
TheGhostofOtto1923
4 / 5 (4) Jan 15, 2014
Incidentally, marsupials are not mentioned
Well this was because the article was about placentals not marsupials. And only a little research would tell you what the authors assumed you already knew;

"Though metatherians diverged in the Jurassic period from the ancestors of placentals,[3][4] the earliest known metatherian fossil, Sinodelphys, is from the Lower Cretaceous of China, about 125 million years ago.[3] The marsupials, the metatherian crown group, diversified shortly after the mass extinction at the end of the Cretaceous."
http://news.natio...ial.html

-or would look up if you were curious. I know, righteous indignation is much more thrilling (for you) but for others it does get tedious.
julianpenrod
1 / 5 (3) Jan 15, 2014
A technique of rejoinders to the truth by liars, change the subject.
The subject of my post was the acceptance of positing the presence of placentals even though there is no evidence in the form of fossils! And TheGhostofOtto1923 can't deal with that!
But, also, what of marsupials? Did every marsupial leave a fossil? If they were much the same size and makeup as placentals, how could they l;eave fossils and not placentals?
TheGhostofOtto1923
3.7 / 5 (3) Jan 16, 2014
A technique of rejoinders to the truth by liars, change the subject.
The subject of my post was the acceptance of positing the presence of placentals even though there is no evidence in the form of fossils! And TheGhostofOtto1923 can't deal with that!
But, also, what of marsupials? Did every marsupial leave a fossil? If they were much the same size and makeup as placentals, how could they l;eave fossils and not placentals?

Indeed and verily is this not what boffins are asking? Without the leading religionist implications that is. IOW they are not asking by assuming that they already know are they?
rockwolf1000
2.3 / 5 (3) Jan 16, 2014
Again, a demonstration of the patent fraud in "science". It is declared that there are no fossils of placental mammals that predate the dinosaurs. This leads to the conclusion that there were no placental mammals before the end of the Age of Dinosaurs. dos Reis is described in the article as "shooting holes in that line of reasoning", by stating that "it's eminently possible that some organisms" left no fossil record. In other words, saying that it's reasonable to accept that something exists, even though there's no proof! And yet they still demand the presence of God claiming no evidence and saying no evidence is proof!
Incidentally, marsupials are not mentioned, indicating fossils for them remain. Is a mouse so different from a marsupial shrew that one leaves fossils and the other doesn't?


You are comparing apples to orangutans... Again.

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