Eye on Science, Science Blog, Michael D. Lemonick, TIME

March 29, 2007 11:17

One More Scientific "Truth" Bites the Dust

Posted by Michael Lemonick | Comments (27) | Permalink | Trackbacks (0) | Email This

We all know—I've written it a dozen times myself, and the textbooks all agree—that the extinction of the dinosaurs paved the way for the rise of mammals. With a whole bunch of ecological niches suddenly empty, our whimpering shrew-like ancestors (OK, maybe they didn't whimper, but gives you a feel for their utter insignificance) went through a burst of evolutionary innovation that led, to elephants, whales, Chihuahuas and us.

It's highly—but a paper published in today's Nature says it's probably wrong, or at least way oversimplified. Using both fossil and DNA evidence to assemble an evolutionary tree whose fruit is about 4,500 of the 4,554 known mammalian species, scientists have shown that the many of the primary groups mammals divide into, including primates and rodents, were already present at least 20 million years before the dinosaurs went bust. So the innovation was already happening long before the event we thought (until yesterday) triggered it.

Not only that: the real flowering of these groups into the thousands of species we know of today didn't happen until millions of years after the dinos were gone—so their demise doesn't explain that one either.

I'm a big proponent of the conventional wisdom in science, which sometimes makes me the target of cranks with supposedly brilliant theories. But watching the conventional wisdom demolished is among my favorite things, when it's done well.

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Reader Comments (27)

kbanginmotown:

Michael,
There are scientific "truths" that are the result of imprecise thinking/methodologies (heavy objects fall faster than light objects, the tongue has taste regions), and there are those are are result from logical conclusions drawn from the best available measurements and/empirical evidence available at the time. As such, the "truth" (up until now) that the extiction of dinosaurs and rise of mammals were causually related appeared to be a reasonable conclusion. That, and the fact that the report in _Nature_ was the cumulation of a *10 year* research project, emphasizes that this was not some sort of obvious answer that lemming-like scientists have overlooked, as the phrase "conventional wisdom" seems to imply.
The challenge now is to propagate this newfound insight into our nation's K-12 science textbooks. But, since they're being reprinted with only 8 planets, now might be a good time. :-P

--An extremely thoughtful and insightful comment. Thank you.
M.L.

Posted by kbanginmotown | March 30, 2007 12:48 AM

JOTHI NARAYANAN:

IS IT POSSIBLE TO CREATE A GM DINOSAUR?

At last, the parallel existence of Mammals and Dinosaurs has been confirmed.The fossil evidence in china says,'Dinosaurs found in Mammal's Belly."It is the first evidence that mammals dined on dinosaurs.
-This information again put the following questions?
Is Dinosaurs are mammals or not?
Still the answer is inconclusive.The most probable answer is Dinosaur is not a mammal but 'mammal like'.
We know that Dinosaur is dined by Mammals? Then what Dinosaurs eat?The answer is plants and other dinosaurs.Again our theory proves that Dinosaurs are Mammals like.
Some one said to add my inquisitiveness, Dinosaurs are AMPHIBIANS.Happy to know that.But again someone said that it resembles crocodile in certain aspects but not amphibian.It is a land
reptile has a shape of monster.
I put one more question,Is 'Dinosaur' a zoological name,since every zoological name will give some insight into the anatomy and origin.But the answer is not convincing.
Dr.Mantell,English doctor,in 1841 discovered the existence of nine types of these different types of reptiles ,and the name Dinosaur was given by him.The basis of his discovery is the teeth of Dinosaurs.
I hope soon we get the news that someone created a
GM Dinosaur which is amphibian,very sensitive to Low Frequency Active Sound waves capable of sniffing any submarine and sensitive to vibration on sea bed.We pray for that day to request US to use this GM Dinosaurs to detect submarines and spare poor,bottle nosed dolphins.phoenixjn@hotmail.com

Posted by JOTHI NARAYANAN | March 31, 2007 10:47 AM

Dave Wisker:

I too found the Nature paper interesting. If its findings are confirmed, then our explanation for the ascendancy of the mammals will have to be re-examined. But I'd also like to put in a word about the 'conventional wisdom' regarding the demise of the dinosaurs. Here the latest 'conventional wisdom' states that the asteroid impact at the end of the Cretaceous was responsible for the dinosaur's extinction. There are other, more interesting (in my humble opinion) ideas emerging from years of paleoecological research that challenge the conventional view. Two things occurred at the end of the Cretaceous that may have had far more impact on extinctions than the asteroid: large-scale sea-level regression and sharply increased vulcanism. These in combination could have produced a catastrophic decrease in "primary production" (ecologists' term for plant biomass, both in the sea and on land--the stuff at the botton of the food chain which supports everything else). Prior to this, the luxuriant primary plant biomass supported elaborate food webs of organisms, both herbivores and the carnivres which feed upon them, with correspondingly complex diversity. The sharp decrease in primary production at the end of the Cretaceous is believed to have resulted in the collapse of these elaborate food webs, with many extinctions. What we see today is the result of the 'sorting out' in the aftermath of the collapse of those ecological systems. Here are a couple of papers explaining the idea in more detail:

Spicer R (1989). Plants at the Cretaceous-Tertiary boundary. Phil. Trans. R. Soc. Lond. B, 325 : 291-305

Briggs J (1991). A Cretaceous-Tertiary mass extinction? Bioscience 41(9): 619-624

From my point of view, the explanation of the decline of the dinosaurs and the rise of the mammals will only become more complex and far more interesting as the years go by and more data is gathered. This can only be good news for biologists.

--Agreed. There's also Gerta Keller, at Princeton, who has interesting evidence that the mass extinction didn't happen all at once at 65 million years B.P., thus muddying the clean precision of the asteroid theory.
M.L.

Posted by Dave Wisker | March 31, 2007 12:03 PM

JOTHI NARAYANAN:

Demise of Dinosaurs-Still A mystery?

Dear Dave Wisker,
We could read on the past existence of many types of Dinosaurs but few on their cause of demise. Extinction theory is still a mystery.One of the agents for its demise is the large no.neutrinos born out of violent stellar collapse theory.I am almost in agreement with this theory.Epidemics of
cancer triggered by bursts of neutrinos of dying stars in our Galaxy wiped Dinosaurs.
New Scientists1 13,Jan,1996 refers,'Neutrinos are reluctant to interact with every day matter.But if
enough passed through the earth in mega then some would collide with nuclei of atoms in living tissue.When this happens,the nuclei will recoil from the collision,such recoils could damage DNA,PRODUCING CANER -CAUSING MUTATIONS.I invite the opinion of ML also who has special interest in
astrophysics.phoenixjn@hotmail.com

--It would have to be a heck of a burst of neutrinos to cause that sort of extinction. I love New Scientist, but they tend to be a little too eager to publish wildly speculative theories that aren't absolutely nuts, but very very dubious.
M.L.

Posted by JOTHI NARAYANAN | March 31, 2007 5:31 PM

Dave Wisker:

Dear Jothi,

I was unaware of this theory, but I'm curious: why weren't mammals and amphibians affected in a similar fashion?

Posted by Dave Wisker | April 1, 2007 9:45 AM

thenekkidtruth:

I don't know if a lot of this is really "breaking news" in a sense - I've been reading about the existence of diverse mammalia coinciding with dinosaurs for years now.

The impression I got was that the "jury wasn't out" about whether the demise of dinosauria led to the (relatively) immediate propagation of mammals as a replacement class. Seemingly, the big news about this announcement is that the evidence has now become available, and there was apparently a gap in time between the two superclasses.

Posted by thenekkidtruth | April 1, 2007 10:29 PM

JOTHI NARAYANAN:

Palingenesist-A MISSING MESSENGER BETWEEN
PALEONTOLOGIST and ASTROPHYSICIST.
Thanks to ML and Dave Wisker.The answer from the neutrino-destructive potentials is 'the effect would be particularly severe in larger animals because of the heavy mass of tissue.The neutrinos are not stopped by the outer layers of the body,the induced recoiling effect is an aggravating factor on sensitive tissue such as bone morrow'.The Asteroid theory has 51.4% and climatic change theory has 14.7% supporting percentage of vote.But the Asteroid
impact also confirms only 70% of total extinction and the balance in partial may be small and medium in size.But we could see that cretaceous period has a temp.drop that affected the marine dinosaurs
and the asteroid effect on land reptiles?
One of the Paleontologists recently made a remark,
the worry is about the origin,mode of life,anatomy and the extinction of Dinosaur not on extinction.
If Paleontologist is on origin,anatomy etc, Astrophysicist only on extinction then who will fill the gap of the survived or reborn species during or after the asteroid /climatic/volcanic effects.The missing messenger is Palingenesist to produce the evidence on the second creation of the few and we need an answer from the nuclear scientist who confirms the survival of cockroach
during nuclear explosion about the survival of the
the species walked along with Dinosaurs during neutrino,climatic impact etc.
Dear Dave,sometimes I wonder that no one talks about Sauropods,the largest animals to live on earth ,80 ton wt. and 40metres long.
phoenixjn@hotmail.com

Posted by JOTHI NARAYANAN | April 2, 2007 1:37 PM

JOTHI NARAYANAN:

CORRIGENDUM
Please,Read the sentence,"one of the Paleontologists.......and the extinction of Dinosaur
is not a matter of concern".phoenixjn@hotmail.com

Posted by JOTHI NARAYANAN | April 2, 2007 9:04 PM

Mrs. S:

I'd like to thank Mike and his audience (kbang and Dave in particular) for discussing complex issues in easy to understand language. As eager as I am for information regarding evolutionary topics, I sometimes get frustrated because the scientists who know the material often present findings with such technical precision, I can't grasp the big picture, let alone the secondary details. As this is a blog, I take everything with a grain of salt, but at least it keeps me thinking.

--That's what we're hoping for. Thanks for the comment.
M.L.

Posted by Mrs. S | April 6, 2007 9:26 AM

Dave Wisker:

I had a chance to read the Nature paper itself (not just a recap, which I originally read), and I don't think it is overturning much conventional thinking at all. The authors were studying only lineages that have living descendants (these are the only ones from whom we can get DNA samples from, after all). So, any timings that the research derived only applied to those groups. The paper can say nothing about lineages that became extinct and left no living descendants. If we look at the mammalian fossil record as a whole, what we see is an incredible explosion of diversity (adaptive radiation) right after the Cretaceous, that is, in the Paleocene, right after the K/T boundary. In fact, this is the greatest increase in diversity in mammalian history. The mammal lineages that are represented by living species today underwent a secondary adaptive radiation later, in the Eocene, and this is what the authors are referring to in their paper.

We are still left with having to explain the explosion of mammalian diversity at the end of the Cretaceous, which also coincides with the elimination of the dinosaurs. It should also be noted that mammals took a tremendous hit at the same time the dinosaurs did, in the late Cretaceous. Almost 2/3 of all mammal species went extinct at about the time of the K/T boundary. So, whatever the cause, asteroid, ecological or both, something big happened, and the mammals look like they were able to weather it and subsequently flourish as they never had before.

Posted by Dave Wisker | April 8, 2007 11:12 AM

JOTHI NARAYANAN:

Dinosaurs Extinction-Is it incorrect?
Thanks for passing the information from the Nature
paper.The neutrino theory on extinction is largely supported by the presence of Iridium(Ir),at the extinction site,which is relatively abundant in space confirms the explosion.During my morning stroll ,I could see few bats,the smallest mammals in our time.If the neutrino explosion caused a radiation hazard from Ir, the ultra sound sensitive mammals like bats could have ensured the
safe hideout,as a shield(probably stuck behind a rock,hill etc.) from radiation hazard.My inquisitiveness makes me to refer Palingenesis theory on' THE UNMODIFIED INHERITANCE OF ancestral characters'.Some argue that it is incorrect to say that dinosaurs are extinct because they have left descendants in the form of cockatoos,cassowaries and their pals just like modern vertebrates are still vertebrates even though their Cambrians ancestors are long extinct.phoenixjn@hotmail.com

Posted by JOTHI NARAYANAN | April 9, 2007 12:07 AM

GOD:

i took a fucking great big asteroid and i slammed it into the planet..why because i was heart broken to see the bastards eating each other....i had greater hopes for mankind thought they could evolve to share my veiw so they would keep themselves sustainably from going extinct,they don,t want to eat each other they just want to fight over what there is...\

--It's kind of awkward when a joke stopped being funny after the fifth or sixth time and everyone but the person telling the joke knows it.
M.L.

Posted by GOD | April 13, 2007 11:33 PM

GOD:

lets hope humour has the common sense to take stock once in a while,and not fly to high to miss sincerity altogether...

Posted by GOD | April 16, 2007 3:53 AM

JOTHI NARAYANAN:

Dear Dave and ML,
Did you notice a photo released by REUTERS of a
Tyrannosaurs rex femur bone.It says that TINY BITS OF PROTEIN EXTRACTED from a 68-year old dinosaur bone have given scientists the first genetic proof that the mighty Tyrannosaurs rex is a distant cousin to the modern chicken.Is this period falls within R/K boundary?Even after the death of species,DNA and
RNA could become active at a certain point to activate fusion?phoenixjn@hotmail.com

Posted by JOTHI NARAYANAN | April 19, 2007 9:43 PM

Learn Chinese:

We should seek more ways or have more innovative method to do research about dinosaurs. Maybe we can find elicitation from the interplanetary explorer or book of changes in ancient China.

Posted by Learn Chinese | August 23, 2007 4:42 AM

JOTHI NARAYANAN:

Dear ML,
The message in the name of LEARN CHINESE is an apt advice to carry out further research on DINOSAUR.
'Scientists have found,particularly at one site in
china,fossils of small carnivorous dinosaurs and others preserved with feathers'.Further scientists believe birds,roughly 150 million years ago,evolved from small feathered carnivorous dinosaurs.
-Reuters.
We should learn Chinese to find out the presence of the amphibian dinosaur that has feathers to fly.
phoenixjn@hotmail.com

Posted by JOTHI NARAYANAN | September 22, 2007 12:39 AM

JOTHI NARAYANAN:

In depth research on the life of Dinosaur is going
on.Did anyone compile an most authentic information on the different type of DINOSAURS
and the cause for the difference in anatomy?.

Posted by JOTHI NARAYANAN | March 27, 2008 9:48 PM

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