Does Dinosaur extinction make sense ?

Question

Why didn't the mammals go extinct also. It just doesn't make sense as to why only Dinosaurs went extinct. Yet Turtles and Crocodiles survived.

Answer 1

Mammals and dinosaurs did indeed live during the same time. However, mammals were not nearly as diversified as the dinosaurs. Most of the mammals that existed before the K-T extinction are believed to have been small, burrowing animals. Of course, there were some dinosaurs which were also small and lived in burrows, as well as reptiles and amphibians.

It is these small animals that would have had the big advantage over larger animals that preyed on them, because they could have escaped the shockwave, high temperatures, and other hazards created by the asteroid that wiped out the dinosaurs and whatever other large animals that were roaming the earth at the time of the impact.

It is possible that there was also a very great diversity of mammals living during the reign of dinosaurs, but that for whatever reason we haven't found as many of their fossils. But the fact is that we find much more in the way of dinosaur fossils than we do in mammalian fossils during that period. Therefore, it is reasoned that most mammals were small, which would help explain the lack of fossils.

Many turtles and crocodilians also live in burrows, so it is very possible that the ancient ancestors of these survived due to this habit of spending at least some of their time underground.

Simply put, fossils only tell us so much, and there is a lot that we still don't know.
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Edited 03/28/07

However, not all scientists believe that the dinosaur extinction spurred a great diversification of new mammalian species.
http://news.yahoo.com/s/ap/20070328/ap_on_sc/mammal_evolution
This is a very, very interesting article...
"NEW YORK - The big dinosaur extinction of 65 million years ago didn't produce a flurry of new species in the ancestry of modern mammals after all, says a huge study that challenges a long-standing theory.

Scientists who constructed a massive evolutionary family tree for mammals found no sign of such a burst of new species at that time among the ancestors of present-day animals.

Only mammals with no modern-day descendants showed that effect.

"I was flabbergasted," said study co-author Ross MacPhee, curator of vertebrate zoology at the American Museum of Natural History in New York.

At the time of the dinosaur demise, mammals were small, ranging in size between shrews and cats. The long-held view has been that once the dinosaurs were gone, mammals were suddenly free to exploit new food sources and habitats, and as a result they produced a burst of new species.

The new study says that happened to some extent, but that the new species led to evolutionary dead ends. In contrast, no such burst was found for the ancestors of modern-day mammals like rodents, cats, horses, elephants and people.

Instead, they showed an initial burst between 100 million about 85 million years ago, with another between about 55 million and 35 million year ago, researchers report in Thursday's issue of the journal Nature.

The timing of that first period of evolutionary development generally agrees with the conclusions of some previous studies of mammal DNA, which argue for a much earlier origin of some mammal lineages than the fossil record does.

The second burst had shown up in the fossil record, MacPhee said. But he said the new study explains why scientists have been unable to find relatively modern-looking ancestors of the creatures known from that time: without any evolutionary boost from the dinosaur demise, those ancestors were still relatively primitive.

Some experts praised the large scale of the new evolutionary tree, which used a controversial "supertree" method to combine data covering the vast majority of mammal species. It challenges paleontologists to find new fossils that can shed light on mammal history, said Greg Wilson, curator of vertebrate paleontology at the Denver Museum of Nature & Science.

William J. Murphy of Texas A&M University, who is working on a similar project, said no previous analysis had included so many mammal species.

But, "I don't think this is the final word," he said.

The study's approach for assigning dates was relatively crude, he said, and some dates it produced for particular lineages disagree with those obtained by more updated methods.

So as for its interpretation of what happened when the dinosaurs died off, "I'm not sure that conclusion is well-founded," Murphy said.

John Gittleman, a study co-author and director of the University of Georgia Institute of Ecology, said the researchers considered a range of previously reported dates for when various lineages split. They found the overall conclusions of the study were not significantly affected by which dates they chose, he said.

Researchers should now look at such things as the rise of flowering plants and a cooling of the worldwide climate to explain why ancestors of present-day mammals took off before the dinosaurs died out, Gittleman said. The cause of the later boom is also a mystery, he said.

The study's family tree includes 4,510 species, more than 99 percent of mammal species covered by an authoritative listing published in 1993. (Nearly 300 species have since been added to the listing, but the researchers said that doesn't affect their study's conclusions.) To construct it, the researchers combined previously published work that relied on analysis of DNA, fossils, anatomy and other information.

S. Blair Hedges, an evolutionary biologist at Pennsylvania State University, said the new work "pushes the envelope in the methods and data, and that's really important."

He said the demise of the dinosaurs may have affected mammal evolution by influencing characteristics like body size rather than boosting the number of new species created. Such changes wouldn't be picked up by the new study, he noted."

Answer 2

Recently on WWW.Archeologynews.com - they reported that the reasons why turtles and other reptiles survived was because many of them were protected in thick layers of mud when the asteroid hit and in a state of Hibernation for periods of time after the fall out diminished which allowed them to exist for a considerable time after that.

That and the fact that the effects were not felt the same way all over the world.

Then you have to remember that there was actually more than just One Extinction! There were several over a long period of time with each having varing effects.

Answer 3

Some scientists think that an asteroid hit somewhere near the Yucatan Peninsula that was responsible for the extinction of the dinosaurs. It is further understood that some mammals evolved from the survivors. Keep in mind, therapods divided themselves into two groups...some ground dwelling, some tree dwelling. The ones in the trees are generally accepted to have evolved into birds, some ground dwellers became mammals.

Perhaps the crocodiles and turtles survived because of their diets of scavaging for carrion (dead meat). Also, being largely underwater they escaped a lot of the worldwide effects of the impact.

Answer 4

The dinosaurs that you're thinking about were very large, requiring very large amounts of food. As the climate changed, the food supply vanished, and with it the large dinosaurs.
Those that required much smaller amounts of food were able to survive. The dinosaurs did not become extinct, only the large ones. Lizards, turtles, etc are still with us.

Answer 5

I would guess that their survival - like ours - is related to adaptation. Darwin, incidentally, never said "survival of the fittest" but rather theorized "survival of the most adaptive". It wasn't the size of the meteorite that extinguished the dinosaurs, but rather the subsequent black clouds which blocked out the sun. Cold-blooded creatures like sharks, tortoises and crocodiles probably don't need sunshine and were safe as long as they remained underwater. Also, only a few of them would have had to survive and propagate.

Answer 6

One of the several theories is that they had very large bodies and required lots of food to survive. But their brain is not large enough to accumulate that quantity of food.
The mammals and dinos hardly lived together. Mammals came into existence in Upper Triassic, somewhat later than the dinos.
Turtles and crocodiles that you are seeing today as survivor are also not the same as those during Mesozoic period. They have evolved, adapted and made them fit to survive and survived.

Answer 7

It doesn't have to "make sense" it is a fact. If you figure out why with definitive evidence you will be famous. Start by doing some reading

Answer 8

It don't make since to me either.I think they are full of peanut butter