who did it to dinosaurs

8/14/2019 Who Did It to Dinosaurs

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Who did it to Dinosaurs?They reigned over the earth for more than 100 million years and suddenly,mysteriously disappeared. What caused the demise of this ubiquitous

group of reptiles which included some of the largest animals to ever walkthe planet?

One of the great mysteries in science is the extinction of the dinosaurs at the

end of the Mesozoic era some 65 million years ago. Who (or more likely what)caused it is unknown and a subject of great debate.

Dinosaurs appeared at the beginning of the Mesozoic era and were thedominant form of life for the next 140 million years. They lived almosteverywhere there was land including Antarctica. We can see their bones in thegeological record laid down over time. The lower stratum of rock contains theearliest and most primitive species of dinosaur, and the upper stratumcontains the newer species. Then, suddenly, at a geological strata line calledthe Cretaceous-Tertiary boundary (often referred to as the K-T Boundary), thedinosaurs disappear.

In fact, not only do the dinosaurs disappear, many other species do too. In the

sea, the great marine reptiles, like the plesiosaur, the mososaurs and theichthyosaur vanished. Nearly half of all invertebrate ocean organisms,(including ammonite cephalopods which had been around for 325 millionyears) were gone. In the sky, the great flying reptiles also disappeared.

Scientists believe that climatic changes might be responsible for most of theseextinctions. There is evidence that shows the temperature dropped at the endof the Mesozoic and the sea levels fell. Such a sudden change in temperature


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By examining insectstrapped in amber in

ancient times

scientists canunderstand the typesof diseases the

dinosaurs faced.

The Bug/Disease Theory

Other scientists think that some of the smallest animals may have beenresponsible for bringing an end to some of the largest. George Poinar, aprofessor of zoology at Oregon State University, believes that during the latecretaceous the number of insects and the number of insect species rapidlyexpanded. Many of these species were biting insects that carried new diseases.Poinar and his wife have examined many of these bugs from that era that have

been preserved in amber and found evidence that they carried forms of leismania and malaria that could infect reptiles. They also examined fossilizeddinosaur dung finding nematodes, trematodes and protozoa that might havegiven the animals dysentery. The dinosaurs probably got these intestinalparasites from insects that had been visiting dung piles and then transferredthem on to the dinosaurs food.

Poinar argues that the high temperatures and the recent evolution of floweringplants would have made the late cretaceous perfect conditions for an explosionin the number of insects and the illnesses they carried. The dinosaurs, whichwould have had little resistance to these new diseases, would have declined inpopulation.

The Double Whammy Theory

It may be that the dinosaurs were not just the victim of a single event, but astring of bad luck. Professor Arens has carefully looked at this idea and hasattempted to measure the extinction rate of species during periods when therewere major asteroid impacts, periods of massive volcanic eruptions and periodswhen neither were happening. Surprisingly, the rate of extinction for each typeof period is about the same. What she discovered, however, is that during


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periods when both massive volcanic eruptions andimpacts were taking placeat the same time extinction rate climbs. This suggests that no single disasterevent might cause mass extinctions, but a combination of two or more areneeded for it to happen, hitting life on earth with a "double whammy."

The fossil record shows that the mass extinction that killed the dinosaurs

wasn't the only one that has occurred in our planet's history. The earth hassuffered a number of such traumatic events over its life. In fact the K-Textinction wasn't even the largest. The Permian-Triassic (P-Tr) extinction event,sometimes referred to as the Great Dying, occurred about 250 million years agoand eliminated 90 percent of known species from the planet. As with the K-Textinction, nobody is quite sure what caused this disaster.

Are They All Dead?

Did any of the dinosaurs survive the extinction? Scientists have very rarelyfound bones of dinosaurs buried above the K-T Boundary. A single Hadrosaurleg bone found in the San Juan Basin, New Mexico, might suggest that a smallpopulation of these dinosaurs survived as long as a half a million years into thefollowing Paleocene era. However, it is also possible that the fossils in question,which are very few in numbers, were unearthed by some geologic event, thenreburied at a higher level.

Occasionally stories still appear about dinosaurs being found still alive today insome remote location of the world (for example, the legend ofmok'ele-mbembein Africa). While there are several famous fictional books like Arthur Conan-Doyle's The Lost Worldon this subject, there is no hard evidence that anydinosaur, other than the birds, their avian decedents, have survived intomodern times.

It is likely scientists will continue to puzzle over the death of the dinosaurs for

many years to come. Part of the mystery of K-T extinction is why certainspecies died out while others survived. Mososaurs went extinct while othermarine reptiles, like crocodiles, are still around. If climate change isresponsible why did the dinosaurs, hearty creatures that lived in all kinds ofconditions all over the planet, die when frogs, who are much more sensitive totemperature change, still survive today?
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who did it to dinosaurs

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