Demise of dinosaurs led to super-sized mammals
As demonstrated by worldwide study:
The demise of the dinosaurs created the ecological opportunity for
the diminutive prehistoric mammals of the time to become the largest
creatures on Earth today, scientists have demonstrated conclusively for
the first time.
A worldwide study of fossilised mammals has demonstrated beyond any
doubt that it was the extinction of the dinosaur some 65 million years
ago that was the key trigger leading to the explosive growth of the
warm-blooded mammals.
Although it was long suspected that this was the reason for the
transition from dinosaur dominance to mammalian supremacy, a thorough
investigation of fossil mammals dating back 140 million years has
confirmed that we would not have elephants today had it not been for the
death of Argentinosaurus, one of the biggest-ever dinosaurs, and others
like it.
The study found that for the first 40 million years or so of their
existence, the mammals were mostly small, shrew-like creatures that
lived in a narrow range of habitats.
However, after the dinosaur disappeared, the mammals evolved
relatively rapidly into much larger creatures capable of exploiting a
wide variety of ecological niches, from leaf-eating giant sloths to
tundra-munching mammoths.
"Basically, the dinosaur disappear and all of a sudden there is
nobody else eating the vegetation. That's an open food source and
mammals start going for it, and it's more efficient to be a herbivore
when you're big," said Jessica Theodor of the University of Calgary in
Canada.
"You lose dinosaur 65 million years ago, and within 25 million years
the system is reset to a new maximum for the animals that are there in
terms of body size.
"That's actually a pretty short time frame, geologically speaking.
" That's really rapid evolution," Professor Theodor said.
The study in the journal Science found that many types of mammals
grew into gigantic forms on different continents.
The biggest was a hornless rhinoceros-like herbivore that lived in
Eurasia 34 million years ago called Indricotherium transouralicum, which
weighed 17 tons and stood 18ft high at the shoulder - four times the
size of a modern elephant.
Being big is an advantage in a habitat with a large landmass of lots
of vegetation, although it can make species vulnerable to sudden
extinction if the environment changes rapidly.
With the dinosaur gone, and no other large animals already on Earth
to take their place, the scene was set for the mammals to evolve into
bigger and bigger forms that could better exploit the natural resources
available to them.
"Nobody has ever demonstrated that this pattern is really there.
People have talked about it, but nobody has ever gone back and done
the math. We went through every time period and said 'OK, for this group
of mammals that's the biggest one?' And then we estimated its body
mass," Professor Theodor said.
John Gittleman of the University of Georgia, who took part in the
study, said that the fossil record for mammals was better than for many
other animals, which was a key factor that helped to nail down the main
conclusion.
"Once dinosaurs went extinct, mammals evolved to be much larger as
they diversified to fill the ecological niches that became available.
"This phenomenon was well documented in North America. We wanted to
know if the same thing happened all over the world," Dr. Gittleman said.
"Having so many lineages independently evolve to such similar maximum
sizes suggests that there were similar ecological roles to be filled by
giant mammals across the globe," he said.
Courtesy: The Independent
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