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Dinosaur Life Span
While we know when dinosaurs first appeared
(during the Triassic period),
and when they finally went
extinct
(at the end of the Cretaceous period),
one common question is how long did individual dinosaur live for?
There is no single answer:
There were many different
types of dinosaurs,
and they ranged in size from chicken-sized or smaller, to over
100 feet (30 meters) long, and each species would have a different
life span (just as different species of birds and mammals have different
life spans). However, a number of different approaches have been
suggested for estimating the life span of a dinosaur:
- One idea is to look at the life span of modern large reptiles.
The common alligator, Alligator mississippiensis,
has a life span of 60 to 70 years, and there are reliable records of
a number of giant tortoises living for over 150 years
(for example, a tortoise named Harriet,
was collected by
Charles Darwin
in the Galápagos islands at about age 5 in 1835,
and died in Australia Zoo in Queensland,
Australia
in 2006,
meaning she lived to about 176 to 181 years old).
Of course, the problem with using these figures, is
that dinosaurs differ in many ways from modern
reptiles - for example, some dinosaurs were massively larger, some
dinosaurs are believed to have been warm-blooded and bird-like, etc.
- Another idea is to use growth rates of modern reptiles. Using this
approach, provided we can find a dinosaur hatchling (or a
egg which
was close to hatching), and compare it to the adult-size of the
same
type of dinosaur,
we can estimate how long it would take for the hatchling to grow to
adult-size.
(Of course, this approach gives us no indication about how long
the adults lived).
The problem is of course the assumption that dinosaurs would have
grown at the same rate as modern reptiles. We simply do not know
whether that is true.
Furthermore, if we actually try this approach, we find that large
dinosaurs (such as
Sauropod dinosaurs), which hatched from comparatively
tiny eggs, could have taken 100 or 200 years to grow to adult-size,
which does seem rather unlikely.
- If we measure the life span of modern animals, we can make a general
observation that larger animals tend to live longer than smaller animals.
Based on this approach, we might expect the largest dinosaurs (the
Sauropods
again) to live on average for 100 years, and smaller dinosaurs to have
much shorter life spans.
This method of course only provides a very rough estimate.
It is also based on the assumption that all animals follow more or less the same formula
- in real-life things are (of course) much more complicated.
All the methods described above, of course, only lead to a very
approximate estimate of life span, and each method is based
on somewhat dubious underlying assumptions.
There is however a method to obtain direct evidence of
dinosaur's age at its death,
by looking at
fossils.
This method uses the fact that animal bones, show annual growth
rings (similar to tree rings) which can be using a microscope
and specialist equipment.
From research into these rings, we are now starting to learn
more about how dinosaurs grew and how long they lived.
The evidence seems to show that dinosaurs grew quickly,
that at least some species
(including Tyrannosaurus rex)
bred while still growing.
Of course, the interpretation of growth rings is itself a subject
that has generated much debate, and new mysteries - such as
unusual variations in the growth patterns of some types of dinosaur.
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