it's true that there are animals today notably the blue whale is the largest
creature ever to inhabit the earth that are bigger
then dinosaurs but, no creature that currently walks
on land gets anywhere close to the size the Super Dino's.
The largest recorded species of dinosaur probably is Amphicoelias Fragillimus,
which measured up to 60 meters and weighed 122 metric tons!
By comparison, the African savanna elephant, the largest modern land animal
clocks in at just three to four meters tall and five and a half tonnes - both herbivores!
So why aren't there land mammals today that are as big as the dinosaurs?
Well, the fossil record gives us some clues as to when and how if not exactly why
mammals hit their limit. After the last of the dinos disappeared around 65 million
years ago the size and diversity of mammals went
totally nuts... Until it didn't.
Around 30 million years ago, a kind of giant Rhino-Giraffe beast
topped out at five meters tall and seven and a half meters long
grabbing the record for the biggest mammal to ever walk the earth.
Scientists think that there are several limiting factors that have kept modern
land animals from approaching super-saurus sizes.
First mammals give birth to live young, a mama dinosaur could just lay a bunch of eggs and walk
away but a mammal has to gestate and nurse and rear babies at a great
energetic cost. Large mammals also have long periods of gestation. Giraffes and
rhinos gestate for about fifteen months
and elephants are pregnant for nearly two years!
And the longer a pregnancy is, the more dangerous they are for both the mother
and the young so on mega-herbivore would probably experience and unfeasibly long
and dangerous pregnancy.
Another theory suggests the dinosaurs grew so large because of Earth's climate
and ecology at the time.
A warmer, muggy climate with a higher carbon content in the air made the
vegetation grow off the hook. Sauropods
basically lived in a massive smorgasbord, and they may may have gotten so Titanic simply
because they could. But the environment changed over time
and herbivores worse today don't live in such prime conditions. Reason number three today's
land mammals are further limited by their skeletal systems. Sauropod fossils
show evidence of
avian in like air sacs that made for a much lighter skeletons than you'd expect in
animals so large.
Some of these dudes were 30 meters long but only weighed an estimated forty tonnes.
A modern land mammal that size would likely weigh nearly twice that and
basically it be too heavy to get around. Finally the fourth
and maybe coolest reason a mega-mammal
would probably cook its own tissues. Mammals as you probably know are
endothermic or warm-blooded. Our bodies generate and maintain their own
temperature internally.
Reptiles meanwhile are ectothermic or cold-blooded
absorbing heat from their environment - like a snake sunning on a rock. There is
actually debate as to whether some dinosaurs were warm-blooded like birds or if they had
some sort of an immediate system that was neither all cold-blooded nor all
warm, but regardless we know a mammal uses way more energy than a
similar-sized reptile.
So it's probable that modern land mammals couldn't get much bigger than
elephants without actually cooking themselves from within.
That's enough to make me perfectly happy being this size.
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