if you're a dinosaur fan you might have
noticed that the way we portray them has
changed over the years I'm not just
talking about the feathers we used to
think of dinosaurs as sluggish
cold-blooded reptilian monsters and at
some point they became the swift active
hunters of Jurassic Park
more like warm-blooded creatures the
dinosaurs might not have been either
cold-blooded or warm-blooded instead
they were probably a little bit of both
ectothermic or cold blooded organisms
like reptiles and fish rely on their
environment to warm their bodies which
helps them conserve energy endothermic
or warm-blooded creatures like birds and
mammals hold their body temperatures
steady in your case that's a toasty 37
degrees Celsius there are advantages to
being warm-blooded since you can stay
active even when it's cold out but it
also takes a lot of energy to maintain
that high temperature which means you
need plenty of food for decades
paleontologists have been debating which
category the dinosaurs fall into since
warm-blooded birds are descended from
dinosaurs there must have been a
transition to endothermy somewhere in
the dinosaur family tree but according
to a study published in 2014 in the
journal Science that might have happened
gradually with dinosaur metabolisms sort
of in-between endotherms and ectotherms
the key was in their bones when bones
grow they lay down growth rings just
like trees by looking at these rings
scientists can calculate how fast the
animal grew even if it's been dead a
hundred million years and they can use
growth ring data to estimate how an
animal's metabolism worked animals with
faster metabolisms use more energy so
they eat more food and grow faster so
the team looked at the growth rings and
dinosaur fossils and compared them to
those of modern animals both endotherms
and ectotherms they pulled published
data on hundreds of vertebrates and
dozens of dinosaurs and crunch the
numbers using statistical analysis they
found that the dinosaurs had a metabolic
rate somewhere between reptiles and
birds meaning they weren't endotherms or
ectotherms they were mezzo therms or
middle blooded mezzo thermy is an
entirely different type of temperature
regulation in which animals generate
their own heat like endotherms but don't
hold their bodies to a specific
temperature like ectotherms they end up
with a body temperature that's a few
degrees higher than their surroundings
but they're still dependent on their
environment to some extent like modern
mezzo therms such as the great white
shark or the echidna dinosaurs might
have relied on their muscles to produce
heat and their large size to retain
it without sticking to a particular
temperature evolutionarily it would make
sense because the dinosaurs would get to
conserve a bit of energy while still
being more active than their cold
blooded competition however some
paleontologists had problems with this
study for one thing not everyone agrees
on how to interpret the growth ring data
using other statistical methods it might
actually support much faster growth
rates giving us warm blooded dinosaurs
for another not all dinosaurs were the
same maybe the more bird-like theropods
had faster metabolic rates than the more
lizardy sauropods lumping them all into
one statistical group like the
researchers did would hide these
potential differences but we might soon
get a much more definitive answer
because there's a totally new way to
study dinosaur fossils that's giving us
a close look at the red blood cells that
could help solve the dinosaur metabolism
problem because the size of red blood
cells is related to metabolic rate
typically the bigger the red blood cells
the more warm-blooded the animal for a
long time paleontologists thought that
the soft stuff like skin and feathers
and blood and tissue were rarely
preserved in fossils but living bones
have lots of soft tissue inside them and
when a group of British researchers
pulled apart 75 million-year-old bones
to look for some of that soft tissue
they found some including red blood
cells it wasn't perfectly intact but it
was enough to make out what the tissue
structure would have looked like when
the dinosaur was alive and the
researchers found soft tissue in nearly
all the bones they searched even though
they weren't all that well-preserved or
anything which means that lots of
dinosaur fossils might still have
squishy organic bits of dinosaur in them
so future studies that look at soft
tissue and more bones should be able to
tell us if dinosaurs were really
cold-blooded warm-blooded or something
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