so dinosaurs are cool hot take the fact
that these
wildly different creatures roamed the
earth millions of years ago is not only
awe-inspiring
but terrifying one thing that has stood
out to paleontologists is the seemingly
odd
rule that carnivorous dinosaurs are
either really huge like the
tyrannosaurus rex
orally small like comp cygnus you know
those creepy ones from jurassic park
that look all cute
and cuddly at first and then they go
nuts stay away take a look at these two
diagrams
first looking at modern day carnivorous
land mammals from kruger national park
in south africa from lions and leopards
all the way down to things like the
small spotted genet you can see in this
ecosystem the size of these animals is
distributed across a gradient pretty
evenly and this is true of other
geographies as well
they all fill their own niche with their
own prey targets but now take a look at
the scale of these carnivorous dinosaurs
all found in the dinosaur park formation
in alberta which have been scaled to
match the largest mammal above
and you'll quickly notice a massive gap
in the middle for perspective
if the modern carnivores were similarly
distributed there would be no carnivores
between the size of an african lion
and a bat-eared fox on top of all this
our understanding of dinosaurs is that
there were way more
large carnivorous species than there
were small which is the opposite of what
we see today in land animals
it tends to be lots of diversity in
small organisms
lower diversity and medium-sized
organisms and then very low diversity in
large organisms which makes sense based
on energetics
so the smaller you are the less food you
need
and the more you can kind of partition
your ecosystem dinosaurs are the exact
opposite
when we look at them at a global scale
most of them are big to understand this
phenomenon we first have to look at the
fossil records dinosaurs weren't super
diverse
compared to the tens of thousands of
mammals and bird species we see today
there are maybe only around 1 500 known
dinosaur species and of these species
a lot more were over 1000 kilograms
than under 60 kilograms but least of all
very few carnivorous dinosaurs existed
between those two sizes
especially around the cretaceous period
which is 145.5
to 65 million years ago turns out
there's something really unique about
massive dinosaurs their babies are small
now that may not surprise you lots of
babies are small but it has more to do
with the fact that they're egg-laying
creatures oviperous animals are those
that lay their eggs with little to no
embryonic development
inside the mother and so dinosaurs
started out weighing no more than 15
kilograms but
a t-rex adult can grow to be 7 000
kilograms compare that with a larger
animal today like a giraffe which weighs
around 68 kilograms when it's born
and ends up around 800 kilograms as an
adult an egg can only be about the size
of a football because of how
gas is exchanged through a shell even a
sauropod that is getting up into the 80
ton range
is just immensely huge are still being
born
like your average border collie size so
how does that impact the size of
other dinosaurs the theory is that these
baby t-rexes would have had an almost
entirely different diet than their
parents because they were physically so
different and because of this as they
became teenagers
they would actually be competing for
resources with other medium-sized
dinosaurs
a niche that would have contained
different foods than what an adult t-rex
was eating for example a young t-rex
likely couldn't take on a triceratops
because they were much more slender than
adults only turning into bone crushers
after a teenage growth spur and so
they instead would go for something
smaller and it looks like they simply
just
out-competed other medium-sized
dinosaurs of course those teenagers
would eventually grow up into adult
t-rexes but their population as
teenagers would have had a massive
impact
on other dinosaur communities and the
ecosystem at large so then why don't we
see this gap in herbivores
they lay eggs too and grow to even more
massive sizes it's more likely that
their young
simply ate the same foliage as the
parents after all you don't have to put
up too much of a fight to take down a
leaf
though i will say rose thorns terrifying
don't wanna be near them don't wanna get
in a fight either way for herbivores the
food barrier just isn't as high
herbivores have their have the
opportunity to partition
their resources and their ecosystem
vertically so they can move
up and down in a tree so a big tall
sauropod can be eating at the tops of
the trees
while a teeny tiny baby sauropod can be
eating at the bottom of the tree
so they're not necessarily resource
limited
in the way that carnivores are resource
limited because a carnivore they're
going to have to be competing with one
another that
explains in part why we don't see it in
herbivores because of this
some even suggest that juvenile
megatheropods like the t-rexes could be
considered their own species
in an ecological type of way obviously
they're technically the same species but
because their diets and impact on the
ecosystem is so different than an adult
in that way they're almost like their
own species in fact when researchers
added juveniles as their own species
into their models the gap in sizes
suddenly disappears which helps further
support the theory that the juveniles of
megatheropods
were actually out-competing other
medium-sized dinosaurs
ultimately leaving a gap in the
diversity of species it wasn't that
there were no medium-sized dinosaurs per
se
it was that the big guys teenagers were
simply taking their place
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peace