reduced natural asteroid stability extinction disasters
According
to
current
hypotheses
,
this
extinction
was
probably
caused
by
a
combination
of
,
including
massive
and
widespread
volcanic
eruptions
,
a
fall
in
sea
level
,
and
a
huge
smashing
into
what
is
now
the
Yucatán
Peninsula
in
Mexico
.
That
collision
produced
forest
fires
and
dust
clouds
.
These
environmental
changes
ecosystem
and
led
to
the
of
most
dinosaurs
along
with
many
other
animal
and
plant
groups
on
land
and
in
the
sea
.
better Respiratory bones fly muscles Endoskeleton hollow breastbone
Skeleton
(
)
Light
weighted
due
to
consisting
of
bones
inside
(
to
help
the
bird
)
.
In
the
,
there
are
strong
connected
to
the
wings
:
helping
birds
fly
.
systems
connected
throughout
the
hollow
.
navigate harder danger directions balanced
Tail
:
Tails
help
birds
stay
during
flight
(
can
fly
without
,
however
)
.
Help
birds
where
they
?
re
headed
(
for
example
,
sensing
if
there
is
any
on
the
way
)
.
The
tail
helps
the
bird
go
in
different
during
flight
as
wel
l
energy temperatur separate four waste carry vessels two lungs blood oxygen nutrients ventricles heart regulating removing
The
circulatory
system
of
birds
includes
a
,
blood
and
Birds'
hearts
have
chambers
.
This
adaptation
makes
it
possible
for
the
body
to
and
,
giving
birds
the
they
need
to
fly
and
keep
up
their
high
levels
of
activity
.
The
heart
had
atria
and
two
that
completely
oxygenated
and
deoxygenated
blood
.
The
left
ventricle
pumps
blood
throughout
the
body
,
the
right
ventricle
delivers
blood
to
the
Birds
can
handle
the
metabolic
needs
of
flying
(
and
running
,
swimming
,
or
diving
)
In
addition
to
providing
oxygen
to
body
cells
and
metabolic
,
the
cardiovascular
system
is
crucial
in
a
bird's
body
stores grit crop liver acid stomach water intestine absorbing esophagus juices gizzard
food
moves
down
a
tube
called
the
and
into
the
,
which
excess
food
so
the
bird
can
digest
it
slowly
.
The
food
then
moves
to
the
first
part
of
the
,
where
it
is
softened
by
gastric
,
mucus
,
and
other
digestive
.
The
second
part
of
the
stomach
,
the
,
grinds
the
food
into
smaller
pieces
,
often
with
the
aid
of
such
as
sand
or
small
stones
the
bird
has
swallowed
earlier
.
Once
the
food
is
sufficiently
broken
down
,
it
moves
into
the
small
intestine
,
where
the
and
pancreas
help
with
nutrients
.
Next
is
the
large
,
which
is
very
short
for
most
birds
.
Where
the
small
and
large
intestines
join
are
the
ceca
,
two
pouches
that
help
absorb
any
remaining
from
the
food
and
finish
the
digestive
process
.