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Skeletal- Cranial 5b
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Splanchnocranium ( MOST Primitive)
supports
pharyngeal arches
but no trace of
neural crest
predates vertebrae
neural crest
origin and cartilage/ bone only in
vertebrates
living agnathans with
elastic cartilaginous support
of
gill pouches
not directly
comparable
to
gnathostome gill arches
Chondrocranium
also known as the
neurocranium
or
endocranium
Sharks lost all dermal bone
the primary "
brain case
"
present in all vertebrates including the
hagfish
may remain as
cartilage
in
adult
or to be
ossified
Chondrocranium: Embryology
develops as a series of
cartilages
under the
brain
and associated with
sense organs
occipitals
probably a modified
anterior vertebrae
fuse during growth to form a
plate
and
occipital arch
Cranium: Embryology
Neural
crest, mesenchyme ->
nasal optic
and possibly
otic
capsules as well as
trabecula
/
ethmoid plate
(sensory organs usually)
Neural
crest mesenchyme->
anterior dermatocranium
(pg6)
Cranium embryology -
Neural crest mesenchyme -> entire splanchnocranium (and its derivatives) Page 7 - figure 7.4
portions of the splanchnocranium may be incorporated into the brain case or be indistinct from rest of skull
Jaws Origin:
serial theory:
mandibular
and
hyoid arches
are modified
anterior pharyngeal arches
composite theory:
anteriormost gill arch
contributes to the
neruocranium
as well as
portions
of the
mandibular arch
Jaws Origin
embryology supports that jaws are
anterior pharyngeal
arches
pharyngeal slit
between
mandibular
and
hyoid
arches retained in some fishes as the
spiracle
and in
tetrapods
as the
eustachian tube
Splanchnocranium
Mandibular arch:
palatoquadrate
(Upper element),
Meckel's element
(lower)
Hyoid arch:
hyomandibula
(
upper
),
ceratohyal
(
middle
),
hypohyal
,
Basihyal
(
bottom
) -> serial homology
I-V branchial arches:
pharyngobranchial. epibranchial
,
ceratobranchial
,
hypobranchial
,
basibranchial
Splanchnocranium-
substantially
reduced
and
modified
in tetrapods (
branchial arches
reduced,
dermal bone
replaces this)
especially in
mammals
where the
mandibular arch
is not involved with the
jaw
at all
alisphenoid
-
homologous
w/
pterygoid
in sharks
Slide
12
for diagrams
Memorize
this chart
Jaw Suspension
paleostyly
(support) in agnathans, NO
JAWS
splanchnocranium
not attached to
rest
of
skull
Lamprey
,
slide 14
Jaw Suspension
euautostyly
in all
placoderms
and
acanthodians
no suspension of
mandibular arch
Jaw suspension:
amphistyly
in primitive sharks and
osteichthyes
(2 supports)
anteriorly by a ligament from the
palatoquadrate
to the
brain case
posteriorly by the
hyoid
to the
brain case
mandible
swings down
immobilized
(jaws just flaps down)
Jaw suspension
hyostyly
in most sharks (hyoid pops out)
mandibular arch
supported only by the hyoid
jaws open downward
Jaw suspension
hyostyly
(modified) in
teleosts
hyoid fixed
and
mobile
symplectic added (open
forward
)
jaws open
forward
Jaw suspension
metautostyly
in most
tetrapods
hyoid
not involved with
jaw stapes
for
hearing
mandibualr arch
reduced to
quadrate
and
articular
(
meckles
in
adults
)
forms joint of jaw made of
dermal bones
Jaw suspension:
Craniostylic
(jaw joint fused by
dermatocranium
) in
tetrapods
(just
mammals
)
hyoid
and
mandibular arch
reduced to
ear ossicles
new jaw joint from
dermatocranium
,
squamosal
and
dentary
Jaw suspension:
articular
and
quadrate
involved with both
jaw
suspension and
hearing
in
lower synapsids
dentary-squamosal
jaw joint assumes
function
Jaw suspension:
exceptional hearing
is a vertebrate specialty ub mammals (small ear bones came from
jaws
)
Dermatocranium (thought to be
homologous
)
synapomorphies
homologous for osteichthyes -(
paired lungs
+
bony bone
has
endochondral
bones)
made of demal bones from the
dermis
,
sinks
in
makes most of the cranium of
osteichthyes
evolutionary trend is
loss
and
function
can be organized as "
series
"
partial organ in brain is
light sensitive
(low ocean dwellers)
Dermatocranium: Trend to
ger rid
of bones as you go on (
reduction
/
fusion
)
Facial
red( snout) -
preamilla
,
maxilla
,
nasal
Orbital blue
( around the
eye
) -
lacrymal
,
prefrontal
,
post frontal
,
post orbital
,
jugal
Temporal green
(
posterior
) -
inter
&
supratemporal tabular
(missing in
sauropsids
but in
mammas
) ,
squamosal
, quadratojugal
Dermatocranium:
Vault -
yellow
(skull roof)-
frontal
,
parietal
,
post parietal
Palatal
-orange
(roof of mouth) -
pterygoid
,
vomer
,
palatine
,
ectopterygoid
,
parasphenoid
(only in ray finned fishes now)
Mandibular-
purple
(
lower
jaw) -
dentary
,
splenials
,
angualr
,
subangular
,
periarticular
,
coronoids
Dermatocranium:
Gular
(
green
) - between dentary bones
opercular
(
purple
) - lateral gill protection, includes branchiostegal
Ostracoderms- jawless
heavy headshield
in many - tendency to
lighten head sheild
+ to become more
active swimmers
no clear relation
to any
gnathostomes dermatocranium
reduction
in
head armour
in
multiple groups
- divided into
parts
possible sister
group to lampreys, loss of gill openings/ filter feeders
active swimmers, did not live on the bottom
Placoderms (heavy headshield -head is different than jawed)
dermatocranium
of placoderms shows little in common with osteichthyan cranial series nor ostracoderm head shields
primary jaw overlaid with
dermal
bone, no
teeth
(made the biting surface get warn down over time)
neck joint may have allowed cranial kinesis (
autostylic
- head could swing up while bottom swung down)
Chondrichthyes
no
dermatocranium
extensive chondrocranium
(bc no dermatocranium)
palatoquadrate immobile
primitively trend to
mobile
jaws
trend for
biting
Acanthodii
dermatocranium
of
anconthodians
might have more in common with
osteichthyans
opercular series
,
large number
of
cranial scales
/
bony plates
primary jaws
Actinopterygii
- ray finned
many bones, trend to
reduce
and
lighten
trend to
cranial kinesis
(lighten to become
mobile
)
trend to
suction feeding
suspensorium
open jaws rapidly (acts as a
lever
pulls back so it pivots
forward
=
forward
opening
jaws
=
great
in
water
=
force
and
fast
)
Actinopterygii
light skull
and
protrusible premaxilla
in
teleosts
perfects
suction feeding
many teeth on jaws and elsewhere
often specialized (backwards facing to trap prey)
Rhipidistians
internal
naris and
external
naris (choana)
tear duct
Non- Amniotes & Lissamphibia
recution
+
simplification
of bones
hyoid
is now the
stapes
(columella)
no
operculars
or
gulars
branchial arches
in
larvae
hyoid apparatus
support
tongue
Lingual feeding
hyoid apparatus
often modified to support
protractile tongue
Amniotes
trend to
temporal fenestrae
Temporal fenestrae
provide space for
jaw musculature
to expand (allows for more
contraction
of the jaw muscles -
temporal
)
Lepidosauria -
diapsid
(snakes and lizards)
tuatara
(NZ) with
basic
diapsid pattern, living fossil - evovled parallel with
lizards
squamates with kinetic skull:
streptostyly
,
mobile quadrate
,
lower temporal bar
lost -
dermal
bone
snakes with highly
kinetic
skulls
dentary symphysis of
loose tissue
Archosauria
- crocs, dino, bird
crocodilians
with
rigid
skulls
bird
skull with greatly expanded
braincase
and
cranial kinesis
upper mandible
can raise sides of
jaw
can
bow
out
Synapsida
-
evolutionary trend
- rigidifying skull
well ossified, akinetic skull, reduction in number of bones - no cranial kinesis EXCEPT in
jaw joint
fewer teeth
in sockets (thecodont)
heterodont dentition
with
precise occlusion
(
bigger teeth
that fit
perfectly together
)
new jaw joint with
mobile mandible
Synapsids -
enlarged auditory bulla
that encase
ear ossicles
large tympanic bulla
extra
pallet
- secondary
pallet
secondary
palate
to allow
chewing
and
breathing
at the same time