Pectoral Girdle
• A pectoral girdle is a skeletal
complex in the body wall
immediately behind the head that
articulates with the anterior fins
or limbs.
•This is a picture of the ray-finned
fish Polypterus, which exemplifies
the basic pattern of all pectoral
girdles.
•Components:
•Scapula & Coracoid: receives
force generated by fins.
•Posttemporal: braces the girdle
against the skull.
•Clavicle: braced against the
opposite clavicle.
•Cleithrum: a major bone.
Pectoral Girdle
•In modern bony fishes
the clavicle has been lost
but the other bones
remain.
•Cartilaginous fishes have
only the endoskeletal
components that do not
ossify (shown in black) and
have none of the dermal
components (shown in
red).
Pectoral Girdle
•Dermal bones predominate in the
pectoral girdle of bony fishes, whereas
replacement bones predominate in
tetrapods.
•Tetrapods
•Early tetrapods are only different in
that they gained the interclavicle and
lost the posttemporal.
• Tetrapods either need clavicles,
coracoids or both to brace the scapula
against the sternum.
•Coracoid
•Develops from embryonic coracoid
plate: anterior ossification centers
give rise to procoracoids and
posterior centers give rise to
coracoids.
•Clavicle
•Absent: urodeles, apodans, and most
nonavian reptiles.
•Present in most mammals.
Pectoral Girdle
•Scapula
•Present in all tetrapods
with vestiges of anterior
limbs.
•Contains the glenoid fossa
for articulation with the
humeral head.
Pectoral Girdle
•Mammalian scapula
•The scapular spine divides the
scapula into supraspinous and
infraspinous fossae, where arm
muscles originate.
•Muscles also attach to the
acromion process near the glenoid
fossa.
•Mammalian clavicle
•Large in mammals with strong
forelimbs used in digging,
climbing, or flying.
•In cats the clavicle is a vestigial
splinter.
•No connections between
scapula and the sternum.
•Allows cats to withstand
the shock of landing upright
on forelimbs.
Test Questions
1. What is the purpose of the posttemporal bone in the Polypterus fish?
2. T/F Cartilaginous fish have both dermal and endoskeletal components to their
pectoral girdle.
3. _________ bones predominate in the pectoral girdle of bony fishes, whereas
__________ bones predominate in tetrapods.
4. What is the purpose of the scapula in tetrapods with anterior limbs?
5. The _________ divides the scapula into the supraspinous and infraspinous fossae.
Answers
1.
2.
3.
4.
5.
The posttemporal bone braces the pectoral girdle against the skull.
False, they lack dermal components.
Dermal; replacement
Contains the glenoid fossa for articulation with the humeral head.
Scapular spine
Pelvic Girdle (Fish)
• Consist of cartilaginous
or bony pair pelvic
Plates that meet in a
midventral pelvic
symphysis.
• No dermal bones in the
pelvic girdle of fishes or
tetrapods.
Pelvic Girdle (Tetrapods)
• Tetrapod embryos
develop cartilginous
pelvic plates.
• Each plate ossifies at two
centers to form a pubis
and a more posterior
ischium.
• At the junction of the
pubis, ischium, and ilium,
a socket, the acetabulum,
accomodates the head of
the femur.
Pelvic Girdle (Tetrapods)
• Reptiles:
– The structure of the pelvic
girdles of reptiles is
correlated with their diverse
body structure and with their
mode of locomotion.
– In most reptiles, the pubis is
directed away from the
ischium, resulting in a
triradiate girdle.
– An epipubic and hypoischial
bone frequently develops in
association with the pelvic
girdle of reptiles.
Pelvic Girdle (Birds)
• The ilia and ischia of
modern birds are
enormously expanded
and united with the
synsacrum.
• There is no ischial or
pubic symphysis.
• Absence of these
provide a wide outlet
for laying eggs.
Pelvic Girdle (Mammals)
• Ilium, ischium, and pubis
ankylose early in postnatal
life to form a left and right
innominate (coxal) bone.
• Sacroiliac joint
• Ischiopubic symphysis
• Since mammalian young are
delivered through the pelvic
outlet, the fibrocartilage is
softened by ovarian
hormone relaxin, which
expands the pelvic outlet
for delivery.
Questions
• There are dermal bones in the pelvic girdle of
tetrapods and fish. -T or F (False)
• What is the junction of the pubis, ischium, and
ilium in tetrapods called? (acetabulum)
• In reptiles, the pubis is directed away from the
ischium. What does this create? (triradiate girdle)
• Why do birds not have an ischial or pubic
symphysis? (Wide outlet for laying eggs)
• What is the ovarian hormone that promotes
expansion of the pelvic outlet? (relaxin)
Girdles, Fins, Limbs & Locomotion
Rays: located in dermis
2 varieties: lepidotrichia, in
bony fish, jointed bony
dermal scales, aligned end
to end.
Ceratotrichia, in
cartilaginous fish, long
horny rays.
Girdles, Fins, Limbs & Locomotion
Fin rays generate from a row of
cartilaginous or bony basalia and one or
more rays of radialia.
Striated muscle mass extends into the
base of the fin and inserts onto available
skeletal elements.
Different taxa exhibit wide variety in
morphology, making identification of
ancestral fin type (archipterygium) highly
unlikely.
Girdles, Fins, Limbs & Locomotion
Fishes have 1, 2, or a
series of dorsal fins, and
may have an anal fin. Act
as keels keeping fish from
rolling left to right.
Girdles, Fins, Limbs & Locomotion
Paired fins:
Lobed-fleshy proximal
lobe containing fin
skeleton and muscles,
membranous distal
portion stiffened by rays
Fin fold- broad base
Ray fins- very flexible fins,
lost components of basal
skeleton, some have no
pelvic fins.
Spiny fins- all extinct.
Tetrapod Limbs
Tetrapods typically have four limbs.
• Some limbs have been modified as wings or
paddles while others have been lost all together.
• Early tetrapods had short limbs.
• In transition from water to land a shift from
horizontal structure to vertical was seen.
• Later a shift from sprawling stance to upright
occurred.
Tetrapod limbs consist of three segments.
• Propdium
• Epipodium
• Autopodium
Propodium and Epipodium
The epipodium (forearm) is composed of the ulna and radius.
•The radius bears most of the weight.
•The ulna is longer than the radius.
•The ulna sometimes fuses with the radius or may be vestigial.
The humerus is the single bone located in the propodium (upper arm).
•The humerus of all tetrapods is very similar, any variations are adaptive
modifications.
Thigh and Lower Leg Bones
The thigh bone is the femur, the tibia and fibula are bones of the lower leg. There is little
difference in these bones from one tetrapod to another (see picture).
The patella (kneecap), which developed in birds and mammals, protects the joint from
abrasive from the tendon.
When the fibula unites with the tibia the tibiofibula is formed (frogs).
In birds the tibia and the proximal row of tarsals fuse to form the tibiotarsus.
Manus: The Hand
• Made up of wrist, palm, and digits
• Very similar among species
• Digits range in number; dominant
is pentadactyl (five-digit) limb
• Carpus (wrist): Three regular rows of carpal bones
– Proximal row: radiale, ulnare, intermedium
• Ulnar end in most reptiles and mammals, sesamoid bone- pisiform
– Middle row: centralia
– Distal row: distal carpals 1-5
• Metacarpals
– Primitively, as many metacarpals as digits
• Digits: Consist of phalanges
– Early formula for pentadactyl
hand: 2-3-4-5-3
– Modern mammals almost
universally 2-3-3-3-3
• Modifications of the manus
– Reduction in number of bones
by evolutionary loss or fusion
• Centralia commonly unite with proximal carpals or disappear; some reptiles
and mammals have single centrale
• Fusion of distal carpals 4 & 5 = hamate bone
• Phalanges or entire digits may be lost (metacarpal becomes vestigial or lost)
– Disproportionate lengthening or shortening (less common)
• Amphibians
– Most have 5 digits on hindlimb,
4 on forelimb, some have less
– Number of wrist bones is
smaller in modern than in
labyrinthodonts
– Line of descent is conjectural,
so no way to tell homologies
• Nonavian reptiles and
mammals
–
–
–
–
Generally pentadactyl, with five metacarpals
Crocodiles: wrist is five bones
Birds: entire manus is reduced
Modifications for various environments
QUIZ
• What is the formula for the phalanges of most modern
mammals?
– A) 2-3-4-5-3 B) 2-3-3-3-3 C) 2-3-3-3-2 D) 2-3-5-3-2
• True or False: In birds, the proximal row of tarsals fuse to form
the tibiofibula
• Name the three regions of tetrapod limbs
• Choose all the bones that are part of the manus:
– Radius, phalanges, radiale, ulna, metacarpals, intermedium, ulnare
• The epipodium is composed of which two bones?:
–
–
–
–
A) Radius, humerus
B) Tibia, fibula
C) Ulna, radius
D) Ulna, femur
QUIZ Answers
•
•
•
•
B
False
Propdium, Epipodium, Autopodium
Phalanges, radiale, metacarpals, intermedium,
ulnare
• C
Flight
• Carpometacarpus- fusion of 3 metacarpals and 3 distal carpals
• 3 fingers present…1st finger called alula (elongated, prominent,
independent)
– Songbirds – broad short wings
– Carnivorous – long, broad wings
– Hummingbird – hand is longer than its arm
• Hands exert a strong breaking force for landing
Flight
• Unlike birds, the hand is
the main part of the
wings in bats
• Normal thumb w/ claw,
but elongated fingersboth metacarpals and
phalanges
• Movement of the hand
responsible for takeoff
and true flight
Girdles, Fins, Limbs & Locomotion
Adaptations for Life in the Water
The “hands” have become
Paddlelike Flippers in well adapted marine
amniotes
Flippers are generally
flattened and stout
In several taxa,
the number of phalanges
has greatly increased
In some Ichthyosaurs
there were as many as 26 phalanges
per digit and more than 100 in a single
hand!
Girdles, Fins, Limbs & Locomotion
Most other swimmers have
skeletons that conform closely
to the tetrapod pattern
Some aquatic animals have
lost their hind limbs…
Use flipperlike “wings” for
thrust, webbed feet for
rudders (ie. Penguins)
Others don’t use foreflippers
for swimming….hind limbs
Questions:
1. Carpometacarpus is the fusion of ____
metacarpals and ____ carpals
– A) 2, 6
– C) 4, 2
--B) 3, 3
--D) 2, 4
2. The first digit in birds that is elongated,
prominent, and independently movable…
A) ulnare
C) alula
B) radiale
D) manus
Questions continued
3. True or False: In the fingers of a bat, both the
metacarpals and phalanges are elongated.
True
4. What adaptation has been vital for aquatic
marine amniotes, and what do they look like
(shape)?
Paddlelike flippers; flattened and stout
5. True or False: Penguins obtain thrust for
swimming solely from their foreflippers?
true
Running and Grasping
• Plantigrade- Digits, wrist,
and ankle rest on ground.
ie. Monotremes,
marsupials, primates
• Digitigrade- Weight borne
on digital arches with wrist
and ankle elevated. ie.
Rabbits, rodents and
carnivores
• Unguligrade- Walk on four,
three, two or one digit with
wrist and ankle elevated on
elongated metatarsals.
ie. Ungulates
Running and Grasping
• Artiodactyles are
paraxonic meaning
their bodyweight is
borne evenly on two
parallel axes.
• Perissodactyles are
mesaxonic meaning
weight tends to be
distributed to the
middle digit
Running and Grasping
• Tibiotarsus- Found in
birds; fused proximal
tarsals and tibia.
• Tarsometatarsus- fused
distal tarsals along with
three fused metatarsals.
• Joint between
tarsometatarsus and
toes allows the bird to
be poised for flight.
Running and Grasping
• In homonoids the
metatarsal arch allows
distribution of weight
over four solid bases;
the heel and the ball of
each foot.
• Hallux- the great toe;
opposable in most
primates but not
humans, aids in
grasping.
Running and Grasping
• 1 - Perissodactyl
• 2 – Canine foot
structure
• 3 – Opposable in
primates
• 4 - Artiodactyl
• 5 – Human foot
structure
•
•
•
•
•
A plantigrade
B digitigrade
C paraxonic
D mesaxonic
E hallux
Hind Feet (Amphibians and Reptiles)
• Comparable with
manus except for
pisiform
• Basal amphibians
display a prehallux
• Reptiles have fused
tarsal bones known as
the astragalocalcaneus
Hind Feet (Birds and Mammals)
• Bird feet are highly
modified, with a
tibiotarsus and fusion of
the distal tarsals with
the metatarsals
• Mammals have no
intratarsal joint, but a
hinge joint at the ankle.
Marine Movement
• Sculling
– Anterior flippers only for
maneuvering
– Lateral undulations of
posterior trunk and flippers
key
– Neck elongated
• Cetaceans thrust forward
by dorsal and ventral
undulations with stiff tail
– “Legless gallop”
Terrestrial Trekking
• Hind flippers switch
from swimming position
into a tetrapod stance
• Flexible wrist joint
further helps
locomotion on land
• Wriggling seals’ hind
limbs are permanently
bound to the tail
Questions
• Name one similarity between reptile hind feet
and bird feet
• Name one difference between amphibian feet
and reptile feet
• Which group of animals lacks an intratarsal joint?
• What pedal feature is exclusively a hominoid
characteristic?
• Name the primary difference in locomotion
between wriggling and fur seals
Answers
•
•
•
•
•
Intratarsal joint
Fusion of the tarsal bones
Mammals
Metatarsal arch
Wriggling seals have a hind limb permanently
bound to the tail, while fur seals can switch
their hind flippers into a tetrapod stance.
Origin of Tetrapod Limbs
Two hypotheses:
•
Modification of pre-existing
structures or
• Formation of new features
Common to both hypotheses are the
origin of proximal elements of the
limb
•
Fig. 10.44 comparison of Devonian
rhipidistian fish’s pectoral fin and
early tetrapod’s forelimb.
Some necessary modifications for
limb development are:
•
•
•
•
Elongation of the two bones of the
epodium (limb bones immediately
above the hand or foot.).
Rotation of long axes of humerus and
femur to parallel the vertebral
column.
Formation of hinge joints
Emergence of definitive manus
(hand) and pes (foot).
Tetrapod forelimb
Rhipidistian pectoral fin
Origin of Tetrapod Limbs
• It is possible that early
Rhipidistian fins were
used for resting on the
water bottom. Minor
modifications could have
led to “walking” on the
muddy floor; and later
venturing onto land.
• Some type of pressure(s)
drove craniates onto land
– so it was inevitable that
a more suitable limb
would evolve.
• (Some fish today use
pectoral fins to move on
land, example: the
Australian lungfish)
•http://cache.eb.com/eb/image?id=2221&rendTypeId=4
Locomotion with no Limbs
• Snakes often combine several
methods of locomotion
• Limbless amphibians on land
use lateral undulation of the
body and tail (like a fish) to
move.
• Marine sea snakes have a
flattened tail that they use
like an oar to propel them
through the water.
• All movements are made
possible by modifications in:
- the skin
- body wall musculature
- ribs
- the vertebral column
http://photos.si.edu/uw/csnake.gif
http://www.projectmosquitia.com/Dermophis_mexicana.jpg
Locomotion with no Limbs
•
The different types of locomotion used by
snakes and other limbless tetrapods are:
Serpentine – uses irregular loops propped
against any stationary object that allow snake
to push off from. Uses waves of muscle
contraction from head to tail.
–
•
•
•
Serpentine is the most common method of
locomotion used by snakes and lizards.
Also referred to as lateral undulation, but
there are slight differences
Rectilinear locomotion – the snake moves in
a straight line. It relies on friction between
the ventral skin and substrate. The ventral
skin acts like a conveyor belt. Belly scutes
alternate pressing and sliding forward on the
substrate to create movement.
Sidewinding – Enables snakes (like
rattlesnakes) to inhabit sandy deserts.
Useful when the other methods would be
clumsy or ineffective. Snakes propel
themselves with modified serpentine
movements while thrusting their anterior
portion forward.
Concertina – Similar to sidewinding.
Movement similar to an accordian.
http://static.howstuffworks.com/gif/snake-motion.gif
Review Questions
1.
Match the following types of
limbless locomotion to the
diagram.
•
•
•
•
2.
3.
4.
Serpentine
Rectilinear Locomotion
Sidewinding
Concertina
1.
2.
What is the most common method
of locomotion used by limbless
creatures?
True or False. It is believed that
tetrapod limbs evolved from fins.
a. the skin
Limbless locomotion is made
b. body wall
possible by modifications in:
musculature
c. Ribs
3.
4.
d. the vertebral column
e. all of the above
5.
Which of the following is not necessary for limb
development
a.
Elongation of the two bones of the epodium (limb bones immediately
above the hand or foot.).
Rotation of long axes of humerus and femur to parallel the vertebral
column.
Formation of hinge joints
Emergence of definitive manus (hand) and pes (foot).
All are necessary
b.
c.
d.
e.