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 Questions1. 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.

Answers1. The posttemporal bone braces the pectoral girdle against the skull.2. False, they lack dermal components.3. Dermal; replacement4. Contains the glenoid fossa for articulation with the humeral head.5. 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 & LocomotionFin 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 & LocomotionPaired 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 LimbsTetrapods 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 EpipodiumThe 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 BonesThe 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 fingers- both metacarpals and phalanges

• Movement of the hand responsible for takeoff and true flight

Girdles, Fins, Limbs & Locomotion

The “hands” have becomePaddlelike Flippers in well adapted marine amniotes

Flippers are generally flattened and stout

In several taxa, the number of phalanges has greatly increased

In some Ichthyosaursthere were as many as 26 phalangesper digit and more than 100 in a single hand!

Adaptations for Life in the Water

Girdles, Fins, Limbs & LocomotionMost 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 --B) 3, 3– C) 4, 2 --D) 2, 4

2. The first digit in birds that is elongated, prominent, and independently movable…

A) ulnare B) radialeC) alula D) manus

Questions continued3. 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 LimbsTwo hypotheses:• Modification of pre-existing

structures or• Formation of new featuresCommon to both hypotheses are the

origin of proximal elements of the limb

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).

• Fig. 10.44 comparison of Devonian rhipidistian fish’s pectoral fin and early tetrapod’s forelimb.

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://www.projectmosquitia.com/Dermophis_mexicana.jpg

http://photos.si.edu/uw/csnake.gif

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.– 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.

Serpentine is the most common method of locomotion used by snakes and lizards.

http://static.howstuffworks.com/gif/snake-motion.gif

Review Questions1. Match the following types of

limbless locomotion to the diagram.• Serpentine• Rectilinear Locomotion• Sidewinding• Concertina

2. What is the most common method of locomotion used by limbless creatures?

3. True or False. It is believed that tetrapod limbs evolved from fins.

4. Limbless locomotion is made possible by modifications in:

1.

3.

2.

4.

a. the skinb. body wall

musculaturec. Ribs

d. the vertebral columne. 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.).

b. Rotation of long axes of humerus and femur to parallel the vertebral column.

c. Formation of hinge jointsd. Emergence of definitive manus (hand) and pes (foot). e. All are necessary