Comp Vert Chapter 9 (Exam 2)

What is the appendicular skeleton?

The paired fins or limbs and their supporting pectoral and pelvic girdles.

What are the main functions of the appendicular skeleton?

Movement, body support, stability, and transmission of muscular forces.

What does the pectoral girdle support?

The pectoral fins of fishes or forelimbs of tetrapods.

What does the pelvic girdle support?

The pelvic fins of fishes or hindlimbs of tetrapods.

How does the axial skeleton differ from the appendicular skeleton?

The axial skeleton includes the skull, vertebrae, and ribs; the appendicular skeleton includes paired appendages and girdles.

What are pterygiophores?

Internal skeletal supports of fish fins consisting of basals and radials.

What are basals in fish fins?

Large supporting skeletal elements located close to the body.

What are radials in fish fins?

Smaller skeletal elements extending outward from the basals.

What are ceratotrichia?

Elastic, protein-based fin rays found in sharks and other elasmobranchs.

What are lepidotrichia?

Segmented skeletal fin rays found in bony fishes.

What are actinotrichia?

Thin supporting rods that strengthen the tips of some bony-fish fins.

What is a chiridium?

A muscular, jointed tetrapod limb with digits.

What are the three regions of a tetrapod limb?

Stylopodium, zeugopodium, and autopodium.

What bones form the stylopodium?

The humerus in a forelimb or femur in a hindlimb.

What bones form the zeugopodium?

Radius and ulna in the forelimb; tibia and fibula in the hindlimb.

What bones form the autopodium?

Forelimb: carpals, metacarpals, phalanges. Hindlimb: tarsals, metatarsals, phalanges.

What are the manus and pes?

Manus is the forelimb autopodium; pes is the hindlimb autopodium.

What is the glenoid fossa?

The pectoral-girdle socket that receives the humerus.

What is the acetabulum?

The pelvic-girdle socket that receives the femur.

What are pitch, roll, and yaw in swimming?

Pitch: head up or down; roll: rotation around long axis; yaw: side-to-side turning.

Why did paired fins evolve?

To control stability, steering, and maneuvering in water.

What characterizes an archipterygial fin?

A central skeletal axis with radials extending on both sides.

What characterizes a metapterygial fin?

A posterior main skeletal axis with most radials extending anteriorly.

Who proposed the gill-arch theory?

Carl Gegenbaur.

What does the gill-arch theory propose?

Paired fins evolved from modified gill arches and gill rays.

What is a weakness of the gill-arch theory?

It poorly explains pelvic-girdle position, dermal shoulder bones, and developmental differences.

Who independently proposed the fin-fold theory?

F. M. Balfour and J. K. Thacher.

What does the fin-fold theory propose?

Continuous ventrolateral body folds became separate pectoral and pelvic fins.

What evidence is discussed for the fin-fold theory?

Early fin-fold fossils, acanthodian spine rows, and shark embryonic lateral thickenings.

What roles do Tbx5 and Tbx4 play?

Tbx5 is associated with anterior appendages; Tbx4 with posterior appendages.

What does Engrailed-1 help establish?

Dorsoventral patterning of developing appendages.

What is the developmental role of Sonic hedgehog (Shh)?

Appendage growth and skeletal patterning.

What is the developmental role of Hox genes?

Patterning skeletal elements and digits.

In what order do tetrapod limb regions form?

Stylopodium, then zeugopodium, then autopodium and digits.

What are agnathans?

Jawless vertebrates; living examples include lampreys and hagfishes.

Do living agnathans have paired fins?

No, modern lampreys and hagfishes lack paired fins.

What were placoderms?

Extinct armored jawed fishes with paired appendages.

What is distinctive about Bothriolepis?

It had heavily armored pectoral appendages.

Which vertebrates are chondrichthyans?

Sharks, rays, and chimaeras; their internal skeleton is primarily cartilaginous.

Name the three main basal regions of a shark pectoral fin.

Propterygium (anterior), mesopterygium (middle), metapterygium (posterior).

What is the scapulocoracoid?

The endoskeletal shoulder support in many fishes.

What is the pubioischiac bar?

A skeletal support of the shark pelvic girdle.

What were acanthodians known for?

Prominent fin spines, sometimes in extra rows between pectoral and pelvic regions.

What are actinopterygians?

Ray-finned fishes with fins primarily supported by lepidotrichia.

What is the cleithrum?

A major dermal bone of the pectoral girdle in ray-finned fishes.

What are sarcopterygians?

Lobe-finned fishes with fleshy fin bases containing internal bones and muscles.

Why is Eusthenopteron important?

Its fin skeleton includes elements comparable to humerus, radius, and ulna.

From which lineage did tetrapod limbs evolve?

Sarcopterygian or lobe-finned ancestors.

Why did the tetrapod pectoral girdle separate from the skull?

To increase independent head movement and reduce transmission of locomotor impact forces.

What are the three major bones of the tetrapod pelvic girdle?

Ilium, ischium, and pubis.

What is the function of the ilium?

The dorsal pelvis connects with the sacral region.

How does the pelvic girdle attach to the axial skeleton on land?

Through a strong skeletal connection to the sacrum.

How does the terrestrial pectoral girdle commonly attach to the trunk?

Through muscular suspension that helps absorb shocks.

How do pelvic and pectoral girdles differ mechanically on land?

The pelvis transmits strong propulsive forces; the shoulder often cushions impacts.

What do polydactyly and pentadactyly mean?

Polydactyly: more than five digits; pentadactyly: five digits.

How many digits did Acanthostega have in its forelimb?

Eight.

How many digits did Ichthyostega have in its hindlimb?

Seven.

How many digits did Tulerpeton have?

Six.

What are the astragalus and calcaneum?

Important proximal ankle bones.

What are the tibiotarsus and tarsometatarsus?

Specialized fused hindlimb elements in birds.

Why did vertebrate limbs require reinforcement on land?

Gravity demands greater weight support than buoyant water does.

Did limb-like structures evolve only after vertebrates lived on land?

No; they began evolving in aquatic ancestors.

What is lateral undulation?

Side-to-side waves of body movement used in swimming and early tetrapod locomotion.

What is thrust in swimming?

The propulsive force that moves an animal forward.

What is a gait?

The pattern and timing of footfalls during locomotion.

What is duty factor?

The fraction of a stride cycle that a foot remains in contact with the ground.

What duty factor generally distinguishes walking from running?

Walking is usually 50% or greater; running is generally below 50%.

What is a diagonal-sequence gait?

Coordination of diagonally opposite forelimbs and hindlimbs.

What is a lateral-sequence gait?

Movement of limbs on the same side in sequence, often supporting stability.

What is cursorial locomotion?

Running-specialized locomotion emphasizing speed and efficiency.

What skeletal posture change is typical of many cursorial animals?

Limbs shift from a sprawling posture toward positioning beneath the body.

What is the sagittal plane of limb movement?

The forward-backward plane where limb motion is concentrated in many runners.

What determines running speed?

Stride length multiplied by stride rate.

What is stride length?

Distance traveled during one complete stride.

What is stride rate?

Number of strides completed per unit time.

What is plantigrade locomotion?

Walking with most or all of the foot contacting the ground, as in humans.

What is digitigrade locomotion?

Walking on digits while the heel stays elevated, as in cats and dogs.

What is unguligrade locomotion?

Walking on digit tips, often protected by hooves, as in horses.

How do pace and trot differ?

Pace moves same-side limbs together; trot moves diagonally opposite limbs together.

What is pronking?

A gait in which all four feet leave and contact the ground together.

How do a bound and a half-bound differ?

In a bound, forelimbs generally land together; in a half-bound, separately.

What are gallop and canter?

Gallop is a fast asymmetric gait; canter is a slower, usually three-beat gait.

Why do animals change gaits as speed increases?

Different gaits are energetically more efficient at different speeds.

How do cheetah and horse running adaptations differ?

Cheetahs use flexible spines for fast sprints; horses emphasize sustained efficient travel.

What are the two major forms of aerial locomotion?

Gliding and powered flight.

Which vertebrate groups independently evolved powered flight?

Birds, bats, and pterosaurs.

What does the arboreal theory propose about bird flight?

Flight evolved from tree-dwelling ancestors progressing from leaping and gliding.

What does the insect-net theory propose?

Feathered forelimbs first helped catch insects, later gaining aerodynamic roles.

What is WAIR?

Wing-Assisted Incline Running: wing movements help animals run up steep surfaces.

What do primary flight feathers mainly do?

Attach near the manus and contribute strongly to thrust and control.

What do secondary flight feathers mainly do?

Attach along the forearm and contribute strongly to lift.

What do contour feathers do?

Streamline the body and help reduce drag.

Name four skeletal adaptations of birds for flight.

Pneumatic bones, enlarged sternum, furcula, and synsacrum.

What is the main role of the downstroke?

Producing much of the lift and thrust in ordinary forward flapping flight.

What is hovering flight?

Remaining nearly stationary in air using specialized wing movements, as in hummingbirds.

What is soaring flight?

Using rising air currents to stay aloft with relatively little flapping.

What are the four forces acting during flight?

Lift, weight, thrust, and drag.

What is the angle of attack?

The angle between a wing reference line and the oncoming airflow; too large an angle can cause stall.

What is a wing stall and how does the alula help?

A stall is major lift loss from airflow separation; the alula helps delay it.

What is fossorial locomotion and what limbs favor it?

Digging and burrowing, favored by short, powerful forelimbs, robust bones, and strong claws.