Chapter 9 Part 2: Appendicular skeleton

Question 1

Pectoral Girdle in Acanthodians

Answer 1

have rows of spines between pectoral and pelvic elements; pectoral spine with the small radials and fused elements at its base

Question 2

Pectoral Girdle in Teleostomi

Answer 2

reduction of dermal elements and expansion of endochondral elements

Question 3

Pectoral Girdle in Actinopterygians

Answer 3

partly endochondral but mostly dermal

Question 4

Pectoral girdle in Sarcopterygians

Answer 4

Only the skeletal elements of the Australian lungfish (Neoceratodus) exhibit features that can be homologized to those of other fishes

• Lacks an interclavicle - includes a crescent of four bones (clavicle, cleithrum, postcleithrum, supracleithrum) and scapulocoracoid

Question 5

Pectoral Girdle in Rhipidistians

Answer 5

interclavicle first appears in them

Question 6

Pectoral Girdle in mammals

Answer 6

The clavicle and interclavicle are present in therapsids and monotremes

Question 7

Pectoral Girdle in Marsupials and Eutherians

Answer 7

interclavicle is absent, the clavicle often is reduced in size, and the scapula becomes the predominant shoulder element

The coracoid (posterior coracoid) is reduced and fused to the scapula as the coracoid process

Question 8

• Be able to describe the dermal and replacement elements of the pectoral girdle

Answer 8

Dermal elements: interclavicle, clavicle, cleithrum, supracletihrum, posttemporal, postcleithrum

Endochondral elements: coracoid, procoracoid, scapula

The old “coracoid”: procoracoid (= anterior coracoid)
A new “coracoid.”: coracoid (= posterior coracoid

Question 9

Pectoral Girdle

Answer 9

A variable series of skeletal elements that functions as a brace for the anterior appendages

Question 10

What is the general trend in the relative contributions of the two types of elements in the evolution from fishes to tetrapods?

Answer 10

Reduction in Dermal Elements: In fish, the dermal skeleton (including scales and bony plates) is highly developed. As tetrapods evolved, there’s a significant reduction in these dermal elements. This change correlates with the shift to a terrestrial environment where heavy dermal armor becomes less advantageous.

Increase in Endoskeletal Elements: The endoskeleton (internal skeleton) becomes more prominent and complex in tetrapods. This includes the development of robust limb bones and vertebrae to support the body’s weight against gravity. The axial skeleton, particularly the vertebral column, strengthens to accommodate the need for effective terrestrial locomotion

Question 11

What is unique about the pectoral girdle of cartilaginous fishes?

Answer 11

They have a liliac process, puboischiac bar instead of coracoid bar, longer/wider stretch of ceratotrichia, and female and male differentiation

Question 12

What dermal elements are lost in the transition from fish to tetrapod?

Answer 12

Dermal scales and bone, ganoid and cosmoid scales

Dermal Scales: Fish generally have dermal scales that provide protection and reduce water resistance. As tetrapods moved onto land, these scales became less useful .
Lateral Line System: This system is either lost or significantly reduced in tetrapods, as they don’t need it in a terrestrial environment.

Ganoid Scales: not present in tetrapods

Question 13

What is the origin of the tetrapod procoracoid?

Answer 13

o In early osteichthyes, seen originally as scapulocorcacoid
o In early tetrapods, the scapulocroacoid splits into 2 bones: scapula and proccoracoid

Question 14

What is the name of the new bone that appears in the amniote pectoral girdle?

What is the fate of that bone in therian mammals?

Answer 14

The new bone that appears in the amniote pectoral girdle is called the interclavicle.

In therian mammals (which include marsupials and placental mammals), the interclavicle is lost or reduced significantly. Instead, the pectoral girdle relies more heavily on the clavicles and scapulae to support and facilitate the movements of the forelimbs.

Question 15

What are the three pelvic girdle bones found in all vertebrates?

Answer 15

Always 3 bones in tetrapods: ilium, ischium, pubis
Shapes of the bones may differ but:
o Ischium oriented caudally
o Ilium oriented dorsally
o Pubis oriented cranially

Question 16

What is the additional bone found in marsupials of the pelvic girdle?

Answer 16

epipubic bone

These bones extend from the pubis towards the midline and are thought to support the abdominal and reproductive organs.

Question 17

Describe the limbs of early tetrapods

Answer 17

Earliest tetrapods were polydactlous (many digits), like 7-8 digits many

Question 18

There are three components to the tetrapod autopodium/limb – what are they?

Answer 18

o Tarsal in Hindlimb/Carpals in Forelimb
o Metatarsals in hindlimb/metacarpals in forelimb
o Phalanges – basic tetrapod limb consist of five digits(pentadactyly)

Question 19

describe some modifications to the tetrapod autopodium

Answer 19

A decrease in the number of bones by loss or fusion; Loss and fusion of metatarsals and metacarpals from early amniote to mammal

A disproportionate lengthening/shortening of some bones; Seen in manus and pes, lengthening of metacarpals in some

Question 20

Describe examples of lengthening and shortening of bones(dispraportionate)

Answer 20

Examples: lizards, artiodactyl, bird, turtles, etc.

Varies from species to species

Birds have reduction of bones near or in autopodium; Autpodium develops carpometacarpus

Question 21

Give examples of loss and fusion from early amniotes to mammals

Answer 21

Sirenians(manatees) have reduction of hindlimb/loss of hindlimb

Cetaceans (killer whales, dolphins, humpback whale, etc) – have forelimbs only