Figure 9.1.

 Exoskeleton or dermal skeleton
 Dermal bony armor of ostracoderms
 Bony scales in ancient fish
 Cranial dermal armor arose from neural crest cells

 Endoskeleton
 Internal to skin
 Where once exoskeleton
 Ex: clavicle, nasal, frontal, and parietal bone
 Other endoskeletal elements were never part of the dermal skeleton
 Ex: scapula, vertebrae, ribs, sternum, brain case, and extremity bones

 All bone develops from mesenchyme
 Neural crest cells
 Membrane bone- arises from mesenchyme without passing through cartilaginous intermediate
 exoskeleton
 Replacement bone- arises from existing cartilage
 endoskeleton

 Visceral Skeleton
 Jaw cartilages and middle ear bones


Weberian ossicles of fish (are referred to as ear ossicles)
Derived from transverse processes of anterior most vertebrae
 Somatic Skeleton
 Remaining internal bones developing from mesoderm proper
 Somite and sclerotome
 Axial Skeleton
 Appendicular Skeleton



Arise from sclerotome cells of somites

Morphogenesis
Sclerotome divides into posterior and anterior halves





Halves join with segments of adjacent sclerotomes
Centrum formed from junction
Vertebrae are intersegmental
Myotome doesn’t move

Posterior segment forms costal process
Site of rib attachment

Figure 9.2. (a) sclerotome divides (b) halves join with adjacent halves of next sclerotome (c) junction forms centrum (see book figure 8.12)
Figure 9.3. Developing vertebral column showing intersegmental position
(see book figure 8.12).




Cartilaginous or bony
From occipital region to tail

Vertebrae types based on centrum structure
Centrum is common feature in all vertebrae







Acelous- flat anterior and posterior surface
Mammals

Amphicelous- concavities of anterior and posterior surfaces
Fish, primitive salamanders

Procelous- concavity on anterior surface
Most reptiles

Opisthocelous- concavity of posterior surface
Most salamanders

Heterocelous- saddle-shaped
Neck of birds and turtles

Figure 9.4. Vertebral types based on articular surface of centra
(book figure 8.4).



Transition from crossopterygians to labyrinthodonts


Different types of vertebrae came from primitive, rachitomous labyrinthodont vertebrae
Two pleurocentra and U-shaped hypocentrum
Hypocentrum is lost and pleurocentrem enlarges and gives rise to centrum of modern amniote
Figure 9.5. Modifications from labyrinthodont to modern amniote vertebrae. Hypocentrum is diagonal lines. Pleurocentrum is red
(see book figure 8.3).



Grouped according to body region

Amphibians
First to possess a cervical vertebrae
Figure 9.7. Regions of vertebral column.
Figure 9.6. Single cervical vertebrae of anuran (book figure
8.13).




Atlas as 1st and axis as
2nd cervicals
Turtle: 8 cervicals, 2 sacrals, 10 dorsals, 16-
30 caudals
Alligator: 8 cervicals, 11 thoracic, 5 lumbar, 2 sacrals, up to 40 caudals
Figure 9.8. atlas and axis cervical vertebrae.
Figure 9.9. Dorsal view of sacral vertebrae of vertebrates.



Possess atlas and axis
13-14 free cervicals, 4 fused thoracics, fused synsacrum, free caudals, pygostyle
Figure 9.10. Pigeon vertebral column (see book figure 8.31).

 Synsacrum
 Fuses with pelvic bone
 Reduction in bone mass
Figure 9.11. Pigeon skeleton: trunk, tail, and pectoral girdle.
Figure 9.12. Synsacrum and pelvic girdle left lateral (a) and ventral (b) views (book figure 8.31).

 Most species have 7 cervicals
 12 thoracic and 5 lumbar compose dorsal vertebrae
 ancestral mammals possessed ~ 27 presacrals
 sacrum 2-5 fused vertebrae (ankylosed)
 caudals are variable
 primates have 2-5 fused into coccyx




Dogfish- develop dorsal ribs


Most teleost- develop ventral ribs
Tetrapods- have dorsal and ventral ribs


Current theory is that the tetrapod rib is homologous to the dorsal rib of fishes
Primitive tetrapods have bicipital ribs - 2 portions articulate with vertebrae
Tuberculum- dorsal head
Capitulum- ventral head
Figure 9.13. Dorsal and ventral ribs
(book figure 8.6 and 8.7).

 Agnathans- no ribs
 Amphibians- ribs never reach sternum
 Birds- flat processes extending off ribs posteriorly (uncinate processes)
Figure 9.14. Uncinate processes of bird (see book figure 8.8).
Figure 9.15. Vertebrae and ribs of alligator
(book figure 8.2).

 Strictly a tetrapod structure
 Amphibians- poorly formed
 Reptiles - cartilaginous plates
 Snakes, legless lizards, turtles have no sternum
 Alligator- extends down belly
 Ribs fused it sternum
 Gastralia
Figure 9.16. Ribs and gastralia of alligator (book figure
8.2).

 Birds- unusual, keeled sternum in carinates
 Mammals- well developed sternum
 Rod shaped
 Segments: manubrium, sternebrae, xiphisternum and xiphoid process
Figure 9.17. Keeled sternum of bird
(book figure 8.8).
Figure 9.18. Tetrapod sterna
(book figure 8.8).

 Develop by endochondral or intramembranous ossification
 In areas subject to continual stress
Ex: Os cordis, rostral bone, os penis, os clitoridis






Os cordis- interventricular septum in deer heart
Rostral bone- snout of pig
Os penis (baculum)- embedded in penis of lower primates
Os clitoridis- embedded in clitoris of otters
Others include falciform, sesamoid, patella, pisiform
Figure 9.19. Heterotopic bones .

 Two functionally independent cartilaginous components derived from replacement bone
1. Neurocranium
(= chondrocranium)
2. Splanchnocranium
Figure 9.20. Dog skull. Sources of the various bones are outlined: dermatocranium (pink), neurocranium (= chondrocranium)-
(blue); splanchnocranium (yellow)

Figure 9.21.





Protects brain and anterior part of spinal cord
Sense organ capsules
Cartilaginous brain case is embryonic adaptation
Four ossification centers
Figure 9.22. Development of cartilaginous neurocranium (book figure 7.3).

 Occipital region
 Sphenoid region
 Ethmoid region
 Otic region
Figure 9.23. Neurocranium of human skull.

 Occipital Region
 Basioccipital, 2 exoccipitals, supraoccipital
 Forms single occipital bone in mammals
 Sphenoid Region
 Basisphenoid, orbitosphenoid, presphenoid, laterosphenoid
 Fuse to form one sphenoid bone in mammals
Figure 9.24. Sphenoid bone.

Figure 9.25. Human skull (a) cribriform plate (b) frontal bone (c) temporal bone
(d) ethmoid bone (e) sphenoid bone (f) foramen magnum.
Figure 9.26. Sphenoid bone.

 Ethmoid Region
 Anterior to sphenoid
 Cribriform plate, olfactory foramina, terminals, mesamoid
 Fuse to form ethmoid in mammals
 Otic Region
 Three bones in tetrapods
 Prootic
 Opisthotic
 Epiotic
 Unite to form petrosal bone in birds and mammals
 Forms temporal in mammals

Figure 9.27. Temporal bone of human skull
(book figure 9.28).
Figure 9.28. Multiple nature of temporal bone of mammals (see book figure 7.53).

Figure 9.29. Intramembranous ossification of human skull. Embryonic, cartilaginous neurocranium is black. Neurocranial bones are red. Other is dermal mesenchyme.

 Viscerocranium, although a misnomer.
- Visceral arches
- Branchial region
Figure 9.30. Primitive splanchnocranium.
Figure 9.31. Splanchnocranium of human.
Skeletal derivatives of 2 nd through 5 th pharyngeal arches (see book Table 7.2).



1st visceral arch- mandibular


Meckel’s cartilage  malleus
Palatoquadrate (quadrate)  incus
2nd visceral arch- hyoid
 hyomandibula  columella (stapes)

 ceratohyal  styloid process and anterior horn of hyoid basihyal  body of hyoid
Figure 9.32. Caudal end of
Meckel’s cartilage and developing middle ear cavity.

 Alisphenoid- part of sphenoid
 Malleus, incus- 1st arch
 Stapes- 2nd arch
 Styloid- 2nd arch
 Hyoid- mainly basihyal
Figure 9.33. Derivatives of the human visceral skeleton (red).

Figure 9.34. Skeletal derivatives of pharyngeal arches (book Table 7.2).




Membrane bone, not replacement bone
Dermal bones of skull
Upper jaw and face, palates, mandible
Figure 9.35. Pattern that tetrapod dermatocrania (see book figure 7.10).

Figure 9.36. Dog skull showing dermatocranium (pink), chondrocranium
(blue), and splanchnocranium (yellow).
Figure 9.37. Hypothetical derivations of skull bones. (Box Essay 7.1)





Nasal, frontal, parietal, squamosal (facial and roofing bones)
Dentary
Vomer, palatine, pterygoid (primary palate)
Premaxilla, maxillary, jugal (secondary palate)
Figure 9.38. Lizard skull.

Figure 9.39. (book figure 7.55).

Figure 9.40. (book figure 7.66).





Pectoral Girdle
Pelvic Girdle
Appendages
Adaptations for Speed

 2 sets of elements: cartilage or replacement bone/membrane bone


Replacement bones
 Coracoid, scapula, suprascapula
Membrane bones
 Clavicle, cleithrum, supracleithrum
Figure 9.41. Pectoral girdle along phylogenetic lines.
Dermal bones are red. Replacement bones are black.

Reduction in number of bones through evolution




Shark- only cartilagenous components
Alligator- retains only replacement bone elements, no dermal bone
Mammals
(a)
 Scapula of replacement bone
 Clavicle of membrane bone
Birds- two clavicles form furcula
(wishbone)
(b)
Figure 9.42. Pectoral girdles of (a) Polypterus and
(b) shark.. Dermal bones are red. Replacement bones are black.

Figure 9.43. (book figure 9.16).

Summary of Pectoral
Girdle Evolution
Figure 9.44. (book figure 9.19).

 No dermal elements
 Three replacement bones
 Ilium, ischium, pubis
 Triradiate pelvic girdlealligator and dinosaur
Figure 9.45. Left halves of pelvic girdles showing parallel evolution.

Figure 9.46. (book figure 9.21).

 Single unit most medial in both fore and hind limbs
 Two units in distal region of fore and hind limb
Figure 9.47. Dorsal view of left forelimb or forefin of Devonian tetrapods.

Figure 9.48. Cladogram of lobe-Fin fishes and amphibians.
Figure 9.49. Basic organization of fore- and hindlimb (book figure 9.23).




Small set of bones at wrist and ankle
Pentameristic pattern of phalanges
Reduction in number and position of phalanges
Figure 9.50. Evolution of fins to limbs.

Figure 9.51. Adaptations in secondarily aquatic tetrapods.
(book figure 9.30)

 Plantigrade
 Flat on the ground
 Primates
 Digitigrade
 Elevated
 Carnivores
 Unguligrade
 Reduction in digits
 Two types
Figure 9.52. Plantigrade, digitigrade, and unguligrade feet. Ankle bones are black. Metatarsals are gray.


Reduction in digits
Perissodactyl
 Odd toed
 Mesaxanic foot
- Weight on enlarged middle digit
 Ex: horse
 Artidodactyl
 Even toed
 Paraxonic foot
- Weight equally distributed on 3 rd and 4 th digits
 Ex: camel
Figure 9.53. Unguligrade adaptations in horse and camel. Bones lost are white
(see book figure 9.39).

Figure 9.54. (book figure 9.58).

 Serpentine
 Lateral undulation
 Wave motion
 Minimum 3 contact points
(a)
 Rectilinear
 Straight line
 Scutes on belly lift
(b)
 Costocutaneous muscles move the skin (c)
Figure 9.55. Serpentine locomotion (a) and rectilinear locomotion (b & c)

 Sidewinding
 Minimum 2 contact points
 Adaptation in sandy habitats
 Concertina
 Minimum 2 contact points
 Allows snake to move up gutter
(a) (b)
Figure 9.56. Sidewinding locomotion (a) and concertina locomotion (b)

Brachiation: Human Limb Engineering
Figure 9.57. (book page 354).
Five to 10 million years have passed since distant human ancestors swung through trees (Kardong, 2013).