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Cranial Divisions of the Skeleton: Postcranial Topic 6: Cranial Osteology Axial Appendicular
What are the components of the skeleton? Divisions of the skeleton Development of bone What are the components of the cranial skeleton? Cranial subdivisions The head skeleton How has the head skeleton evolved? The skull The jaws and pharyngeal arches Fenestration Cranial kinesis
Liem et al. Fig. 8 15, 8 18; Dean 1895
Developmental Subdivision Developmental Subdivision
______ Endochondral ossification Cartilaginous precursor Calcification or ossification of cartilage ______ Base of brain case ______ Limbs & girdles Dermal/membranous Vertebrae ossification Ribs & sternum Connective tissue membrane Ossification of membrane ______ Most of head skeleton Clavicle & Interclavicle More later Gastralia Liem et al. Fig. 5 11; histology world.com © ucmp.berkeley.edu; plesiosauria.com
The Cranial The Cranial Skeleton Skeleton
Can also use developmental units ______ Forms braincase Reduced in many Head skeleton vertebrates ______ ______ ______ Jaws & visceral arches ______ Reduced in many vertebrates Based on ______functional units Forms much of skull in many vertebrates Absent in which taxon?
© digimorph.org Liem et al. Fig. 7 4
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Salamander Chondrocranium Splanchnocranium
Endochondral ossification What kind of ossification would you expect?
Forms ______ Ventral Forms Lateral Part of ______ ______apparatus Gill Arches Components Inner ear bones Otic capsule Occipital bones Sphenoid bones Contributions are highly Ethmoid bones variable, depending on taxon
Liem et al. Fig. 7 1 Liem et al. Fig. 7 3, 7 15
Dermatocranium Putting the Crania Together
Dermatocranium How do you think this overlies the would ossify? chondrocranium and splanchnocranium
Forms: ______of skull Splanchnocranium ______of skull is highly modified in Most of ______most taxa Opercular bones in fishes
Liem et al. Fig. 7 4A, 7 13 Liem et al. Fig. 7 4
Evolution of Chondro & Evolution of Chondro & Dermatocranium Dermatocranium
Chondrichthyes (sharks & allies) Bowfin fish (Amia) Chondrocranium but no Chondrocranium highly reduced dermatocranium Ventral & posterior braincase All cartilaginous ______takes over Clue to endochondral origin Dorsal & lateral braincase ______ Jaws No sutures or joints Opercular bones ______ ______ Functionally forms entire Many jointed elements skull
Liem et al. Fig. 7 7 Liem et al. Fig. 7 7, 7 9
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Evolution of Chondro & Evolution of Chondro & Dermatocranium Dermatocranium
Trend continues with tetrapods Sutures evolved to make bones tightly integrated Ontogenetic & Dermatocranium covers evolutionary trend chondrocranium (and parts of splanchnocranium) Replacement of position Why would this be Replacement of function/role useful? Subsequent solidification with sutures
Liem et al. Fig. 7 12 Liem et al. Fig. 7 20; © Bone Clones, microscopy uk.org.uk
Evolution of Chondro & Evolution of Chondro & Dermatocranium Dermatocranium
Also trends towards 1. Replacement of chondrocranium ______by dermatocranium Bones reduced in area Bones reduced in 2. Transformation of the thickness dermatocraium from ______loosely articulated to 1 Why might this evolve? solidly articulated elements
Other trends to solidify or reduce or increase mobility 2
Liem et al. Fig. 7 16, 7 22; scienceblogs.com Liem et al. Fig. 7 7, 7 9, 7 12
Evolution of the Evolution of the Splanchnocranium Splanchnocranium
Salamander Start as loosely articulated Further reduction and fusion cartilaginous elements of elements in tetrapods
7 Unmodified arches Support of tongue and Who has this? throat muscles Turtle
Anterior modification ______cartilages ______arch ______arch Human ______bones ______arches Hyomandibula Collumela Stapes Bird Palatoquadrate Quadrate Incus Increased robustness of Meckel’s CartilageArticular Malleus elements and articulations
Liem et al. Fig. 7 5, 7 3, © T. Derting Liem et al. Fig. 7 15, 7 21
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Evolution of the Evolution of the Splanchnocranium Splanchnocranium Lamprey
1 Evolution of Jaws Shark Highly specialized for Gill arch I Meckel’s ______feeding + palatoquadrate 1 Some salamanders Jaw suspension Chameleons Gill arch II Hyomandibula 2 Hyomandibula Columella Amphibian Chameleons 2 Palatoquadrate Quadrate, Tongue supported and shoots off Meckel’s cartilage Articular processus lingualis Branchial arch VII lost 3 Arch VI Larynx cartilage Other elements: Reptile Basihyal 3 Arch VI lost Ceratohyal Arch IV + V Larynx 4 st 1 Ceratobranchial 4 Columella Stapes Quadrate Incus Mammal Articular Malleus
© S. Huskey, digimorph.org, Anderson et al. 2010 © S. Huskey, digimorph.org, Anderson et al. 2010
Evolution of Temporal Evolution of Temporal Fenestration in Amniotes Fenestration in Amniotes
Temporal region of the skull is posterior to the orbit A fenestra is an opening in a bone (L. – “window”)
______ An~ none No fenestra Syn~ one 1 fenestra ventral to postorbital & squamosal ______ Di~ two 2nd fenestra dorsal to postorbital & squamosal
Which fenestra is homologous between synapsids and diapsids? Lepidosaurs, Crocodylians, Birds © Biodidac
Evolution of Temporal Evolution of Temporal Fenestration in Amniotes Fenestration in Amniotes
Not simply 012 fenestrae Mammalia Anapsid is ancestral Diapsid modification But turtles are derived ‘Lizards’ Tuatara has a typical diapsid skull 3 1. ______1 Lizards have lost the ventral temporal bar 2. Diapsida Serpentes 4 Snakes have lost the 3. Loss of ______postorbital squamosal bar 4. Loss of postorbital 5 Euryapsids squamosal bar 2 Testudines Why might this be adaptive? 5. Reduction in dorsal 6 fenestra 6. ______of fenestrae Crocodylia 7. Fusion of fenestrae with orbit Aves Liem et al. Fig. 7 18, 7 22 7 © www.digimorph.org
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Cranial Kinesis C Rank these skulls from most kinetic to least
A
D
B
© OUM, digimorph.org
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