10 Questions
What is the main focus of the lecture described in the text?
The evolution of the mammalian skull and jaw
What is the key difference between the jaw muscles shown in image A and image B?
Image A shows the jaw muscles of a basal synapsid, while image B shows a therapsid close to the mammal transition
What is the main purpose of the 'Learning Objectives' section in the text?
To outline the key topics that will be covered in the lecture
Which of the following is characteristic of major vertebrate lineages?
Jaw suspension
What is the main evolutionary transition described in the text?
The transition from therapsids to mammals
Which of the following is not a learning objective mentioned in the text?
Describe the evolution of the vertebrate spinal column
What is the key difference between the jaw muscles shown in image B and image C?
Image B shows a lateral view, while image C shows a posterior view
Which of the following is not a major topic covered in the lecture described in the text?
The development of the cranial skeleton
What is the significance of the 'therapsid close to the mammal transition' mentioned in the text?
Therapsids were the ancestors of mammals, and this transition represents a key evolutionary step
What is the primary purpose of the three skull divisions mentioned in the text?
To protect the brain and sensory organs
Study Notes
Cranial Skeleton
- Has three primary functions: protecting soft tissues, facilitating food gathering and processing, and providing passage for respiratory flow
- Composed of three distinct components: chondrocranium, splanchnocranium, and dermatocranium
- Chondrocranium:
- Forms around the three major sensory capsules (nasal, optic, and otic)
- Developed from neural crest and mesodermal mesenchyme
- Primarily endochondral
- Splanchnocranium:
- Associated with pharyngeal arches
- Derived from neural crest
- Primarily endochondral
- Dermatocranium:
- Superficial bones encasing the chondrocranium and splanchnocranium
- Developed from neural crest and mesoderm
- Primarily membrane bone
Components of the Cranial Skeleton
Chondrocranium (Neurocranium)
- Forms around the tripartite brain (nasal, optic, and otic capsules)
- Notochord extends to the pituitary of the brain and parachordals form on either side
- Trabeculae extend rostrally to surround the nasal capsules, uniting to form the ethmoid plate
- Occipital elements develop from mesodermal sclerotomes and form the occipital arch
Splanchnocranium (Visceral Skeleton)
- Composed of skeletal elements that arise from the pharyngeal (branchial) arches
- Developed in aquatic vertebrates, adding elasticity and powerful suction to the pharynx
- First visceral arch = mandibular arch:
- Consists of dorsal palatoquadrate and ventral mandibular cartilage (Meckel's cartilage)
- Forms the basic architecture of jaws
- Second visceral arch = hyoid arch:
- Composed of dorsal hyomandibula and ventral series including ceratohyal
- Often articulates with and provides support for the mandibular arch
Types of Jaw Attachments
- Metautostyly:
- Jaws attached to braincase through articulation of the quadrate and articular
- Found in Lissamphibia and Reptilia
- Craniostyly:
- Upper jaw incorporated into braincase
- Articulation is with dermal squamosal of the temporal bone and the dermal dentary
- Found in derived Synapsids (Mammalia)
Cranial Skeleton of Early Tetrapods
- Similar to rhipidistian fishes
- Facial part of skull increased in length, resulting in longer jaws
- Internal nostrils (choanae) present, indicating lungs
- Branchial apparatus lost, enabling head to move independently of the trunk
- Caudal portions of palatoquadrate and mandibular cartilages ossified as quadrate and articular bones
- Hyomandibula of hyoid arch formed an ossified rod called the columella
Cranial Skeleton of Lissamphibians
- Skull became broad and flat to accommodate sheets of muscles in the floor of the mouth and pharynx
- Basioccipital region absent, two condyles borne on exoccipitals
- Many dermal bones of the circumorbital and temporal series absent
- Mandibular cartilage remains unossified, but encased in dentary, angular, and sometimes splenial bones
Anapsid Skull of Early Amniotes (Reptilomorphs)
- Early amniotes were small, insectivorous captorhinids
- Smaller, higher, and narrower skulls than early tetrapods
- Temporal region of skull complete (anapsid)
- Single occipital condyle, teeth simple and conical
Temporal Fenestration in Amniotes
- Openings in temporal series of dermatocranium in major amniote lineages
- Evolution corresponds to changes in complexity and orientation of jaw-closing (adductor) muscles
- Anapsid - without arches, condition of early amniotes
- Synapsid - single arch, condition of Synapsida (including mammals), single temporal fenestra located low on each side of the skull
- Diapsid - double arch, condition in living Reptilia, two openings develop, one below and one above the postorbital and squamosal bones
Test your knowledge on the components of the cranial skeleton with this quiz focused on the functions and distinct embryonic origins of the Chondrocranium, Dermatocranium, and Splanchnocranium.
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