Lec 6 Mammals Flashcards
What are the features of mammals?
Cranial:
1. Dentary only lower jaw bone
2. Squamosal-dentary jaw joint
3. Dentary: high coronoid process and mandibular fossa
4. well-differentiated, marginal, diphyodont dentition
5. 3 ear bones: stapes, quadrate -> incus, articular -> malleus
6. Ectotympanic
7. Single bony naris
8. Double occipital condyle
9. Large temporal fenestra
10. Large zygomatic arch, dorsally bowed and laterally flared
11. No pineal foramen
12. No postorbital
13. Secondary palate
Postcranial:
1. Limbs erect, almost below body
2. Limbs move in parasagittal plane
3. girdles developed dorsally
4. Slender tail
5. No lumbar ribs -> have diaphragm
6. No cervical ribs
7. Vertebral column bends dorsoventrally, not laterally -> longer stride + ventilation
What are the two clades of cynodonts?
Cyanognathia, Probainognathia
Describe the main steps in jaw joint to middle ear transition
- Jaw joint: quadrate in skull and articular in lower jaw. Quadrate already contacts stapes
- Surangular meets squamosal -> 2 joints in tandem
- Surangular lost, so dentary contacts squamosal. Quadrate and articular shift medially
- Dentary-squamosal contact takes over as main articulation. Dentary enlarged to become a condyle
- Articular and quadrate lost contact with squamosal -> free to become incus and malleus
- separation of middle ear from jaw joint:
a) quadrate and articular displace medially and posteriorly
b) become smaller
c) Meckel’s cartilage re-absorbed
What is the phylogenetic sequence of jaw joint to middle ear transition?
Thrinaxodon, Probainognathus, Pacbygenelus, (Brasilodon), (Sinoconodon), Morganucodon,
New bonnes in early Mammals
Alisphenoid, Orbitophenoid
Features of Morganucodontid
Dentary-squamosal jaw joint
molars and premolars
Diphyodont tooth replacement
no lumbar ribs lost
still have coracoid
When did Mammalia evolve?
Jurassic
