The Synapsida and the Evolution of Mammals

Lecture 18

What are the 3 major Amniote clades?

Synapsida, Parareptilia, Eureptilia

What is the primary Synapsida synap and what other unrelated vertebrate clades are confusingly similar?

The major synap of synapsida is the single post orbital (temporal) fenestra. Other groups with one fenestra are Diapsids

What is the crown clade of Synapsida?

Mammalia

What is an outdated term for the stem Synapsida?

“Mammal-like reptiles”

What is the crown clade of Therapsida?

Mammalia

What is an outdated term for the stem Therapsida?

Mammal like reptiles

What is the crown clade of Cynodontia?

Mammalia

What are 4 morphological characters found in some early Cynodontia fossils which many indicate these were endothermic?

1. At least some may have had hair

2. Erect limbs allowing for parasagittal gait

3. Highly vascularized bones

4. Absence of growth rings in bones

Relatively agreed upon evidence: Turbinates (chonchae)

What are turbinates? What is their function? Why are they important for endothermy?

Turbinates are long, thin, bony structures in the nasal passage that are covered in tissue. Their functions include: warm and moisten inhaled air, extract heat and moisture from exhaled air.

For endothermy, metabolic rates of mammals is much higher than reptiles, allowing for increased activity levels. More respiration is needed to obtain O2 needed for higher metabolic rates. Complex turbinates allow for rapid breathing without drying the lungs. They also reduce the energy needed to keep the body temp at a high and constant temperature.

What are two synaps of Mammaliaformes?

1. A dentary-squamosal jaw articulation

2. Occlusion between the upper and lower molars

In what way did early Mammaliaformes differ from later species?

Early Mammaliaformes were the size of a small rat or shrew.