Mammals

Mammals are endothermic animals with a very high metabolism. Endothermy and high metabolic rates reflect active lifestyles, and mammals are highly active and alert to their surroundings.

The mammalian skull has several characteristic features:

1. Nasal turbinals (aka nasal turbinates, nasal conchae) form from the maxillae, nasals, and/or mesethmoid

2. Most circumorbitals are lost, and the postorbital is either reduced or lost altogether

3. The braincase is relatively large

4. Three ear ossicles are present and enclosed in an auditory bulla on the basicranium

5. Upper teeth are present on the maxilla and premaxilla only

6. Mandible composed solely of the dentary

Monotreme skulls can be distinguished from those of other mammals by:

1. Absence of auditory bullae

2. Absence of teeth in adult individuals (not true for some ancient monotremes)

Marsupial skulls can be distinguished from those of placentals by:

1. Participation of the jugal in the jaw joint at the glenoid (mandibular) fossa

2. Presence of posterior palatal vacuities

   
   

3. Primitive dental formula of 5134/4134

Placental skulls can be distinguished by:

1. Disproportionately large braincase

2. Absence of posterior palatal vacuities (there are exceptions)

3. Absence of the jugal in the mandibular fossa

   
   

Fish

Bird

Reptiles

Amphibians

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