TWENTY-THREE
Emergent Mammals II
"The mammals arose within the therapsid radiation in the Late Triassic (252 - 201 mya), initially small and shrewlike. These Mesozoic (252 - 66 mya) animals [co-existed] with a terrestrial fauna then dominated by dinosaurs, especially the sauropsids" (Vertebrates, 2012, p. 122).
DEVONIAN PERIOD
(419 - 359 mya)
JURASSIC PERIOD
(201 - 145 mya)
JURASSIC PERIOD
(201 - 145 mya)
TRIASSIC PERIOD
(252 - 201 mya)
FOSSIL MAMMALIAN SKELETAL CHARACTERISTICS
(adapted from Vertebrates, 2012, p. 123)
1) The mammal possesses a chain of 3 bones in the middle ear, that conduct sound from the eardrum to the inner ear (reptiles have only one primary middle ear bone);
2) Whereas several bones comprise the reptilian lower jaw, mammals posses only a single, dentary, bone; and
3) Whereas reptiles have additional bones to complete the jaw joint, mammals have a joint between the dentary and squamosal bones of the jaw.