an emergent
website design
by
peter jay stein, md, ma
atmosphere
asthenosphere
lithosphere
regolith
biosphere
hydrosphere
This 54 page synopsis of the evolution
of the Earth, the origin and progression of life, and the
emergence of humans as descendants of the hominin lineage, divides the last 4.57 billion years into progressively overlapping, imagistic, time segments, to outline our place in biological existence.
magnetosphere
ionosphere
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.