Mammalian evolution began with the evolution of the first synapsids. what is the defining synapomorphy of synapsis?
a. the possession of the amniotic egg
b. a single temporal fenestra
c. the dentary squamosal joint
d. respiration with a diaphragm
e. endothermic metabolism

b. a single temporal fenestra

Explanation:

Synapsids have a temporary fossa in the lower part of the temporal bone. These reptiles mamiferoides only have a single inferior temporal fenestra.

The synapsids were the first amniots to diversify and appeared  in the middle of the Carboniferous. These first synapses were characterized by the presence of a single temporary fenestra behind each orbit, through which the mandibular muscles pass.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

im not in connections yet but i might can you some questions. what grade are you in?