Which mammal possesses both reptilian and mammalian characters?

Note the following:
$I.$ Dentition is heterodont.
$II.$ Canines are poorly developed.
$III.$ Incisors are chisel-like,poorly developed.
$IV.$ Herbivorous and diastema is present.
$V.$ The dental formula is $I \frac{2}{1}, C \frac{0}{0}, P m \frac{3}{2}, M \frac{3}{3}$.
Which of the above are true for $Oryctolagus$?

Echidna is found in

What do warm-blooded animals possess?

Point out the mammalian characters.

Which of the following mammals is adapted for aquatic life?