Reptiledom

It is generally allowed that birds have risen out of reptiledom.

Source: wiktionary

It is common enough practice for them to turn cannibals and eat their own offspring — rather despicable business, this eating of one's own children, but possibly considered good form in reptiledom.

Source: wiktionary

For hibernation means more than taking a long sleep when it is very cold and the metaphorical wolf is at the door; it means a definite imperfection in the warm-bloodedness, and a peculiar lapse towards reptiledom, with very remarkable constitutional changes in heart and blood, in breathing and excretion.

Source: wiktionary

Leaning against bookcases filled with medical works were huge test tubes of alcohol and formalin preserving the remains of many of the most dangerous characters of reptiledom.

Source: wiktionary