The sentience scale was a numeric scale used by humans to rate the intelligence of various species.
- Alphane and Medusan intelligence was comparable to that of humans.
- Treecats of Sphinx:
- real intelligence ≈ 1.00
- dissimulation = 0.83
- Gremlins of Beowulf < 0.83 (slightly)
- Dolphins of Earth < 0.83 (slightly)
- Amphors of Barstool = 0.70 (SK1)
- Barthoni ? 
Other animals that might also be considered a sentient species:
- the herbivorous Growlers, a degenerated form of the Alphanes. (HHA1.2: AGT)
- the carnivorous Gilgamesh River Devils, a semi-sentient animal species. (HHA4.4: LGTP)
Terran great apes were not mentioned.
There were twenty-seven sentient nonhuman species discovered to 1920 PD. (Companion)