Here is the full list of all 28 Endling - there are Extinction is Forever achievements.
Let Molly pet you.
Do not kill any animal (fish, mouse, rabbit, pigeon, chicken) for five days.
Don't feed your cubs trash for six days in a row.
Enter your lair with a full stomach.
Reach the second lair.
Find all traces of the missing cub in the river area.
Pet a scared cub.
Release the Badger from the trap.
Bark at the Roamer.
Reach the first lair.
Bark three times in a row when it's raining.
Finish the game with all cubs alive.
Finish the game with at least three cubs alive.
Finish the game with at least two cubs alive.
Finish the game with at least one cub alive.
Reunite the Badger's cub with their mother.
Rescue the missing cub.
Reach the third lair.
Finish the game.
Find all traces of the missing cub in the forest.
Find all traces of the missing cub near the dumping ground.
Learn all cub skills.
Let the Scavenger pet you.
Let your cubs eat every kind of food in the game.
Pet your cubs at least once for five days straight.
Hunt a chicken for the first time.
Have your cubs eat the Easter Egg.
Unlock every other achievement in the game.