Apex Level animals are stronger variants of their original ARK Alpha counterparts and only spawn in designated areas such as Monster/Carno Island, but can occasionally be found roaming the ark depending on the lifetime of that ark.
Apex is considered the upgraded versions of ARKs original Alpha Predators, meaning that the Alpha Rex, Carno and Raptor are the only currently available Apex Predators around. However, due to the Scorched Earth DLC, there may be more Apex predators in the future, but this is speculation without consistent proof from the Annunaki Dev Team.
Apex Creatures cannot be tamed by any means, including the forcetame cheat command (Performing this command on an Apex creature may result in saves crashing and/or corrupting). Apex Creatures can also apply Bleeding Debuffs to the character and their dinos in a battle, which causes health to drip away at a solid rate over time. Because of this, Apex Predators are considered to be incredibly dangerous and it is recommended to only attack these creatures with many hard hitting and high health animals, or with certain Boss creatures such as Megapiths, Dragons/Wyverns & Broodmothers.
Upon death, Apex creatures drop large amounts of Raw Prime Meat and Raw Meat, large quantities of Hide and each nearby player is awarded an Apex Costume, which can make their creature look like the one defeated. (Quantities of all drops except costumes are dependent on the servers resource gathering rate.)
User:Elfshot has also discovered that Apex Predators are capable of laying eggs naturally, which can result in a player taking the egg to hatch at their own place. However, it appears that Apex Creatures only drop an Alpha version of their own being. (For example: An Apex Tyrannosaur will only lay an Alpha Tyrannosaur Egg.)