Found it in the wild or more likely in an expensive incubator.
Mostly buying legendary incubator.
As per my understanding, Epics/Hybrid Epics can be found in wild but not Legendaries. So can’t be from hunting.
Also, looking at the level, obtaining this from park event wouldn’t be ideally possible (assuming there was a park event for Allosinosaurus)
There was a legendary incubator a month or so ago that guaranteed 200 legendary DNA. Could be that.