It had been a simple plan... no really, it was! With the animal rights groups armed to the teeth these days, getting human 'volunteers' was infinitely easier to getting your hands on lab animals!
So when it was proposed to mutate creatures that were plentiful into species of extinct or engaged animals, it had fallen upon the human race to shoulder the burden. After all, let's put those 'worthless' people who asked for loose change because they lost their job through the company going under to some actual good use! That was how it was sold, and that was how the public bough it! Some parents had to hold their kids back from the option of becoming dinosaurs.
The transformation wasn't 'perfect' but that was fine for those who 'signed up', that they'd still go on two legs, and have opposable thumbs... but they couldn't hope for much else. But the scientists were sure with some more testing they could work out these 'bugs.'
But the extinct species they brought back... were not the ones they were expecting. The DNA of the animals identified as some species of equine, or unknown dinosaur, or extinct Japanese canine, or the like... as it turned out... were something entirely differently.
First was the instincts, losing any sense of modesty, and being driven by the wants and needs of their new form, just as smart, and with all their memories of their former lives... but those didn't seem really as important afterwards.
Not when dragons have hoards to build, unicorns had their own ecco-restoration to do, kitsune and tanuki had a rivalry going to see who could trick and manipulate the most humans, and all the rest... the scientists and medical personnel were of course shocked at what their subjects had turned into... And the unknown type of energy these creatures gave off (IE, magic).