Selachii
This is a work in progress, and we'll get to the sharks in a while... First, the birds...
"Being able to fly is all well and good" thought Karen, "but I've lost so much".
Until a few weeks ago, Karen had been a middle aged mother of two children, enjoying a job in a large corporation and when the Divergence occurred she suddenly became a one metre high, fully functioning bird. Since this also happened to all the people in the same area, many were involved in the accidents that occurred as the result, and she was not affected as fortunately at that moment she and the rest of her team were enjoying a soft drink in the sun outside. One moment human and the next avian was tremendously disorientating, and it took a while to figure out what had happened and who she now was.
There was nothing left to indicate that any of these huge birds were originally human - and since beaks and the vocal apparatus are not built for speech, no matter how much she tried the sounds all came out very similar, as slight variations on 'caw'.
In the couple of weeks since the change happened a number of things had happened - the 'flock' had dispersed along the coast, as houses and flats were no good to huge birds. They had individually figured out that they could eat both grain and flesh, and fresh fish as well as small creatures were delicious. A persistent bird had sorted out a keyboard and computer, on which it was possible to type, one letter at a time with the tip of the beak. Karen had tried it and found it both a relief to be able to communicate, and a literal pain in the neck to do such fiddly movements. At a rate of about ten characters a minute, this was hard going, especially as their eyes looked either side of their heads, so it was an act of supreme concentration to focus on the spot at the very front of the vision in both eyes to keep the keyboard and the tip of the beak in focus.
Somehow she had retained all her life memories, and also inherited the skills that the body required to fly, keep the body and feathers in good condition, and sleep on a roost with the long claws at rest wrapped hard around a branch.
As soon as neighboring cells of recognisably human people realised that this area was no longer populated with people they began to move in, spreading like a tide through the neighborhoods, selecting the best places to inhabit, finding the keys to the best cars, and so on.
Karen was not bothered by the loss of her material possessions, but she was really sad that she could not find her children or husband. Life was reduced to finding food and good quality rooting places.