[sim (OP)]

The species paradox

http://gamahucherpress.yellowgum.com/wp-content/uploads/SPECIES-PARADOX.pdf

who did the first bird mate with who did the first dog mate with

an individual of species A gives birth to a individual of the new species B so who did this new individual of new species B mate with to continue the new species
either
1)there was no one to mate with- so how did the new species B become common
or
2)a whole lot of species A gave birth toa whole lot of new individuals of species B at the same time so that these new individual members of species B could mate together

if this 2) was the way it happened
we have a major problem
it would mean something made a whole lot of members of species A give birth to a whole lot new members of species B at the same time
we are told species form due to random mutations
so
it is beyound possibility that the same random mutation took place in a whole lot of different members of species A at the same time

[Kryptid]

That's not how evolution works. The transition between species is a gradual process so there would have been no problems with new individuals finding mates that they could breed with it. Species have blurry boundaries over time (in most cases).