Thank you for all the responses. Just to be clear: the dog wasn't hurt in any way, just scared. My partner is not at all an aggressive person but has a tendency to bottle things up, take too much on board and I fear he is under a lot of pressure that he doesn't know how to deal with.
I'm not going to leave him over this incident: he is my child's father and has been a supportive and loving partner to be for over 6 years. The problem is that he went into a sort of rage for a moment and it was out of character. He apologised to me and to the dog afterwards and his explanation was that he's just stressed from work.
I suppose I'm looking for advice as to how to make him aware of how serious that kind of behaviour is, and how to stop it or learn techniques to manage stress or anger. I've explained that while life with a young toddler is exhausting, these are the good times and there may come much more trying times in the future and I need confidence that he won't freak out like that again. I don't obviously want our children growing up in a house with a father prone to angry outbursts or worse.
In the years since I've known him I have been surprised, on a small handful of occasions, of his overreactions to small things: throwing a laptop that won't work or hitting a cupboard door...not at me, or as a threatening gesture towards me, but still an overreaction to a minor situation. Again these have only been a small number of occasions. His response tends to be that we are both under pressure and outbursts will happen but I suppose (and I'm probably being gendered here) its a lot more scary when a big man goes mental at a dog than when I throw a few clothes out of my wardrobe!
I suppose its complex. But if I could narrow down the question it would be: does anyone have experience of a husband or partner who has worked at managing stress or anger? Or how do you convince someone or help them to at least acknowledge there might be a problem that needs dealing with?
While I'm grateful for all the responses telling me to leave is a little premature. With my past experience I will always be mindful of these things, and would never let my child grow up in a threatening environment, hence why I'd appreciate constructive advice relating to moving forward rather than "just leave him", which seems a bit hasty.
**also, the dog gets plenty of exercise and while it is tough with a toddler around he has his own space, a big garden and is treated well