C# Reflection Get base Constructor Parameters

I am trying to get the Base Constructor parameters of a class using Reflection.

public class A : B
{
   public A (Param1, Param2) : base(Param3, Param4)
   {
     ...
   }
}

I have tried:

var cons = type.GetConstructor();

var con = ctors[0];

ParameterInfo[] par = con.GetParameters();

But it Only returns param1 and param2, how can I get param3 and param4?