Abstract Type vs Type parameter

abvsTypeDep.scala

trait AnimalMouth
class Beak extends AnimalMouth

//================================Generic type works as in the following =======================

trait Animal[Mouth <: AnimalMouth] {
  def mouth : Mouth
  def feedAnother(m: Mouth): Unit = ()
}

class Bird extends Animal[Beak] {
  def mouth: Beak = new Beak
}

object Test{
  def feed[Mouth <: AnimalMouth, A <: Animal[Mouth]](mother: A, child: A) : Unit = mother.feedAnother(child.mouth)
}
 
//==============Make mouth an abstract type and it would be hard =========================== 

trait Animal {
  type Mouth <: AnimalMouth
  def mouth : Mouth
  def feedAnother(m: Mouth): Unit = ()
}

class Bird extends Animal {
  type Mouth = Beak
  def mouth: Mouth = new Beak
}

object Test{
  def feed[A <: Animal](mother: A, child: A) : Unit = mother.feedAnother(child.mouth) //won't compile, no way to write something like this? 
}

//=============== Work Around using Aux ================

trait Animal {
  type Mouth <: AnimalMouth
  def mouth : Mouth
  def feedAnother(m: Mouth): Unit = ()
}

object Animal {
  type Aux[Mouth0] = Animal { type Mouth = Mouth0 }
}

object MotherFeed {
  def feed[Mouth](mother: Animal.Aux[Mouth], child: Animal.Aux[Mouth]) : Unit = mother feedAnother child.mouth
}