Declaring classes that inherit from another class

The following lines show the code for the Animal base class in Swift. The class header doesn't specify a base class, so this class will become our base class for the other classes:

public class Animal {
    public static var numberOfLegs: Int {
        get {
            return 0;

        }
    }
    public static var averageNumberOfChildren: Int {
        get {
            return 0;
        }
    }
    
    public static var abilityToFly: Bool {
        get {
            return false;
        }
    }
    
    public var age: Int
    
    init(age : Int) {
        self.age = age
        print("Animal created")
    }

    public static func printALeg() {
        preconditionFailure("The pringALeg method must be overriden")
    }
    
    public func printLegs() {
        for _ in 0..<self.dynamicType.numberOfLegs {
            self.dynamicType.printALeg()
        }
        print(String())

    }
    
    public static func printAChild()...