At most, their forelegs grow vestigial spurs where wing membrane might have been. 最终，它们本应长为翅膀的前肢会退化为薄膜。
Immediately behind the shoulders ribs are flattened enough to allow free movement of the forelegs, becoming rounder behind. 肩胛后面的肋骨立即变平，允许前肢能自由运动，随后逐渐变圆。
