Which anatomical features do scientists use to classify gruiform birds?

The order Gruiformes is a diverse group of birds defined by a collection of anatomical characters rather than a single, universal feature. Because these traits are often internal or subtle, they are not always readily apparent in live birds.1

Scientists classify these birds by examining a variety of anatomical and biological features, including:

• Skeletal and muscular structure: The type of palate (osteologically), the configuration of pelvic musculature, the number of cervical vertebrae, and the presence of specific muscle groups like the caudo-femoral muscle.12
• External morphology: The condition of the feet and toes (such as whether they are lobed or webbed), the presence or absence of a hallux (hind toe), the shape of the nostrils, and the presence of an aftershaft on body feathers.12
• Wing and feather characteristics: The number of wing and tail feathers, and whether the wing is eutaxic or diastataxic (the presence or absence of the fifth secondary flight feather).12
• Internal systems: The number of carotid arteries and the presence or absence of a crop.12
• Developmental behavior: The behavior of the young, specifically whether they are nidifugous (precocious) or nidicolous (dependent).12