These are birds about the size of a small domestic Turkey, with a small head and a rather fowl-like bill. The legs are of moderate length, but very thick and strong, and naked for a considerable distance above the ankle joint; the toes are very long, the third and fourth being connected at base by a short membrane.
The wings are large, broad, and rounded, with the third quill longest, and each wing is provided on the carpal portion with two curious, powerful spurs, the front one being much the larger. The plumage is composed of rather soft feathers, especially on the neck; the tail, of fourteen or twelve feathers, is broad and nearly half as long as the wings. The Screamers possess, also, a number of other marked peculiarities, the principal one being the absence of uncinate processes to the ribs, a condition not known in any other living birds, and suggesting at once the reptiles. The bones of the skeleton are very highly pneumatic, and the skin and underlying tissue to the depth of nearly half an inch is so completely filled with minute air spaces that it produces a crackling sound when pressed. According to Newton, the Screamers share with the Penguins the distinction of having the body continuously feathered, that is, without apteria, but other observers record the presence of a small bare space under each wing.
There has been much discussion as to the systematic position of the Screamers, and even now it can hardly be regarded as definitely settled. Some would regard their characters as of sufficient importance to entitle them to ordinal rank, but, all things considered, it seems least inconvenient to consider them as an aberrant family of the present order. They number but three species, which are placed in two well-marked genera; all are natives of South America.