Diagnostic features of living birds

Among living vertebrates, birds possess a remarkable and largely unique suite of diagnostic features (Figure 10.1 and Table 10.1).

Feathers. All living birds have feathers - complex, distinctive structures that consist of a hollow, central shaft that decreases in diameter toward the tip. Radiating from the shaft are barbs, feather material that, when linked together along the length of the shaft by small hooks called barbules, form the sheet of feather material called the vane (Figure 10.1a). Feathers with well-developed, asymmetrical vanes are usually used for flight and are therefore called flight feathers. Feathers in which the barbules are not well developed tend to be puffy, with poorly developed vanes, and are called down, and, as we know from sleeping bags, comforters, and ski parkas, are superb insulation.

Loss ofteeth. No living bird has teeth. The jaws of birds are covered with a rhamphotheca.

Large brains and advanced sight. Living birds have well-developed brains protected by a large braincase.

Carpometacarpus. The wrist and hand bones in the hand of modern birds are fused into a unique structure called the carpometacarpus1 (Figure 10.1b). The carpometacarpus is composed of three fused fingers, now generally thought to be digits I (the thumb), II, and III.

Legs and feet. Birds are fully bipedal, and have an erect stance (see Chapter 4). The twin shin bones (tibia and fibula; together, the "drumstick" on the dinner table) are unequal: the tibia is large, but the fibula thins to a sliver close to the ankle.

The feet of all living birds are clawed and have three toes in front (digits II, III, and IV), and a smaller toe (digit I) at the back. The three central metatarsals (foot bones, to which the

Table 10.1. Diagnostic features of living birds

Modern birds

Teeth (-) Swollen braincase Pygostyle (+)

Carpometacarpus (+); fused digits I, II, III

Legs:

1. Bipedal

2. Tarsometatarsus

Foot:

3. Claws

Pneumatic bones Furcula

Rigidified trunk

1. Carinate sternum

2. Synsacrum

4. Flying adaptations

The plus sign (+) indicates character present; the minus sign (-) indicates character absent.

1. Spiced and served with beer, we call them "buffalo wings."

Bird Vertebrae

Figure 10.1. The skeleton of a pigeon, showing major features of its skeletal anatomy. (a) Detail of feather structure; (b) carpometacarpus with digits labeled; (c) tarsometatarsus; (d) synsacrum (fused pelvic bones) with pygostyle; (e) hollow bone with pneumatic foramina; (f) sternum with large downward-projecting keel; and (g) furcula.

Figure 10.1. The skeleton of a pigeon, showing major features of its skeletal anatomy. (a) Detail of feather structure; (b) carpometacarpus with digits labeled; (c) tarsometatarsus; (d) synsacrum (fused pelvic bones) with pygostyle; (e) hollow bone with pneumatic foramina; (f) sternum with large downward-projecting keel; and (g) furcula.

toes attach; in this case II, III, and IV) are fused together and with some of the ankle bones, to form a unique structure called a tarsometatarsus (Figure 10.1c).

Pygostyle. No living bird has a long tail skeleton. Instead, in most cases, the bones are fused into a compact, vestigial structure called a pygostyle (pygo - rump; stylus - stake; Figure 10.1d).

Pneumatic bones. Living birds breathe unidirectionally with a complex system of air sacs (see Box 8.1). Their bones are pneumatic and have pneumatic foramina (Figure 10.1e).

Rigid skeleton. Bird skeletons have undergone a series of bone reductions and fusions to produce a light, rigid platform to which the wings and the muscles that power them attach. Fused vertebrae in the back are connected with a well-developed breastbone, or sternum, by ribs with upper and lower segments. The sternum is large and, in flapping flyers, has a broad, deep keel, or downward-protruding bony sheet, for the attachment of flight muscles (Figure 10.1f). The pelvic region is fused together into a synsacrum, a single structure consisting of many sacral vertebrae fused together (Figure10.1d). The pubis is very slender and points posteriorly.

In the shoulder, pillar-like coracoid bones buttress against the front of the sternum, the shoulder blade (scapula), and against paired, fused collarbones2 (furcula; Figure 10.1g). No living organism except birds has a furcula.

Flight musculature. In modern flying birds, the downward stroke of the wing is obtained by the pectoralis muscle, which attaches to the front of the coracoid and sternum, and to the furcula and humerus. The recovery stroke is carried out by the supracoracoideus muscle. The supracoracoideus attaches at the keel of the sternum, runs up along the side of the coracoid bone, and attaches via a tendon at the top of the upper arm bone through a hole (the trioseal foramen) formed by the coracoid, furcula, and scapula (Figure 10.2). This is an adaptation unique to living birds.

+1 0

Responses

  • Sarah
    Why are birds tibia and fibula fused?
    7 years ago
  • semolina
    Are bird skeletons fused?
    7 years ago
  • Tomacca
    What is the most diagnostic feature of birds?
    7 years ago
  • VELI-MATTI HAGMAN
    Why furcula why is it fused together?
    7 years ago
  • donte blanton
    Which bones of birds are fused together?
    7 years ago
  • rorimac
    Are feathers diagnostic of birds?
    7 years ago
  • Lalli
    What is the pneumatic foramina?
    7 years ago
  • luwam
    What are the diagnostic features of birds?
    4 years ago
  • dominik
    What are the diagnostic features of bird?
    2 years ago
  • costanzo
    What Is Diagnostic Feature Of A Living Organism?
    2 years ago
  • madihah
    What is the diagnostic feature of a bird?
    1 year ago
  • bildad
    WHAT ARE THE DIANOSTIC FEATURES OF BIRD?
    1 year ago
  • Annett
    What is diagnosic of features of birds?
    11 months ago
  • tobold diggle
    What Is The Diagnostic Feautures Of Bird?
    11 months ago
  • ronald
    What are diagnosis features of birds?
    11 months ago
  • michael
    What is the diagnostic featuers of birds?
    11 months ago

Post a comment