Vertebrate Zoology

Additional grouping of the subphylum Vertebrata:

• group pisces (fish)
  Classes
1. Myxini
2. Cephalaspidomorphi
3. Chodrichthyes
4. Osteichthes
• group tetrapoda
  Classes
1. Amphibia
2. Reptilia
3. Aves
4. Mammalia
• group anamniota
  Classes
1. Myxini
2. Cephalaspidomorphi
3. Chodrichthyes
4. Osteichthes
5. Amphibia
• group amniota
  Classes
1. Reptilia
2. Aves
3. Mammalia

Adaptations

• Living Endoskeleton
1. Advantages
   • Growth - can grow with the body, thus allowing very large size and nearly unlimited body size.
   • Jointed scaffolding for muscles - provides jointed attachment structure for muscles which in turn support, protect, and cushion the skeleton.
2. Composition

    

Cartilage

• translucent elastic tissue;
• the basic form is called hyaline cartilage which has a clear, glassy appearance;
• is composed of cartilage cells called chondrocytes surrounded by a firm, complex protein gel interlaced with a meshwork of collagen protein fibers.
• The endoskeleton of some spp. is composed exclusively of cartilage.

Bone

• living tissue having significant deposits of inorganic calcium salts laid down as an extracellular matrix.
• Most bones develop from cartilage (endochondral bone).
• Embryonic cartilage gradually erodes away; bone-forming cells deposit calcium salts around strand-like remnants of the original cartilage.
• Bone is the major component of most vertebrate endoskeletons with some cartilage present as well.

 

Advantages of bone over cartilage:

1. Bone serves as a reservoir of phosphate in the form of calcium phosphate; phosphate is important for energy production (ATP), membrane formation (phospholipids), and nucleic acids (DNA and RNA).
2. Bone is extremely strong.

 

• Pharynx and efficient respiration
1. Circulation to the internal gills of aquatic animals is more efficient through the pharyngeal gill slits and openings over most invertebrate forms of aquatic respiration which occurs by variously modified means.
2. The ventral heart, closed circulatory system, and distinct pulmonary and systemic components of the circulatory system allow for more efficient aquatic and terrestrial gas exchange and eventual circulation of oxygenated blood throughout the body.
• Advanced nervous system
1. Centralization of the nervous system:
1. Cephalization - anterior, true head of a cranium containing and protecting the brain and certain external, paired sense organs.
2. Sense organs suited for distance perception.
2. Specialization of paired sense organs:
1. Eyes with lenses and specialized retinas.
2. Pressure receptors such as paired ears designed for equilibrium and sound reception.
3. Chemical receptors, such as taste receptors and olfactory organs for smell.
• Paired limbs
  Pelvic and pectoral appendages are present in most vertebrates in the form of paired fins or jointed limbs. Jointed appendages are suited for life on land because they permit levering motions against a substrate.

Fossil Record of Vertebrate Animals

Jawless Ostracoderms (shell, skin)

Deepest vertebrate fossils are fragments of bony armor discovered in Ordovician rock [geological period corresponding to approx. 500 million to 425 million years before present (BP) in geological or atomic years based on radioisotope dating] in Russia and in the US.

The fossils represented organisms that were small, jawless forms collectively called ostracoderms (shell, skin).

The ostracoderms belong to the Agnatha superclass and consisted of three groups:

• Heterostracans - lacked paired lateral fins.
• Cephalaspids (head, shield) - had paired lateral fins; largest genus was Cephalaspis - had a bony shield around head and a bony armor protecting the remainder of the body.
• Anaspids (without shield) - had paired lateral fins but lacked the bony shield around the head.

Jawed Placoderms (plate skin)

Deepest jawed vertebrate fossils are of two placoderm groups:

• Devonian placoderms - large bony plates below epidermis; few, large fins.
• Acanthodians - several, small bony plates below epidermis; several, small fins.