grouping of the subphylum Vertebrata:
- group pisces (fish)
- 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.
- translucent elastic tissue;
- the basic form is called hyaline cartilage which has a clear,
- is composed of cartilage cells called chondrocytes surrounded
by a firm, complex protein gel interlaced with a meshwork of collagen
- The endoskeleton of some spp. is composed exclusively of cartilage.
- 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:
- 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).
- Bone is extremely strong.
Pharynx and efficient respiration
Advanced nervous system
- 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.
- 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.
- Centralization of the nervous system:
- Cephalization - anterior, true head of a cranium containing and protecting
the brain and certain external, paired sense organs.
- Sense organs suited for distance perception.
- Specialization of paired sense organs:
- Eyes with lenses and specialized retinas.
- Pressure receptors such as paired ears designed for equilibrium and
- Chemical receptors, such as taste receptors and olfactory organs for
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
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
- 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,
- Acanthodians - several, small bony plates below epidermis; several,