Marine Phyla Pages -- Coastal Carolina University
VERTEBRATA
Vertebrata
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| Great White Shark | Sea Turtles | Phoca vitulina |
Defining Characteristics 1
The Vertebrata, or vertebrates, is a very diverse group. It includes all craniates, except hagfishes, and are characterized chiefly by a vertebral column, hence their name.
Systematics 2
Vertebrates first evolved in the ocean. The invertebrate ancestors of vertebrates had gill slits, but these were used primarily for filter feeding; these organisms took up most of the oxygen they needed through the skin. As early vertebrates grew larger and developed bony scales or plates between their tissues and the water, they developed gills for taking up oxygen from the water. Gills are complex, highly branched and folded structures; this increases the surface area for taking up oxygen. Because water is heavier and more viscous than air, fish must pump water through their mouths, through their gill chambers, and out the gill slits. When you see an aquarium fish gulping water you will also see the gill cover opening and the gills fluttering, as water is drawn over the gills and the fish breathes. Very active fish increase oxygen uptake by swimming rapidly, forcing water into the mouth and over the gills by a sort of "ramjet" action.
Habitat 2
Vertebrates are found from the tropics to the polar regions, from the deep sea to high mountains, and even the air -- vertebrates and insects being the only groups of animals to have mastered powered flight.
Other Information 1
The majority of the extant vertebrates are the jawed vertebrates, or gnathostomes, but lampreys are jawless vertebrates. However, in Late Silurian or Early Devonian times, about 420 to 400 million years ago, the situation was reverse, and the majority of the vertebrate species were jawless fishes (the "ostracoderms", presumably more closely related to the gnathostomes than to lampreys). The decline of the jawless vertebrates and the subsequent rise of the gnathostomes took place about 380 million years ago.
Vertebrata Links
1. http://tolweb.org/tree?group=Vertebrata&contgroup=Craniata
2. http://www.ucmp.berkeley.edu/vertebrates/vertintro.html