EXERCISE 12 (Vertebrates).docx - EXERCISE 12 12.1 Vertebrates Introduction The Vertebrata or vertebrates is a very diverse group ranging from lampreys

EXERCISE 12 (Vertebrates).docx - EXERCISE 12 12.1...

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EXERCISE 12 Vertebrates 12.1. Introduction The Vertebrata, or vertebrates, is a very diverse group, ranging from lampreys to Man. It includes all craniates, except hagfishes, and they are characterized chiefly by a vertebral column, hence their name. 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 reversed, 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. 12.2. Gnathostomata The Gnathostomata, or gnathostomes, are the majority of the Middle Devonian (380 million years ago) to Recent vertebrates. They differ from all other craniates or vertebrates in having a vertically biting device, the jaws, which consist of an endoskeletal mandibular arch and a variety of exoskeletal grasping, crushing, or shearing organs, i.e. the teeth, and jaw bones. Among Recent vertebrates, the gnathostomes include sharks, rays, chimaeras, ray-finned fishes, lobe-finned fishes and land vertebrates. Extant gnathostomes fall into two major clades, the Chondrichthyes and Osteichthyes. The Chondrichthyes are characterized by a special type of hard tissue lining the cartilages of the endoskeleton: the prismatic calcified cartilage. Another chondrichthyan characteristic is the pelvic clasper, as special copulatory organ derived from the metapterygium, i.e. the posterior part of the pelvic fin. The Osteichthyes are characterized by endochondral ("spongy") bone in the endoskeleton, dermal fin rays made up by lepidotrichiae (modified, tile-shaped scales), and three pairs of tooth-bearing dermal bones lining the jaws (dentary, premaxillary and maxillary). The Osteichthyes include two major clades, the Actinopterygii and the Sarcopterygii. Hammer head shark (Question 1a) Marlin (Question 1b) ( ) 12.3. Eastern Red-backed Salamander The Red-backed Salamander, along with all salamanders within the family Plethodontidae, are lungless. Nearly all of their respiration takes place through cutaneous gas exchange. This means that they breathe through their skin. The remaining gas exchange takes place through buccopharyngeal (within the mouth) respiration. The Red-backed Salamander is characterized by the red stripe, which begins immediately behind the head and extends nearly to the tip of the tail. The red stripe is usually very straight throughout its entire length along the body and generally covers the entire back of the salamander. In some populations the red color of the stripe is replaced by dark gray (right). This is called the lead-backed phase.
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  • Fall '19
  • Gnathostomata

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