Lab3Chondrichthyes - The Vertebrates Structure Function and...

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The Vertebrates: Structure, Function and Evolution (BIOEE 2740) Lab 3 – Chondrichthyes, the cartilaginous fishes. Goals for this lab: 1. Learn the morphological features that define the Gnathostomata , the jawed vertebrates. 2. Learn what morphological features define the Chondrichthyes , and how this group is related to other major vertebrate groups. 3. Explore the diversity, structure and function of the Holocephalans and the Elasmobranchs , the two major groups within the Chondrichthyes . 4. Become familiar with the internal anatomy of the Chondrichthyes through dissection of a spiny dogfish shark, Squalus sp. Station 1. The Gnathostomata – phylogenetic context and synapomorphies Remember from last week’s lab that the Gnathostomata (=”jaw mouth”) include all of the Vertebrata except for the Petromyzontiformes , the lamprey. Some major morphological synapomorphies of the gnathostomes are: 1. Jaws – enable gnathostomes to seize and eat a wider range of food items than non-jawed craniates. Major concepts The evolution of jaws allowed vertebrates to eat and specialize upon a diversity of foods The evolution of 2 sets of paired appendages lead to greater maneuverability and more efficient swimming Think about the innovations in morphology which allowed transitions in feeding ecology among taxa in last week’s and this week’s labs: 1. filter-feeding with cilia (urochordates and cephalochordates) 2. Filter-feeding with a muscular pharyngeal pump (larval lamprey) 3. Jaws and active predation = large active predators, like sharks (and other gnathostomes) !
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2. Calcified teeth – allow gnathostomes to eat a variety of prey items, and to specialize their diet via morphological specialization of the teeth. Tooth replacement is also present. Remember from lecture that most cartilaginous fishes have polyphyodont teeth (= continuous replacement) and homodont dentition (= all teeth in the mouth are the same shape; note the interesting exception to this pattern at station #6!). In contrast, most mammals have diphyodont teeth (= 2 sets of teeth, “milk” and adult) and heterodont dentition (= differentiated tooth shapes within the jaw). Examine the representative jaws at this station to familiarize yourself with homodont vs. heterodont dentition. 3. Three semicircular canals – these are the fluid-filled tubes in the inner ear involved in balance and movement. Having three tubes allows for three- dimensional orientation (remember that having at least two semicircular canals is a synapomorphy of the Vertebrata – lampreys have two canals; hagfish have only one). 4. Paired appendages – increase stability, maneuverability, and efficiency in movement. Paired appendages are possible because of the evolution of the pelvic and pectoral girdles (you will learn more about the girdles at station #5). 5.
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Lab3Chondrichthyes - The Vertebrates Structure Function and...

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