BIO 474 Lecture Notes - Lecture 1: Gnathostomata, Branchial Arch, Placodermi
Conodants
Early group of fish with mineralized tissue, notochord, cranium, but lacked pharyngeal slits
Where did vertebrate life originate?
The efficiency of the vertebrate kidney at removing water from the body points to vertebrate life
originating in freshwater where there was an abundance of water. On the other hand, the earliest
vertebrate fossils are found exclusively in marine environments.
Agnathans
Paraphyletic group of jawless extant vertebrates without reproductive ducts who reproduce externally
Hagfishes
Essentially the only extant Agnathans who are found at 1% males in a population (possibly
hermaphroditic). They lack jaws, vertebra, external armor, are found worldwide (except for polar
waters) \, and feed as scavengers.
Distribution vs. range
Range refers to the distance an individual will travel while distribution refers to the regions in which a
species can be found.
Lampreys
Have small simple vertebrae, feed as parasites by drinking blood, have well-developed kidneys to allow
them to reproduce in freshwater (making them Anadromous), and are sedentary filter-feeders as larvae.
They respire via gill tissue where water exits it's gills, using tidal ventilation instead of flow-through
ventilation since they may be fixed to their prey at times.
Benefits of jaws
Bite, chew, eat larger prey than self, speak, grip, facial expressions, talk, defense, digging,/burrowing,
forceful ventilation. Jaws likely developed from mutated gill arch bones. Jawed teeth are derived from
the jaw bone, unlike previous teeth, which were dermal bone.
Placoderms
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Early jawed fish derived from ostracoderms that lacked teeth. They were covered with a thick bony
shield that was separated in to a head and trunk portion unlike ostracoderms. They began as marine
organisms but the fossil records show an evolution to fresh water living. They have an extra pelvic lobe
similar to that of sharks called "claspers" used for copulation believed to be the origin of sex since the
placoderms fertilized internally.
Viviperous
Offspring born living
Oviperous
Offspring born from an egg
Acanthodians
After Placoderms, these had 6 pairs of fins.
Buchal pumping
using muscular contractions to force water out of the Buchal (oral) cavity
Ram ventilation
Swimming with an open mouth to allow water to flow through the gills for respiration
Gill tissue structure
Primary lamellae with secondary lamellae that have capillaries within them with a thickness of 1 cell to
allow for gas exchange. The primary lamellae have abductor muscles that when contracted allow water
to flow between the lamellae rather than around, increasing oxygen uptake.
Countercurrent exchange
Blood and water flow in opposite directions within the gill tissue to maximize O2 uptake rather than
them equilibrating as it would if they flowed in the same direction (lateral to medial blood flow).
Increased O2 uptake allows for increased activity due to more metabolic resources. Also used for
thermoregulation where heat is maintained in the organism's core. It allows muscle temperatures to
drop more slowly than outside water temperature.
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Labyrinth form organ
A flattened, highly folded and invaginated organ found in fish that breathe surface air that allows for gas
exchange from the air. Lung was not derived from this, but rather a swim gas bladder next to the
digestive tract.
Differences in eyes between land animals and fish
Water and air have different light refractive indexes, and thus the eyes must differ in their location of
the retina behind the eye to allow for clear image.
Anapleps
A fish with "4 eyes" that allowed it to sit at the surface of water and have a clear image below and above
the water based on the shape of it's oval lens.
Lateral line system
A sensory system in fish that allows them to detect minute and rapid changes in water pressure to
better navigate water. The neuromast organ is within a canal running anterior to posterior that is
accessible through pores in the skin
Neuromast organs
Sensory organs within the lateral line system canals that are composed of sensory cells with kinocilia
that are attached to a cupula that is moved by water. When the cupula moves the kinocilia, they
mechanically open and close ion gates to depolarize or repolarize the cell and create an action potential
sent to the brain. These organs are afferently and efferently innervated so that the brain can regulate
how much sensory input it gets.
Sensory field
An area of the surroundings to which an organ is sensitive to changes. Many sensory fields often
overlap.
Ampullary organ
Organ located within skin pores that are filled with gel that has cells within it that can sense
electromagnetic fields. this organ is derived from the lateral line system. This allows sharks to accurately
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Document Summary
Early group of fish with mineralized tissue, notochord, cranium, but lacked pharyngeal slits. The efficiency of the vertebrate kidney at removing water from the body points to vertebrate life originating in freshwater where there was an abundance of water. On the other hand, the earliest vertebrate fossils are found exclusively in marine environments. Paraphyletic group of jawless extant vertebrates without reproductive ducts who reproduce externally. Essentially the only extant agnathans who are found at 1% males in a population (possibly hermaphroditic). They lack jaws, vertebra, external armor, are found worldwide (except for polar waters) \, and feed as scavengers. Range refers to the distance an individual will travel while distribution refers to the regions in which a species can be found. Have small simple vertebrae, feed as parasites by drinking blood, have well-developed kidneys to allow them to reproduce in freshwater (making them anadromous), and are sedentary filter-feeders as larvae.
