Gnathostome Lecture Flashcards
Gnathostome aka
“jaw mouth”
Gnathostome key synapomorphies
- jaws
- appendages (fins)
Other Gnathostome synapomorphies
- 3 pairs semicircular canals
- notochord partially/completely replaced by centra
- neural & hemal arches extend from notochord (surface are a for muscle attachment & more maneuverability)
- horizontal septum divides trunk musculature divided into epaxial (dorsal) & hypoxia (ventral) portions for increased muscular coordination)
jaws =
skeletal elements (bone or cartilage) that support borders of mouth
jaws derived…
evolutionarily & developmentally from pharyngeal arches (neural crest)
jaws first appeared in which fishes?
placoderms
benefits of jaws (2)
- permitted more effective predation
- increased size of prey that would be captured
ancestral condition of pharyngeal arches
cartilaginous elements around pharyngeal slits
jaws provide
structural support for gills
1st pharyngeal arch =
mandibular arch
- palatoquadrate (dorsal)
- mocker’s cartilage (ventral)
2nd pharyngeal arch =
hyoid arch
- hyomandibula (dorsal element)
paired appendage benefit
- greater body control in 3D space
- increased surface are (fins) allows for greater speed & maneuverability
True or false: about 1/3 of described extant chordate species are fishes
False (it’s 1/2)
Major clades of Gnathostomes: (5)
- Placodermi - placoderms (extinct)
- Aconthodii (extinct)
- Chondrichthyes - sharks, ray, chimaeras
- Osteichthyes - bony fishes (paraphyletic)
- Tetrapoda
Placodermi
Most basal gnathostome lineage (extinct)
Subclass Chondrichthyes
sharks, rays chimaeras
Chondrichthyes skeleton?
cartilaginous
Elasmobranchii is part of
Chondrichthyes
Elasmobranchii animals = body styles
sharks (fusiform) & rays (depressed)
Elasmobranchii tail
heterocercal (swim “lift”)
Elasmobranchii intestine valve
spiral valve in intestine
- increases time food in intestine
- increased SA for diffusion
Elasmobranchii fertilization
internal fertilization via clasper on male
Clade Neoselachii part of
Subclass Elasmobranchii
Sublcass Holocephali animals
chimaeras/ratfishes
Holocephali diverged from
earliest shark lineage (sister lineages to shark)
Holocephali habitat
marine/deep ocean
Lateral Line System structure & function
grooves/canals w/ neuromasts - mechanoreception (sensing mechanical disturbances)
Lateral Line System senses
water movements + directionality of course
- used for navigation & predation/evasion
Electroreception happens by
ampullae: (of Lorenzini, for example) specialized sensory cells detected electric current in water
- gives off electric potentials during neuromuscular activity
electroreception role
in prey detection
who has electroreception?
Chondrichthyes & platypus
who has a lateral line?
cartilaginous & bony fish & larval amphibian stage & soemtimessss adult amphibians retain lateral line (only ones that are fully aquatic)
electric rays generate
high power electrical output (nearly one kW)
electric organs:
electrocytes (modified muscle cells that produce electricity)
electric organs function
- stun prey
- protection from predators
electric organs homologous to
muscle cells
Elasmobranchii reproduction #1
oviparous (egg laying)
- some sharks & rays deposit into egg case (often with tendrils for attachment to objects)
Elasmobranchii reproduction #2
vivaporous (live-bearing t.f. young derives nutrients from mother)
- some have extensions of oviductal wall into embryo’s mouth that secrete milky substance
- some ovulate eggs that embryos eat in utero (or eat siblings in embryo!)
- some develop placenta-like structure w/ an umbilical cord that provides direct blood exchange
Integument & Teeth of Elasmobranchs
placoid scales (denticles)
- dermal and epidermal components
- resemble teeth of other vertebrates (pulp cavity, dentine, covered by enamel)
Elasmobranch Teeth attached
loosely to jaws & polyphyodont (constantly being replaced “multiple rows at any time”)
scales are homologous to
teeth of any vertebrate
Osteichthyes aka
“bony fishes”
Osteichthyes include
Actinopterygii & Sarcopterygii
Osteichthyes monophyletic or paraphyletic?
paraphyletic (when tetrapods not included)
Are all fishes as a whole (bony & cartilage) monophyletic or paraphyletic?
paraphyletic
Class Actinopterygii aka
“ray fin / wing”
t.f. Ray-Finned fishes
Actinopterygii appendage (fin) skeleton & musculature where
w/in body
Chondrostei part of?
Actinopterygii
Chondrostei monophyletic or paraphyletic?
paraphyletic group
Chondrostei animals
sturgeons. bichirs, paddlefishes
Chondrostei skeleton
cartilaginous (reversal)
Teleostei part of
Actinopterygii
Teleostei monophyletic or paraphyletic?
monophyletic clade
Teleostei scales
cycloid or ctenoid scales
- lighter & more flexible
- effect: greater mobility & speed
Teleostei scales derived
dermally (t.f. analogous)
Teleostei tail
homocercal tail (most)
Teleostei bladder function
gas reabsorption & secretion by gas bladder
- effect: buoyancy control
Teleostei jaw suspension modification for
suction feeding
Teleostei suction feeding
expansion of buccal (oral) cavity generates (-) pressure to draw in food
Teleostei diversity
~96% of fishes & nearly 1/2 of all vertebrates
Class Sarcopterygii aka
“flesh fin/wing”
t.f Lobe-Finned fishes
Sarcopterygii skeleton & musculature where
inside fins
Sarcopterygii groups
- Actinistia (coelacanths)
- Dipnoi (lungfishes)
- Rhipidistia (extinct sarcop.’s that share more recent common ancestor w/ tetrapods than do extant sarcop.’s)
Sarcopterygii & Rhipidistia (when tetrapods excluded) monophyletic or paraphyletic?
paraphyletic
