Ch.3 Flashcards
Trends in Paleozoic continental drift: Cambrian
Super continent
South Pole
O2 still increasing
Temp stable
Shallow sea eats
—> better deposit for fossils
Trends in Paleozoic continental drift: Ordovician
Glacieration —> less water in ocean
More area for life
Temp decreased
Trends in Paleozoic continental drift: Devonian
Jawless and jawed fish diversified
Now in fresh water too
Trends in Paleozoic continental drift: Permian
Super continent
Some Land masses inhabitable, temp increased
Aminotes
—> evolved, diversified
Worst mass extinction
Cyclostomata
(cyclos = round, stoma = mouth)
Most Basel group of verts
• Myxiniformes (hagfish)
• Petromyzontiformes (lampreys)
• Diagnostic characters include:
1. Monorhiny – single nostril
2. Branchial basket – gill arches without joints (more rigid)
3. Gill arches lateral to gill tissues (internal)
4. Velum – pumps water to gills
5. Tongue with keratinous teeth
6. Notochord remains in adults (not completely replaced by vertebrae)
Cyclostome pharyngeal structures
Lamprey
Gill arches (branchial basket)
Gills lateral, fill tissue inside
Sharks
Gills point out laterally
Gill structures medial
Jawless vertebrates
Myxiniformes
• 75 species of hagfish
• Primarily scavengers, can hunt
• Rows of keratinized open sideways
• Single median fin
• Chemoreception strong, other
senses weak
• Vestibular system with single semicircular canal
• Body maintained at same osmotic concentration as sea water
• Do control concentration of some ions
• Produce slime as defense
• Combination of mucus and protein threads
Jawless vertebrates
Petromyzontiformes
• 40 species of lampreys
• Larvae are filter feeders
• Adults are parasitic or non-feeding
• Keratinous teeth all around buccal funnel
• 2 dorsal fins
• Good vision
• Vestibular system with two semicircular canals
• Parasitic forms use tidal ventilation (water flows in and out through gill openings)
• Most species anadromous
• Mates create nests of stones in
stream beds for developing eggs
• Larvae known as Ammocoetes, long thought to be independent species
Gnathostomes
• Diagnostic characters include:
1. Diplorhiny – paired nostrils
2. Gill arches with joints
3. Gill arches medial to gill tissues
4. Vestibular system with 3 semicircular canals
5. 2 pairs of tribasic fins
6. Mineralization of vertebral
elements
7. Myomeres separated into epaxial and hypaxial sections by horizontal septum
Evolution of jaws
• Developmental domains
1. Premandibular: No Hox genes,
helps anchor jaws to cranium
2. Mandibular arch: Becomes the upper and lower jaws
3. Hyoid arch: Hox gene expression begins, hyoid structures support the jaws
4. Carotid arch: Supports first set of gills, carotid artery develops
5. Branchial arches: support gills
Significance of the nostrils
• Early vertebrates: Midian nasal sac develops connected to pituitary, overlies forebrain
• Premandibular domain compact
• Gnathostomes: Nasal sac paired, separated from pituitary, moves anteriorly
• Premandibular domain elongated
• Neural crest cells migrate in, providing support
Why are jaws beneficial?
• More efficient respiration
• Increase the volume of the pharynx
• Draw more water in
• Pump water over the gills
• Allow intake of larger food items
Early gnathostomes
• Jaws evolved before teeth
• Some early “teeth” were elaborations of jaw bones
• Teeth might have evolved from outside in
• Some fish scales are composed of dentine and enamel
Paired fins
Another gnathostome character
Types of fins
• Cyclostomes and early vertebrates had midline fins, simple myomeres
• Gnathostomes have midline fins, paired fins, complex myomeres
• Trunk muscles originate from somitic mesoderm
• Limbs develop from lateral plate mesoderm
Fin structure and support
• Limbs are supported by girdles
• Distal girdle elements develop as
dermal bone
• Central girdle elements develop as endochondral bone
• Scapula, coracoid, basal elements
• Tribasic = 3 basal elements distal to scapula/coracoid
