Lecture 2 – August 27, 2008
1. A few more phylogenetic terms.
2. Building a tree
a. synapomorphies & homologies
b. swapping branches
3. Defining Characters of Craniates vs. Cephalopods
- cranium, 3 part brain, nephrons, unpaired fins
4. Defining Characters of Myxiniformes vs. Petromyzontiformes + Gnathostomata
- vertebrate, 2 or more semi-circular canals, lateral line
5. Defining Characters of Gnathostomata
- jaws, 3 or more semi-circular canals, paired fins
6. Details on hagfish
7. Details on lampreys
8. (time permitting) details on jawless fossil fishes
Terms
homology – possession by two or more species of a trait derived, with or without
modification, from their common ancestor
synapomorphy – shared derived character state.
We use homologies & synapomorphies to identify & define monophyletic groups. These
kinds of traits inform us about the evolutionary history of a group.
Outgroup – a taxon that diverged from a group of other taxa before they diverged from
each other
Sister group – closest evolutionary relative to a taxa
Group Activity – See powerpoint file
taxa
notochord
Cranium
3-part
brain
gill
pouches
Vertebrae
Cephalochordates
Myxiniformes Hagfish
Petromyzontiformes
- Lamprey
Gnathostomata
-Jawed Vertebrates
present
present
absent
present
absent
present
absent
present
absent
absent
2 or more
semicircular
canals
absent
absent
present
present
present
present
present
present
present
present
present
present
present
present
taxa
lateral line
unpaired
fins
jaws
paired
fins
Cephalochordates
Myxiniformes
Petromyzontiformes
Gnathostomata
absent
absent
present
present
absent
present
present
present
absent
absent
absent
present
absent
absent
absent
present
3 semicircular
canals
absent
absent
absent
present
notochord - present in all choardates
- firm rod that provides support
draw picture of development
vertebrae develop around the notochord (intersect with muscles)
- in higher vertebrates, only present during development
cranium (skull) – brain case made out of cartilaginous (and often bony) tissue
3-part brain – Cephalochordates just have a nerve cord that ends. Craniata has a larger
mass at the anterior end of the fish that has three lobes
Gill pouches – water comes in through the mouth and out a hole to the exterior. The
pouch is the site of respiration (specialized for respiration – sites for feeding and
breathing are separate).
Unpaired fins = dorsal fin, anal fin, and caudal fin – in lampreys, The unpaired fins
are the dorsal and caudal fins, which are strengthened by numerous,
thin cartilaginous radials associated with radial muscles.
paired fins = pectoral fins, pelvic fins
lateral line - A system of mechanoreptors that detect water
movement or pressure change near fish’s body
Semi-circular canals – parts of the inner ear that allow for sound detection
After you put all of this up in the matrix have the students make the tree for
Cephalochordates, Myxiniformes, Petromyzontiformes, and Gnathostomata
Myxiniformes – details
-show map – 43 species – all marine
- narrow range of salinity tolerance, always in cold water, usually deep
• Slime eels: 70-200 pairs of slime glands
– 50 cm hagfish can produce 8 liters of slime /5 min.
• Function of slime?
– To suffocate fish when attacking dying fish?
– Protection from digestive juices when scavenging?
– Repulsion of competing scavengers?
– Stabilization of burrow walls?
– Anti-predator device?
• Hagfish can suffocate in its own slime
– Gets rid of it by tying knot and sliding through it
• Knot can also be used to feed
– scavengers
• Four hearts (open circulatory system) – low b.p.
• No larval stage
no functioning eyes,
no pineal gland (gland on top of head to detect light)
gut is a straight line
SHOW VIDEO (Blue Planet, The Deep at 31:45)
Petromyzontiformes – details
show map – 41 sp. fw & anadromous
- eye & pineal gland are present
- 7 openings for gill pouches
- single heart – closed circulatory system & high b.p.
- larval stage (ammocoete) – blind 10-15 cm
- they can be in this stage for 5-7 years, settle in mud and filter feed.
- two life-styles ( parasitic and non-parasitic)
- Non-parasitic species are thought to have evolved from parasitic species.
(draw out phylogeny)
- ammocoetes are indistinguishable,
same number of myomeres (or muscle blocks)
hypothesis – larval period is extended and parasitic period is deleted.
- spawning
- males travel to a rocky area and make a spawning pit; actually move rocks
around either with mouth or with tail
- nonparasitic ones are thought not to travel as far; parasitic ones travels far
- males circle around the female and “squeeze eggs out” over the course of 2-9
days; both then die.
- large # of chromosomes (140-170)
SHOW VIDEO from Youtube
Ostracoderms –
- paraphyletic group (actually two groups)
• Appeared in Cambrian/Ordovician, extinct in Devonian
• No jaws
• The first vertebrates- cartilaginous internal skeleton
• Bony exoskeleton armor-1st true bone (dermal)
• Small (< 15 cm)
• No paired fins that articulate with endoskeleton, some with reverse hypocercal
tail
• Bottom dwellers