6-8: Vertebrate Origin, Jawed Vertebrates, Fish Evolution Flashcards
Chordates are spilt into…
Cephalochordates, urochordates, vertebrates
Vertebrates are split into…
Cyclostomes, gnathostomes
Fundamental structures of chordates
Notochord + myomeres, dorsal nerve chord, pharyngeal gills and endostyle
What’s the notochord + myomeres?
Rigid rod along body. In vertebrates, the notochord becomes vertebrae. Allow lateral undulations for swimming. Without, would have a slug/leech-like movement
What’s the dorsal nerve chord?
Runs along top of back (dorsal). In invertebrates, the nerve chord is ventral. Often a brain attached to anterior end
What are the pharyngeal gill slits and endostyle?
Breathe in through mouth, water passes out over gills.
Used in combination with the endostyle for filter feeding in early chordates.
In higher vertebrates, become gill arches and thyroid
Features of cephalochordata
Small, filter feeding marine animals
Also called lancelets
Simple morphology
They are the typical chordate, seen in basic diagrams
Features of urochordata
Tunicates/sea squirts
Marine invertebrates
Can be colonial, pelagic, can form a mucus ‘house’ around themselves- called a test
Filter feed using siphons
Juvenile has the chordate features, anchors itself and digests brain etc
What are cyclostomes? (agnatha)
Jawless vertebrates: lampreys and hagfish
What are gnathostomes?
Jawed vertebrates
What is the neural crest in vertebrate development?
A migratory multipotent cell population.
It can become parts of te brain, endocrine glands, head/face, teeth and jaws, circulatory system etc
How many whole genome duplication events have vertebrates undergone?
2
What genes control body plan layout?
Hox genes
Lamprey features
Anguilliform (eel-like) Parasitic freshwater-marine lifecycle Show semelparity- have a single breeding event No bones/jaws, just cartilage Oral suckers with keratinous teeth Sucking velum apparatus Vertebrae Brain, cranium, sensory organs Single dorsal nasal opening
Lamprey development
Larval stage (ammocoetes) Ammocoetes make burrows and are filter feeders Blind No oral suckers Anatomically similar to cephalochordates Metamorphosis to adult stage
Lamprey scientific name
Petromyzontida
Hagfish scientific name
Myxinoidea
Hagfish features
Anguilliform Blind Deep marine scavenger/predator Secrete gross gelatinous slime, twist to escape No bones/jaws, just cartilage Burrow int carcasses Rasping keratinous teeth- bite by rasping Velum and tongue apparatus Anterior single nasal opening
Hagfish development
Don’t know much about them
Eggs hard to grow in lab as they are deep sea creatures
Discovered neural crest in 2007
Gnathostome features
Paired pectoral and pelvic fins Bones and dentine Hinged jaws Paired nostrils Ribs and ventral vertebrae Internal gill arches
What is taphonomy?
The study of fossilisation
Look at current anatomy and how it decays
Decaying organisms lose synapomorphies, and so appear more primitive
Can estimate what features should be present after decay
Allows us to look at fossils and group them
What are ostracoderms?
Fossil jawless fish
Means ‘bony skin’
Lots of different types
What are conodonts?
Ostracoderms- ‘cone teeth’
Tooth-like elements with dentine
Body with eyes
Muscle blocks, tail fin
What are thelodonts?
Ostracoderms- ‘nipple teeth’
Shark-like scales on body
Maybe a bit like sharks?
The evolution of teeth could have started on the body
What are Placoderms?
Fossil jawed vertebrates Have simple hinged jaws Don't have proper teeth, just an extension of the jaw Predators with a strong bite Earliest example of live birth
What is the traditional segmentalism theory of jaw evolution?
Hyoid and mandibular arches are specialised anterior gill arches
But little evidence to support
What is the specification of upper and lower jaw theory of jaw evolution?
Hox gene expression specifies the arch identity along the body
Dlx expression specifies upper and lower jaws
