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
Who lost the End Devonian extinction?
Ostracoderms
Placoderms
Who survived the End Devonian extinction?
Chondrichthyes
Actinopterygii
Tetrapods- became us!
What are Chondrichthyes?
Cartilaginous fishes
What are Chondrichthyes split into?
Elasmobranchii and Holocephali
Features of Chondrichthyes
Placoid scales- dermal denticles, homologous with teeth, reduce drag
Pelvic claspers- males use them to attach to females to inject sperm
Lateral line system- line of sensory cells (neuromasts) across bodies of many fish,. Mechanoreception detects small changes in water pressure
Ampullae of Lorenzini- network of jelly filled pores for electroreception
What are Elasmobranchii?
Sharks and rays
Features of elasmobranchs
Usually 5 gill openings Spiracle opening Rigid fins Shed their continually growing teeth Grow around 12 teeth a day 2 clades
What are elasmobranchii split into?
Selachii (sharks) and Batoidea (rays
What are Selachii?
Sharks
What are Batoidea?
Rays
What are Holocephali?
Rat fish
Holocephali features
Pre-pelvic claspers
Frontal tentaculum- don’t really know what its for
Tooth plate- part of the upper jaw, fused to the skul
What are Actinopterygii?
Ray-finned fish
What are actinopterygii split into?
Chondrostei
Holostei
Teleostomi
What are Chondrostei?
Type of actinopterygii
Include sturgeons, paddlefish, reedfish
What are Holostei?
Type of actinopterygii
Include bowfins and gars
What are Teleostomi?
Type of actinopterygii
Around 25,000 modern species
Anatomy of actinopterygii
Bony endoskeleton Fin rays Air filled swim bladder Operculum (flap covering a single gill opening) Overlapping bony scales
What’s the slim bladder for?
Filled with gas to maintain position in the water column
What are Sarcopterygii?
Lobe-finned fish
What are Sarcopterygii split into?
Actinistia (Coelocanths), Dipnoi, Tetrapods
Sarcopterygii anatomy
Fleshy lobed fins
Humerus is the single connection to the supportive girdle
How do Osteichthyes maintain buoyancy?
Swim bladder- connected to the gut, or can be entirely internal
Lactic acid secretion at a gas gland causes oxygen to be released from the blood
Homologous with tetrapod lungs
How do Chondrichthyes maintain buoyancy?
Don’t have a swim bladder
Have a large oily liver (squalene oil) for lift
Dynamic lift from pectoral fins and tail
Types of breeding (8)
Oviparity Ovoviviparity Ovuliparity Viviparity Hermaphroditism Sexual dimorphism Parthenogenesis Sexual parasitism
Oviparity
Internal fertilisation
Female lays eggs that develop externally
Eg. mermaids purse from sharks
Ovoviviparity
Embryos develop inside the female, egg hatches inside
Get nourishment just from the egg
Eg. basking sharks, anacondas
Ovuliparity
External fertilisation
Broadcast spawning- all release egg and sperm into the water
Eggs develop externally
Eg. Cnidaria, Ctenophora, Echinoderms
Viviparity
Embryos develop inside female
Nutrients from the adult, no eggs
Eg. seahorses, humans, cattle
Hermaphroditism
Change sex over time
Male to female = protogyny
Female to male = protoandry
Eg. Indo-Pacific cleaner wrasse. Form harems of one large male and smaller females. If male dies, largest female becomes male within 2 weeks!
Sexual dimorphism
Males and females look different
Eg. Peacock spiders (jumping spiders). Some debate as to whether sexual dimorphism exists- Wallace (vital energy causing intensified colour), Peckham says yes.
Eg. sneaker males that look like females, so can sneak past the guarder male to mate with females
Parthenogenesis
Females produce offspring asexually
Seen in sharks and teleosts, and some species of scorpion
Sexual parasitism
Deep sea angler fish exhibit extreme dimorphism
Male is tiny, attaches permanently to female like a parasite
Teleosts are split into
Acanthomorpha
Non-acanthomorpha
Acanthomorpha
Eg. Cod, dories
Over 18,000 species (out of 25,000)
Very diverse shapes
Protrusion feeding
Non-Acanthomorpha
Eels, herring, carp, tetras
Protrusion feeding
Use premaxilla to estimate distance of protrusion
Increased over time
Now 21.4% of original distance
Swimming forms (4)
Anguilliform eg. eels
Carangiform eg. mackerel
Thunniform eg. tuna
Ostraciiform eg. puffer fish
ACTO! Less laterally flexible
Anguilliform
Eg. eels
Lots of head movement
Carangiform
Eg. mackerel
A fair bit of head movement
Thunniform
Eg. tuna
A little bit of head movement
Ostraciiform
Eg. puffa fish
Basically no head movement
