Vertebrate origins Flashcards
What is a chordate?
- Dorsal, hollow nerve cord
- Notochord
- Pharyngeal slits
- post anal tail
What is a vertebrate?
- Vertebrae
- Neural crest cells (origin of vertebrate skeletal tissue)
- Dermal bone
-Often: paired appendages, cephalisation, skull, closed circulation, red blood cells
What are the subphylums of Chordata?
- Urochordata
- Craniata
- Cephalochordata
What are craniates?
Chordates w/ cephalisation and bone/cartilage.
Especially vertebrates, but may lack vertebrae
How many vertebrates are there?
55,000 known living species
-27,000 tetrapods (0.5k marine)
- 28,000 fishes (16k marine)
What is cartilage?
- Tough, semitransparent, elastic, flexible
- Glycoprotein strengthened by collagen
What can mineralised skeleton be?
- External (dermal) bone
- Internal, derived from cartilage precursors (endochondral)
Why is bone important?
-Solid support for attachment of muscles
- Fast, efficient locomotion – avoid predators and catch prey
-Storehouse of chemicals (e.g. phosphates) for metbolism
- protection
What are examples of early vertebrate-like finds?
- Conodonta (superclass) - 475 mya
- Myllokunmingia & kin – 525 mya
- Cephalochordates (e.g. pikaia) – 525 mya
- Urochordates - 540 mya
What are the Ostracoderms?
Dominant fishes in the silurian
What are features of the Ostracoderms?
- Bony shields over head + thorax
- Often small, but some large (>1m)
- Bony – still no jaws
What are some vertebrate innovations of the Ostracoderms?
- Cellular bone
- Dentine-like tissue
- Paired limbs
- Intricate sensory line systems
- Complex eye muscles
- Inner ear with 2 semi-circular canals
How many extinct superclasses are in Ostracoderms?
5
What are the extinct superclasses of Ostracoderms?
- conodonta
- Pteraspidomorphi
- Anaspida
- Thelodonti
- Osteostracomorphi
What are features of the superclass Pteraspidomorphi? X
- 10-20cm, but some up to 1.5m
- Benthic filter feeders
- Evolved reduced armour, narrower head shield, lateral projections
What are features of the superclass Anaspida? X
- <15cm, fusiform, compressed
- Benthic parasitic/ detrital feeders: marine –> freshwater
- Overlapping tuberculate scales
- Fin-like projections + muscles + internal skeleton –> manoeuvrability
What are features of the superclass Thelodonti? X
– 10-20cm, fusiform, depressed, large head, horizontal mouth
- Hypoceral tail, dorsal + anal fins: benthic
– Forktail form - supra-benthic!
– Covered with characteristic scales or denticles ( like sharks)
- Stomach
– Lateral line
What are features of the superclass Osteostracomorphi? X
- Abundant and diverse
- Large, anterior, bony shield with eye, nose & pineal openings
– Ossification of endoskeleton
– Epicercal tail, body form and paired fins creates lift
– complex brain
How many living superclasses are in Ostracoderms?
2
What are the living superclasses of Ostracoderms?
- Myxinomorphi
– Petromyzontomorphi
How many species and classes are in the superclass Myxinomorphi?
70 living species in 1 class: Myxini
What are the preferred conditions of Myxinomorphi?
- Temperate/cold temperate oceans, below 30m
- Restricted to seawater: isosmotic!
What are the features of Myxinomorphi?
- Sister group to vertebrates: lack even primitive vertebrae
- No true eyes
- Mud-burrowing species extremely hypoxia tolerant
- Predators of benthic inverts and scavengers (burrow into prey)
- 70-200 pairs of slime glands: exude mucous and thread cells
How many species and classes are in the superclass Petromyzontomorphi?
38 living species in one class: Petromyzontida
What are the preferred conditions of Petromyzontida?
- Freshwater species: may be parasitic
- Anadromous species: all are parasitic
– migrate to upper streams for spawning
What are features of Petromyzontomorphi?
- Functional eyes
- Cerebellum
- Separate ventral & dorsal roots of the spinal nerves (a vertebrate feature)
- Olfactory and respiratory pathways are separated
What is an example of a Hagfish?
Myxine glutinosa
What is an example of a Lamprey?
Petromyzon marinus
What are similarities between Hagfishes and Lampreys?
- Eel-like, scale-less, jawless forms
– Produce pathogen-specific defensive substances: “variable lymphocyte receptors” (vs. antibody proteins in gnathosomes) - Tongue posses keratinous, replaceable teeth
– No stomach
What are differences between Hagfishes and Lampreys?
- Hagfishes produce mucus
– FINS – H: continuous caudal, L: 1 or 2 dorsal, caudal
– Mouth – H: terminal, L: Sub-terminal
– Gill-openings – H: 1-16, L:7
– Reproduction – H: repeat spawning, direct dev. from egg – L: terminal spawning, larval ammocoetes
– Tongue – H: biting & tearing, L: rasping & sucking
