early vertebrates? primitive fish? Flashcards
(24 cards)
What is a fish?
A vertebrate that isn’t a tetrapod
Give 5 characteristics of the early Cambrian fossilised vertebrates
Cranium W-shaped myomeres Heart and fin rays Lack mineralised tissues Soft bodied
When are the early Camrbian fossils from?
535 mya
Where were the early Cambrian fossils found?
Chengjiang, China
When did mineralised tissue appear in the fossil records?
Late Cambrian
When did bone fragments appear in the fossil records?
Early Ordovician - 480 mya
When did complete fossils first appear in the record?
Late Ordovician
Where were the first complete fossils found?
Bolivia and Australia
Give an example of a complete fossil from late Ordovician Bolivia
Astraspis
Give 5 characteristics of Astraspis
Torpedo shaped Jawless External armour, head shield and bony plating Gill openings Sensory canals
What did the Astraspis use its sensory canals for?
Detecting changes in water pressure (like modern day fish)
Why may the Astraspis have needed external armour?
Protection from large marine invertebrates
What are conodonts?
Microfossils spanning fossil records from Cambrian to Triassic, turned out to be teeth
What are conodonts made of?
Apatite
What are jawless fish called?
Agnatha
What are the 2 classes of agnatha?
Myxinoidea
Petromyzontia
Give 8 general characteristics of jawless fish
Slender eel-like bodies Naked skin (no scales) Cartilaginous skeleton/cranium Notochord persistent No vertebrae or jaws 5-16 pairs of gills Distinct brain No distinct stomach
How many species of hagfish are there?
65
Why don’t hagfish lose ions or water to the surrounding environment?
They have an osmotic equilibrium with seawater
How do hagfish defend themselves against predators?
They produce slime which clogs up a predator’s mouth and gills, making it hard to breathe
Describe the hagfish circulatory system
Low pressure
1 main heart with 3 accessory hearts
What are Myxinoidea known as?
Hagfish
What are Petromyzontia known as?
Lampreys
Give 4 morphological characteristics of hagfish
Single nasal opening
Single semi-circular canal
Degenerate, skin-covered eyes
Mucoid bag
