The Vertebrate Story Flashcards
1
Q
Vertebrates - defining features
A
- vertebrae (backbone) forms around notochord
- internal and elaborate skeleton (cartilage or bone)
- defined head with braincase (skull), and sensory organs
2
Q
Cephalochordate
A
- lacks jaws
- earliest vertebrates share this feature
- later vertebrates developed jaws by modifying gill arches
3
Q
Agnatha
A
- vertebrates: jawless fishes
- were once (495-360 mya) a very divers group of animals
- early forms had exoskeleton of bone in skin - may even have had electroreception
- nowadays only two small groups exist - lampreys and hagfish (both blood-sucking parasites of fish)
4
Q
Evolution of Jaws
A
- jaws derived form gill arches of chordates
- earliest jawed fishes - late silurian (420 mya)
- some had dermal armour e.g. Placoderm
5
Q
Cartilaginous Fish
A
- cartilaginous skeleton
- maintaining water balance is a major issue (high levels of urea in blood)
- reproducition sexual and mostly internal
- embryo encased in leathery egg-case
- some sharks give birth to live young
6
Q
Bony (ray finned) Fish
A
- rigid bony skeleton (cartilage replaced)
- paired fins (ray like structure)
- swim bladder for buoyancy
- usually a single dorsal fin
- incredibly diverse
7
Q
Evolution of legs
A
- most bony fishes have fins made of long rays of bone (ray-finned fishes)
- some fishes developed more substantial bones in the fins (lobe-finned fishes) e.g. lungfish
8
Q
The first tetrapods: The amphibians
A
- had unsual limbs
- about 350 mya some of lobe-finned fishes, living in shallow lagoons, developed these bones to be able to ‘walk’ (paddle in shallow water)
- these early amphibians had both gills and lungs e.g. lungfish
- still needed water
9
Q
Amphibians
A
- water crucial for reproduction
- eggs do not have shells
- some have ingenious ways to keep damp
10
Q
Class: Reptiles
A
- tetrapod vertebrates
- evolved form advanced reptile-like amphibians
- adapted to life on dry land
- many extinct groups e.g. dinosaurs
- modern reptiles inhabit all continents except Antarctica
- Key features:
- have scutes or scales
- “cold blooded” - ectothermic
- most lay eggs
- no aquatic larval stage
- not a monophyletic group
- strictly speaking should include birds
- reproduction sexual and internal
- usually eggs, some product live young
11
Q
Appearances of the major groups of tetrapods
A
- Amphibians = 350 mya
- Reptiles = 330 mya
- Mammals = 190 mya
- mammal-like reptiles = 320 mya
- dinosaurs and crocodieles = 230 mya (after Permian extinction)
- Birds = 150 mya
12
Q
Dinosaurs
A
- dinosaurs come from the same lineage as crocodiles (archosaurs)
- unlike crocodiles, many walked upright
- Eoraptor - an early dinosaur (230 mya)
13
Q
The origin of birds
A
- one group of small dinosaurs, the dromaeosaurs
- In 1861, Germany, a new fossil discovered that had dromaeosaur characteristics but also had feathers, wings - first evidence for evolutonary origin of birds from dinosaurs
- birds = archosaurs
- Archaeopteryx*
14
Q
The evolution of mammals
A
- first mammal-like reptiles = 320 mya
- at first very reptile-like e.g. Dimetrodon
- many were large and carnivorous (powerful jaws)
- smaller mammal-like reptiles evolved (possibly with fur)
- upright stance evolved (legs tucked under body)
15
Q
A change of stance
A
- hip joints and upper limb bones changed in mammals and dinosaurs
- changed stance
- change of stance enabled quicker locomotion (longer legs)
