The Vertebrate Land Invasion

1
The Vertebrate Land Invasion

• Amphibians and Early Reptiles

2
Learning Goals

• What does life on land versus life in the ocean
  require?
• What evidence supports that the Rhipidistians
  were the first on land?
• What group may have given rise to the mammals?
• What are dinosaurs? What living animals are they
  most closely related to?

3

• We have the oxygen, we have the plants and bugs
  to chew on.. Next are the land vertebrates!
• Late Devonian
• Pg. 373-376

4

• Rhipidistians (Devonian lobe fins) poised to
  invade land
• Why the Rhipidistians?

5

• Shallow water ambush predators lived close to
  land
• 2. Respiration - had an air-breathing lung
• 3. Both upper and lower jaw moves - allows them
  to move into shallower water

6

• 4. Powerful ventral lobe fins - chase prey into
  very shallow water and land

5. Coelacanth (and probably the Rhipidstians)
limbs (fins) same as all modern terrestrial
tetrapods
7

• Limbs and Feet why become an amphibian?
• 1. Traditional answer pool hoping - Drought in
  the continent

8

• 2. Basking?
• Sunning on a mud bank could speed digestion
  would have grown / matured faster
• Requires support thorax has to move to respire
  strengthening of pectoral fins to take the weight

9

• 3. Reproduction?
• Isolated pools ideal for spawning out of the
  way of most predators
• Warm with a rich supply of invertebrates ( FOOD)

10

• 4. Latest idea
• Limbs did not develop for any land-based
  locomotion!
• Adaptation for moving around in swampy, root
  tangled environments.

11

• Developments required for living on land
• water tight skin
• strengthening of vertebral column and ribs to
  support new muscles / internal organs

12
The Early Amphibians
An ancestor of all of us!
13

• Earliest Amphibian / True Tetrapod fossil
  Elginerpeton, late Devonian, Scotland (368Ma)
• Large! Jaw alone 40cm long

14

• Diversified into the Devonian
• Still relied on the water ambush predators like
  crocodiles today
• Many rhipidistian characteristics - spine, skull,
  tail fin, but have stiff back bone and ribs to
  support internal organs out of water

15
The Early Reptiles

• First reptile fossil - Early Carboniferous
• Early reptiles are small compared to the
  amphibians

Westlothiana around 20cm long
16

• Why are early reptiles so small?
• Adaptation to catching small insects
• Small creatures can heat up quicker
• Early reptiles much like modern lizardsFlexible
  neck, rapid movement
• Suggested that reptiles evolved on the forest
  floor or in the canopy of the Carboniferous
  forests.

17

• Breaking The Final Links With the Water The
  Amniotic Egg
• Amphibians still linked to water to reproduce.
• Reptiles fewer eggs, more of an investment in
  protecting them Air-tight space ship
• Due to embryo being surrounded by membranes /
  shell reptiles had to develop internal
  fertilization
• Very successful The Amniotes major vertebrate
  clade.

18
The Reptile Radiation
19

• Late Carboniferous major reptile groups
  developed
• Classified on number of openings in skull behind
  eye
• Anapsid - no holes (turtles, Permian / Triassic
  reptiles)
• Synapsid - one hole (mammal like reptiles)
• Diapsid - two holes (lizards, dinosaurs, snakes,
  crocs)
• Edges of holes - muscle attachment areas.

20

• ANAPSIDS
• Earliest - probably small insect eaters
• SYNAPSIDS
• First mammal-like reptiles
• Mostly small insectivores in Early Permian
• Later Permian Therapsid pelycosaur radiation
• 1. Larger carnivores, e.g. gorgonopsians
• ?Endothermic (warm blooded) - adapted to running
• Lycaenops late Permian gorgonopsian 1m long

21

• 2. First herbivorous land vertebrates, e,g.
  dicynodonts
• Ranged in size from rat - cow
• Very successful in Permian - range into Triassic

22

• 3. Significant for us Cynodonts
• Whiskers, hair?
• Will give rise to the mammals in the late
  Triassic
• Dvinia - late Permian cynodont

23

• DIAPSIDS The Triassic Takeover
• Competitive replacement
• Extinction of Synapsids followed by radiation of
  dinosaurs

24
What ARE dinosaurs?
Synapsid Reptiles (Mammal-like reptiles)
Mammals
Archosaurs
Other Reptiles
Amphibians
Diapsid Reptiles two holes behind eye socket
Read pg. 384-388
AMNIOTES Land creatures that internally
fertilize eggs
Land animals with 4 limbs - TETRAPODS
25

• True dinosaurs evolve in late Middle Triassic
  mostly bipedal carnivores

Eoraptor skull 2.5cm
Coelophysis 2.5 long - common in N-America
Herrerasaurus 3-6m long
26

• LABS EOS-Main 101
• start next Wed. (Oct. 15) Group B
• Fri (Oct. 17) Group C
• Mon (Oct 20) Group A