ANIMALS COLONIZE LAND

Question 1

Vertebrate Evolution: jawless fish (Cambrian) => fish w/ jaws (Silurian, Acanthodians & Placoderms) => Devonian Period “Age of Fishes” => Rhipidistian “lobe fin” fish (Devonian) => by Devonian early tetrapods (i.e. amphibians like Ichthyostega) Jaws are modified gill arches

Answer 1

○ Acanthodians - earliest jawed fish (appeared at late Silurian)
○ Placoderms - heavily armored jawed fish (appeared at late Silurian)
○ Rhipidistian fish - lobe-finned fish. Developed nostrils and internal air passages by late devonian; the transitory form for tetrapods (Acanthostega, Panderichthys, Eusthenopteron)
Many transitional forms from fish to tetrapods exist in fossil record (Ichthyostega, Tiktaalik)

Question 2

Both rhipidistian fish and early amphibians (Ichthyostega) have labyrinthodont teeth, other lines of morphological evidence? Remember, amphibians reproductive biology bound to aquatic environment (must lay eggs in water)

Answer 2

○ Shoulder/limb bones
○ Wrist/ankle bones
○ Tiktaalik doing push ups, which leads to evolution of actual limbs
○ Tiktaalik’s amphibian-like traits: flat head, flexible fins, actual neck bones (fish don’t have necks, while amphibians do), ribcage
○ Tiktaalik’s fish-like traits: scales, fins, gills
Amphibians have inefficient lungs and have to absorb oxygen through their skin

Question 3

Carboniferous: Temnospondyl Amphibians (labyrinthodont teeth) & Tetrapod Radiation

Answer 3

○ Amphibians ruled throughout the Carboniferous
○ Temnospondyls - large, flat bodied amphibians. Most common group
Anthracosaurs - thought to be reptile ancestors

Question 4

How would evolution of first forest canopy facilitate tetrapod radiation in Devonian?

Answer 4

○ Damp climate was the ideal environment for these early tetrapods
○ Lots of food (insects) that was not found in the water
○ No predators on land
Protected wetland environments from intense sunlight

Question 5

Parallel evolutionary between seed plants & amniotes?

Answer 5

Amniotes and plant seeds decoupled reproductive biology from aqueous environments, made it possible for life to habitat drier climates inland

Question 6

Anthracosaur amphibians lack otic notch => earliest reptiles – when? First reptiles – when?

Answer 6

○ Late carboniferous/Early Permian
○ Lack of otic notch in Anthracosaurs suggest that they evolved into reptiles
Hylonomus: one of the first reptiles

Question 7

Pelycosaurs (Permian) => synapsids => Therapsids (mammal-like reptiles)

Answer 7

○ Synapsids - one temporal opening (mammal-like reptiles)

Diapsids - two temporal openings (dinosaurs, crocs, birds, snakes, etc)

Question 8

Therapsids likely warm-blooded (endothermic)

Answer 8

○ Upright posture and complex chewing apparatuses suggest they are warm-blooded
○ Therapsids diversified and spread out very quickly - advantage of being warm-blooded?
Temperature control, able to live in cooler environments than cold blooded organisms