BIOL360 Lecture Notes - Lecture 13: Edaphosaurus, Hylonomus, Thrinaxodon
12 May 2018
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Reptiles
What are the key events that took place in Mesozoic?
The Mesozoic started after Permian extinction and ended with cretaceous mass
extinction. It was the age of reptiles and conifers. Wide shallow seas began to form
and first mammals and flowering plants appeared.
End of Triassic -> Pangea began to rift apart
Early Jurassic -> dinosaurs spread across Pangea
Late cretaceous -> new ones begin to open
Reptiles
• Amphibians only made it half-way on to land; depended on water for egg-
laying (i.e. frogs, toads, salamanders, newts)
• Reptiles made clean break
• lay eggs on dry land habitat
• They have two types of eggs -> cleidoic egg and amniotic eggs
• The eggs were enclosed within tough semipermeable shells (calcareous,
leathery)
3 groups based on skull opening:
Anapsids have 2 openings in the skull -> a large opening and a nostril. Comprised of
turtles and reptiles
• Turtles do not have teeth, but earlier forms did (ex. Proganochelys)
• Turtles live on land in ponds and in the sea; early marine turtles in
Cretaceous reached 3 m
Synapsids have 3 openings in the skull. They were insectivores and carnivores with
some earliest forms being herbivores. Comprised of mammal-like reptiles and true
mammals (ex:
thrinaxodon
–-> a dog-like synapsid with hair that laid eggs -> 6 bones
in lower jaw to single jaw bone = transition to mammals)
• Earliest -> pelycosaurs; later representatives -> dimetrodon and
edaphosaurus
Document Summary
The mesozoic started after permian extinction and ended with cretaceous mass extinction. It was the age of reptiles and conifers. Wide shallow seas began to form and first mammals and flowering plants appeared. End of triassic -> pangea began to rift apart. Late cretaceous -> new ones begin to open. Anapsids have 2 openings in the skull -> a large opening and a nostril. Comprised of turtles and reptiles: turtles do not have teeth, but earlier forms did (ex. Proganochelys: turtles live on land in ponds and in the sea; early marine turtles in. They were insectivores and carnivores with some earliest forms being herbivores. Early forms-> lizards, snakes, crocs, dinosaurs and birds: mammals and reptiles (dinosaurs) appeared around the same time (late. Triassic/early jurassic) -> coexisted: reptiles did not give rise to mammals -> mammals quickly evolved after dinosaur extinction, ex: megaxostrodon -> earliest mammal.
