Mesozoic Era
Life
Mesozoic Life
• Known as “Age of Reptiles”
• Mammals and angiosperms evolve
Marine Invertebrates
Plankton
• Coccolithophores
– 1st appeared (Jur)
– Abundant (K)
– Continue today
• Diatoms (SiO2)
– 1st evolved (K)
– Cold H2O
• Dinoflagellates
– Warm H2O
• Foraminifera
– Exploded
• Most plankton extinct (end K)
Marine Invertebrates
Corals & Echinoderms
• Corals & Echinoderms proliferated
Scleractinians
Echinoderm
Mollusks
Brachiopods & Gastropods
• Significant invertebrate fauna
• Brachiopods
– Never fully recovered from
Permian extinction
– Minor invertebrate
• Gastropods
– Largest, most varied class
– Marine, fresh H2O, terrestrial
– Herbivore & carnivore
Mollusks
Bivalves
• Burrowing organism
– Escaped predators
– i.e., oysters, clams
– Rudists significant
 Formed large tropical reefs
 Excellent guide fossils
Mollusks
Cephalopods
Cephalopod
Nautilus
• Important invertebrate group
• Ammonites
– Complex sutures
– Abundant (Jr & K), extinct (end K)
• Nautiloids and belemnoids survived
Mesozoic Life
Fishes and Amphibians
• Bony fish
– ↑ abundance
• Amphibians
– Frogs and salamanders appear
– Greatest diversity (Permian)
Mesozoic Life
Plants
• Primary producers – base of food chain
• Gymnosperms
– Gingkos
– Conifers
– Cycads
Modern cycads
• Gymnosperms replaced by angiosperms
Gymnosperm
Angiosperm
Plants
Angiosperms
• Adapted to nearly every terrestrial habitat
• Factors to success:
– Method of reproduction
 Evolution of flowers
• Pollinators
 Evolution of enclosed seed
• Seeds dispersed by wind, fruit, burr
Mesozoic Life
Reptiles
• Diversification began during Penn
– Evolution of protorothyrids
 1st to lay amniote egg
 All other reptiles evolved
• Thecodontian (L. Per-Tri)
– Small, agile reptiles with
long tails, short limbs
– Teeth set in sockets
 i.e. crocs, dinos, &
mammal-like reptiles
– Quadrupedal, ran bipedal
– Herbivores & carnivores
– Dinosaur ancestors
Warm-Blooded Dinosaurs
• Ectotherm – “cold-blooded”
– Animals whose body temp
varies in response to outside
temp
• All reptiles ectothermic
• Endotherm – “warm-blooded”
– Capable of maintaining a
constant body temp regardless
of outside temp
• Mammals & birds endothermic
• Dinosaurs believed to be
endothermic
Warm-Blooded Dinosaurs
• Endotherm requirements
– Dino bones numerous
passageways = blood flow
 Crocs, turtles have similar
bone structure = ectotherm
– High metabolic rates  need to
eat more
 Dinosaurs  3.5% prey pop’n
 Similar to present-day mammals
– Complex nervous system 
large brain
 Many dinos have small brains
 Small carnivores = large brain
– Active flight requires endothermy
 Pterosaurs = hair-like feathers
Triceratops brain cavity
Mesozoic Life
Dinosaurs Relationships
• Two independent orders evolved
1. Saurischia “lizard-hipped”
– Theropod & Sauropod
2. Ornithischia “bird-hipped”
Dinosaurs
Saurischia Theropod
• Theropods – “Carnivores”
– Bipedal locomotion
– Various sizes
 60 cm to 15 m
 2 kg to 8 tons
– Tyrannosaurus (largest
terrestrial carnivore)
– Deinonychus – “terrible claw”
Dinosaurs
Saurischia Sauropod
• Sauropods – “Herbivores”
– Quadruped locomotion
– Largest land animals to
ever exist
 20 to 35 m in length
 10 to 55 tons
Camasaurus “Brontosaur”
Brachiosaurus
Diplodocus
Mesozoic Life
Dinosaurs Relationships
• Two independent orders evolved
1. Saurischia
– Theropod & Sauropod
2. Ornithischia
Dinosaurs
5 groups
Ornithischia
1. Duck-billed dinos (K)
– Colonial nesting, cared for
young, herbivores, bipedal
2. Pachycephalosaurs
– Dome-shaped skull,
bipedal, butting
3. Ankylosaurs
– Armored, quadrupeds, tail
w/ club-like growth
4. Stegosaurs
– Quadruped, herbivore with
spike on tail
5. Certopsian
– Triceratops, quadrupedal
herbivores
Mesozoic Life
Winged Dinosaurs
• Pterosaurs
– 1st flying vertebrates
– Flight adaptations
 Winged membrane
supported by elongated
finger
• Pteranodon (K)
– Pterosaur
– Could actively fly
Mesozoic Life
Birds
• Few Meso birds
– Archaeopteryx
 Jur strata, Germany
– Protoavis (Tri)
 Crow sized
 Hollow bones
Mesozoic Life
Early Mammals
• 1st mammals (Tri)
– Small, rodent-like mammals
– Evolved from Therapsids
 Mammal-like reptiles
• Cynodonts
– Most abundant
mammal-like reptile
Early Mammals
• Monotremes
Cynodonts
– Egg-laying
– i.e. today’s platypus & string
anteater
• Eupantotheres
– Marsupials – pouched (E. K)
– Placental mammals
– All living mammals related to this branch
Mesozoic Life
From Reptile to Mammal
• Used skeletal structure to classify fossils
– Skull – Middle ear – Lower jaw – Teeth
–
–
–
–
Mammal’s middle ear attached to dentary
Reptiles = 1 ear bone; mammals = 3
Reptile = several jaw bones; mammals = 1
Teeth = distinct types
Reptile vs. Mammal
Comparison
Mesozoic Era
Mass Extinction
• Impact Theory
– Huge asteroid or comet
– Cloud of dust into
atmosphere
– Reduced sunlight
 Plants die first
 Herbivores followed
 Then, carnivores starved
Mass Extinction
Evidence
• Large impact basin
• Iridium-rich clay layers
– Rare crustal rock
– More in meterorites
• Clay layers, New Mexico
Mass Extinction
Problems
• Selective extinction
– Dinosaurs completely extinct
– Corals, clams, snails – some extinction
– Tropical plants, crocodiles, mammals,
turtles, snakes, & birds unaffected
• Why weren’t all organisms affected equally?