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 Important invertebrate group Ammonites Nautilus Important invertebrate group Ammonites Complex sutures Abundant (Jr & K), extinct (end K) Nautiloids and belemnoids survived

Mesozoic Life Fishes and Amphibians Cartilaginous 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 captorhinomorphs 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 Ornithischia 5 groups 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 Protoavis (Tri) 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 Cynodonts Monotremes 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?