Mesozoic Life

Life of the Mesozoic Era Age of Reptiles –most diverse and abundant land dwellers Mammals appear Birds appear Flowering plants appear Some marine invertebrate groups recover Pm\Tr Another big extinction at end K

Mesozoic Marine Life Permo-Triassic extinctions left voids that were rapidly filled. Several important invertebrate phyla radiated, as did certain fishes Predator/prey relationships changed Appearance of marine reptiles at top of marine food chain

Just before the Mesozoic: Permian\Triassic Extinctions Many major Paleozoic invertebrate groups extinct a) Trilobites b) Rugose and tabulate corals c) Blastoids (echinoderms) d) Fusulinid foraminifera e) Brachiopods and crinoids severely reduced

Replacement radiations New marine groups assumed ecological roles of extinct organisms a) New corals and planktonic foraminifera b) Several classes of mollusks Ammonites radiate - Clams replace many brachiopod groups- –Rudistid clams become reef formers Marine Reptiles replace fish as top marine predators

The diversification of Mollusks Bivalves replaced most brachiopods in benthic community Oysters were successful, abundant in shallow Atlantic and Gulf ocean. Ammonites underwent a tremendous radiation

Rudists Bizarre rudistid bivalves (clams, oysters) Shells had large cone-shaped valve, smaller lid valve Shells up to 1meter long grew in masses, formed reefs They replaced corals as dominant reef- formers by Middle Cretaceous

Ammonites Greatest mollusk diversification was among cephalopods Nautiloids and ammonoids had appeared in Paleozoic Ammonites were ammonoid cephalopods that underwent tremendous radiation They were differentiated on the basis of their complex suture patterns The evolutionary purpose of the intricately folded septa –Complex infolding sustained shell against great water pressure at depth

Cephalopod shell morphology (living today) (extinct end K)

Ammonites Ammonites were rapidly evolving, free- swimming predators A favorite food of mosasaurs (huge marine lizards) Among most important Jurassic and Cretaceous index fossils –Rapid evolution of sutures –Widespread, many facies

Scleractinian Corals 1) Scleractinian corals replaced rugose, tabulate corals (a) First appeared in Middle Triassic (b) Soft-bodied sea anemones possible ancestors (c) Scleractinian corals formed large reefs by end of Triassic

Success of Scleractinian corals Skeletons faster growing –Crowd out other benthic organisms Symbiotic relationship with algae (zooxanthelae) responsible (found in fossils) Algae supply food, oxygen to coral Coral furnishes home to algae in shallow, sunlit waters

Echinoids Stalked echinoderms largely gone at Paleozoic end. A few crinoids still survive. Varieties of echinoids flourished in the benthic environment Sea urchins Sand Dollars

Microfossils

Foraminifera Foraminifera greatly reduced after Perm-Triassic extinctions, radiated again Benthic until Jurassic Period Planktonic foraminifera then inhabited surface waters Thinner-walled, globular–shaped tests Important index fossils

Coccolithophorids Unicellular gold-brown algae Calcareous shells consist of microscopic disk-shaped plates First appearance in Jurassic Major component of Cretaceous chalk deposits, along with forams Chalk deposits represent the original reference section that defined the Cretaceous System both sides of the English Channel

Mesozoic Fishes Bony Fishes continued to dominate Especially Teleosts Sarcopterygians reduced to a few species

Marine Reptiles Several groups of Triassic diapsid and euryapsid reptiles became successful marine predators They developed streamlined bodies Flipperlike modifications of limbs Large size Ichthyosaurs Mosasaurs Plesiosaurs

Mosasaurs - Marine Lizards A really big ”Goanna” or Monitor Lizard Lived offshore near here Diapsids

Euryapsid Marine reptiles Placodonts (Triassic) 1) Short-necked, body < 2m 2) sea floor dwellers 3) Crushed shellfish for food Nothosaurs (Tr-J) 1) Contemporary with placodonts 2) Streamlined bodies elongated necks 3) Ancestral to plesiosaurs Plesiosaurs 1) Found in Jurassic and Cretaceous rocks 2) Short bodies, flipperlike limbs, and long necks 3) Ate fish. Up to 12 meters in length Icthyosaurs Tr to Late K, long snouts, fishlike bodies like sharks and dolphins; convergent evol. Rapid swimmers Mosasaurs (Cretaceous) 1) Giant marine lizards up to 15 meters long 2) Flattened tails and flipperlike limbs 3) Ate fish and cephalopods Plus Marine Crocodiles

Placodonts Ichthyosaurus Plesiosaurus Mosasaurs marine predators in Cretaceousc, mostly ate fish and ammonites

Land Plants Gymnosperms Cycads – Cylindrical trunks and large-fernlike leaves – Dominant during Jurassic, common until Cretaceous Conifers –most modern conifer types –dominated Cretaceous forests as cycads declined Ginkgoes –Common in Mesozoic forests –Single surviving species like Mesozoic ancestors

Cycad: Sago palm

Ginkgo biloba

Cycads and cycadeoids in Jurassic Scenes

Angiosperms - Flowering Plants Most significant Mesozoic evolutionary event Reproductive adaptations out compete gymnosperms Flower uses color and scent to encourage insect pollination Higher pollination success rates than gymnosperms that use wind Manufacture of seeds with a food supply Animals became important in distributing seeds from fruits Demo, cones and Magnolia seed sheath after flowers wilt.

Flowering Plants - Primary Producers on land Triassic and Jurassic land plants consisted of seedless vascular plants and gymnosperms with seeds. Angiosperms (flowering plants) appear in Early Cretaceous, similar to magnolias SAYREVILLE The evolution of flowers and an enclosed seed ensured their success No more relying on wind

Mammal-Like reptiles Therapsid reptiles recovered from Permo- Triassic extinctions Dicynodonts were common until end of Triassic –Gondwana Lystrosaurus found on all southern continents Cynodonts radiated in Early Triassic Gondwana carnivorous Cynognathus found in Africa and South America Herbivorous cynodonts lived until Middle Jurassic

Triassic Therapsids Thrinaxodon Lystrosaurus

Mesozoic Therapsids

Origin of Mammals Therapsids gave rise to cynodonts, which evolved into the mammal class –skeletal structure is used to identify mammals in the fossil record –differences in the lower jaw and ear in particularly distinguish mammals

Late Triassic Morganucodon Mammaliaformes descended from Cynodonts ~ 200 mya Mesozoic groups: multituberculates, monotremes, marsupials and placentals

Roy Chapman Andrews In the Gobi desert of Mongolia, found the first dinosaur nests and evidence of parental care in the dinosaurs Protoceratops Modern studies of Dinosaurs still test his theories Discussion: Oviraptor Protoceratops Was looking for early humans

Dinosaur Ancestry Archosaurs, reptiles that radiated in Permian and especially Early Triassic Large quadrupedal “galloping” crocodile-like forms. Hind limb much longer. Small bipedal forms probably ancestral to dinosaurs and birds

Phytosaurs Basal Archosaurs Herrerasaurus Common fossil near campus Rutiodon

Archosaurs and the Origin of Dinosaurs Archosaurs gave rise to crocodiles, pterosaurs, dinosaurs, and birds Dinosaurs two groups distinguished by hips: –Saurischia –Ornithischia Saurischian Hip Ornithischian Hip

First dinosaur found: Iguanodon First dinosaur discovered in Richard Owen “dinosaur” Dinosaurs are terrestrial, so they are rare fossils Hypsilophodon Mary Anning

Dinosaurs Back of hip this side Front of hip this side SaurischianOrnithischian

Dinosaurs Saurischians –theropods were bipedal carnivores –sauropods were the giant, quadrupedal herbivores Ornithischians –Ornithopods (duckbill) –Pachycephalosaurs –Ankylosaurs –Stegosaurs –Ceratopsians

Saurischian Dinosaurs Theropods, the carnivorous dinosaurs And Sauropods, the long necked giants

Theropods Dennis Neary Trenton NH Museum Larger relative of Velociraptor Dilophosaurus

Theropods

Sauropods Sauropods Parental Care, Herds, Land

Ornithischian Dinosaurs Stegosaurs (plate-backed dinosaurs) Ornithopods including Hadrosaurs (duckbills) Ankylosaurs (armored dinosaurs) Pachycephalosaurs (thick-headed dinosaurs) Ceratopsians (horned dinosaurs)

Ornithischians

Social behavior in duckbill dinosaurs Maiasaura Jack Horner Parasaurolophus Crest dimorphism, function Colony nesting also known in Protoceratops Roy Chapman Andrews

Armored dinosaurs

Pachycephalosaur Pachycephalosaur

Ceratopsians

Flying Reptiles The pterosaurs were the first vertebrates to fly –common from Late Triassic to Cretaceous –wing membrane supported by an elongated fourth finger –light hollow bones –development of brain areas associated with coordination and sight –likely to have been endothermic

Principle pterosaur groups Rhamphorynchoids Pterodactyloids Long keeled tail, teeth No tail, strong crest Discussion: stability and steering in flight Pitch, Yaw and Roll

Some have fine “hair”

Jurassic Bird Archaeopteryx

Archeopteryx lithographica Late Jurassic, Solenhofen Germany Coelurus

Luis and Walter Alvarez The K\T ash layer in Alberta Shocked Quartz Hell Creek Formation

Cretaceous-Tertiary boundary

The Chicxulub structure

K-T Mass Extinction - A Crisis in the History of Life n Cretaceous-Tertiary extinction claimed dinosaurs, flying reptiles, marine reptiles, and many marine invertebrates

Dust cloud reached stratosphere Blocked the sun Plants need light Herbivores eat plants Carnivores eat herbivores Hibernating survivors can sleep through it. Uh, oh. That can’ t be good.

The End of the Age of Reptiles

ZZZZZZZZZ ZZZZZZZZZ ZZZZZZZZZ Meanwhile, mammals able to hibernate could sleep through the cold dark crisis,

getting up occasionally for a supper of stored seeds

and underground insects and worms