Mesozoic LifeMesozoic Life

Life of the Mesozoic EraLife 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 LifeMesozoic 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:Just before the Mesozoic:Permian\Triassic ExtinctionsPermian\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 radiationsReplacement 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 ofThe diversification of MollusksMollusks• Bivalves replaced most brachiopods in

benthic community

• Oysters were successful, abundant in shallow Atlantic and Gulf ocean.

• Ammonites underwent a tremendous radiation

RudistsRudists

• 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

AmmonitesAmmonites

• 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 morphologyCephalopod shell morphology

(living today)(extinct end K)

AmmonitesAmmonites

• 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 CoralsScleractinian 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 coralsSuccess 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

EchinoidsEchinoids

• 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 Microfossils

ForaminiferaForaminifera

• 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

CoccolithophoridsCoccolithophorids

• 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 FishesMesozoic Fishes

• Bony Fishes continued to dominate

• Especially Teleosts

• Sarcopterygians reduced to a few species

Marine ReptilesMarine 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 LizardsMosasaurs - Marine Lizards

A really big ”Goanna” or Monitor Lizard

Lived offshore near here

Diapsids

Euryapsid Marine reptilesEuryapsid Marine reptiles

Placodonts (Triassic)1) Short-necked, body < 2m2) sea floor dwellers3) Crushed shellfish for food

Nothosaurs (Tr-J)1) Contemporary with placodonts2) Streamlined bodies elongated necks3) Ancestral to plesiosaurs

Plesiosaurs1) Found in Jurassic and Cretaceous rocks2) Short bodies, flipperlike limbs, and long necks 3) Ate fish. Up to 12 meters in length

Icthyosaurs Tr to Late K, long snouts, fishlike bodieslike sharks and dolphins; convergent evol.Rapid swimmers

Mosasaurs (Cretaceous)1) Giant marine lizards up to 15 meters long2) Flattened tails and flipperlike limbs3) Ate fish and cephalopods

Plus Marine Crocodiles

Placodonts

Ichthyosaurus

Plesiosaurus

Mosasaurs marine predators in Cretaceousc, mostly ate fish and ammonites

Land Plants GymnospermsLand 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 palmCycad: Sago palm

Ginkgo bilobaGinkgo biloba

Cycads and cycadeoids in Jurassic Scenes

Angiosperms - Flowering PlantsAngiosperms - 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 landFlowering 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 reptilesMammal-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 TherapsidsTriassic Therapsids

Thrinaxodon

Lystrosaurus

Mesozoic TherapsidsMesozoic Therapsids

Origin of MammalsOrigin 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 MorganucodonLate Triassic Morganucodon

Mammaliaformes descended from Cynodonts ~ 200 mya

• Mesozoic groups: multituberculates,

• monotremes,• marsupials and

placentals

Roy Chapman AndrewsRoy Chapman Andrews

In the Gobi desert ofMongolia, found the first dinosaur nests

and evidence of parental care in the

dinosaurs Protoceratops Modern studies ofDinosaurs still test

his theoriesDiscussion: Oviraptor

Protoceratops

Was looking for early humans

Dinosaur AncestryDinosaur 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 ArchosaursHerrerasaurus

Common fossil near campus

Rutiodon

Archosaurs and the Archosaurs and the Origin of DinosaursOrigin 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:First dinosaur found:

Iguanodon Iguanodon

•First dinosaur discovered in 1822

•1842 Richard Owen “dinosaur”

•Dinosaurs are terrestrial, so they are rare fossils

•Hypsilophodon

Mary Anning

DinosaursDinosaurs

Back of hip this sideFront of hip this side

Saurischian Ornithischian

DinosaursDinosaurs • Saurischians– theropods were

bipedal carnivores– sauropods were

the giant, quadrupedal herbivores

• Ornithischians– Ornithopods (duckbill)

– Pachycephalosaurs– Ankylosaurs– Stegosaurs– Ceratopsians

Saurischian DinosaursSaurischian Dinosaurs

• Theropods, the carnivorous dinosaurs

• And Sauropods, the long necked giants

TheropodsTheropods

Dennis NearyTrenton NH Museum

Larger relative of Velociraptor

Dilophosaurus

Theropods

SauropodsSauropodsSauropods

Parental Care, Herds, Land

Ornithischian DinosaursOrnithischian Dinosaurs

• Stegosaurs (plate-backed dinosaurs)

• Ornithopods including Hadrosaurs (duckbills)

• Ankylosaurs (armored dinosaurs)

• Pachycephalosaurs (thick-headed dinosaurs)

• Ceratopsians (horned dinosaurs)

Ornithischians

Social behavior in duckbill dinosaursSocial behavior in duckbill dinosaurs

MaiasauraJack Horner

ParasaurolophusCrest dimorphism, function

Colony nesting also known in ProtoceratopsRoy Chapman Andrews

Armored dinosaursArmored dinosaurs

PachycephalosaurPachycephalosaur

CeratopsiansCeratopsians

Flying ReptilesFlying 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 groupsPrinciple pterosaur groups

Rhamphorynchoids PterodactyloidsLong keeled tail, teeth No tail, strong crest

Discussion: stability and steering in flightPitch, Yaw and Roll

Some have fine “hair”

Jurassic BirdJurassic Bird Archaeopteryx Archaeopteryx

Archeopteryx lithographicaLate Jurassic, SolenhofenGermany

Coelurus

Luis and Walter Alvarez

The K\T ash layer in Alberta

Shocked Quartz

Hell Creek Formation

Cretaceous-Tertiary boundaryCretaceous-Tertiary boundary

The Chicxulub structureThe Chicxulub structure

K-T Mass Extinction - A Crisis in the History of Life

Cretaceous-Tertiary extinction claimed dinosaurs, flying reptiles, marine reptiles, and many marine invertebrates

Dust cloud reached stratosphereBlocked the sunPlants need lightHerbivores eat plantsCarnivores eat herbivoresHibernating survivors can sleep through it.

Uh, oh. That can’ t be good.

The End of the Age of Reptiles

ZZZZZZZZZZZZZZZZZZZZZZZZZZZ

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

getting up occasionally for a supper of stored seedsgetting up occasionally for a supper of stored seeds

and underground and underground insects and wormsinsects and worms