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 reefformers 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, freeswimming 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
Diapsids
A really big ”Goanna”
or Monitor Lizard
Lived offshore near here
Euryapsid Marine reptiles
Mosasaurs (Cretaceous)
1) Giant marine lizards up to 15 meters long
2) Flattened tails and flipperlike limbs
3) Ate fish and cephalopods
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
Nothosaurs (Tr-J)
1) Contemporary with placodonts
2) Streamlined bodies elongated necks
3) Ancestral to plesiosaurs
Icthyosaurs
Tr to Late K, long snouts, fishlike bodies
like sharks and dolphins; convergent evol.
Rapid swimmers
Placodonts (Triassic)
1) Short-necked, body < 2m
2) sea floor dwellers
3) Crushed shellfish for food
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 PermoTriassic 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
Lystrosaurus
Thrinaxodon
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
Was looking
for early
humans
Roy Chapman Andrews
Protoceratops
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
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
Basal Archosaurs
Herrerasaurus
Common fossil near campus
Rutiodon
Phytosaurs
Archosaurs and the
Origin of Dinosaurs
• Archosaurs gave rise to
crocodiles, pterosaurs,
dinosaurs, and birds
• Dinosaurs two groups
distinguished by hips:
Saurischian Hip
– Saurischia
– Ornithischia
Ornithischian Hip
First dinosaur found:
Iguanodon
Mary Anning
•First dinosaur
discovered in 1822
•1842 Richard
Owen “dinosaur”
•Dinosaurs are
terrestrial, so they
are rare fossils
•Hypsilophodon
Dinosaurs
Saurischian
Back of hip this side
Ornithischian
Front of hip this side
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
Dilophosaurus
Larger
relative of
Velociraptor
Dennis Neary
Trenton NH Museum
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
Colony nesting also
known in Protoceratops
Roy Chapman Andrews
Maiasaura
Jack Horner
Parasaurolophus
Crest
dimorphism,
function
Armored dinosaurs
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
Discussion: stability and steering in flight
Pitch, Yaw and Roll
Rhamphorynchoids
Long keeled tail, teeth
Pterodactyloids
No tail, strong crest
Some have fine “hair”
Jurassic Bird Archaeopteryx
Archeopteryx lithographica
Late Jurassic, Solenhofen
Germany
Coelurus
The K\T ash layer in Alberta
Shocked Quartz
Hell Creek Formation
Luis and Walter Alvarez
Cretaceous-Tertiary boundary
The 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 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