Review of Mesozoic Earth History
• Main Happenings in Mesozoic
– Breakup of Pangaea
– Lots of mountain-building in western North America
– Appearance + extinction of dinosaurs
– More detail in the geologic record
• More climate information!
The hydrologic cycle and climate
Water moves heat around the planet;
tectonics determines how effectively this
heat can move
• Mountains and continental shape/size determine whether
the hydrologic cycle can transport heat effectively
–
–
–
–
–
Mountains can block rainfall
Massive continents tend to have dry interiors
Coastal regions benefit from water cycle climate controls
Circumpolar currents cut off polar access to warm waters
N/S currents & waterways moderate polar climate
End Permian land and oceans
• Pangaea was shaped
like a ‘C’
• Inside ocean: Tethys
Sea
• Outside ocean:
Panthalassa
Panthalassa
Panthalassa
Tethys sea
Breakup of Pangea 1: Triple Junctions
• Seafloor spreading
creates a triple
junction: a point
where 3 tectonic
plates diverge
• North America split
off from S America
and Africa
Seafloor spreading raises sea
level
• Seafloor spreading causes bulges in ocean
basins
• Big enough bulges and/or lots of them
lowers the ocean volume
• This can cause flooding of the continents.
Western Interior Seaway
www.isgs.uiuc.edu/dinos/westernseaway.gif
Cordillera Orogenies
• General term refering to complex period of mountainbuilding Jurassic-Cenozoic
• Farallon plate goes below N American plate
– Nevadan orogeny – Late Jurassic/Early Cretaceous
• Orogeny near the current W coast
• Slope of subducting Farallon plate decreased ->
– Sevier orogeny – Late Cretaceous
• Further east (Utah)
– Laramide orogeny – Late Cretaceous/Cenozoic
• Even FURTHER east! Rockies
Triassic
• Arid, red beds
• Lots of fern prairies – no grasses yet
• Dinosaurs first appear
Triassic
• Dinosaurs evolved from reptiles
• Special hips and ankles that allow them to stand on 2
feet
• Speed, agility and less need for water gives them
edge
Jurassic
• Pangaea is breaking up – causes SL to rise
Jurassic
• Climate wetter than Triassic
• Forests replace deserts, still fern prairies
• Dinosaurs diverse and abundant
• Giant marine reptiles
Cretaceous
• SL still rising as breakup of Pangaea continues
• Atlantic only about 300 km wide
Cretaceous
• Abundant flying reptiles
• First flowers
• Birds with feathers
Isolation
• Pangaea began fragmenting
– during the Triassic and continues to do so
• Organisms had increasing difficulty
– migrating between continents as a result
• In fact, South America and Australia
– became isolated island continents
– their faunas evolving in isolation
– became quite different from those elsewhere
Mesozoic Marine Revolution
• Many predators in ocean
– Marine reptiles
– Fish, sharks
– Crabs, lobsters – could crush shells
Mesozoic Marine Revolution
• Many predators in ocean
– Marine reptiles
– Fish, sharks
– Crabs, lobsters – could crush shells
• Marine animals had to adapt:
– Burrow/hide (eg. clams, gastropods)
– Thick shells
– Swim
Echinoderms
• Metazoans
(animals) but not
vertebrates or
even chordates
• 5-fold symmetry
www.humboldt.edu/~natmus/Exhibits/Life_time/Cretaceous.web/327.jpg
Marine Vertebrates
• Numerous bony fish
• Cephalopods most common swimming animals
– Squids, octopus, ammonites
• Marine reptiles – not dinosaurs, not fish!
Ichthyosaurs
– Plesiosaurs
– Mosasaurs
Ichthyosaurs
• The streamlined, rather porpoiselike
ichthyosaurs
– varied from species measuring only 0.7 m long
– to 15-m-long giants
• Evolved from small animals
Ichthyosaurs
• fully aquatic animals
• evolved from
land-dwelling
ancestors
Ichthyosaurs evolved from reptiles
http://www.ucmp.berkeley.edu/people/motani/ichthyo/intro.html
Plesiosaurs
• The plesiosaurs,
• Mesozoic marine reptiles,
– belonged to one of two subgroups:
– short necked and long-necked
• Most were modest sized animals 3.6 to 6 m
long,
– one species found in Antarctica measures 15 m
Plesiosaurs
• Although the
plesiosaurs
– were aquatic
animals,
• their fipperlike
forelimbs
– probably
allowed them
to come out
onto land
Mosasaurs
• Mosasaurs were Late Cretaceous marine
lizards
– related to the present-day
– Komodo dragon or monitor lizard
• Some species measured no more than 2.5 m
long,
– but a few such as Tylosaurus were large,
– measuring up to 9 m
• Mosasaur limbs resemble paddles
– and were used mostly for maneuvering
– whereas the long tail provided propulsion
Tylosaurus
• Tylosaurus
was
– a large,
– Late
Cretaceous
– mosasaur
– It measured
up to 9 m
long
Mosasaur Skull
• Mosasaur skull on display
– in the Museum of Geology and Paleontology,
– University of Florence, Italy
Mosasaurs Were Predators
• All mosasaurs were predators,
–
–
–
–
and preserved stomach contents indicate
that they ate fish, birds, smaller mosasaurs,
and a variety of invertebrates
including ammonoids
And on land…
Land Plants
• Important changes took place
– in land plant communities
– flowering plants evolved during the Cretaceous
– soon became widespread and numerous
• The major groups of Paleozoic land plants
persisted,
– but now they constitute less than 10% of all species
Seedless Vascular Plants
and Gymnosperms
• Seedless vascular plants and gymnosperms
– were prolific
• until angiosperms
– replaced many of them during the Mesozoic
Angiosperms
• The long dominance of seedless plants and
gymnosperms
– ended during the Early Cretaceous/Late Jurassic,
– many were replaced by angiosperms, or flowering
plants
• Angiosperms probably evolved
– from specialized gymnosperms
Fossil Angiosperms
• From the lower
Cretaceous
– Potomac Group
– of the eastern United
States
• Sapindopsis,
– Cecil County,
Maryland
The Diversification of Reptiles
• Reptile diversification began
– during the Mississippian Period
– with the evolution of the first animals to lay
amniotic eggs
• From this basic stock of so-called stem reptiles
– all other reptiles, as well as birds and mammals,
evolved
Reptiles and Birds
• Relationships among fossil and living reptiles
and birds
First Dinosaurs
• Evolved from archosaurs (reptiles)
• Late Triassic
• Small, only 3 ft long
• Major characteristics
– Can walk fully upright - bipedal
– Special hip and ankle structure
Archosaurs and the
Origin of Dinosaurs
• Reptiles known as archosaurs
• archo meaning "ruling" and sauros meaning "lizard”
– include crocodiles, pterosaurs (flying reptiles),
dinosaurs, and the ancestors of birds
• Including such diverse animals
– in a single group implies
– that they share a common ancestor
– and indeed they possess several characteristics that
unite them
Dinosaurs Orders
• All dinosaurs possess
– a number of shared characteristics,
– yet differ enough for us to recognize two distinct orders
• the Saurischia
• and Ornithischia
• A distinctive pelvic structure characterizes each order
– 3 bones in pelvis: illium, ischium, and pubis
– Saurischian: pubis points down
– Orinischian: pubis points back
Distinctive Pelvic Structure
• Saurischian dinosaurs
– have a 1izardlike pelvis
– and are thus called lizard-hipped dinosaurs
• Ornithischians
– have a birdlike pelvis
– and are called bird-hipped dinosaurs
• Convergent evolution
– ‘birdlike’ pelvic structure reinvented in Saurischian
descendents (avian dinosaurs = birds)
Saurischians
www.enchantedlearning.com/subjects/dinosaurs/dinoclassification/Saurischian.html
Saurischian Dinosaurs
• The saurischians,
– include two distinct groups
– known as theropods and sauropods
• All theropods
– were carnivorous bipeds
– ranging in size from tiny Compsognathus
– to giants such as Tyrannosaurus
• and similar species
• that might have weighed
• as much as 7 or 8 metric tons
Dinosaur Cladogram