early mesozoic era - university of northern...

Earth History, Ch. 16 1

Early Mesozoic Era

Jurassic

System

Triassic

System

Late

Early

Early

Middle

Middle

Late

142

206

251

Jurassic System named

in early 1900’s for classic

exposures in the Alps.

Triassic System named

in 1834 by von Alberti

in Germany. Triassic is

bounded by mass extinc-

tions above and below.


Today’s outline

• Life in the Early Mesozoic (aftermath of the

end-Permian mass extinction)

– Marine realm

• Benthic life forms

• Pelagic life forms

– Terrestrial realm

• Plants

• Animals


Early Mesozoic marine life

• End-Permian mass extinction wiped out:

– Corals, fusulinids, blastoids, trilobites, most crinoids,

most brachiopods, most bryozoans

• Paleozoic invertebrate faunas were dominated by

sessile, filter-feeding organisms

• End-Permian mass extinction caused a complete

reorganization of marine communities



• Earliest Mesozoic marine realm was

dominated by mobile, predatory mollusks

– Ammonoids (radiated from 1 to 100 genera in

early Triassic)

– Bivalves

– Gastropods


Sepkoski’s three faunas

(marine invertebrate world)



• Reef communities were decimated by the end-Permian mass extinction

• No reefs in early Triassic

• Middle Triassic reefs resembled late Permian ones (sponges, algae)

• New coral reefs (hexacorals) appeared in middle Triassic (small, deep-water reefs)

• By late Triassic, large, shallow water reef structures were forming


Triassic hexacorals

Hexacorals probably are not

related to Paleozoic corals,

but evolved indepently from

sea anemonies.

Explosive adaptive radiation

started in late Triassic time.


Hexacoral

radiation

Note: No early

Triassic corals


Early Mesozoic marine realm

• Planktonic microrganisms diversified in Jurassic time

– Dinoflagellates (algae)

– Calcareous nannoplankton (coccoliths)

• Swimming organisms rebounded

– Ammonoids, belemnoids (fossil cigars)

– Conodonts (became extinct at end-Triassic)

– Bony fishes and sharks


Pelagic organisms

Calcareous

nannoplankton

Ammonoids and belemnoid


Early Mesozoic marine realm

• Swimming reptiles (a curious return to aquatic habitats) diversified in Triassic time

– Nothosaurs (early Triassic, seal-like)

– Placodonts (turtle-like)

– Plesiosaurs (middle Triassic, giant, up to 40 feet long)

– Ichthyosaurs (dolphin-like)

– Crocodiles


Nothosaur


Placodont


Plesiosaurs


Ichthyosaur


Early Mesozoic terrestrial realm

• Triassic flora was dominated by ferns and seed ferns

• Early Mesozoic trees were dominantly gymnosperms

– Cycads

– Cycadeoids

– Conifers

– Ginkos


Early Mesozoic gymnosperms

modern Ginko leaf Jurassic Ginko leaves


Cycadeoid (palm-like fern)


Early Mesozoic terrestrial

animals

• Therapsids (mammal-like reptiles) barely

survived end-Permian mass extinction

– Then gave rise to true mammals in late

Triassic time

• Earliest mammals were small and

inconspicuous

– No larger than a house cat


Origin of the dinosaurs

• Thecodonts were small early Triassic

reptiles that gave rise to earliest dinosaurs

• Early dinosaurs were small, but by end of

Triassic some reached up to 20 feet in

length

• By early Jurassic time, many kinds of huge

dinosaurs existed


Thecodonts and early mammal


Allosaurus

(Jurassic)


Dinosaur phylogeny

thecodont


Origin of the

dinosaurs

thecodonts

Bird-hipped dinosaurs

were all herbivorous

Reptile-hipped dinosaurs

were both herbivorous

and carnivorous


Dinosaur pelvises

Saurischian pelvis Ornithischian pelvis


Jurassic dinosaurs

• Morrison Formation (extends from

Montana to New Mexico) has best

assemblage of Jurassic dinosaurs in world

• Dinosaur collecting wars

– Cope vs. Marsh feud

– Gun battles and railroad cars full of bones!!


Earliest Flight

• Pterosaurs (late

Triassic reptiles)

were earliest flying

animals

• Probably clumsy

upon take-off and

landing, but well

suited for soaring

through the air


Earliest birds

• First true birds

appeared in late

Jurassic time

(evolved from

saurischian

dinosaurs)

• Last of the

vertebrate classes

to originate


Archaeopteryx from Solnhofen

Limestone (Germany)

early mesozoic era - university of northern...

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