L10- Triassic Terrestrial Ecosystems

Triassic World:

  • pangea, everything is together, have to cross central-pangean mountain range to get from top to bottom, two deserts (deposits here are sandstone), Tethis ocean, islands, large ocean

  • CO2 levels are higher than today, greenhouse world, no ice at the poles, O2 levels are low→ problems for terrestrial animals (lower altitude limit)

  • poles are warm temperate, 6 months of winter and 6 months of sunshine, get forests at the poles


Plants:

  • mesophytic vegetation, not much change

  • Bryophytes

  • Lycopsids

  • Ferns and Horsetails→ understories

  • Pteridosperms→ glossopterids

  • Pteridosperms→ bennettites (new group- have flower-like reroductive structures, distinctive cuticle structures)

    • cuticle prep→ dissolve leaf out of rock, film them, stain them, study the structure of cells and stomata

  • Cycads

  • Gingkos

  • Conifers→ diversify, most modern conifer groups appear in the Triassic

  • reconstruction of Triassic plants:

    • conifer forest, cycads, understory of ferns

  • transition from palaeophytic to mesophytic from west to east

End Permian:

  • animals→ minimal survival, Lilliput effect- survivors are small groups, longer recovery

  • plants→ get wiped out but come back, ecological reorganisation of the same group of plants


Insects:

  • few insect deposits:

  • not much change→ no major groups get wiped out, get some new modern groups e.g. flies

Fish:

  • get change from lobe-finned fish dominance to ray-finned fish dominance

  • basal chondrichthyes get wiped out, still don’t have the modern group of sharks and rays- possibly diversify at the end

  • lots of groups get wiped out at end Triassic, modern groups diversify after this


Tetrapods:

  • severely affected by end Permian mass extinction

  • find lots of Lystrosaurus→ restricted fauna, survived by the nature of its ecology

  • initial recovery is very slow, synapsid dominance in the Permian is replaced with Diapsid dominance in the Triassic→ mass extinction changed the course of tetrapod evolution

  • shift from warm/moist→ hot/dry environment with low O2


Amphibians:

  • many groups go extinct at the P/T mass extinction

  • radiation of Lissamphibia→ modern groups make it through and start to diversify


Reptiles:

  • may groups wiped out, dicynodonts re-radiate but die at the next mass extinction, cynodonts make it through→ give rise to mammals, many anapsids gone, diapsids radiate after

  • Archosaurs→ are important as they give rise to dinosaurs and crocodiles

  • dinosaurs appear in middle-late triassic in Argentina/Brazil

    • small, bipedal

  • Diapsids→

    • groups reinvade the sea, eating fish e.g. placodonts, ichthyosaurs

    • Pterosaurs→ first true fliers, bias to marine deposits but weren’t all fish eaters, morphologically diverse

Amniotes:

  • diapsids diversify following the P/T mass extinction→ gives rise to the groups that dominate the Triassic/Jurassic (crocodiles/dinosaurs)

  • appear after P/T, hit hard at Triassic mass extinction, give rise to mammals→ evolved mammal like characters sequentially over 30-40million years so cannot say when the first mammal evolved

  • fossil taxa progressively become more mammal like


Mass extinctions:

  • huge extinction at P/T 250mya→ slow re-radiation- lots of herbivores, start to get dinosaurs, major groups are there but are small

  • extinction at Mid Triassic→ lose herbivores from Carnian and replaced with Ornithiscians and Sauropods, major carnivore groups still there, therapods diversify a bit

    • caused by change from wet/damp/humid environment to drier environment

  • extinction at End Triassic→ phytosaurs and rauischia go extinct

    • caused by super heating

→ 3 mass extinctions rearrange therapods

  • get classic dinosaur biotas in the Jurassic