Climate change as a selection pressure: Triassic - Jurassic mass extinction:
Triassic life and climate pre-extinction -
The Triassic was a time of recovery and diversification after the mass extinction at the end of the Permian. The climate was getting hotter and dryer in general and the continents were still united as a super-continent Pangaea and there was little to stop tetrapod animals migrating except climate.
The climate of the Triassic was much warmer than today, there were no polar ice caps, so the world’s climate was generally hot and dry with monsoonal polar regions as a result of carbon dioxide levels being about three times higher than today.·The vegetation was dominated by the forked seed-fern, Dicroidium with abundant horsetails, club-mosses, ginkgoes, ferns, conifers such as pines and Araucarians. Aquatic environments were dominated by fish and Labyrinthodont amphibians alongside sharks, bony fishes and Ichthyoaurs. On land the first dinosaurs, Prosauropods, early Ornithopods, small predators such as Eoraptor and Herrerasaurus appeared. At the same time the mammal-like reptiles were declining in numbers while the long-tailed pterosaurs dominated the air. Early crocodiles, lizards and turtles also thrived; as well as insects such as cockroaches and dragonflies. Primitive mammals were starting to appear also in the Triassic period.
Causes of extinction - The end Triassic extinction remains unsolved, but several theories include: gradual sea level change, and temperature fluctuations, but these theories don’t explain the suddenness of the extinction event in the marine realm. Another theory points to an asteroid impact but so far no crater of sufficient size has been dated to coincide with the Triassic-Jurassic boundary extinction. One widely supported theory states that a likely cause was the eruption of the Central Atlantic magmatic province, as shown on the diagram below, from which over 2 million cubic kilometres of lava erupted over many centuries, and quadrillions of kilograms of the aerosol sulphur was released, causing intense global cooling.
The Triassic was a time of recovery and diversification after the mass extinction at the end of the Permian. The climate was getting hotter and dryer in general and the continents were still united as a super-continent Pangaea and there was little to stop tetrapod animals migrating except climate.
The climate of the Triassic was much warmer than today, there were no polar ice caps, so the world’s climate was generally hot and dry with monsoonal polar regions as a result of carbon dioxide levels being about three times higher than today.·The vegetation was dominated by the forked seed-fern, Dicroidium with abundant horsetails, club-mosses, ginkgoes, ferns, conifers such as pines and Araucarians. Aquatic environments were dominated by fish and Labyrinthodont amphibians alongside sharks, bony fishes and Ichthyoaurs. On land the first dinosaurs, Prosauropods, early Ornithopods, small predators such as Eoraptor and Herrerasaurus appeared. At the same time the mammal-like reptiles were declining in numbers while the long-tailed pterosaurs dominated the air. Early crocodiles, lizards and turtles also thrived; as well as insects such as cockroaches and dragonflies. Primitive mammals were starting to appear also in the Triassic period.
Causes of extinction - The end Triassic extinction remains unsolved, but several theories include: gradual sea level change, and temperature fluctuations, but these theories don’t explain the suddenness of the extinction event in the marine realm. Another theory points to an asteroid impact but so far no crater of sufficient size has been dated to coincide with the Triassic-Jurassic boundary extinction. One widely supported theory states that a likely cause was the eruption of the Central Atlantic magmatic province, as shown on the diagram below, from which over 2 million cubic kilometres of lava erupted over many centuries, and quadrillions of kilograms of the aerosol sulphur was released, causing intense global cooling.
Life and climate post extinction (early Jurassic) -
The early Jurassic period brought a much warmer and wetter rainforest type of climate and as such it encouraged reptile expansion [5]
in the post extinction environment which once again had left behind a gap that allowed new species to flourish throughout the Jurassic. The largest dinosaurs of the Jurassic were the gigantic sauropods, such as the famous Brachiosaurus. Other herbivorous dinosaurs of the Jurassic included the armour plated Stegosaurs with predatory dinosaurs such as Allosaurus. The Jurassic also marked the appearance of the first birds, including Archaeopteryx, probably from coelurosaurian ancestors. [1]
The early Jurassic was crucial in the development of marine reptiles such as ichthyosaurs which shared the oceans with the plesiosaurs, marine crocodiles and with early sharks and rays. These existed alongside cephalopods: relatives of the squids, octipi and nautilus of today's oceans. These Jurassic cephalopods included the ammonites which had survived from the Triassic, and the belemnites, (close relatives of modern squid but with heavy, calcified, partially internal shells). [2] Among the plankton in the oceans, the dinoflagellates [3] became numerous and diverse during this period, as did the coccolithophorids (microscopic single-celled algae with an outer covering of calcareous plates). [4]
Land plants were numerous in the Jurassic, but different from today's equivalents. There were no palms or flowering plants in a modern sense in the Jurassic. Instead, ferns, ginkgoes and bennettitaleans were widespread in this period. Conifers were also present, including close relatives of living redwoods, cypresses, pines, and yews. Amongst all these were the small early mammals that survived the mass extinction.
The early Jurassic period brought a much warmer and wetter rainforest type of climate and as such it encouraged reptile expansion [5]
in the post extinction environment which once again had left behind a gap that allowed new species to flourish throughout the Jurassic. The largest dinosaurs of the Jurassic were the gigantic sauropods, such as the famous Brachiosaurus. Other herbivorous dinosaurs of the Jurassic included the armour plated Stegosaurs with predatory dinosaurs such as Allosaurus. The Jurassic also marked the appearance of the first birds, including Archaeopteryx, probably from coelurosaurian ancestors. [1]
The early Jurassic was crucial in the development of marine reptiles such as ichthyosaurs which shared the oceans with the plesiosaurs, marine crocodiles and with early sharks and rays. These existed alongside cephalopods: relatives of the squids, octipi and nautilus of today's oceans. These Jurassic cephalopods included the ammonites which had survived from the Triassic, and the belemnites, (close relatives of modern squid but with heavy, calcified, partially internal shells). [2] Among the plankton in the oceans, the dinoflagellates [3] became numerous and diverse during this period, as did the coccolithophorids (microscopic single-celled algae with an outer covering of calcareous plates). [4]
Land plants were numerous in the Jurassic, but different from today's equivalents. There were no palms or flowering plants in a modern sense in the Jurassic. Instead, ferns, ginkgoes and bennettitaleans were widespread in this period. Conifers were also present, including close relatives of living redwoods, cypresses, pines, and yews. Amongst all these were the small early mammals that survived the mass extinction.
References:
[1] http://en.wikipedia.org/wiki/Coelurosauria
[2] http://www.thinktank.ac/page.asp?section=504§iontitle=fossil
[3] http://www.ucl.ac.uk/GeolSci/micropal/dinoflagellate.html
[4] http://www.mbari.org/staff/conn/botany/phytoplankton/phytoplankton_coccolithophorids.htm
[5] http://www.jurassictimes.com/jurassic-period-facts
[1] http://en.wikipedia.org/wiki/Coelurosauria
[2] http://www.thinktank.ac/page.asp?section=504§iontitle=fossil
[3] http://www.ucl.ac.uk/GeolSci/micropal/dinoflagellate.html
[4] http://www.mbari.org/staff/conn/botany/phytoplankton/phytoplankton_coccolithophorids.htm
[5] http://www.jurassictimes.com/jurassic-period-facts