Mesozoic

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<span style="font-size: 120%;">Lasting little more than half the duration of the Paleozoic, this was a spectacular time. The generalized  archosaurian reptiles of the  Triassic gave way to the dinosaurs, a terrestrial megafauna the like of which the Earth has not seen before or since. While dinosaurs dominated the land, diverse  sea-reptiles ruled the oceans, and invertebrates, especially ammonites, were extremely diverse.  Pterosaurs and later  birds took to the sky. Mammals however remained small and insignificant. Climatic conditions remained warm and tropical worldwide. The supercontinent of Pangea broke up into Laurasia and Gondwana, with different dinosaurian faunas evolving on each. During this era modern forms of corals, insects, new fishes and finally flowering plants evolved. At the end of the Cretaceous period the dinosaurs and many other animals abruptly died out, quite likely the result of an asteroid impact and associated extensive volcanism (acid rain).</span>
<span style="font-size: 120%;">Lasting little more than half the duration of the Paleozoic, this was a spectacular time. The generalized  archosaurian reptiles of the  Triassic gave way to the dinosaurs, a terrestrial megafauna the like of which the Earth has not seen before or since. While dinosaurs dominated the land, diverse  sea-reptiles ruled the oceans, and invertebrates, especially ammonites, were extremely diverse.  Pterosaurs and later  birds took to the sky. Mammals however remained small and insignificant. Climatic conditions remained warm and tropical worldwide. The supercontinent of Pangea broke up into Laurasia and Gondwana, with different dinosaurian faunas evolving on each. During this era modern forms of corals, insects, new fishes and finally flowering plants evolved. At the end of the Cretaceous period the dinosaurs and many other animals abruptly died out, quite likely the result of an asteroid impact and associated extensive volcanism (acid rain).</span>
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==Introduction==
The supercontinent Pangea divides into Laurasia in the north and Gondwana in the south. The climate is hot and tropical worldwide. On land, the  dinosaurs reign supreme. In the oceans are various kinds of marine reptiles, as well as ammonite and belemnite molluscs and many other invertebrate groups. Plants include ferns and gymnosperms. Mammals are small and insignificant, but probably numerically common.
The supercontinent Pangea divides into Laurasia in the north and Gondwana in the south. The climate is hot and tropical worldwide. On land, the  dinosaurs reign supreme. In the oceans are various kinds of marine reptiles, as well as ammonite and belemnite molluscs and many other invertebrate groups. Plants include ferns and gymnosperms. Mammals are small and insignificant, but probably numerically common.
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==Geography==
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== ''' Mesozoic  Life''' ==
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During the early [[Jurassic]], the [[supercontinent]] [[Pangaea]] broke up into the northern supercontinent [[Laurasia]] and the southern supercontinent [[Gondwana]]; the Gulf of Mexico opened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following [[Cretaceous]] Period, when Gondwana itself rifted apart. The [[Tethys]] Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of [[glaciation]]. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed.
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[http://en.wikipedia.org/wiki/ wikipedia]
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== ''' Mesozoic  Life''' ==
The Mesozoic came after the Paleozoic.  The Paleozoic Era ended with the Permian Period, which ended with a sort of general meltdown, sometimes called the "PT" or "End-Permian" extinction.  We still aren't certain exactly what happened, but the fact that much of central Siberia turned into a sort of volcanic bubble bath for a few million years didn't help.  This caused, bar none, the worst mass extinction in the last 600 My.  Don't get this one confused with the "KT" extinction at the end of the Mesozoic -- the one which finished off the dinosaurs 200 My later.  That was a sumo match by comparison.  That is, it eliminated some very large and conspicuous folks very quickly, but it was all very quick and civilized.   
The Mesozoic came after the Paleozoic.  The Paleozoic Era ended with the Permian Period, which ended with a sort of general meltdown, sometimes called the "PT" or "End-Permian" extinction.  We still aren't certain exactly what happened, but the fact that much of central Siberia turned into a sort of volcanic bubble bath for a few million years didn't help.  This caused, bar none, the worst mass extinction in the last 600 My.  Don't get this one confused with the "KT" extinction at the end of the Mesozoic -- the one which finished off the dinosaurs 200 My later.  That was a sumo match by comparison.  That is, it eliminated some very large and conspicuous folks very quickly, but it was all very quick and civilized.   
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=== '''Other Invertebrates''' ===
=== '''Other Invertebrates''' ===
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=== '''Annelida''' ===
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==== '''Annelida''' ====
The fossil record of Mesozoic annelids, like the fossil record of all annelids, is poor.  We can only make a few, general remarks.   
The fossil record of Mesozoic annelids, like the fossil record of all annelids, is poor.  We can only make a few, general remarks.   
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The end-Permian extinction more or less destroyed the entire Paleozoic benthic fauna.  The Mesozoic benthic communities, developed an entirely new style, possibly (i.e., this is complete speculation) based on the very few anoxia-tolerant detritivores who would have flourished in the benthic carnage of the end-Permian.  Whatever their origin, Mesozoic and Cenozoic benthic communities are dominated by infaunal (burrowing) deposit-feeders, rather than epifaunal suspension feeders.  This was surely good for the annelids who are quite handy with low-oxygen, burrowing ways of making a living.  Oligochaetes probably evolved in the Late Jurassic.  However, they were unable to employ the usual annelid skills on land until the Late Cretaceous, when angiosperms began creating large quantities of humus, permitting the evolution of the oligochaete earthworms.   
The end-Permian extinction more or less destroyed the entire Paleozoic benthic fauna.  The Mesozoic benthic communities, developed an entirely new style, possibly (i.e., this is complete speculation) based on the very few anoxia-tolerant detritivores who would have flourished in the benthic carnage of the end-Permian.  Whatever their origin, Mesozoic and Cenozoic benthic communities are dominated by infaunal (burrowing) deposit-feeders, rather than epifaunal suspension feeders.  This was surely good for the annelids who are quite handy with low-oxygen, burrowing ways of making a living.  Oligochaetes probably evolved in the Late Jurassic.  However, they were unable to employ the usual annelid skills on land until the Late Cretaceous, when angiosperms began creating large quantities of humus, permitting the evolution of the oligochaete earthworms.   
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=== '''Brachiopoda''' ===
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==== '''Brachiopoda''' ====
Brachiopods suffered greatly during the end-Permian extinction.  They were able to make a considerable come-back during the Late Triassic, but ultimately declined and were ecologically replaced by bivalves.  Their fate may have been tied to substrate.  The brachiopods of the Late Triassic resurgence were strongly associated with carbonate shelves, the classic reef environment of the Late Paleozoic and Early Mesozoic.  The rise in sea levels during the Jurassic and Early Cretaceous drowned these platforms on a global basis.  That is, the residents of the carbonate platforms gradually found themselves too deep in the water column for sunlight to sustain photosynthesis, and the shelf ecosystems collapsed.  This permitted the bivalves to "mussel" their way in, as they were better adapted to the and unstable sand & mud sea bottoms within the new photic zone. In fact, with the evolution of the rudists, the bivalves were able to make their own quick and sloppy reefs on even the softest substrate.
Brachiopods suffered greatly during the end-Permian extinction.  They were able to make a considerable come-back during the Late Triassic, but ultimately declined and were ecologically replaced by bivalves.  Their fate may have been tied to substrate.  The brachiopods of the Late Triassic resurgence were strongly associated with carbonate shelves, the classic reef environment of the Late Paleozoic and Early Mesozoic.  The rise in sea levels during the Jurassic and Early Cretaceous drowned these platforms on a global basis.  That is, the residents of the carbonate platforms gradually found themselves too deep in the water column for sunlight to sustain photosynthesis, and the shelf ecosystems collapsed.  This permitted the bivalves to "mussel" their way in, as they were better adapted to the and unstable sand & mud sea bottoms within the new photic zone. In fact, with the evolution of the rudists, the bivalves were able to make their own quick and sloppy reefs on even the softest substrate.
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Mesozoic brachiopods, like many other invertebrates, show considerable differentiation between Tethyan (tropical) and Boreal (subtropical and temperate) types in the Late Triassic and Jurassic.  Also like many other invertebrates, these distinctions broke down in the Cretaceous when rising sea levels and flattened climate zonation homogenized most marine fauna.   
Mesozoic brachiopods, like many other invertebrates, show considerable differentiation between Tethyan (tropical) and Boreal (subtropical and temperate) types in the Late Triassic and Jurassic.  Also like many other invertebrates, these distinctions broke down in the Cretaceous when rising sea levels and flattened climate zonation homogenized most marine fauna.   
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=== '''Bryozoa''' ===
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==== '''Bryozoa''' ====
Early Mesozoic bryozoans were largely cheilostomes and cyclostomes. During the Early Cretaceous, however, the cyclostomes declined while cheilostomes diversified. The reasons for this replacement is unclear. Both suffered massive extinctions in Maastrichtian time, possibly coinciding with the more general KT extinctions.  The cheilostomes rebounded during the Cenozoic.  The cyclostomes generally did not.  McKinney & Taylor (2001).
Early Mesozoic bryozoans were largely cheilostomes and cyclostomes. During the Early Cretaceous, however, the cyclostomes declined while cheilostomes diversified. The reasons for this replacement is unclear. Both suffered massive extinctions in Maastrichtian time, possibly coinciding with the more general KT extinctions.  The cheilostomes rebounded during the Cenozoic.  The cyclostomes generally did not.  McKinney & Taylor (2001).
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=== '''Cnidaria''' ===
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==== '''Cnidaria''' ====
Mesozoic cnidarians are mostly known from their greatest success story, the scleractinian corals.  Several groups of scleractinians developed tight symbiotic relationships with photosynthetic zooxanthellae with a resulting huge boost to their productivity.  The scleractinians suffered considerably from the drowning of the carbonate platforms on which their reefs were based during the Late Jurassic and Cretaceous.  However, they recovered quickly after the KT extinctions.   
Mesozoic cnidarians are mostly known from their greatest success story, the scleractinian corals.  Several groups of scleractinians developed tight symbiotic relationships with photosynthetic zooxanthellae with a resulting huge boost to their productivity.  The scleractinians suffered considerably from the drowning of the carbonate platforms on which their reefs were based during the Late Jurassic and Cretaceous.  However, they recovered quickly after the KT extinctions.   
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=== '''Echinodermata''' ===
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==== '''Echinodermata''' ====
The End-Permian extinction at the end of the Paleozoic Era took a heavy toll on the stemmed echinoderms.  The blastoids became extinct at that time and the crinoids suffered heavy losses.  In general, Paleozoic echinoderms were epifaunal suspension and detritus feeders.  Like so many high school students, their strategy was to sit more or less stationary on the sea bottom with their mouths open and wait for food to come to them.  In the Mesozoic and Cenozoic, the echinoderms became more like undergraduates -- still bottom-feeders, but now willing to dig for it (infaunal detritus feeders) or, if sufficiently pressed, to go and hunt for it (armored herbivores and carnivores).   
The End-Permian extinction at the end of the Paleozoic Era took a heavy toll on the stemmed echinoderms.  The blastoids became extinct at that time and the crinoids suffered heavy losses.  In general, Paleozoic echinoderms were epifaunal suspension and detritus feeders.  Like so many high school students, their strategy was to sit more or less stationary on the sea bottom with their mouths open and wait for food to come to them.  In the Mesozoic and Cenozoic, the echinoderms became more like undergraduates -- still bottom-feeders, but now willing to dig for it (infaunal detritus feeders) or, if sufficiently pressed, to go and hunt for it (armored herbivores and carnivores).   
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Williston, SW (1898) Mosasaurs, The University Geological Survey of Kansas, Volume IV, Paleontology, Part V, pp. 81-347
Williston, SW (1898) Mosasaurs, The University Geological Survey of Kansas, Volume IV, Paleontology, Part V, pp. 81-347
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{{Mesozoic}}
<center>[[image:Palaeos logo small.gif|Palaeos com page]]<br>'''[http://www.palaeos.com/Mesozoic/Mesozoic.htm Palaeos com - Mesozoic]'''</center>
<center>[[image:Palaeos logo small.gif|Palaeos com page]]<br>'''[http://www.palaeos.com/Mesozoic/Mesozoic.htm Palaeos com - Mesozoic]'''</center>
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combined paleogeography page MAK091117
this material may be freely used
this material may be freely used

Revision as of 06:37, 18 November 2009

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