by A W Drake

Created on: April 14, 2009   Last Updated: April 16, 2009

The age of the dinosaurs, or the Mesozoic Era began 240 million years ago after a mass extinction towards the end of the Palaeozoic Era. This was a phase of geographical upheaval as land that we know as Europe and Asia collided with North America to form one large Land mass called Pangea. This huge "C" shaped land mass protected the Tethys Ocean which was encircled by the Panthalassic Ocean. There were no shallow waters surrounding Pangea and only the coast would have had cool moist air.

Climate Evidence

Generally land and sea temperatures were higher throughout the Mesozoic Era than before with a more tropical, dryer climate. Sea levels were lower and different land masses with more deserts and less marshy conditions were ready for dinosaurs to exploit. However, throughout the Triassic, Jurassic and Cretaceous periods of the Mesozoic Era there were wide variations in climatic conditions that saw temperature and seasonal differences.

Much of the evidence for this has come from the ocean beds which have provided information on changes in carbon cycling that at times changed erratically. It is thought for instance that ocean surface temperatures could have varied as much as 6 degrees Celsius during certain parts of the Cretaceous Period. This may seem a small figure but it would have caused significant climatic effects.

In 2001 geoscientists, studying rocks in Shatsky Rise in the east of Japan found evidence for variations in carbon cycling and nitrogen fixation which gave clues to a changing climate. It was estimated that during the Cretaceous Period temperatures could have been between 30 degrees Celsius and 38 degrees Celsius with two significant cooling phases of 4 degrees Celsius. By comparison tropical sea surface temperatures are presently around 30 degrees Celsius.

The Antarctic

It has long been established that dinosaurs inhabited Antarctica, and whilst it has puzzled palaeontologists how they managed to survive long cold and dark winters, this may not have been the case.

Antarctica was a lush forest with tall trees which in some instances have been preserved as fossils. Interestingly the fossil wood does not have signs of any frost rings which can be seen in modern trees even in temperate climates. There are signs in the fossil trees however there was a growing season indicating that perhaps during the long dark days vegetation went through a "maintenance only" phase.

More importantly this is good evidence that the Antarctic climate did not cool as previously thought, and it is possible that dinosaurs did not need to migrate to warmer areas during the season of long dark days.

Further evidence of a warmer climate in the Antarctic has been found in the fossilised leaves of other vegetation. It has been observed that in colder climates the leaves of plants tend to have rough edges, and in more tropical conditions leaf edges are much smoother. By studying the percentage of plants with either smooth or rough leaf edges it is possible to estimate the mean temperature of a region. Using this strategy alongside the fossil tree evidence, it has emerged that during the time of the dinosaurs Antarctica had a warm tropical climate.

The overwhelming evidence strongly supports a climate throughout the Mesozoic Era that was much warmer than it is today, with phases of dramatic climatic change. There is also good evidence that the tropical warm condition even extended to the poles providing habitats that allowed dinosaurs to thrive globally.

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