THE  THERAPSIDS 

Therapsids
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The Therapsids
Introduction

The Cynodonts
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Pangean End Game  —  the End-Permian Mass Extinction

Not all of Pangea was accessible to the therapsids. Toward the end of the Permian, a final piece of the jigsaw puzzle of slow-motion, moving land masses fell into place.  The ancient continent Angara  (now Siberia and Central Asia )  pressed even closer to Pangea proper, creating land bridges which opened up fresh habitat areas to the east  for the therapsids.

One therapsid which took advantage of this windfall was the dicynodont, Diictodon ('two weasel teeth' - skull 10cm), related to Robertia who we met earlier.  Diictodon lacked tusks but did have a sharp bone 'process' where its tusks would have been.  These 'caniniform processes' may have acted like wire-cutters, snipping through tough stems and rhizomes.

Diictodon also had long sharp claws – good for raking up food but also good for digging. We know for certain that Diictodon scraped out burrows. Fossilized Diictodon have been found curled up inside their burrows – likely caught there during a flash flood.  Diictodon probably excavating these complicated burrows as shelters and as breeding chambers.

As Angara collided with Pangea,  those land bridges would  rise and subside repeatedly. Diictodon and the lumbering pareiasaur (Shihtienfenia) were descendants of the animals
which had migrated from what is now European Russia.  But, the collision of Angara with
the growing supercontinent of Pangea was also a ticking time-bomb. The buckling of the earth's crust had triggered immense volcanic eruptions.  For half a million years, sulphur-rich lava poured onto the surface of Angara, poisoning a world that was already in trouble.

The End-Permian mass extinction was the most devastating die-off of all time. Waves of extinction swept through the therapsids. The most highly adapted – the fittest – were the first to die in this changing world. But, there were survivors.

Lystrosaurus  ( 'shovel reptile' - 10cm skull ) could be the 'poster child' for impoverished ecosystems. From humble beginnings in the latest Permian, these homely animals would go on to cover the planet. The remains of Lystrosaurus have been found in Africa, India, Australia, Antarctica, Russia, and Central Asia  –  in fact, all these widespread fossils of Lystrasaurus species helped to confirm the earlier existence of  Pangea for geologists.

Once thought to be semi-aquatic, it seems that the lystrosaurs' success was due to their being well-adapted  to very dry habitats. That odd, turned-down face gave Lystrosaurus
a jaw movement that allowed  it to tackle the driest, toughest of plant material.  When the familiar Glossopteris flora became extinct at the end of the Permian, the tubby lystrosaurs were perfectly positioned to move out of their fringe habitats and to take over the world !

Another survivor was the cynodont, Galesaurus ( 'cat reptile' - 40cm long). And lucky for us, too. Little Galesaurus, and the related Triassic cynodont, Thrinaxodon, are part that line which led to all living mammals.  Without them,  we would not be here to read this !

The Cynodonts
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