The Therapsids

Earliest Therapsids
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Eotitanosuchids  –  the Dawn Therapsids in Russia
The therapsids came into their own in what is now the west of Russia. During the Permian, this area sat near to the equator.  It was one vast, densely forested floodplain cut with meandering rivers.  This region provided a wealth of habitats for therapsids and other animals – fast- flowing water and still pools, silt-ladened deltas, overgrown riverbanks, and thickly-treed hilltops. Fortunately, conditions were also perfect for creating a wonderful, near-complete fossil record of life at that time.

The earliest Russian therapsids were the eotitanosuchids.*  The most complete fossils of these 'dawn therapsids' belongs to Biarmosuchus. Although not very large, there's no doubt that this animal was a hunter. Big canine teeth would have delivered a killing bite to any prey Biarmo- suchus could reach. And this therapsid was built to chase down prey.

Early therapsids would have needed to be good swimmers to survive on those ancient Russian floodplains.  But, it was on dry land that these 'dawn therapsids' would have excelled as hunters.  Their secret was in the arrangement of their hips and hind legs.

The hip design of early therapsids allowed them to use two gaits – a low sprawl and a high walk. The energy-saving low sprawl was used to move from place to place, while
the high walk was reserved for lunging at prey. Modern crocodiles use these same two
modes of locomotion.  We tend to think of crocodiles on land as slow-moving animals. But, younger crocodiles are quite capable of a bounding gallop and even of jumping.

'Dawn Therapsids':   Biarmosuchus tener in the foreground with Eotitanosuchus olsoni behind  –  top left
Eager to escape with its lunch is Biarmosuchus ('double- shouldered crocodile' – skull 18cm, length 1.0m). Roused from its slumber bankside is Eotitanosuchus  (the 'giant dawn crocodile' - skull 35cm), likely top predator on land.

Eotitanosuchus was at least 6.0m long, weighing 500kg  –  the bigger 'dawn therapsid' remains attributed to other genera probably represent very large individual Eotitanosuchus (reptiles grow continually throughout their lives, therapsids likely did too). Younger Eotitanosuchus would have strongly resembled an adult Biarmosuchus.

*  Opinion is divided on this group name.  Some argue that these animals represent different species to the same genus – Biarmosuchus. If so, both the group name eotitanosuchid and the species name Eotitanosuchus disappear – leaving one big happy biarmosuchid family.

Earliest Therapsids
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