The Therapsids

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"It Slices,  It Dices"  —  the Two Tusked Dicynodonts and their 'Jaw Mill'

Cistecephalus ('box head' - 34cm long, bottom, left) was a full-time tunnel dweller. Like modern moles, Cistecephalus would have used powerful forelimbs as spades before kicking away the loosened soil with its short hindlegs. Safe from predators below ground, Cistecephalus would have ready access to rich food sources: both burrowing insects and rhizomes –  the soft, root- like underground stems of ferns and horsetails which were abundant in the Permian.

The hunting Lycaenops ('terrible wolf face' - 1m long — centre, left) was the first gorgonopsid studied in detail. The re-assembled fossil skeleton of Lycaenops gave us our first hints at the likely appearance of this family of sabre-toothed killers. [see: Portrait Gallery of Gorgonopsids]

Dicynodon ('two dog teeth' - skull 29cm, length 1.5m –  top, left )  was among the most general- ized of the dicynodonts. Neither fast nor agile, Dicynodon's barrel-like body shape suggests a non-stop eating machine. The secret to dicynodont success was in their jaw arrangements. The distinctive dicynodont 'jaw mill' was the first complex chewing mechanism in a land vertebrate.

The operation of the dicynodont 'jaw mill' is shown below. The lower jaws slide foreward and aft to process food.  Some dicynodonts had horny plates to shred plant material (as shown), others had rasping teeth or tooth/plate combinations. The jaw muscles shown are

A – (yellow) depressor mandibuli

B –  (red)  the  internal adductor 

C and D –  (blue) elements of  the external adductor

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