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Dinosaur beaks

>      Which dinosaurs had beaks?

All ornithischians except the most primitive members of the group
had beaks.

Among theropods, oviraptorosaurs and ornithomimosaurs probably had
beaks.  (In oviraptorosaurs it would explain why the upper jaw falls
short of the length of the mandible; a keratinous beak would have
made up the difference.)  Birds had beaks (and still do); most likely
they evolved independently in ornithurines and enantiornithines.

The bizarre tyrannosauroid _Alioramus_ may also have had a beak; the
furrowed texture of its upper jaw elements suggests that they may have
been ensheathed in a layer of horn.  I've heard this argument used
for a beaked _Carcharodontosaurus_, for the same reason.