Ankylosauria

   Ankylosauria consists of three main groups, Ankylosauridae, Nodosauridae, and Polacanthidae, plus some basal forms. All ankylosaurians had armor over much of their bodies, mostly scutes and nodules, with large spines in some cases. The scutes, or plates, are rectangular to oval objects organized in transverse (side to side) rows, often with keels on the upper surface. Smaller nodules and plates filled in the open spaces between large plates. In all three groups the first two rows of plates tend to form a sort of half-ring around the neck; in nodosaurids, this comes from adjacent plates fusing with each other (and there is a third row as well), while ankylosaurids usually have the plates fused to the top of another band of bone. The skull has armor plastered on to it, including a distinctive piece on the outside-rear of the lower jaw. Feeding was generally accomplished similarly to how Scelidosaurus did it, with precise meeting of the teeth leading to a puncture-crush style like a mortar and pestle.
        Besides body armor, which is also known lower in Thyreophora, all ankylosaurians (except Mymoorapelta) rewalled the acetabulum (the socket for the femur; it is open in most dinosaurs) for strength and flared the upper surface of the ilium outward. Ankylosaurians were very tubby beasts, suggesting that their somewhat feeble teeth were backed up by an impressive internal digestion system.
    Ankylosaurians are a mostly K group from North America and Asia, although isolated finds put them in a number of odd places, including the Campanian (LK) of Antarctica, the late Maastrichtian (LK) and the Toarcian (EJ) of India, and the Campanian-Maastrichtian (LK) of Argentina. Interestingly, ankylosaurians as a group are also the second-most common dinosaurs, next to hadrosaurids, found in marine sediments; this likely is due to their solid construction and (inferred) spacious digestive tracts and other viscera, allowing whole bodies to float out to sea with surprising buoyancy despite the armor.
    These classifications of Ankylosauria and Ankylosauridae presented here are very tentative; much new material has been found in recent years, and these classifications will doubtless be altered. For one new look at these armored beasts, see The Tree of Life's ankylosaur pages, and for anyone wishing to read more about armored dinosaurs in general, and who isn't daunted by the technical literature, there is The Armored Dinosaurs, 2001, Kenneth Carpenter (ed), which is where I got much of the material for the reclassifications I've undertaken here.  

<--Ankylosauria
      |-->Nodosauridae
      |-->Polacanthidae
      `-->Ankylosauridae

Ankylosauria i.s.:

Nodosauridae, Polacanthidae, and Ankylosauridae:  Next come the good old nodosaurids, the spiky, nodosaurid-like polacanthids, and the (usually) tail-clubbed, squat-bodied ankylosaurids.