The thyreophorans, the armored dinosaurs, evolved in the early Jurassic and soon grew to be the dominant low browsers of the middle Mesozoic evolving into (among other things) the famous stegosaurs.  Stegosaurs went extinct soon after the end of the Jurassic, but the more heavily armored thyreophorans survived, and by the end of the Cretaceous, existed in two groups, the immense, tank-like, club-tailed ankylosaurs, and the somewhat smaller, less well armored nodosaurs.  Both groups diversified throughout the early and middle Cretaceous, with the ankylosaurs ranging across Asia and North America, while the nodosaurs spread across the globe.  Nodosaur fossils have been found on every continent on Earth, a fact that no doubt saved them from the disaster wrought upon their kin.

Fossils indicate that ankylosaurs and nodosaurs were faring well all the way up to the Campanian (70 million years ago).  However, the very latest Cretaceous deposits in North America fail to turn up any evidence of other herbivore group, while revealing abundant hadrosaurs, ceratopsians, and other ornithiscians.  Apparently, some disaster other than the Chixulub bolide was responsible for the abrupt extinction of all ankylosaurs and nodosaurs in the Northern Hemisphere. 

As far as Spec's preliminary paleontology has implied, whatever killed the ankylosaurs acted upon both our time-lines, and the massive club-tailed beasts are just as extinct here as in our home timeline.  However, the nodosaurs, with their global distribution, weathered the storm a little better. 

While nodosaurs in Asia, Europe, and North America went extinct with their ankylosaur cousins 70 million years ago, they maintained a toe-hold in the southern continents.  Early South America (and presumably Africa and Antarctica) had an abundance of armored plant-eaters, but while several nodosaur species have been recovered from South American Eocene strata, their numbers dwindle until, some time during Pliocene, they cease altogether.  Paleontologists theorize that the spread of grasslands, combined with the South American asteroid impact, and the invasion of hadrosaurs from the North combined to kill off the South American nodosaurs.  Today, their niche has been partially filled by other South American natives, the panzertoitals, giant meiolaniid tortoises with armor plates and spiked tails very much like the nodosaurs' extinct cousins, the ankylosaurs.

AUSANKYLOSAURIDAE (Dreadnaughts and pyoros)

The nodosaurs perished in South America, but another line, an offshoot from somewhere at the base of the ankylosaurian family tree, survived the upheavals of the Cenozoic.  Australia, ancient home of the famous Minmi, managed to keep its thyrophorans, and it is on this island continent, land of so much strangeness and novelty, that one is still able to see live ankylosaurians. 

The Ausankylosaurids are clearly related to Minmi in that they share this odd creatures mosaic of features, fitting into none of the recognized thyrophoran group. The skull has the cranial armour configuration of a scelidosaur, the overall proportions of a nodosaur  and the hornlets of an ankylosaurid.  An ausankylosaur's dorsal (and ventral) armor (numerous rows of small spines/scutes set in a chainmail of tiny scutes that extends across the belly) is quite unlike any Laurasian ankylosaurian. Paleontologists usually place Minmi alone as a basal member of Ankylosauria, but in Spec, with several Minmi-like species surviving, and no other ankylosaurs of any kind, biologists have erected the new family Ausankylosauridae to accommodate these animals.

Australia's ausankylosaur fossil record is poor, but it seems that the descendants of, Minmi, stayed fairly conservative throughout most of their evolution, present in Australia's primal forests as low-level browsers much like their Cretaceous ancestors.  With the drying of Australia and the ascent of the euclasaurs, however, these creatures must have begun to die out, and only a single dwarf species of this old, forest-dwelling group remains on the island of papua.  The tropical low-browsing niche has since been left to the pig-like psittacosuids, much smaller than the ausankylosaurians, and so better able to cope with the recent environmental stresses.  The descendants of Minmi did not entirely fade into the background, however, one group, the dreadnaughts, managed to adapt to Australia's increasing aridity, and still survive today.  Also called 'ankies', dreadnaughts are the largest of Australia's herbivores, the largest species often surpassing 2 tonnes.  Dreadnaughts live in Australia's braken meadows and dry schlerophyl forests, utilizing their ankylosaur cutting teeth and chewing jaws to eat a variety of spiny and (to other herbivores) extremely unappetizing herbage, including the poisonous braken, young p-eukalyptus, and thorncrown bushes.  Enormous, rare, and specialized, the drednaughts are truly some of the most impressive of Australia's dinosaur fauna.

Diminutive, ill-tempered, and loud, the pyoro is the last of the small ausankylosaurs, the single of species of its genus, and endemic to the island of Papua.  These round-bodied little creatures trundle like oversized beetles through Papuan jungle's understory, eating fungi, small plants, roots and bulbs, and bark.  Pyoros are not at at shy or skittish, and their blue and white hides show up well against the backdrop of the forest, a fact which has lead biologists to wonder how these little creatures avoid predators.   Poison has been proposed as a means of predator deterrent, and if this theory is true, it would be the only known instance of such a substance used by an ornithischian dinosaur. 

 

 

(fig. 1) Pyoro Pyoro pyoron (Papua)

Analysis of pyoro muscle has revealed no toxic compounds, but an as-yet untested theory proposed by some workers suggests the presence of a toxin-secreting bacterium that infests the pyoros' skin.  This theory would explain the elaborate cleaning ceremonies employed by the pyoros, as well as their seeming invulnerability to predation.
 

    The great aussie ankie, or great dreadnaught, is second only to the great euclasaur in size. It exists in disjunct eastern and western populations whose habitats range from semi-arid scrub to the wet coastal woodlands. They are unfussy eaters and are one of the few dinosaurs that will gladly feed on poisonous bracken ferns.

 

 

 

Works Cited:

 http://tolweb.org/tree?group=Nodosauridae&contgroup=Ankylosauria
 

=Ankylosauria=Ausankylosauridae=Dreadnaughtius maximus (The Great Aussie Ankie)
             
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