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 in the Middle Jurassic. Stegosaurs went extinct soon after the end of the Jurassic, in the Early Creataceous (but with a possible Late Cretaceous record), but the more heavily armored thyreophorans, the ankylosaurs, survived, and by the end of the Cretaceous, existed in two major groups, the immense, tank-like, club-tailed ankylosaurids, and the somewhat smaller, less well armored nodosaurs. Both groups diversified throughout the Early and middle Cretaceous, with the ankylosaurs ranging across Eurasia and North America, while the nodosaurs spread across the globe. Nodosaur fossils have been found on almost every continent on Earth, a fact that no doubt saved them from the disaster wrought upon their kin.
Fossils indicate that ankylosaurs in general were faring well all the way up to the Eocene (50 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 ornithischians. Apparently, some disaster other than the Chicxulub bolide was responsible for the abrupt extinction of most if not all of the ankylosaurs and nodosaurs in the Northern Hemisphere.
In Asia and South America, they seemed to cling to life, though barely. Over millions of years, all of the Asian ankylosaurs were wiped out in the Miocene epoch by the arrival on new herbivores, the nearly the same fate befell their South American cousins the Pliocene epoch with the invasion of various species from North America when both it and South America were linked up about 3.3 million years ago. The only difference is that less than a handful of ankylosaurs thrive in the America's, however, they have seen much more success in the Australasia region, most notably in Australia which seems to be their main bastion while the majority of their relatives marched into extinction.
As far as Spec's preliminary paleontology has implied, whatever killed the ankylosaurs acted upon both our timelines, 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 and Europe went extinct with their ankylosaur cousins 70 million years ago, they maintained a toe-hold in the Americas. 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 neohadrosaurs from the North combined to kill off most of the North American South American nodosaurs. Today, their vast majority 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 ankylosaurids, and the vanguards, armored ornithopods descended from Thescelosaurus. However, in Australia and Oceania and in they still thrive.
AUSANKYLOSAURIDAE (Dreadnaughts and pyoros)[]
The ankylosaurs native to the New World suffered heavy loses through out the Cenozoic, however, they still thrive to this very day as semi-aquatic creatures. On the other hand, another line, an offshoot from somewhere at the base of the ankylosaurian family tree, survived the upheavals of the Cenozoic. Australia,the ancient home of the famous Minmi and the recently discovered Kunbarrasaurus, managed to keep its thyreophorans, 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 thyreophoran group. The skull has the cranial armor 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 few 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 some of the largest of Australia's herbivores, the largest species often surpassing 2 tons. Dreadnaughts live in Australia's bracken meadows and dry sclerophyll 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 bracken, young Eucalyptus, and thorncrown bushes. Enormous and specialized, the dreadnaughts are truly some of the most impressive of Australia's dinosaur fauna. Recently, a new species of ankylosaur was found in New Caledonia. As of now, it is estimated that less than a dozen species of ankylosaur are left in the world, or this area to be more specific.
Pyoro (Pyoro pyoron)[]
Pyoro, Pyoro pyoron (Papua)
Diminutive, ill-tempered, and loud, the pyoro (Pyoro pyoron) is one of the last of the small ausankylosaurs, the single 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 all 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. 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.
Great Aussie Ankie (Dreadnaughtis maximus)[]
Great Aussie Ankie, Dreadnaughtius maximus (Australia)
The great aussie ankie, or great dreadnaught (Dreadnaughtis maximus), is second only to the great euclasaur in size. It exists in disjunct eastern and western populations whose habitats range from semiarid 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.
But when Australia finally broke off and drifted north to the equator, combined with a dryer environment (thanks to the ice ages) and the arrival of grass killing off much of the population, the ecosystem turned from a tundra-forest to a desert-like "out-back". Luckily, ankylosaurs had already adapted a effective strategy commonly used to survive long winters without plant-material, this is because, despite being known as a family of herbivores, ankylosaurs would occasionally eat rotting wood filled with maggots and beetle-grubs, providing them with the vital proteins.
Works Cited
- Daniel Bensen and Brian Choo