When first the massive, low-slung, and armored vanguards also known as "pseudopeltas" or "nodornithopods" were found trundling across the temperate and warm grasslands, forests, and deserts of North America and South America, biologists assumed them to be ankylosaurs, descendants of such great armored creatures like Edmontonia, which roamed North America until shortly before the end of the Cretaceous. Upon closer inspection of the vanguards' internal anatomy, however, it soon became clear that these armored herbivores owed their allegiance to a different branch of herbivorous dinosaurs altogether; the vanguards were not ankylosaurs, but ornithopods.
At the end of the Cretaceous, ornithopods like Thescelosaurus were fleet-footed, bipedal browsers, and it is difficult to see these dinosaurian deer in the same group as the lumbering, spiny vanguards. Some clues to their ansestry remain, however. Vanguard cranial anatomy is obviously ornithopodan, and, indeed, the skulls of the anatomically conservative baa van is virtually indistinguishable from that of Cretaceous Thescelosaurus.
Vans first appear in the fossil record in the late Eocene, with fossil forms essentially indistinguishable, save for details of armor and spines, from modern forest vanguards. Vans became far more omnipresent during the Miocene, evolving elephantine grazing forms as the drying climate caused a slow decline of long-running groups like ceratopsians, anklyosaurs, ornithomimids, and pachycephalosaurs to enter a terminal decline. Unlike their jackalope cousins, vans never managed to gain a foothold in Eurasia, with the only evidence of their presence fragmentary fossils of dubious phylogeny. Vans did establish themselves in South America when the Panama isthmus formed, although they've remained comparably small and rare forms, unable to fully supplant the panzertortiles as predominant large armored herbivore of the Neotropical realm.
Outward resemblance to the ornithopods stops at a vanguard's head. Their bodies are large, supported by four pillar-like legs (though vanguards still retain the ability to rear onto their hind legs for short periods). Armor that began as dermal scutes on the ancestral ornithopods has grown into an imposing thicket of spines and plates, protecting these flow-moving herbivores from predators. The tail has become thicker, no longer a balancing organ, but an anchor for leg muscles and a support for a rearing vanguard. The neck has become long and flexible, able to reach out from under this spiny armor to variously nip buds, chew through small trees, dig up tubers, graze upon grass, or munch cactus.
Vanguards probably evolved as low-level forest browsers some time during the Eocene, spreading into deciduous forests across North America. Asia may have seen vanguards as well, though the fossils are not conclusive, but in any case, this ecological success was short-lived. As the world dried and cooled in the Miocene and Pliocene, the forests retreated and the vanguards suffered. Some species adapted to the new conditions, however, and the grazing vanguards found a home among the megahadrids on North America's grasslands. Upon the coming of the Ice Age, vanguards were pushed south, disappearing from all land north of Virginia, while holding onto survival along the Gulf of Mexico. It is here that the forest vanguards may still be found, living much as their ancestors must have. Prairie vanguards have expanded north with the retreat of the glaciers, and one cold-tolerant species may be found in southern Canada. The newly-evolved desert vanguards, looking very much like the Australian dreadnaughts, inhabit a range that extends from Arizona to central Mexico.
Spiny Van (Aridovangaurda paiweiae)
The spiny desert van is the smallest of the desert vans, and only a distant relative of the dew-licker. In this species the spines have retained the original defensive purpose, and few predators would attempt to tackle this rather small and otherwise unassuming herbivore.
Spiny vans are primarily root-eaters, digging up the water-filled tubers so abundant in Spec's North American Southwest.
Hoplite Van (Aridovanguarda armatus)
The larger of the two species of Aridovanguarda, these are more heavily armored and can be seen living solitary lives as well. Unlike their smaller relatives, the eat other plant life found in the desert environments.
Dita (Vangaurda ditae)
Most common of the vangaurds, the dita is a small-to-medium browser that inhabits meadows, deciduous forests, and river margins across most of southern and central North America. Wide-ranging in diet, ditas prefer shoots and bulbs, leaves, young grass, and a variety of water plants.
Unusually social for vangaurds, juvenile ditas collect into all female groups of up to six (usually closely related) individuals. Upon reaching sexual maturity (three years after birth), ditas will pair up with nomadic males and leave the bachelorette herd.
Ditas pairings are monogamous, and even out of the mating season, the mated pair will remain in close physical proximity, foraging and eating together. Why the marital bond is so strong in a species without much social complexity or extended child-rearing is a question asked by spec-biologists since the discovery of this species. The tentative conclusion is that, while other vangaurds are either large or well-armored enough to be in little danger from predators, ditas, unremarkable in size, and relatively poorly armored, must rely on each other to repulse predators. Draks or errosaurs may easily maneuver past a single dita's swiping tail and dorsal armor to slash the soft belly, but a mated pair, both twisting and swinging spines presents a far more difficult ordeal. United in this way against an enemy, ditas are nearly unassailable.
Kappa-gwa (Hylekkivangaurda gascongneae)
The kappa-gwa, largest and one of the last forest vangaurds, lives along the coast of western North America, taking advantage of the prodigious temperate rainforest of this part of the continent. Kappa-gwas are selective eaters, browsing along the forest floor or rearing to nip buds and shoots from low-growing branches.
The armor plating of other vanguards has, in the kappa-gwa, been fused into a series of large spines, vaguely reminiscent of the plates of a stegosaur. To complete the image, kappa-gwas also possess a gruesome array of spines on their tails, which they wield against any predators that make the mistake of attacking these prickly herbivores.