Many aspects of the Spec-Australian biota are unique and bizarre, none more so than the 30 species of rhynchoraptors, carnivorous ornithopods that dominate the large predator guilds of this continent. They are amongst the most highly specialized ornithischians in the world and are the first non-theropodian big-game land predators to have evolved since at least the Late Triassic.Their ancestry can be traced to small, basal euornithopods of the same stock that produced the euclasaurs and viriosaurs. Many small, normally herbivorous ornithopods even today will often take insects and small animals and in the Late Paleocene, one family became increasingly adapted for omnivory. The poorly understood extinction event of the Late Eocene cleared out Australia's top predators (abelisaurids and deinonychosaurs). In the ensuing ecological vacuum, two dinosaurian lineages - the early rhynchoraptors and the coelurosaurian ancestors of the Cedunasauria - competed for supremacy in the large predator guilds, a competition in which the rhynchoraptors were ultimately successful.
The skull of a rhynchoraptor immediately betrays both its predatory nature and its ornithopod heritage. The predentary bone has become a long, curved stabbing structure. The front pairs of teeth have become similarly adapted for stabbing. The upper pair (the sole remaining premaxillary teeth) slide around the narrow predentary when the mouth is closed whilst the bottom pair (the first two dentary teeth) slot into a pit just behind the premaxilla.
Unlike theropods, the rhynchoraptors are precision biters using their specially adapted dentition to crush or pierce the jugular or some other vital structure on their victim. The foreclaws have become long and curved to aid in securing the victim. Smaller rhychoraptors run on two legs whilst the larger species are facultative quadrupeds. An odd feature: the smaller forms are primarily egglayers whilst the large species are viviparous.
Recent DNA analyses reveal that some purported species are actually complexes of similar forms, in particular, so-called Papuan subspecies of Australian diamondbacks and jagdpanthers are separate species in their own right. Additionally recent surveys of Melanesia have uncovered many previously unknown forms. In fact, if anything the rhynchoraptor stranglehold on the predatory guilds on these islands is even more complete than in Australia, although diversity tapers off west of Wallace's line.
DASPLETODONTIDAE
With their bipedal postures and protruding fangs, daspletodontids---the aptly-named anklebiters---bear a strong (if entirely superficial) resemblance to the ancient heterodontosaurs. These little predators are, however, rynchoraptors, only distantly related to the heterodontosaurs.Uncommon on mainland Australia, ankelbiters are the dominant (often the only) predators of the Melanesian islands. Many species are found on Papua as well (although there they play second fiddle to their larger cousins).
The smallest rhynchoraptor is an agile hunter of mammals and small dinosaurs on the forest floor. Understandably, this form was initially described as a possible heterodontosaur.
(fig. 2) A protective mother piggy-beak guards her offspring from a marauding anklebiter
RHYNCHORAPTORIDAE
All large rhynchoraptors are ambush predators that subdue their prey with their forelimbs before dealing a lethal precision bite. They started out as small bipeds (ie. anklebiter) - however as they began to target larger, more dangerous prey their forelimbs became increasingly large and well-muscled while their frontal osteology became robust and reinforced to hand the rough-and-tumble activity (they are a lot more solidly built than a comparable sized theropod). Eventually the larger rhynchoraptors (formally Rhynchoraptoridae) were too front heavy for practical bipedalism.
This majestic predator is found throughout the continent from semi-desert to rainforest-edge. It is largely nocturnal and hunts in small packs, often tackling animals far larger than themselves but will also run down smaller prey.
The greater diamondhide (Rhynchoraptor regius) is the principal predators of the forests of southern Australia. Typical rhychoraptors, diamondhides hunt in packs, running their prey to exhaustion before wrestling it to the ground and dispatching it with a bite to the throat.
In Australia, species generally grow smaller as one progresses northwards, and the lesser diamondhide (Rhynchoraptor minimus) is no exception. This 1.8 meter-long predator lives in Australia's northeastern forests where it mammals, reptiles, and small dinosaurs, including birds and other rhyncoraptors.
The blacktip is a fox-sized rhyncoraptor that lives in southwestern Australia.
The largest terrestrial carnivore on the continent, the strumtiger is a solitary hunter that stakes out a huge territory in a wide variety of habitats. It primarily hunts large, slow moving herbivores but also does a significant amount of scavenging. For it's size, the strumtiger is surprisingly agile and swims well.
The Sturmtiger and Jagdpanther seem to share a deep hatred for one another and both species will go to great lengths to violently remove the other from their respective territories. One documented sighting involved a pack of 7 jagdpanthers that attacked a young male sturmtiger, eventually tearing him to pieces after losing 3 of their number.
Brian Choo and Daniel Bensen
