Leaellynasaura is known from several specimens including two nearly complete skeletons and two fragmentary skulls. It has been variously described as a hypsilophodontid, a primitive iguanodontian and primitive ornithischian (Genasauria). The most recent assessment describes it as a non-iguanodontian ornithopod. Unlike more advanced ornithischians, Leaellynasaura lacked ossified tendons in its tail. The tail is noteworthy as among the longest relative to its body size of any ornithischian: the tail was three times as long as the rest of the body combined. It also has more tail vertebrae than any other ornithischians except for some hadrosaurs.
Biology and ecologyEdit
Leaellynasaura was an Australian polar dinosaur. At this period in time, Victoria would have been within the Antarctic Circle. Although this latitude is very cold today, it was less frigid in the mid-Cretaceous. However, because of the Earth's tilt, Leaellynasaura and its contemporaries would still have been living under conditions with extended periods of daylight and night. Depending on latitude, it is possible that the sun might not have risen for several weeks or months in the winter, which means that Leaellynasaura would have had to live in the dark for perhaps months at a time. This is particularly relevant to the fact that a skull fragment interpreted as being from Leaellynasaura shows enlarged eyes and the suggestion of proportionally large optic lobes, as if it had evolved to be routinely active in low-light conditions.