Leaellynasaura amicagraphica
Rich and Rich 1989

Click image to enlarge
Leaellynasaura

Information
PRONOUNCED
    Lee-ell-lin-ah-saw-rah
MEANING
    Leaellyn's reptile
CLASSIFICATION
    Genasauria, Ornithopoda,
    Cerapoda, Ornithischia
AGE
    Early Cretaceous (Albian) 106 MYA
FORMATION
    Otway Group
    Referred specimens: Strzelecki Group
SIZE
    1 metre (3 feet) long
LOCATION
    Dinosaur Cove, Victoria

Leaellynasaura was a small bipedal herbivorous ornithopod, and in my opinion the cutest dinosaur of them all. It was named after Leaellyn Rich, the daughter of palaeontologists Tom Rich and Patricia Vickers-Rich. It is one of many dinosaurs whose partial remains have been dug (and blasted) out of the solid sand- silt- and mud-stones of Dinosaur Cove in the south east of Australia. The holotype for Leaellynasaura (NMV P185990-3) is a partial skeleton with an almost complete skull, and many small isolated bones have also been attributed to Leaellynasaura sp. The holotype is of a juvenile about 75 cm (2.5 feet) long and 30 cm (1 foot) high, although adults probably reached almost 1 metre (3 feet) in length. The reconstruction shown here is of the juvenile type specimen.

In 2009 Matthew Herne of the University of Queensland gave a talk during the annual SVP (Society of Vertebrate Paleontology) meeting, held that year in Bristol (U.K.), about the postcranial osteology of Leaellynasaura. He reveiled that its tail most likely made up 75% of its total length. See a modified version of the above illustration here showing just how long its tail may have been. Rather than being stiffened by ossified tendons like the tail of 'true' hypsilophodontids, the tail of Leaellynasaura was stiffened by enlongated projections on the upper forward sections of the verterbae.

Originally the small ornithopods found in south eastern Australia were thought to be hypsilophodontids, however subsequent studies have failed to find any characteristics that would place them firmly within this family. Currently their ornithopod affinities can not be determined any better than the Genasauria level - a grouping that includes ornithopods, armoured dinosaurs such as Stegosaurus, and horned dinosaurs such as Triceratops. Australian ornithopods in general may well represent a separate family of 'primitive' ornithopods unique to the Australian continent.

These small herbivores probably fed on ferns and horsetails that grew in the understory of the forest. Perhaps they also scrambled into the trees, in much the same way as goats do, but they weren't really built for climbing. The polar forest that Leaellynasaura lived in included conifers (like araucarians and podocarps), and ginkgo trees. Flowering plants would have been extremely rare, and probably restricted to small ground plants, which small ornithopods may also have eaten.

During the Early Cretaceous southern Australia was joined with Antarctica, and would have had 3 to 5 months of complete darkness each year (see polar dinosaurs). The fact that dinosaur remains are here at all, and also to be found in the Arctic, suggests that their metabolism was probably not like modern reptiles. An enlarged optic lobe in an excellantly preserved endocast of the brain may indicate that Leaellynasaura was well adapted to living for extended periods in the winter darkness (an endocast is formed when sediment fills the cavity inside a skull where the brain has rotted away, and solidifies to form a natural cast of the brain itself).

Having such a long tail in a polar environment would at first seem to be a disadvantage, since heat loss might be expected to have been a problem with such a high surface area to volume ratio. If however the long tail was covered in bushy 'protofeathers', and was flexible enough to be bent side-to-side, then perhaps it was used as a kind of scarf to wrap around the body while asleep, just as arctic foxes use their bushy tails. Such a bushy tail could also be raised or swished from side to side in order to make the ornithopod appear larger than it actually was, as a way of intimidating rivals or potential predators. If the hypothetical protofeathers could also be raised like the hackles of a cat, then it would have made the tiny herbivore look even larger still. No integumentary structures are known for any of the non-avian dinosaur species known from Australia though, so this idea is purely speculative. Similar protofeathers have been indentified in the Chinese heterodontosaurid Tianyulong, therefore it is not impossible that other ornithiscians also had such integumentary structures. In fact, it is hard to imagine how a small creature like Leaellynasaura could have survived in polar conditions without some sort of 'dinofuzz'.

Leaellynasaura
skull: stereo photo
A stereo photograph of the skull of Leaellynasaura. The grey area at the base is the cast of the brain. The bump to the left is an optic lobe.

Rich, T.H. and P.V.Rich 1988. A juvenile dinosaur brain from Australia. National Geographic Research. 4(2):148.

Galton, P. M. 1989 Crania and endocranial casts from ornithopod dinosaurs of the families Dryosauridae and Hypsilophodontidae (Reptilia: Ornithischia). Geologica et Palaeontologica 23: 217-239

Rich, T.H. and P.V.Rich 1989 Polar dinosaurs and biotas of the Early Cretaceous of southeastern Australia. National Geographic Research 5:15-53.

Rich, T.H. & P.Vickers-Rich 1999 The Hypsilophodontidae from Southeastern Australia In Y.Tomada, T.H.Rich and P.Vickers-Rich (Eds) Proceedings of the Second Gondwana Dinosaur Symposium. National Science Museum Monographs, No.15. Tokyo. pp.167-180


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