Timimus hermani
Rich and Vickers-Rich 1993

Click image to enlarge
Timimus

Information
PRONOUNCED
    Tim-mime-us
MEANING
    Tim's mimic
CLASSIFICATION
    Incertae sedis (?Ornithomimidae),
    Coelurosauria, Tetanurae, Theropoda
AGE
    Early Cretaceous (Aptian) 106 MYA
FORMATION
    Otway Group
SIZE
    3.5 metres (11.5 feet) long, 1.5 metres (5 feet) at hip
LOCATION
    Dinosaur Cove, Victoria

Timimus is yet another dinosaur whose remains have been found at Dinosaur Cove in the south east of the Australian continent. Two femora (thigh bones) and some vertebrae have been attributed to this species. The reconstruction is based on the two femora, one measuring 432 mm from an adult animal (Holotype P186303), and one at 195 mm from a juvenile (P186323), each found within 1 metre of each other in the sandstone deposits. It was named after Timothy Rich (son of Drs Tom Rich and Patricia Vickers-Rich) and Tim Flannery, and in honor of John Herman.

At the time of its discovery it was thought to have belonged to an ornithomimid, the first such remains from Australia. Re-examination of the material has reclassified it as Coelurosauria incertae sedis, meaning that it can not be classified with any more detail beyond that it probably belonged to the Coelurosaurs. My reconstruction was completed before hearing of this news, so it can probably be considered out of date. Then again, it could just as likely have been an ornithomimid as any of the other families within the Coelurosauria, and the history of dinosaur research is full of instances where the original classification is re-adopted (Gorgosaurus libratus for example).

Timimus (if ornithomimid) is distinguished from other ornithomimid species by the absence of an intercondylar groove on the anterior surface of the femur. It shows some similarities to the Late Jurassic Elaphrosaurus bambergi, a possible early ornithomimisaur from Africa. A pubis (P186058) and vertebrae from southern Victoria are also thought to be ornithomimid, with a possible ornithomimid claw having been found in 1996.

The proportions of the adult Timimus femur suggests that the animal had unusually slender legs. Most theropod femora are more robust, since the majority of the leg's length is below the knee. Australia seems to be the world leader in isolated and unusually slender theropod limb bones (see Kakuru kujani).

The juvenile reconstruction is based on alterations of the adult reconstruction. Young animals are not merely scaled down versions of adults, since different body parts grow at different rates. The young of many species have relatively larger, rounder heads, with especially larger eyes, and often relatively larger limbs as compared to their body size. By taking the relative difference between various skeletal elements (as compared to femur length) of skeletal reconstructions of a Gallimimus adult and a juvenile, I was able to apply the same difference in ratios to the adult Timimus reconstruction.

Most ornithomimisaurs are known from the Late Cretaceous of Asia and North America, with only fragmentary remains known from the Early Cretaceous and the Late Jurassic. Most of the oldest remains seem to come from the southern Gondwanan continents, suggesting that ornithomimisaurs may have originated there and later spread to Laurasia. Although Timimus is no longer considered an ornithomimid with any certainty, their presence in Africa suggest that Gondwanan ornithomimisaurs did exist elsewhere. So far an ornithomimid claw, pelvic fragment, and vertebra have been found at the Flat Rocks site near Inverloch, south eastern Australia, so even if Timimus itself is not ornithomimid their remains are still known from Australia. Protoceratopsian remains (in the form of an ulna) dating to the Early Cretaceous of southern Australia may suggest a similar Gondwanan origin for ceratopsians, such as the giant Triceratops horridus of North America. Possible Early Cretaceous caenagnathid remains have also been found in southern Australia. It was once thought that ceratopsians, ornithomimisaurs and caenagnathids were northern hemisphere Laurasian species, but evidence from Gondwana seems to contradict these views.

Timimus material

Adult and juvenile Timimus femora from Dinosaur Cove

Rich, T.H. and P.Vickers-Rich 1994 Neoceratopsians and ornithomimosaurs: dinosaurs of Gondwanan origin? Research and Exploration 10:129-131.


Index