Тіммус: Австралиялық динозаврдың сипаттамасы

Extinct genus of dinosaurs

Timimus is a genus of small coelurosaurian theropod dinosaur from the Early Cretaceous of Australia. It was originally identified as an ornithomimosaur, but now it is thought to be a different kind of theropod, possibly a tyrannosauroid.

In 1991, two femora (thighbones), one from an adult and one from a juvenile, were found within a metre of each other at the Dinosaur Cove East site, in the small "Lake Copco" quarry, at the southern tip of Australia. The type species, Timimus hermani, was formally named and shortly described by Dr Thomas Rich and his wife Patricia Vickers Rich in 1993/1994. The generic name means "Tim's Mimic" and combines the name of both the discoverers' son Timothy Rich and palaeontologist Tim Flannery with a Latin mimus, "mimic", a reference to the presumed affinity of the species with the Ornithomimosauria. The specific name honours volunteer John Herman who, for many years, assisted the Dinosaur Cove project. The holotype specimen, NMV P186303, was found in a layer of the Eumeralla Formation, dating to the Albian faunal stage in the early Cretaceous, some 106 million years ago. It consists of a left femur of an adult individual. The second femur, that of a juvenile, was assigned as the paratype specimen NMV P186323. However, based on differences between the two femora that were likely unrelated to conspecific allometry or ontogeny, later researchers have suggested that the paratype femur may instead represent an indeterminate maniraptoran. The slenderness of the bone suggest a lithe animal. The paratype femur is 19.5 centimetres long. The femora show several features that were considered diagnostic. There is no extensor groove between the condyles of the lower joint, which would have been a basal trait for an ornithomimosaur.

In 1994, the describers assigned Timimus to the "Ornithomimosauridae", with which the Ornithomimidae were meant. Ornithomimosaur remains from Gondwana are rare and dubious; Timimus was thus presented as proof that the group was indeed present in the Southern Hemisphere and would even have originated there. Immediately, however, a position within the Ornithomimosauria was doubted by Thomas Holtz. Today, it is recognised that Timimus shares no derived traits, synapomorphies, with the Ornithomimosauria and thus any proof it would belong to this group is lacking. It perhaps belongs to some coelurosaurian group; some workers consider it a nomen dubium. A 2012 study found it to be a valid tyrannosauroid,

The habitat of Timimus consisted of polar forests with mild summers but cold and dark winters due to the closer proximity of the area to the South Pole during the Early Cretaceous. In 1996, Anusuya Chinsamy, an expert on the microstructure of fossil bones, examined bone material from Timimus and Leaellynasaura and discovered they exhibited different bone histology. The ornithischian showed a continuous rate of bone deposition, while the coelurosaur had a cyclical pattern of bone formation, which suggested Timimus may have hibernated in colder months. A possible Timimus hermani or related form from the Strzelecki Group near Inverloch, Victoria left a fossil of the first phalanx of its third toe with a depressed fracture on the plantar surface.