| Timimus | |
|---|---|
 | |
| Holotypic left femur ofT. hermani, NMV P186303 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Genus: | †Timimus Rich & Vickers-Rich, 1993 |
| Species: | †T. hermani |
| Binomial name | |
| †Timimus hermani Rich & Vickers-Rich, 1993 | |
Timimus is agenus of smallcoelurosauriantheropoddinosaur from theEarly Cretaceous ofAustralia. It was originally identified as anornithomimosaur, but now it is thought to be a different kind of theropod, possibly atyrannosauroid.[1]
In 1991, twofemora (thighbones), one from an adult and one from a juvenile, were found within a metre of each other at theDinosaur Cove East site, in the small "Lake Copco" quarry, at the southern tip ofAustralia.Thetype species,Timimus hermani, was formally named and shortly described by DrThomas Rich and his wifePatricia Vickers-Rich in 1993/1994. The generic name means "Tim's Mimic" and combines the name of both the discoverers' son Timothy Rich and palaeontologistTim Flannery with aLatinmimus, "mimic", a reference to the presumed affinity of the species with theOrnithomimosauria. Thespecific name honours volunteer John Herman who, for many years, assisted the Dinosaur Cove project.[2]
Theholotype specimen, NMV P186303, was found in a layer of theEumeralla Formation, dating to theAlbianfaunal stage in the earlyCretaceous, some 106 million years ago. It consists of a left femur of an adult individual.[2]
In 1994, Dr. Thomas Rich commented that, while it would have been more ideal to have had the most complete specimen possible as aholotype, it was highly unlikely that future material ofTimimus would be found, due to the limited nature of sites to be explored in the area. Also, the holotype would have had characteristics which both identified it as an ornithomimosaur and a new genus within that group. Thus the name would serve as a reference point for the material within paleontological literature. Rich stated: "By themselves, the names of dinosaurs are like telephone numbers - they are labels that go with specimens and the ideas that flow from the analysis of the material. Confusing labels, like an inaccurate telephone book, lead to an unworkable system, so one must be careful in putting names or labels on things. But the act of doing so is not creating those specimens or the ideas associated with them; it is merely creating a convenient "handle" for purposes of communication".[3]
The second femur, that of a juvenile, was assigned as theparatype specimen NMV P186323. However, based on differences between the two femora that were likely unrelated toconspecificallometry orontogeny, later researchers have suggested that the paratype femur may instead represent an indeterminatemaniraptoran.[1] Somevertebrae from the site have been referred to the also been referred toTimimus, as well as some other South Australian material.[citation needed]
The holotype thighbone is 44 centimetres long. From this, a total length of the animal of 2.5 metres has been extrapolated.[4] 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.[4] The femoral head is anteroposteriorally flattened. The anterior trochanter is in a high position and reaches the level of the major trochanter. In 2016 the NMV P186303 specimen was estimated to be 4.3 meters (14 ft) long, and 200 kg (441 lbs) in weight.[5]
In 1994, the describers assignedTimimus to the "Ornithomimosauridae", with which theOrnithomimidae were meant. Ornithomimosaur remains fromGondwana are rare and dubious;Timimus was thus presented as proof that the group was indeed present in theSouthern Hemisphere and would even have originated there. Immediately, however, a position within the Ornithomimosauria was doubted byThomas Holtz.[6] Today, it is recognised thatTimimus 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 anomen dubium.[7] A 2010 study classifiedTimimus withinParaves, specifically asDromaeosauridae? indet. cf.Unenlagiinae.[8] A 2012 study found it to be a validtyrannosauroid,[1] a conclusion supported by Delcourt and Grillo (2018) who recoveredTimimus as a tyrannosauroid in two phylogenetic analyses but as a sister taxon of Tyrannoraptora (outside Tyrannosauroidea) in one analysis.[9]
Thehabitat ofTimimus consisted ofpolar forests with mild summers but cold and dark winters due to the closer proximity of the area to theSouth Pole during the Early Cretaceous. In 1996,Anusuya Chinsamy, an expert on the microstructure of fossil bones, examined bone material fromTimimus andLeaellynasaura and discovered they exhibited different bone histology. Theornithischian showed a continuous rate of bone deposition, while the coelurosaur had a cyclical pattern of bone formation, which suggestedTimimus may have hibernated in colder months.[10] A possibleTimimus hermani or related form from theStrzelecki Group nearInverloch, Victoria left a fossil of the first phalanx of its third toe with a depressed fracture on theplantar surface.[11]
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