Siamotyrannus

*Siamotyrannus isanensis*

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***Siamotyrannus***, name meaning "Siamese tyrant", is an extinct genus of theropod dinosaur which lived during the early Cretaceous period in what is now Thailand.

*Siamotyrannus* was a large theropod, with estimates suggests an average length of 7 meters (23 feet) and a weight of around half a ton.

Siamotyrannus is a large theropod. Buffetaut estimated its length at seven meters. In 2010, Gregory S. Paul estimated the length at six metres, the weight at half a ton. A possible autapomorphy, unique derived trait, is the possession of two vertical ridges on the ilium. The second and third sacrals are strongly transversely flattened.

As evidenced by its name, it was originally thought to be a tyrannosauroid and even a tyrannosaurid, though due to lacking some of the primary tyrannosauroid synapomorphies that define the clade, its position here is not certain. Some analyses have categorized Siamotyrannus as a primitive carnosaur rather than a basal tyrannosauroid, and it has several features that may determine it to be an allosaurid or a sinraptorid. In 2012 Matthew Carrano e.a. found a position in the Metriacanthosauridae.

## Discovery

In 1996, Eric Buffetaut, Varavudh Suteethorn and Haiyan Tong named and described the type species Siamotyrannus isanensis. The generic name is derived from the old Thai kingdom of Siam, and a Latinised Greek tyrannus, meaning "tyrant", in reference to a presumed membership of the Tyrannosauridae. The specific name is derived from Thai isan, "northeastern part", referring to the provenance from northeast Thailand.

## Classification

As highlighted by its genus name, *Siamotyrannus* was originally identified as a tyrannosaur. However, as it lacks some of the fundamental features of a tyrannosaur, its position in the group is not clear. Some scientists refer to *Siamotyrannus* as a primitive carnosaur, rather than a basal tyrannosauroid, as it possesses several features that occur in some allosaurids and sinraptorids. In 2012, Matthew Carrano e.a. found a position in the Metriacanthosauridae

## JPInstitute.com Description

Siamotyrannus is the earliest known member of the family that includes Tyrannosaurus rex. Discovered in Thailand, this medium-sized carnivore seems to be about halfway evolved into a T. rex. A number of scientists believe tyrannosaurs originated in Asia and this discovery supports that theory.

The genus is based on pelvic and tail vertebrae, no skull material was discovered for Siamotyrannus. It has features that seem to show an intermediate stage of evolution between the allosaurs and the tyrannosaurs.

## Links

http://web.archive.org/web/20040214163205fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_siamotyrannus.html

## References

1. ↑ Paul, G.S., 2010, *The Princeton Field Guide to Dinosaurs*, Princeton University Press p. 91
2. ↑ Buffetaut, E., Suteethorn, V. and Tong, H. 1996. The earliest known tyrannosaur from the Lower Cretaceous of Thailand. *Nature* **381**: 689-691
3. ↑ Rauhut, Oliver W. M. Special Papers in Palaeontology: *The Interrelationships and Evolution of Basal Theropod Dinosaurs* (No. 69). The Palaeontological Association: 2003
4. ↑ Holtz, Thomas R. et al. (2004). "Basal Tetanurae." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): *The Dinosauria*, 2nd, Berkeley: University of California Press. p. 101 ISBN 0-520-24209-2
5. ↑ Carrano, M. T.; Benson, R.B.J.; Sampson, S.D., 2012, "The phylogeny of Tetanurae (Dinosauria: Theropoda)". *Journal of Systematic Palaeontology* **10**(2): 211–300