Siamotyrannus

Siamotyrannus
Live reconstruction of Siamotyrannus at the Sirindhorn Museum in Non Buri, Thailand
Temporal occurrence
Lower Cretaceous ( Barremium )
130.7 to 126.3 million years
Locations
Sao Khua formation ( Thailand )
Systematics
Lizard dinosaur (Saurischia) Theropoda Tetanurae Avetheropoda Allosauroidea Siamotyrannus
Scientific name
Siamotyrannus
Buffetaut , Suteethorn & Tong , 1996
Art
Siamotyrannus isanensis

Siamotyrannus is an extinct genus of the Allosauroidea from the theropod group . The only known species of the so far monotypical genus is Siamotyrannus isanensis from the Sao Khua formation ( Barremium ; approx. 130.7 to 126.3 million years ago) from Thailand .

Etymology and history of research

The generic name is derived from the name of Thailand ( Siam ), which was used in the West until 1939, and the Latin word "tyrannus" ("sole ruler", "tyrant", "despot"). The additional species " isanensis " refers to Isan ( Thai : อีสาน ), the north-eastern region of Thailand.

In 1976 dinosaur fossils were discovered for the first time in the Sao Khua formation of the administrative district of Phu Wiang in the province of Khon Kaen in the Isan region as part of a uranium prospecting campaign . A closer examination of the area by a Thai-French research team in 1981 revealed a rich fossil deposit and the find area was placed under protection as Phu Wiang National Park in December 1991 .

"Site No. 9 “, the site of Siamotyrannus isanensis in the Phu Wiang National Park

In 1993, the Thai geologist Somchai Triamwichanon discovered the remains of a large theropod at the so-called Phu Wiang 9 site (“PW.9” for short or simply “Site No. 9”). After the find was recovered, the fossils were replaced by replicas and the original find was restored to the original. The site was covered and is now accessible to visitors to the national park.

The first description was in 1996 by Buffetaut, Suteethorn & Tong. The authors first described Siamotyrannus isanensis as a basic representative of the Tyrannosauroidea .

A single, isolated tibia as well as several, also isolated, large theropod teeth were also assigned to this species by Buffetaut & Suteethorn in 1998. However, no conclusive evidence of belonging to Siamotyrannus isanensis could be provided.

In 2001, Holtz also noted several synapomorphies with the Tyrannosauridae , but at the same time also referred to the absence of the diagnostically significant skull and saw Siamotyrannus as a possible representative of a progenitor line outside the actual Tyrannosauridae.

2003 Rauhut contradicts this finding, finds no synapomorphies with the Tyrannosauridae and evaluates Siamotyrannus in his phylogenetic analysis of the basal theropods as an independent “operational taxonomic unit” (OTU). In 2004, Holtz et al. Followed this assessment.

In 2012, Carrano et al. Siamotyrannus together with Metriacanthosaurus ( type genus ) and Sinraptor in the group of Metriacanthosaurinae .

Fossil record

Illustration of the pelvis and caudal vertebrae

Since the isolated tibia and theropod teeth from the Sao-Khua formation cannot be clearly assigned, only the holotype (PW.9-1) of Phu Wiang 9 of Siamotyrannus isanensis is known with certainty. This consists of an articulated partial skeleton with the left half of the pelvis, the sacrum , five dorsal vertebrae and 13 caudal vertebrae with some chevron bones facing the trunk .

features

The bones found suggest a theropod with a length of about 6.5 meters.

The main anatomical feature that defines the genus and species is two parallel, vertical bone ridges on the outside of the ilium above the hip joint opening ( acetabulum ). This feature also plays a central role in the systematic classification of Siamotyrannus .

Systematics

Siamotyrannus was first described as a primitive tyrannosauroid . A key argument for the assignment was the double bone crest described above on the outside of the ilium. The representatives of the Tyrannosauroidea have a similar feature, but they only have a simple, but strong, developed crest. The trait is also not limited to the Tyrannosauroidea, but is particularly widespread among the basal representatives of the Tetanurae.

Other properties of Siamotyrannus , such as a spur-like appendage anterior to the actual spinous process of the caudal vertebrae, do not occur at all in the Tyrannosauroidea, but for example in Allosaurus or Sinraptor and some other theropods. Rauhut therefore classified Siamotyrannus as a basal carnosaur in 2003 . In 2004, Holtz et al. who saw in Fukuiraptor the closest known relative of Siamotyrannus and put both together in a clade.

In 2012, a comprehensive phylogenetic analysis of the Tetanurae by Carrano et al. some results that are essential to the systematic position of Siamotyrannus :

• The Carnosauria are classified by the authors as a paraphyletic group and a three-way division with the monophyletic clades Megalosauroidea , Allosauroidea and Coelurosauria is proposed. Allosauroidea and Coelurosauria can be further summarized to the Avetheropoda , which are rated as a sister group to the Megalosauroidea within the Tetanurae .
• The taxon of the Sinraptoridae Currie & Zhao, 1994 is recognized as the junior synonym of the Metriacanthosauridae Paul, 1988 and discarded according to the priority rule.
• Siamotyrannus is placed together with Metriacanthosaurus and Sinraptor in the group of Metriacanthosaurinae in the clade of Metriacanthosauridae within the Allosauroidea.

Siamotyrannus is not one of the oldest representatives of the Tyrannosauroidea, but rather one of the youngest representatives of the Metriacanthosauridae.

Systematic position of Siamotyrannus within the Allosauroidea (after Carrano et al., 2012):

Allosauroidea

Metriacanthosauridae *)    Yangchuanosaurus   Metriacanthosaurinae    Shidaisaurus      "Sinraptor" hepingensis      Metriacanthosaurus      Sinraptor      Siamotyrannus  Allosauria   Allosauridae   Allosaurus     Saurophaganax   Carcharodontosauria    Neovenatoridae   Neovenator      Chilantaisaurus   Megaraptora    Australovenator      Fukuiraptor      Aerosteon      Megaraptor   Carcharodontosauridae    Eocarcharia      Concavenator      Acrocanthosaurus      Shaochilong   Carcharodontosaurinae    Carcharodontosaurus   Giganotosaurini    Tyrannotitan      Giganotosaurus      Mapusaurus

*) Junior synonym: Sinraptoridae

Paleecology

Despite the only fragmentary fossil material, Siamotyrannus can be assumed to have a purely carnivorous diet. Siamotyrannus lived approximately simultaneously in the same region with the Sauropoden phuwiangosaurus , the at least partially aquatic living Megalosauroiden siamosaurus and the Ornithomimosaurier Kinnareemimus . Fossil remains of freshwater sharks, bony fish, turtles, crocodiles and an unspecified bird complete the picture of the fauna of the Sao Khua formation.

The sediments of the Sao Khua formation were deposited in a low-energy fluvial system with meandering river courses and extensive alluvial plains . The Qin Ling Mountains (in what is now central China) are presumed to be the delivery area for the sediments , which were only separated spatially later in the course of the collision of the Indian subcontinent with Eurasia. Stable oxygen isotopes from vertebrate teeth and fish scales indicate an alternately humid tropical climate with seasonal heavy rainfall of up to several thousand millimeters per year.

Pollen analyzes from the Sao-Khua formation indicate a growth of common conifers from the group of Cheirolepidiaceae , ferns from the order of the Schizaeales and other representatives of the real ferns as well as subordinate deciduous mosses , tree ferns from the families of the Cyatheaceae or the Dicksoniaceae , royal fern plants , Representatives of the Bärlappigen and Bennettitales , as well as araucaria plants .

literature

• David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 .
• Éric Buffetaut , Gilles Cuny , Jean Le Loeuff & Varavudh Suteethorn (Eds.): Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia , The Geological Society, London, Special Publications, No. 315, 306 pp., 2009, ISBN 978-1-86239-275-5 .

Individual evidence

1. ↑ S. Tumpeesawan, Y. Sato, & S. Nakhapadungrat: A new species of Pseudohyria (Matsumotoina) (Bivalvia: Trigonioidoidea) from the Early Cretaceous Sao Khua Formation, Khorat Group, northeastern Thailand. In: Tropical Natural History , Vol. 10, pp. 93-106, 2010. (digitized version )
2. ↑ ^{a b} N. Boonchain, PJ Grote & P. ​​Jintasakul: Paleontological parks and museums and prominent fossil sites in Thailand and their importance in the conservation of fossils. In: JH Lipps & BRC Granier (eds.): PaleoParks - The protection and conservation of fossil sites worldwide. Carnets de Géologie / Notebooks on Geology, Chapter 7, pp. 75–95, Brest, 2009. (CG2009_BOOK_03 / 07) (digitized version )
3. ^ ^{A b} W. Songtham & B. Sektheera: Phuwiangosaurus sirindhornae. 106 pp., Department of Mineral Resources, Ministry of Natural Resources and Environment, Bangkok, 2006. ISBN 978-974-226-410-9 (digitized version )
4. ↑ ^{a b} E. Buffetaut, V. Suteethorn & H. Tong: The earliest known tyrannosaur from the Lower Cretaceous of Thailand. In: Nature , Vol. 381, pp. 689-691, 1996. doi: 10.1038 / 381689a0
5. ^ ^{A b} E. Buffetaut & V. Suteethorn: Early Cretaceous dinosaurs from Thailand and their bearing on the early evolution and biogeographical history of some groups of Cretaceous dinosaurs. In: SG Lucas, JI Kirkland & JW Estep (Eds.): Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History Bulletins, No. 14, pp. 205–210, 1998. (digitized version )
6. ↑ Th. Holtz: The Phylogeny and Taxonomy of the Tyrannosauridae. In: DH Tanke & K. Carpenter (eds.): Mesozoic vertebrate life: new research inspired by the paleontology of Philip J. Currie. Chapter 7, pp. 64-83, Indiana University Press, Bloomington, 2001. (digitized)
7. ↑ ^{a b c d} O. WM Rauhut: The interrelationships and evolution of basal theropod dinosaurs. In: Special Papers in Palaeontology , No. 69, 213 pp., The Palaeontological Association, London, 2003. (digitized version)
8. ↑ ^{a b c} T. R. Holtz Jr., RE Molnar & Ph. J. Currie: Basal Tetanurae. In: DB Weishampel, P. Dodson & Halszka Osmólska (eds.): The Dinosauria . 2nd Edition, pp. 71-110, University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 .
9. ↑ ^{a b c d e} M. T. Carrano, RBJ Benson & SD Sampson: The phylogeny of Tetanurae (Dinosauria: Theropoda). In: Journal of Systematic Palaeontology , Vol. 10, No. 2, pp. 211–300, 2012. (digitized version )
10. ↑ PJ Currie & X.–J. Zhao: A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People's Republic of China. In: Canadian Journal of Earth Sciences , Vol. 30, No. 10, (1993), pp. 2037-2081, 1994. (Abstract)
11. ^ GS Paul: Predatory Dinosaurs of the World . 464 pp., Simon & Schuster, New York, 1988. ISBN 0671619462 , ISBN 9780671619466
12. ↑ Ch. Hendrickx, SA Hartman & O. Mateus: An Overview of Non-Avian Theropod Discoveries and Classification . In: PalArch's Journal of Vertebrate Palaeontology , Vol. 12, No. 1, pp. 1-73. ISSN 1567-2158, 2015. (pdf)
13. ^ E. Buffetaut, V. Suteethorn & H. Tong: An early 'ostrich dinosaur' (Theropoda: Ornithomimosauria) from the Early Cretaceous Sao Khua Formation of NE Thailand. In: E. Buffetaut, G. Cuny, J. Le Loeuff & V. Suteethorn (Eds.): Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia , The Geological Society, London, Special Publications, No. 315, pp. 229–243, 2009. doi : 10.1144 / SP315.16 (pdf)
14. ↑ H. Tong, J. Claude, V. Suteethorn, W. Naksri & E. Buffetaut: Turtle assemblages of the Khorat Group (Late Jurassic– Early Cretaceous) of NE Thailand and their palaeobiogeographical significance. In: E. Buffetaut, G. Cuny, J. Le Loeuff & V. Suteethorn (Eds.): Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia , The Geological Society, London, Special Publications, No. 315, pp. 141–152, 2009. doi : 10.1144 / SP315.11 (pdf)
15. ^ R. Amiot, E. Buffetaut, Ch. Lécuyer, V. Fernandez, F. Fourel, F. Martineau & V. Suteethorn: Oxygen isotope composition of continental vertebrate apatites from Mesozoic formations of Thailand; environmental and ecological significance. In: E. Buffetaut, G. Cuny, J. Le Loeuff & V. Suteethorn (Eds.): Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia , The Geological Society, London, Special Publications, No. 315, pp. 271–283, 2009. doi : 10.1144 / SP315.19 (pdf)
16. ^ A. Racey & JGS Goodall: Palynology and stratigraphy of the Mesozoic Khorat Group red bed sequences from Thailand. In: E. Buffetaut, G. Cuny, J. Le Loeuff & V. Suteethorn (Eds.): Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia , The Geological Society, London, Special Publications, No. 315, pp. 69–83, 2009. doi : 10.1144 / SP315.6 (pdf)