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XENOTARSOSAURUS

a meat-eating ceratosaurian theropod dinosaur from the Late Cretaceous of Argentina.
Pronunciation: zen-o-TAR-so-SOR-us
Meaning: Strange-ankle lizard
Author/s: Martinez et al. (1986)
Synonyms: None known
First Discovery: Chubut, Argentina
Chart Position: 260

Xenotarsosaurus bonapartei

The strangest thing about the strange ankle lizard's strange ankles is that they weren't much stranger than those belonging to any other ceratosaur. Its astragalus (ankle) is completely fused to the calcaneum (heel) which are then fused to the widened lower end of the tibia (shin), and there were no pathologies (physical abnormalities that result from disease or trauma), suggesting this was a natural feature rather than a "club foot" formed by severe breakage and healing, or infection.

Xenotarsosaurus has a gracile femur, similar to the comparable part of Carnotaurus sastrei which suggests an affinity with abelisaurids. However, its other parts are quite different, and its tibia bears a striking similarity to that of Ceratosaurus, which is a ceratosaurid.

Funnily enough, a nearly complete left maxilla (tooth-bearing bone of the upper jaw) with features of both Carnotaurus and Ceratosaurus was discovered in 2002 on the same land - "Ocho Hermanos" - which hints at the prescence of a possibly weird abelisaurid-ceratosaurid-type predator in the area. Unfortunately, there are no body parts to link this strange jaw to the strange ankle lizard, and until a strange ankle turns up attached to a more complete skeleton Xenotarsosaurus will remain enigmatic.
(Bonaparte's strange-ankle lizard )Etymology
Xenotarsosaurus is derived from the Greek "Xenos" (strange), "tarsos" (tarsus =ankle and heel) and "sauros" (lizard).
The species epithet, bonapartei, honors Argentine paleontologist José Bonaparte.
Discovery
Strangely, the first known fossils of the strange ankle lizard (UNPSJB PV 184: the first of 2 cotypes) are two back (dorsal) vertebrae which were discovered in the "lower member" of the Bajo Barreal Formation, 6 km north of the Ocho Hermanos ranch, Departamento Sarmiento, Chubut, Argentina, by Juan Carlos Sciutto in 1980.
The "strange ankle", along with a 611 millimetre (24.1 in) long thigh (femur), a shin (tibia) and a calf (fibula) from the right leg (PVL 612: the 2nd of 2 cotypes) were discovered some time later by a team led by Argentinian paleontologist José Bonaparte. To say all remains are from the same individual would be presumptuous.
Estimations
Timeline:
Era: Mesozoic
Epoch: Late Cretaceous
Stage: Cenomanian-Turonian
Age range: 99-89 mya
Stats:
Est. max. length: 6 meters
Est. max. hip height: ?
Est. max. weight: 2 tons
Diet: Carnivore
References
• (1986) "Xenotarsosaurus bonapartei nov. gen. et sp. (Carnosauria, Abelisauridae), a new Theropoda from the Bajo Barreal Formation, Chubut, Argentina". IV Congreso Argentino de Paleontologia y Bioestratigrafia 1:23-31.
• Rodolfo A. Coria and Jorge Rodriguez (April 2001) "On Xenotarsosaurus bonapartei Martínez, Giménez, Rodríguez and Bochatey, 1986; a problematic Neoceratosauria (Novas, 1989) from the Cretaceous of Chubut". Ameghiniana 30(3):326-327.
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To cite this page:
Atkinson, L. "XENOTARSOSAURUS :: from DinoChecker's dinosaur archive".
›. Web access: 29th Mar 2017.
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