Pronunciation: zen-o-TAR-so-SOR-us
Meaning: Strange-ankle lizard
Author/s: Martinez et al. (1986)
Synonyms: None known
First Discovery: Chubut, Argentina
Discovery Chart Position: #325
Xenotarsosaurus bonapartei
The strangest thing about the strange ankle lizard's strange ankles is that they're not much stranger than those belonging to any other ceratosaurian dinosaur. Its astragalus (ankle) is completely fused to the calcaneum (heel) which are both 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 abelisaurid ceratosaurs. However, its other parts are quite different, and its tibia bears a striking similarity to that of Ceratosaurus, which is a ceratosaurid ceratosaur.
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 Xenotarsosaurus will remain enigmatic until a strange ankle turns up attached to a more complete skeleton.
Xenotarsosaurus has a gracile femur, similar to the comparable part of Carnotaurus sastrei which suggests an affinity with abelisaurid ceratosaurs. However, its other parts are quite different, and its tibia bears a striking similarity to that of Ceratosaurus, which is a ceratosaurid ceratosaur.
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 Xenotarsosaurus will remain enigmatic until a strange ankle turns up attached to a more complete skeleton.
(Bonaparte's strange-ankle lizard )Etymology
Xenotarsosaurus is derived from the Greek "xenos" (strange), "tarsos" (ankle), 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.
