Open Paleo

Achillesaurus

Martinelli & Vera, 2007 a-KILL-ee-SOR-us Disputed

Named for Achilles' heel from Greek mythology, referencing diagnostic features found in the heel anatomy; combined with Greek 'sauros' meaning 'lizard'. The species name honors Professor Rafael Manazzone.

85.7–83.6 million years ago Santonian, Late Cretaceous
Late Cretaceous stages

Achillesaurus is a genus of alvarezsaurid theropod dinosaur from the Santonian-aged (Late Cretaceous) Bajo de la Carpa Formation of Rio Negro, Argentina. It contains one species, Achillesaurus manazzonei.

Under dispute

Achillesaurus manazzonei is a basal alvarezsaurid closely allied to Alvarezsaurus. Makovicky and colleagues (2012) argued that the features separating the two are ontogenetic and that Achillesaurus may be a junior synonym of Alvarezsaurus; the describing authors (Martinelli and Vera, 2007) and Meso and colleagues (2024) retain it as a distinct genus while noting that it is unstable and incompletely known.

Diagnosis

  1. Biconcave caudal vertebra (possibly the fourth) with the cranial articular surface 30% larger in diameter than the caudal articular surface.
  2. Lateral fossa present on the proximal caudal centra (small, subcircular depression on proximal half of the centrum).
  3. Brevis shelf of the ilium does not reach the base of the ischial pedicel.
  4. Supraacetabular crest of the ilium almost entirely undeveloped.
  5. Lateral malleolus of the tibia at the same level as the medial malleolus.

Species

Achillesaurus manazzonei Martinelli & Vera, 2007 Disputed

Type species

Named for Professor Rafael Manazzone, an amateur paleontologist whose knowledge of Patagonian fossils and localities assisted the researchers on their field trips.

Holotype
MACN-PV-RN 1116 , Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’
Material
Last sacral vertebra, two procoelous caudals with articulated chevron, partial proximal biconcave caudal (possibly fourth), distal caudal centrum fragment, left ilium, proximal left femur, distal left tibia articulated with astragalus, proximal left metatarsals II-IV.
Horizon
Bajo de la Carpa Formation, Santonian, Late Cretaceous , 85.7–83.6 million years ago
Locality
Paso Córdova, Río Negro, Argentina

References

  1. Martinelli, A. G.; Vera, E. I. (2007). Achillesaurus manazzonei, a new alvarezsaurid theropod (Dinosauria) from the Late Cretaceous Bajo de la Carpa Formation, Río Negro Province, Argentina. Zootaxa 1582(1). Magnolia Press. doi:10.11646/zootaxa.1582.1.1 martinelli2007a
  2. Makovicky, P. J.; Apesteguía, S.; Gianechini, F. A. (2012). A New Coelurosaurian Theropod from the La Buitrera Fossil Locality of Río Negro, Argentina. Fieldiana Life and Earth Sciences 5: 90-98. Field Museum of Natural History. doi:10.3158/2158-5520-5.1.90

    Argued Achillesaurus may be a junior synonym of Alvarezsaurus, its distinguishing features ontogenetic.

    makovicky2012a
  3. Meso, J. G.; Pol, D.; Chiappe, L.; Qin, Z.; Díaz-Martínez, I.; Gianechini, F.; Apesteguía, S.; Makovicky, P. J.; Pittman, M. (2024). Body size and evolutionary rate analyses reveal complex evolutionary history of Alvarezsauria. Cladistics 41(2): 135-155. Wiley. doi:10.1111/cla.12600 meso2024a