[D] Achillesaurus manazzonei [~/~]
Martinelli, & Ezequiel 2007
Cretaceous Late Santonian
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Alvarezsauridae
Bajo de la Carpa Formation, Río Negro Province, Argentina
Genera - Typespecies
A relatively large alvarezsaurid different from Alvarezsaurus calvoi (from the same Age and Formation) in having a lateral fossa in the proximal caudal centra, a less developed supraacetabular crest, the brevis shelf not reaching the base of the ischial pedicel, and the lateral malleolus of the tibia at the same level of the medial one.
Achillesaurus differs from Patagonykus puertai, from the Portezuelo Formation (Neuquén Province, Argentina), by the presence of an almost undeveloped supracetabular crest of the ilium and the unfused condition of the astragalus and the calcaneum. The new species is excluded from the Asian Mononykinae due to the unreduced fibula distally and a non-arctometatarsalian pes. The autapomorphies of Achillesaurus are the presence of a biconcave caudal vertebra (possibly the fourth) with the cranial surface 30% larger in diameter than the caudal one.
The inclusion of Achillesaurus in a phylogenetic framework resulted in an unresolved polytomy among the new taxon, Alvarezsaurus, and Patagonykus plus Mononykinae, the latter clade being weakly supported. The result here presented shows a basal stem radiation of South American alvarezsaurids. New material of the Patagonian alvarezsaurids is necessary to evaluate relevant traits to test further the phylogenetic relationships of the basal alvarezsaurids.
Achilles (Latin), in reference to Achilles’ heel, the weak point of Achilles in the book “Iliad” written by Homer, because the holotype has diagnostic features in this portion of the skeleton. Manazzonei, in honor to Prof. Rafael Manazzone, an amateur paleontologist who provided valuable data about Patagonian fossil localities, and assisted to several paleontological field trips.
MACN-PV-RN 1116, last sacral vertebra and the following two procoelous caudals with an articulated chevron, a partial proximal biconcave caudal (possibly the fourth), a portion of a distal caudal centrum, left ilium, proximal end of the left femur, distal end of the left tibia articulated with the astragalus, proximal portion of the left metatarsals II, III, and IV, and cast of the ilium and the vertebrae as originally found prior to disarticulation.
Relatively large alvarezsaurid with the following autapomorphies: presence of a biconcave, possible fourth, caudal vertebra with the cranial surface 30 % larger in diameter than the caudal one. Achillesaurus differs from Alvarezsaurus calvoi in the presence of a lateral fossa in the proximal caudal centra, less developed supraacetabular crest, brevis shelf not reaching the base of the ischial pedicel, and lateral malleolus of the tibia at the same level of the medial one. Achillesaurus differs from Patagonykus and [Mononykinae] in the presence of an almost undeveloped supraacetabular crest, unfused astragalus and calcaneum, and from Mononykinae in the distally unreduced fibula and a non-arctometatarsalian pes.