Achillesaurus

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

Achillesaurus Temporal range: Santonian ~85 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Illustration
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Genus:	†Achillesaurus
Species:	†A. manazzonei
Binomial name
†Achillesaurus manazzonei Martinelli & Vera 2007

Discovery and naming

The holotype specimen of Achillesaurus, MACN-PV-RN 1116, was discovered in 1995 by a team of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” led by Dr. José F. Bonaparte. It was found in the Paso Córdova Locality, Río Negro Province, northern Patagonia, where the Santonian-aged Bajo de la Carpa Formation outcrops.^[1]

Its genus name was chosen in reference to Achilles' heel, because diagnostic features are found there for these animals, while the species name honors Professor Rafael Manazzone, an amateur paleontologist whose knowledge of Patagonian fossils and localities assisted the researchers on their field trips.^[1]

Description

The genus was a relatively large, basal alvarezsaurid, and a contemporary of Alvarezsaurus. It is only known from MACN-PV-RN 1116, a partial skeleton including a sacral vertebra, four tail vertebrae, part of the left thighbone, shin and foot, and the left ilium. Agustín Martinelli and Ezequiel Vera, who described the specimen, performed a phylogenetic analysis and found their new genus to be an alvarezsaurid with an unresolved relationship to Alvarezsaurus and more derived alvarezsaurids.^[1]

However, Makovicky, Apesteguía & Gianechini (2012) argued that Achillesaurus might actually be a junior synonym of Alvarezsaurus, which, according to the authors, "is known from the same formation and from which it [i.e. Achillesaurus] differs trivially."^[2]