Genus: Muyelensaurus CALVO, GONZALEZ-RIGA & PORFIRI, 2007
Etymology: Muyelen, of the names of the Colorado river after the Mapuche indigenous language (Erize, 1988), and Greek, sauros, "lizard."

Species: pechenae emend CALVO, GONZALEZ-RIGA & PORFIRI, 2007
Etymology: In honor of Dr. Ana Maria Pechen, Main head of the National University of Comahue (2002-2006), who supported the study of the dinosaur fossils in Neuquen Province, Patagonia.
= Muyelensaurus pecheni CALVO, GONZALEZ-RIGA & PORFIRI, 2007
Note: The authors named the species after Dr. Ana Maria Pechen and gave the wrong ending, it should be -ae (for a woman/female) not -i (for a male/man).
= Titanosauridae incertae sedis CALVO & GONZALEZ RIGA, 1999, 2004

Holotype: MRS-PV 207

Locality: Loma del Lindero site, 10km West to Rincon de los Sauces City, Neuquen Province, Patagonia, Argentina.

Horizon: Portzuelo Formation, Rio Neuquen Subgroup, Neuquen Group.
= Rio Colorado Formation, Neuquen Group, CALVO & GONZALEZ RIGA, 1999, 2004.

Biostratigraphy:

Age: Neuquenian Tetrapoda Assemblage, Late Turonian Stage, Uppermost Gallic Subepoch- Coniacian Stage, Lower Senonian Subepoch, Lower Gulf Epoch, Late Cretaceous.

Material: A braincase including partial frontal and parietal, basioccipital, incomplete basipterigoid process, supraoccipital, exoccipital, basisphenoidals tubers, orbitosphenoids, and incomplete parasphenoids.

Paratypes:

MRS-Pv 50-54, 128, 141, 142, 166, 168, 242, 273, 274, 378, 379: Metatarsals.

MRS-Pv 55-58, 143, 144-147, 165, 237: Phalanges.

MRS-Pv 59, 60, 337: Premaxillae.

MRS-Pv 65, 66, 121, 122, 204, 229, 230, 232, 279, 391, 392, 420, 422, 428: Cervical vertebrae.

MRS-Pv 67, 68, 224, 404, 412, 421: Dorsal vertebrae.

MRS-Pv 70, 132, 212, 352, 357, 387: Humerii.

MRS-Pv 71, 139: Radii.

MRS-Pv 72, 182, 243, 353: Ulnae.

MRS-Pv 87, 199, 247, 251: Ischiae.

MRS-Pv 88, 154, 204, 371: Pubii.

MRS-Pv 89, 91, 352, 356, 358, 389, 429: Femora.

MRS-Pv 90, 245, 246, 258, 271, 369, 375: Fibulae.

MRS-Pv 125: Sternal plate.

MRS-Pv 127, 152, 157, 181, 198, 231, 235, 236: Metacarpals.

MRS-Pv 131, 134, 202, 399: Ilia.

MRS-Pv 135, 147, 164, 170, 171, 173, 174, 189, 190, 193, 200, 209, 214, 252, 377, 408: Caudal vertebrae.

MRS-Pv 161, 162, 257, 266: Tibiae.

MRS-Pv 187: Astragalus.

MRS-Pv 355: Sacrum.

MRS-Pv 259, 396, 397: Scapulae.

Referred material:

MRS-Pv 123, 203, 419, 431: Posterior dorsal vertebrae.