Najash rionegrina, APESTEGUIA & ZAHER, 2006

Zaher, Hussam, Apesteguía, Sebastián & Scanferla, Carlos Agustín, 2009, The anatomy of the upper cretaceous snake Najash rionegrina Apesteguía & Zaher, 2006, and the evolution of limblessness in snakes, Zoological Journal of the Linnean Society 156, pp. 801-826 : 803-804

NAJASH RIONEGRINA APESTEGUÍA & ZAHER, 2006

Diagnosis: As for the genus, of which this is the only known species.

Holotype: Museo Provincial Carlos Ameghino , Cipolletti, Río Negro, Argentina ( MPCA) 389–400. The holotype consists of a series of associated materials, including a large fragment of the left dentary and anterior portion of the corresponding splenial ( MPCA 390 ), and a nearly complete and articulated postcranial skeleton, composed of 16 sections bearing a total of at least 122 articulated vertebrae (109 presacrals, two sacrals, and 11 caudals), a pelvic girdle, and hindlimbs. The holotype is represented by the following articulated and associated postcranial elements: an articulated section bearing the axis, four anterior presacral vertebrae, and the broken anterior part of the fifth vertebra ( MPCA 391 ); a section bearing a continuous string of 47 articulated presacral vertebrae, with associated ribs and two isolated vertebrae ( MPCA 392 ), from which the proximal head of a middle presacral rib ( MPCA 389 ) was prepared separately; three sections bearing no more than six, seven, and nine presacral vertebrae, respectively ( MPCA 393 ); two sections bearing only associated ribs ( MPCA 394 ); one section bearing five articulated midpresacral vertebrae, and the broken anterior part of a sixth vertebra ( MPCA 395 ); two articulated caudal vertebrae ( MPCA 396 ); eight fragmentary sections bearing a total of 18 articulated presacral vertebrae ( MPCA 397 ); five undetermined and fragmentary elements ( MPCA 398 ); several fragmentary associated presacral vertebrae ( MPCA 399 ); a section containing the pelvic girdle and hindlimb elements, articulated with eight posterior presacral, two sacral, and nine caudal vertebrae ( MPCA 400 ).

Referred material: Five specimens: (1) a fragmentary skull comprising the posterior half of the braincase, and associated vertebrae of a small specimen ( MPCA 385 ); (2) several associated cranial and vertebral elements of a larger individual, probably twice as large as the holotype, including an incomplete left dentary ( MPCA 380 ) , two undetermined cranial elements (possibly mandibular fragments) ( MPCA 381 and 382), axis ( MPCA 383 ) , and associated presacral and caudal vertebrae ( MPCA 384 ); (3) a right quadrate and five associated presacral vertebrae ( MPCA 387 ); (4) four associated sections of articulated vertebrae, and one fragment totaling 16 middle presacral vertebrae ( MPCA 386 ); (5) a posterior presacral vertebra of a large individual ( MPCA 388 ) .

Stratum typicum: Mid to upper layers of the Candeleros Formation, basal unit of the Neuquén Group, early Upper Cretaceous. The bearing strata, about 40 m under the boundary with the overlying Huincul Formation, are considered as having been deposited around 92–94 Mya, during the Cenomanian. The fission track study on a tuff in the overlying Huincul Formation gave an age of 88 ± 3.9 Myr ( Corbella et al., 2004).

Locus typicus: La Buitrera, Rentería Mesa, 30 km north-west from the town of Cerro Policia.