A new ichno-taxon from the Argentinean Northwest (Neogene of the Salta Province)

TINEO, DAVID; PÉREZ, LEANDRO; BONA, PAULA; COMERIO, MARCOS; NORIEGA, JORGE I.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

International Palaeontological Association

The Argentinean trace fossil record of vertebrate footprints is abundant and profusely studied, however the one referred to Aves is particularly scarce and less known. Although there are some works about fossil footmarks referred to this taxon of archosaurs, there are not any detailed descriptions or taxonomical assignations of those traces. Here we describe a new huge ichno-taxon, ascribing it to a bird activity. Footprints were found at Río Iruya section (62 Km NW from San Ramón de la Nueva Orán city, Sierras Subandinas Australes), from lower levels of Guandacay Formation (Río Guanaco Formation; Mio-Pliocene). They were preserved as convex hyporeliefs in brownish-grey conglomerates of fine to medium grain; the base of the level is in contact with reddish - reddish brown mudstones and very fine sandstones. The new ichno-taxon is defined on the base of a track of three well preserved tridactyle footprints. This track presents a stride of 96 cm long, a track width of 13.6 cm, a step angle of 178º and a femoro-acetabular height of 65.2 cm, approximately. Footmarks present a mean length of 16.3 cm, a mean width of 10.9 cm and the following combination of characters: romboidal overall outline with a width/length radio of 0.67 and the minor axis posteriorly displaced; thick digits (D) broader in their middle sector; DIII longer than DII and DIV, respectively; continuity between DIII and the rounded meta-basipodial distal end; DII - DIV internal angle of 62º; DII and DIII with a tapered outline and a well-defined knuckle and mark of claws at the ungueal phalanges; ungueal impression of DIII externally curved and DIV with an oval outline noticeably separated from the meta-basipodial distal end. The presence of a single knuckle by digit, the orientation of the DIII ungueal impression and the absence of a DI (hallux) suggest that these footprints could have been generated by a Rheidae, differing from those referable to other similar sized birds (e.g. Phorusrhacidae). The presence of probable rheid footprints was mentioned for the stratigraphic units outcropping at Quebrada del Yeso (Mio-Pliocene) in La Rioja Province and at the paleo-ichnological site of Pehuen-Co (late Pleistocene) in Buenos Aires Province.