CONICET | Buscador de Institutos y Recursos Humanos

This contribution presents a preliminary neoichnological study in a parabolic dune located near the Gran Salitral saline lake from southwestern La Pampa province, which is developed under a semiarid and temperate climate. The study area was divided into three subenvironments with sparse shrubby vegetation: saline mudflat, dune and interdune. The saline mudflat exhibits halophyte plants with dominance of Heterostachys ritteriana, the dune contains psammophyte vegetation especially Salsola kali and Baccharis spartioides (both accounting for 37.5 %), whereas the interdune exhibits a greater species diversity and dominance of Baccharis spartioides (37.5%), Suaeda divaricata and Allenrolfea vaginata (both 17.5 %). This research was carried out mainly in the dune subenvironment, where root systems as well as invertebrate and vertebrate traces were observed. The more conspicuous root-like structure are long stems or roots arranged parallel to the ground surface with evenly spaced shoots, typically produced by Prosopis strombulifera and Distichlis scoparia. This kind of unidirectional growth is a response to sand mobility and wind stress. Recognized animal traces include trails, trackways and burrows of invertebrate and vertebrate origin. Invertebrate traces include trackways of scorpion, spider and insect (Tenebrionidae), two types of jumping traces of unknown arthropods, mole-cricket and stiletto fly larva burrows, and bee cells. Scorpion trackways (incipient Paleohelcura) are 2.80 cm wide and composed of sets of three circular to tapered (1 mm wide) imprints arranged as lines oblique to the midline with opposite symmetry. Average stride length is 2.56 cm. Spider trackways (incipient Octopodichnus) are 5.45 cm wide, with sets of four and three 0.27 cm wide imprints, arranged at different angles with the midline, with circular and tapered imprints sometimes leaving drag marks, two additional marks may be related to the pedipalps. Tenebrionidae trackways (incipient Hexapodichnus) are 2.22 cm wide and display alternate symmetry, with sets of three elongate imprints, two of them oriented parallel and the third oblique to the midline. Two different arthropod jumping traces were found. The first type of jumping trace comprises sets of four imprints measuring 2.84 cm in width and 2.49 in length, spaced 5.41 cm apart. These sets are composed of two tracks parallel and two oblique to the midline. The second type of jumping trace is smaller and consists of an oval depression (0.94 cm wide and 1.31 long) probably caused by the body, accompanied by two pairs of small appendage imprints in one tip of the depression, no discrete trackway was recognized. Invertebrate burrows include those assigned to mole crickets and stiletto fly larvae. Mole cricket burrows (incipient Palaeophycus) are 0.7 mm wide subcylindrical open burrow systems showing acute branching angles that are produced just under the sediment surface, and appears as 3 cm wide surface ridges. Similarly, sinusoidal shallow ridges (incipient Cochlichnus) with about 0.3 cm of amplitude are assigned to stiletto fly larvae (Therevidae). A single bee cell (incipient Celliforma) about 1.77 cm long and 0.69 cm wide was found in situ on a deflation surface. Bee cells may be connected with profuse inclined burrow openings seen on the dune surface. Vertebrate traces comprise trails assigned to snakes, several rodent and lizard trackways, and also lizard burrows. A sinusoidal trail with a wavelength of 20 cm and wave amplitude of 7.8 cm is tentatively assigned to snakes, probably of the genus Phylodrias. Several rodent trackways were identified, the small ones are attributed to Ctenomys, Microcavia and Tympanoctomys; whereas the largest are assigned to Dolichotis patagonum. Small tetradactyl rodent trackways are 3.5 cm wide and display a pace angulation of 160˚, where the manus is placed in front of the pes, manus are 1.4 cm wide and 2.1 cm long, and pes are 1.7 cm wide and 2.4 cm long, the digits have claw marks. The trackway made by Dolichotis patagonum (incipient Dolichotichnus) is very distinctive and includes a tetradactyl manus 3.6 cm wide and 4.8 cm long, and a 3.4 cm wide and 7.2 cm long tridactyl pes, both with clear claw marks. The trackway of the small lizard Liolaemus consist of pentadactyl footprints showing a marked asymmetry in digit length and a medial tail drag impression, manus footprints are 0.98 cm wide and 1.22 cm long, and pes footprints are 1.33 cm wide and 1.22 cm long, the digits are strongly clawed. Liolaemus burrows have an overall flattened U-shape with two entrances on each branch, although only one was active. The main tunnel is 3.11-4.88 cm wide and 2.29-2.04 cm high, with a plano-convex cross-section and shows a widening near one of the entrances (5.14 cm wide and 3.56 cm high), as well as a blind tunnel of cylindrical cross section. The ceiling of the Liolaemus burrow is heavily ornamented with sets of four thin parallel scratch marks. The described biogenic structures display a high diversity (minimum 13) which contrasts with the low to moderate ichnodidersity seen in fossil counterparts. However, the typical components of trace fossil assemblages from eolian dunes were recorded, including mammal (rodent), as well as spider and scorpion trackways.