Wolf spider burrows from a modern saline mudflat: morphology and potential of preservation

FATIMA DEL ROSARIO MENDOZA BELMONTES; RICARDO NESTOR MELCHOR

Cape Town

Congreso; Second International Conference of Continental Ichnology; 2017

University of Cape Town

We describe burrows excavated by the wolf spider Pavocosa sp. (Lycosidae) from the Gran Salitral saline lake, La Pampa province, Argentina. The burrows were only found in the sparsely vegetated siliciclastic-evaporitic mudflat on the edge of the saline lake. The general morphology is a simple, nearly vertical (66-88°) and cylindrical burrow, with a slight widening in the lower half, roughly comparable with the ichnogenus Skolithos (Fig. 1A). Entrance is circular, slightly narrower than the burrow, and display silk and some sediment pellets. During a wet period, the burrow entrance was surrounded by small sediment pellets. Active burrows were occupied by an individual and contained an egg sac. Burrow casts are about 10.4-12.3 cm long, the maximum diameter is 1.9-2.9 cm, and the diameter at the entrance is 1.1-1.3 cm. The burrow wall was covered with silk (Fig. 1B) and displayed a surface ornamentation in the form of sets of two linear parallel grooves about 2.8-4 mm long and 2.8-3 mm wide (Fig. 1C), matching the size and shape of the wolf spider fangs. Predation by armadillos makes the entrance funnel-shaped, similar to the ichnogenus Monocraterion. Pavocosa burrows show a particular environmental distribution (sparsely vegetated saline mudflat) and moderate potential of preservation due to the presence of silk. Although the fossil record of Lycosidae dates back to the Neogene (probably to the Late Cretaceous), until now no fossil Lycosidae burrow has been recognised. Distinctive features of these burrows are a cylindrical shape with a slight widening and a characteristic surface ornamentation.