Burrow systems of the extant South American fossorial rodent Ctenomys: keys to its recognition in the fossil record

CARDONATTO, MARÍA CRISTINA; RICARDO NESTOR MELCHOR; FATIMA DEL ROSARIO MENDOZA BELMONTES

Cape Town

Congreso; Second International Conference of Continental Ichnology; 2017

University of Cape Town

Burrow systems of Ctenomys azarae (Ctenomidae) were studied in central Argentina. The area has a temperate continental climate and the vegetation includes the pampean steppe and the caldenal (Prosopis forest). Ctenomys azarae is a small (average body mass of 138 g), fossorial, scratch-digging and solitary rodent. The genus Ctenomys is recorded since the Pliocene (3.5 Ma). The burrow systems are complex (Fig. 1A), large (covering 13.2 to 49 m2), dominantly subhorizontal (dip up to 27°), and shallow (15- 60 cm deep). The systems include a main tunnel and secondary tunnels, and have several entrances plugged by sediment. Tunnel segments are connected by T or Y junctions to short blind tunnels, grass-stuffed tunnels and rare chambers. Tunnels exhibit an elliptical cross-section with a larger vertical diameter (average vertical diameter: 77.3 mm, average horizontal diameter: 67.7 mm). The grass-stuffed tunnels are filled by compacted grass and separated from the main tunnel by a sediment plug (Fig. 1B). Elevated organic content renders these structures of high potential of preservation. The ceiling and lateral walls of the burrow contain a surface ornamentation in the form of 12 mm-wide sets of three parallel scratch marks (Fig. 1C) that are oblique to the tunnel axis (average 53°). The diagnostic features for recognition of fossil Ctenomydae burrows are: 1) subhorizontal burrows with massive fill, 2) size and elliptical cross-section (vertical to horizontal diameter ratio ≥ 1), 3) sets of three parallel scratch marks forming an acute angle with burrow axis, and 4) presence of grass-stuffed tunnels.