Large mammal burrows in late Miocene calcic paleosols from central Argentina: paleoenvironment, taphonomy and producers

MELCHOR, RICARDO NÉSTOR; CARDONATTO, MARÍA CRISTINA

PeerJ

PeerJ

Año: 2018 vol. 6 p. 1 - 36

Large cylindrical sediment-filled structures interpreted as mammal burrows occurwithin the loess-paleosol sequence of the late Miocene Cerro Azul Formation of centralArgentina. A total of 115 burrow fills from three localities were measured. They aretypically shallowly dipping, subcylindrical, unbranched structures with rounded endsand lacking enlargements. The horizontal diameter of the burrows range between 0.15and 1.50 m, with most of the burrows in the interval of 0.39 to 0.98 m. Geometricmorphometric analysis of transverse cross-sections support their distinct subcircularand elliptical (horizontally flattened) shapes. Burrow fills are typically laminated inthe lower part and massive in the upper part. The laminated intervals reflect pulses offlowing water entering the abandoned burrow during moderate rains, whereas massiveintervals reflect mass flow input of dense sediment-water mixtures during heavy rainsthat produced sheet floods. Approximately 1% of the burrows contained fragmentary,disarticulated and weathered mammal bones that were introduced in the open burrowby currents along with other sedimentary particles. Analysis of the tetrapod burrowfossil record suggests that Miocene burrows, including those studied herein, reflect aremarkable increase in the average size of the fossorial fauna.Weconclude that large lateMiocene mammals dug burrows essentially as a shelter against environmental extremesand to escape predation. The simple architecture of the burrows suggests that theproducers essentially foraged aboveground. Several mammal groups acquired fossorialhabits in response to cold and seasonally dry climatic conditions that prevailed duringthe late Miocene in southern South America. The considerable range of horizontaldiameters of the studied burrows can be attributed to a variety of producers, including dasypodids, the notoungulate Paedotherium minor, Glyptodontidae and Proscelidodonsp.