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Middle Triassic burrows from Argentina

From: Ben Creisler

A new online paper:

Veronica Krapovickas, Adriana C. Mancuso, Claudia A. Marsicano, Nadia
S. Domnanovich & Cesar L. Schultz (2012)
Large tetrapod burrows from the Middle Triassic of Argentina: a
behavioural adaptation to seasonal semi-arid climate?
Lethaia (advance online publication)
DOI: 10.1111/j.1502-3931.2012.00329.x

We report the discovery of large burrow casts in the early Middle
Triassic Tarjados Formation, at Talampaya National Park, north-western
Argentina. Facies analysis indicates the burrows are preserved in
sandbars deposited by an ephemeral river under semi-arid and seasonal
climatic conditions. The structures are mostly preserved in
longitudinal cross-section and consist of an opening, an inclined
tunnel (ramp), and a terminal chamber. The ramp is 8–14 cm in height,
up to 130 cm in length and penetrates 49–63 cm bellow the
palaeosurface with an inclination of 22°–30°. We studied burrow cast
dimensions, overall architectural morphology, surficial marks, and
compared them with other large burrows of both invertebrate and
vertebrate origin. A tetrapod origin of the burrow casts was
established based on: distinctive architecture, and size, which is
more than twice the most common size range for large terrestrial
invertebrate burrows. Comparison with other Upper Permian and Triassic
tetrapod burrows allows us to identify three general morphological
groups: (1) simple inclined burrows; (2) helical burrows; and (3)
burrow network complexes, representing different behaviours. A study
of tetrapod body fossils preserved within other Upper Permian and
Triassic burrows shows that the Tarjados structures were most likely
produced by non-mammalian cynodonts. The environmental and climatic
context suggests that aridity and seasonality played a fundamental
role selecting burrowing behaviour in therapsids and that by the
Early–Middle Triassic their burrowing behaviour attained a complexity
comparable to modern mammals.