Triassic megaherbivore comm una latrines: evidence of social behaviour and herbivory in dicynodonts

FIORELLI, L. E.; DESOJO, J. B.; EZCURRA, M. D.; HECHENLEITNER, E. M.; ARGAÑARAZ, E.; TABORDA, J. R. A.; BACZKO, M. B.; TROTTEYN, M. J.; LECUONA, A.

La Rioja

Jornada; XXVII Jornadas Argentinas de Paleontologia de Vertebrados; 2013

Communal defecation latrines or ?dung piles? are a common behaviour in extant mammal megaherbivores such as rhinoceros, horses, tapirs,elephants, antelopes, and camelids. This behaviour has important social functions as well as biological and ecological consequences for thespecies, plant populations and vegetation dynamics. Communal latrines of mammal megaherbivores are extremely rare in the fossil recordand currently unknown among non-mammal fossil vertebrates. Here we report the discovery of several fossil communal latrines with copiousamounts of coprolites from the Middle Triassic lower lithological unit (Top Ten locality) of the Chañares Formation in La Rioja Province, Argentina.The characteristics of the communal latrines and the multiplicity, density, and morphology of thousands of in situ coprolites suggestthat they belonged to gregarious species with a complex social behaviour comparable to that of extant megaherbivores. The communal latrinesurfaces range from 400 to 900 m2 and have an average density of 60 coprolites/m2. The latrines are separated ~1500 meters from each other.Several lines of evidence ?such as the size of coprolites (c. 0.5 to 30 cm), density, and presence of plant microfragments within the coprolitesand their association at the same level with juvenile and adult kannemeyeriiform dicynodonts? suggest that large dicynodonts (>2 m long)could have been the producers of the latrines. The abundant coprolite associations described here are the first record of communal latrinesin dicynodonts and non-mammal fossil vertebrates. This behaviour matching that observed in extant megaherbivore mammals predates byover 200 million years the oldest known record.