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

FIORELLI, LUCAS E; DESOJO, JULIA B; EZCURRA, MARTIN D; HECHENLEITNER, E. MARTÍN ; ARGAÑARAZ, ELOISA; TABORDA, JEREMÍAS R A; VON BACZKO, M B; TROTTEYN, M JIMENA; LECUONA, AGUSTINA

La Rioja

Jornada; XXVII Jornadas Argentinas de Paleontología 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 the species, plant populations and vegetation dynamics. Communal latrines of mammal megaherbivores are extremely rare in the fossil record and currently unknown among nonmammal fossil vertebrates. Here we report the discovery of several fossil communal latrines with copious amounts of coprolites from the Middle Triassic lower lithological unit (Top Ten locality) of the Chañares Formation of the La Rioja Province, Argentina. The characteristics of the communal latrines and the multiplicity, density, and morphology of thousands in situ coprolites suggest that belonged to gregarious species with a complex social behaviour comparable to that of extant megaherbivores. The communal latrine surfaces range from 400 to 900 m2 and have an average density of 70 coprolites/m2. The latrines are separated around 1500 meters from each other. Several lines of evidence suggest that large dicynodonts (>2 m long) should have been the producers of the latrines, such as the size of coprolites (ca. 0.5 to 30 cm), density, and presence of plant microfragments within the coprolites and their association at the same level with juvenile and adult kannemeyeriiform dicynodonts. The abundant coprolite associations described here are the first record of communal latrines in dicynodonts and non-mammal fossil vertebrates; this behaviour that matched that observed in extant megaherbivore mammals predates the oldest record over 200 million years.