The number of pores per area of the eggshells is not always a reliable indicator of Rheidae species.Archaeofauna. International Journal of Archaeozoology.

NAVARRO,J.L:; GARCIA, K. A.:; GONZALEZ, G. ; MARTELLA, M.B.

Archaeofauna:International Journal of Archaeozoology

Universidad Autónoma de Madrid:Llaboratorio de Arqueozoología

Lugar: MADRID; Año: 2020

1132-6891

The use that humans have made of the two Rheidae species present in the Pampas and Chaco regions (greater rhea, Rhea americana), and in the Patagonia (lesser or Darwin´s rhea, Rhea -formerly Pterocnemia- pennata) of Argentina has been registered in various archaeological sites dating from the late Pleistocene until the end of the late Holocene. Bones and, mainly, abundant fragments of eggshells of these birds constitute frequent archaeofaunistic remains in these deposits. In search of taxonomic classification methods of Rheidae eggshell fragments that were more reliable than the determination based only in the geographical location of a given archaeological site, other authors proposed counting the pores on the surface of the shell as a method to determine more precisely which of both species corresponds to a particular fragment. In the present work, by using a destructive method to facilitate the counting process, we assessed the reliability of that classification procedure, with a broader sample of eggs. As it has already been published, we have found that the greater rhea eggshells have on average a pore density greater than that of the lesser rhea. However, the high variability observed in the pore density of both species and even within sectors of the same egg, can lead to erroneous classifications of shell fragments. This happens especially when total pore density per cm² of an eggshell fragment falls close to the lower values for greater rhea or to the higher values for lesser rhea. The most frequent mistake was to consider a fragment of eggshell as belonging to a lesser rhea egg when, instead, it belonged to the other species, but the converse could also occur. The probability of making this mistake depends on the fragment?s original position at the eggshell. This potential flaw could be because the method was not verified initially on the full pore density range of both species. Our work shows that the classification of eggshell fragments of Rheidae eggs based on pore counts adopted in previous papers is not as straightforward as proposed and its accuracy deserves to be corroborated more exhaustively, using a larger sample size belonging to a broader spectrum of populations of both Rhea species.