Fritz Tsao

Evolutionary foundations of number: spontaneous representation of numerical magnitudes by cotton–top tamarins

Marc D Hauser, Elizabeth S Spelke, E. Spelke, 2003, Proceedings of the Royal Society of London. Series B: Biological Sciences.

General Intelligence in Another Primate: Individual Differences across Cognitive Task Performance in a New World Monkey (Saguinus oedipus)

Valen E. Johnson, Christopher F. Chabris, Marc D. Hauser, 2009, PloS one.