References - A Brief History of Butts

Martín-Durán, J. M., Passamaneck, Y. J., Martindale, M. Q. & Hejnol, A. The developmental basis for the recurrent evolution of deuterostomy and protostomy. Nat Ecol Evol 1, 1–10 (2016).

Heldstab, S. A., van Schaik, C. P. & Isler, K. Being fat and smart: A comparative analysis of the fat-brain trade-off in mammals. J Hum Evol 100, 25–34 (2016).

Hejnol, A. & Martín-Durán, J. M. Getting to the bottom of anal evolution. Zoologischer Anzeiger - A Journal of Comparative Zoology 256, 61–74 (2015).