Specializing in both paleontology and behavioral ecology with interests in Paleogene mammals, early primate evolution, prosimians (lorises, lemurs, and tarsiers), and birds, he synthesized multiple fields of study in order to better understand evolutionary processes.

Born in Salt Lake City, Utah in 1958, Rasmussen grew up in the Sonoran Desert, which he frequently explored as a child and young adult.

His interest in the natural world and native cultures began during his childhood with his exploration of the surrounding Sonoran Desert.

Courses he taught at WUSTL included the history of physical anthropology and human osteology, primate biology, evolution, functional morphology, paleobiology and phylogeny.

He spent several summers with his colleague, Glenn Conroy, in the Uintah Basin of Utah searching for the fossils of early mammals.

Other fossil collecting trips included locations such as Egypt, Kenya, Libya, Ethiopia, Namibia, South Africa, Madagascar, Ecuador, and Colombia.

[11] During his tenure at WUSTL, he was acknowledged with the Excellence in Mentoring award twice by the Graduate Student Senate of College of Arts and Sciences.

[12] A symposium in celebration of Rasmussen's influence on biological anthropology was held as a part of the 84th annual meeting of American Association of Physical Anthropologists on March 27, 2015.