Molecular analyses corrected many of these misgroupings and the superordinal hierarchy of placental mammals was recently assembled into four clades.
Jan Ole Kriegs, Gennady Churakov, Martin Kiefmann, Ursula Jordan, Jürgen Brosius,Jürgen Schmitz 2006, 'Retroposed elements as archives for the evolutionary history of placental mammals.',PLoS Biologyhttp://europepmc.org/articles/PMC1395351?pdf=render. Retrieved from PLOS CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)