Stephanie E. Pierce; Jennifer A. Clack; John R. Hutchinson (2012). Three-dimensional limb joint mobility in the early tetrapod Ichthyostega. Nature.486: 524–527. doi: 10.1038/nature11124
plos.org
journals.plos.org
Swartz, B. (2012). "A marine stem-tetrapod from the Devonian of Western North America". PLoS ONE.7 (3): e33683. doi:10.1371/journal.pone.0033683