Smithson, T. R.; Carroll, R. L.; Panchen, A. L.; Andrews, S. M. (1993). "Westlothiana lizziae from the Viséan of East Kirkton, West Lothian, Scotland, and the amniote stem". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 84 (3–4): 383–412. doi:10.1017/S0263593300006192. ISSN1755-6929. S2CID129807712.
Smithson, T. R.; Carroll, R. L.; Panchen, A. L.; Andrews, S. M. (1993). "Westlothiana lizziae from the Viséan of East Kirkton, West Lothian, Scotland, and the amniote stem". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 84 (3–4): 383–412. doi:10.1017/S0263593300006192. ISSN1755-6929. S2CID129807712.
stratigraphy.org
"Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
Smithson, T. R.; Carroll, R. L.; Panchen, A. L.; Andrews, S. M. (1993). "Westlothiana lizziae from the Viséan of East Kirkton, West Lothian, Scotland, and the amniote stem". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 84 (3–4): 383–412. doi:10.1017/S0263593300006192. ISSN1755-6929. S2CID129807712.