Cope’s rule, the tendency towards phyletic size increase in lineages over time has long been accepted by the vast majority of evolutionary ecologists and paleontologists. Recently, the validity of this rule has been questioned. Advocates of Cope’s rule have been searching for mechanisms to explain the obvious trend (Hallam, 1975; Kingsolver and Pfennig, 2004; Hone and Benton, 2005) while those in opposition have taken a wider look at the trends and discovered several biases which may have been present in earlier studies (Arnold et al., 1995; Jablonski, 1997). Although the work of Hallam (1975) may show strong trends towards size increase, it may be somewhat outdated compared to later studies examined in this paper. The major downfalls of the paper are that it only uses two main taxa and that it assumes that there are selective advantages to being larger. The more recent study by Kingsolver and Pfennig (2004) did take into account more taxa, but did so in a biased sense. They sampled more individuals from some taxa than others and did not consider that these unfairly sampled taxa may not have followed Cope’s rule and would have changed their end results.