My favorite papers are always the older papers, with rare exception. It is not because I am a traditionalist or that I find current science to be less educated or informed, it is totally the language used. Scientific papers are dry by nature, something that will probably never change, but the language of the earlier paleontologists is from a different time and, in my opinion, makes the reading that much more interesting despite its dry nature. With that in mind, I picked out two papers- out of a virtual stack not to mention a good portion of Oceans of Kansas' chapter on fish- one of which is from 1997 and the other 99 years older, from 1898, that redescribes and makes new observations on Xiphactinus.
The 1997 paper, by Schwimmer, Stewart, and Williams, discusses the different Xiphactinus discoveries in North America and the distribution of the species Xiphactinus vetus in the Eastern US. The paper is a short communication and thus is not very highly in depth, but it does address some questions of distribution and poses a question near the end of what kind of evolutionary relationship existed between the two species of Xiphactinus.
The older paper, O.P. Hay's 1898 observations and redscription, does exactly what it says it is going to do; Hay makes observations on Cope's and Leidy's two "distinct" genera of fish. Hay goes on to talk about multiple species but does make an important note that Cope's genus, Portheus, and Leidy's genus, Xiphactinus, possess "no serious discrepancy between Cope's description of his Portheus thaumas and my specimen [Leidy's Xiphactinus]." Additionally, as has been made often here, Hay compares Xiphactinus with extant tarpon regularly throughout the paper. It is a fairly good read.