The Third Lower Premolar of the Cottontail, Genus Sylvilagus, and Its Value in the Discrimination of Three Species

Abstract

The enamel pattern of the third lower premolar of Sylvilagus is derived from its Blancan ancestor, Nekrolagus. The posterobuccal re-entrant of Nekrolagus is short and a fossettid lies opposite it. In Sylvilagus, the fossettid joins the re-entrant to form a broad reentrant. The enamel at the tooth base consists only of thin radial enamel. Ameloblasts above the tooth base deposit additional lamellar enamel to the basal radial enamel at the anterior and posterior ends of the tooth and at the anterior wall of the posterobuccal re-entrant. At the occlusal surface these areas consist of enamel thicker than that of the rest of the pattern. A small area of the occlusal surface of Nekrolagus fossettid shows tangential enamel. Two types of cementum are distinguished, and herein named. Deeper re-entrants and the Nekrolagus fossettid are filled with structural cementum but the outer surfaces are covered with coating cementum. The anterior wall of the posterobuccal re-entrant of p3 is without crenulations or simple in S. nuttallii and usually so in S. floridanus. Sylvilagus audubonii usually has the anterior wall of the re-entrant moderately to strongly crenulated. Crenulation of the anterobuccal re-entrant wall does not separate species of cottontails in all cases but is helpful in separation of species where only isolated teeth are available and in mixtures of species as in some cave deposits.