Systematics of Sylvilagus Gray, 1867 (Lagomorpha: Leporidae) from Southwestern North America

Abstract

A multivariate morphological analysis of 26 cranial, mandibular, and dental characters was carried out on five taxa of cottontails: Sylvilagus floridanus chapmani (J. A. Allen, 1899), S.f. cognatus (Nelson, 1907), S. f. holzneri (Mearns, 1896), S. f. robustus (Bailey, 1905), and S. nuttallii pinetis (J. A. Allen, 1894). Discrete characters of upper P2 and P3 and lower p3 were examined in the above taxa, S. n. grangerii (J. A. Allen, 1895), and S. a. audubonii in the context of cladistic analyses. In the latter series of analyses, particular attention was paid to inter- and intrapopulational variation in the S. f. floridanus (J. A. Allen, 1890) and robustus taxa and in S. audubonii (Baird, 1857). I describe dental variation among holotypes and topotypes of these three taxa. My principal objective was to assess whether or not S. robustus was a subspecies of S. floridanus . An analysis of variance indicated that robustus differed from other taxa in six characters (greatest length of skull, condylobasal length, breadth of rostrum, interbasioccipital length, width of tympanic bullae, and mastoid breadth). Principal component analysis indicated ontogenetic differences between robustus and remaining taxa. Neighbor joining analysis in every case correctly classified each specimen examined to its predetermined taxon. Besides a large difference in size, several discrete differences in cranial and dental morphology separated S. robustus from the parapatric S. f. chapmani and from the nominal subspecies, S. f. floridanus ;, characters based on premolar enamel pattern in particular differentiated between S. f. floridanus and robustus . In phylogenetic analyses of 24 dental characters, S. cognatus , S. robustus , and S. holzneri were successive sister taxa to an unresolved clade consisting of two paraphyletic S. nuttallii “subspecies” and two subspecies of S. floridanus (sensu stricto). I propose that Sylvilagus robustus is a species distinct from S. floridanus and its subspecies, some of which probably also constitute distinct species. These results help clarify biogeographic problems inherent in the genus Sylvilagus under the current taxonomic framework.