Introduction

Castoridae are known from the late Eocene or early Oligocene to modern times with varying numbers of genera; one today and over 23 described from the Tertiary (McKenna and Bell 1997). The earliest radiation of beavers was the one of palaeocastorine beavers (Subfamily Palaeocastorinae Martin 1987) known from North America only. Xu (1996) saw Agnotocastor (Stirton 1935) as sister taxon to this subfamily of beavers, Rybczynski (2007, figure 3) indicated Castorinae and Castoroidinae as sister groups to Agnotocastor sp. and Palaeocastorinae. The phylogenetic relationship within this subfamily is still little resolved. Korth (2001) included Palaeocastor (Leidy 1869), Euhapsis (Peterson 1905), Capacikala (MacDonald 1963), Fossorcastor (Martin 1987) and Pseudopalaeocastor (Martin 1987) (Xu 1996 assigned this to Nannasfber Xu 1996) in this subfamily. A review of the group was given by Martin (1987). In more recent reviews of Castoridae, Capacikala and Palaeocastor were retained as separate genera by McKenna and Bell (1997). The synonymization of Capatanka (McDonald 1963) to Palaeocator suggested by McKenna and Bell (1997) has been followed by Korth (2001) and Rybczynski (2007).

Geographically these Palaeocastorinae come from Oregon, South and North Dakota, Wyoming and some from Nebraska. Stratigraphically the earliest occurrence of this group is in the Whitneyan, Latest Oligocene: Palaeocastor nebrascensis (Leidy 1869) from the Mauvaises Terres of White River, represented by fragmented skulls and jaw material and teeth (Leidy 1869:338, pl 26, figures 7, 8); now not numbered at the Academy of Natural Sciences in Philadelphia (Xu 1996). The Palaeocastorinae are known to be fossorial, and some species are directly associated with the burrows Daimonelix Barbour 1892 (Martin and Bennett 1977; Martin 1994).

The genus Capacikala was nominated about 40 years ago by MacDonald (1963) and has been included in the revision of palaeocastorine beavers by Martin (1987) and in the analysis of Castoridae by Xu (1996) but it still seems poorly understood. There is ample material from the Wounded Knee, Sharps Formation (Martin 1987) and some from Muddy Creek Wyoming (Xu 1996) and the John Day Formation. "Capatanka," also nominated by McDonald, has been synonymized to Palaeocastor, and other species have been assigned to different genera by different authors indicating difficulties in understanding this group of beavers. A good understanding is further complicated by the nomination of several new species that are scarcely illustrated and documented only with little material and few measurements, but some details on the infraorbital foramen and lower jaws are explained in Martin (1987) and Xu (1996).

I discuss the subject of teeth in this report because it is not discussed in great detail anywhere. More specifically, morphology and morphometry of larger samples of teeth are focused on here. Discriminant analyses of several measurements can help to reveal taxonomic differences. The goal of this study is to better understand the systematics of palaeocastorine beavers, especially those assigned to Palaeocastor, Capacikala and "Capatanka" mainly on the basis of tooth morphology and morphometry under consideration of wear stages of the material. Some aspects of skull morphometry will also be considered and discussed to hopefully contribute some new aspects to the discussion of the taxonomic status of these beavers.