Widanelfarasia, a diminutive placental from the late Eocene of Egypt

Abstract

The lower dentition of Widanelfarasia (new genus), a diminutive late Eocene placental from the Fayum Depression in Egypt, is described. Widanelfarasia exhibits a complex of features associated with incipient zalambdodonty and at least three unequivocal apomorphies [loss of P(1), an enlarged I(2) (relative to I(3)), and a basal cusp on I(2)], which provide weak support for its placement as a possible sister taxon of either a tenrecid-chrysochlorid clade or of solenodontids. The former hypothesis gains additional support from biogeographical evidence, but both scenarios are currently tenuous as Widanelfarasia is clearly not truly zalambdodont. Phylogenetic hypotheses positing affinities with tenrecids alone or chrysochlorids alone must invoke either convergent acquisition of zalambdodonty in these taxa or autapomorphic reversal in Widanelfarasia. Given these considerations, a relationship with more generalized taxa from the Laurasian Paleogene (e.g., geolabidids, nyctitheriids, leptictids) cannot yet be ruled out. Comparisons with other Paleogene Afro-Arabian forms are generally inconclusive. A relationship with the earlier Eocene Chambilestes from Tunisia-currently represented by a single specimen preserving P(4)-M(3)-seems possible based on the geometry and predicted occlusal relationships of these teeth, but cannot be confidently determined until these two taxa come to be represented by common diagnostic elements. Todralestes (late Paleocene, Morocco) exhibits general phenetic similarities to Widanelfarasia, but it is not yet known whether this taxon shares any of Widanelfarasia's unequivocal dental apomorphies. Pending the recovery of more informative material, we tentatively refer Widanelfarasia to Placentalia incertae sedis. Truly zalambdodont placentals remain conspicuously absent from the Paleogene of Afro-Arabia.

Figure 1

Lingual views of DPC 15637, Widanelfarasia bowni, right P₂–M₃ (A), and cast of CGM 41878, W. bowni, left P₄–M₃ (reversed) (B). Labial views of DPC 15637, W. bowni, right P₂–M₃ (C); cast of CGM 41878, W. bowni, left P₄–M₃ (reversed) (D); and DPC 17427, W. rasmusseni, right P₂ and P₄–M₃ (note that labial views are taken from slightly different orientations) (E). (F) Labial view of DPC 17779 (W. bowni), left dentary containing I₂, root of I₃, and C–P₄. Note the loss of P₁, the large cross-section and slightly procumbent orientation of the broken canine, and the enlarged I₂ with posterior basal cusp. (G and H) Occlusal stereophotos of the holotypes of W. bowni (G, DPC 15637) and W. rasmusseni (H, DPC 17427). Note that a thin layer of matrix adheres to the hypoflexids of M₁–M₂ of DPC 17427. (Bars = 1 mm.)

Figure 2

Three of many feasible options for Widanelfarasia's systematic position given differing assumptions of placental interrelationships. Possible lower dental synapomorphies are given at selected nodes. (A) The option preferred (but still weakly supported) by this study, under the assumption that tenrecids and chrysochlorids are sister taxa, Solenodon is unlikely to be the extant sister taxon of a tenrecid–chrysochlorid clade, and the extant sister taxon of the tenrecid–chrysochlorid clade is currently unclear—molecular data (e.g., ref. 12) suggest that it is some segment of “Afrotheria.” Nodes: 1, loss of P₁, enlarged I₂ with basal cusp, possibly deep hypoflexids and a semimolariform P₄; 2, marked reduction of molar talonids, possibly a reduction of the lower canine. This option gains additional support from biogeographic considerations. (B) Possible relationships under the assumption that living and extinct zalambdodont placentals are monophyletic. Nodes: 1, semimolariform P₄; 2, loss of P₁, increased depth of hypoflexids; 3, marked reduction of molar talonids; 4, relatively large I₂. (C) Widanelfarasia mapped onto a cladogram of Lipotyphla as suggested (in part) by Butler (33). Lower dental features considered in this paper are quite labile given this scenario. Nodes: 1, loss of P₁, enlarged I₂ with basal cusp, deep hypoflexids; 2, marked reduction of molar talonids, possibly a reduction of the lower canine; 3, increased dilambdodonty.