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SUBFAMILY Leimacomyinae

Author:new subfamily..

Type genus–Leimacomys Matschie, 1893. Definition–medium-sized terrestrial, insectivorous muroid with a scantily haired (caudal hairs length of one tail scale), tapering tail much shorter than length of head and body (TL/HBL = 32%), four digits and rudimentary fifth on front foot, five on hind foot, claws nearly straight, and dense pelage without guard hairs; cranium robust, rostrum moderately long and wide, and tapering distally in lateral perspective; interorbit wide; prominent supraorbital ridges border wide wedge-shaped postorbital region merging with wide braincase outlined by weak temporal ridging; occiput squarish, interparietal wide and narrow; broad zygomatic plate with prominent anteriorly projecting spine (deep zygomatic notch), masseteric tubercle weakly developed; zygomatic arches stout and not bowed outward; braincase moderately deep, with convex dorsal outline, and overhangs occipital condyles; expansive parietals form dorsal sides of braincase along with squamosal; incisive foramina narrow and very long, extending to lingual roots of first molar and close to posterior palatine foramina; bony palate wide, and posterior to third molar merges with adjacent pterygoids to form shelf roofing more than half of mesopterygoid fossa (extending almost to basisphenoid-presphenoid suture); auditory bullae small; dentary with high ramus, elongate coronoid process, deep emargination between condyloid and angular processes, incisor alveolus ending in prominent knob anterior to root of coronoid process, not extending into condyloid process; upper incisors slender, proodont, shallowly grooved on anterior enamel faces, those surfaces oriented as the arc of a circle (closely similar to form in Tateomys; see illustration in Musser and Durden, 2002); lower incisors very slender; molars with primitive number of roots; upper molar rows diverging anteriorly; upper molars with simple laminae, most formed by broad coalesence of two cusps (outlines of individual cusps on anterocone and posterior lamina of M1, and posterior lamina of M2 not evident), second lamina on M1 and anterior lamina on M2 chevron-shaped and formed by three broadly coalesced cusps (a cingular lingual cusp, protocone, and paracone); posterior cingulum, cusp t7, cingular cusplets, anterolabial cusp on M2 and M3, longitudinal grooves separating cusp rows, and mures (longitudinal crests) absent from upper molars; anterolabial and posterolabial cusplets, and posterior cingula absent from lower molars; anteroconid broadly fused with chevron-shaped anterior lamina; M3 and m3 moderately reduced compared to first and second molars (Misonne, 1966; Rosevear, 1969; Dieterlen, 1976a; Denys et al., 1995; Denys, 1993). Contents–only the type genus.

Compared with Steatomys and Lophuromys by Matschie (1893) who placed Leimacomys in Dendromurinae, kept there by G. M. Allen (1939), but transferred to Murinae by Ellerman (1940) and Simpson (1945), and subsequently regarded as an enigmatic dendromurine (Carleton and Musser, 1984; Rosevear, 1969). Conformation of body and skull is murine or deomyine, not dendromurine; cranial configuration is strikingly similar to the deomyine Lophuromys, but the resemblance has been interpreted as convergent, not phylogenetic, reflecting similar terrestrial and insectivorous habits (Dieterlen, 1976a). Nothing about Leimacomys’s external and cranial morphology suggests affinity with dendromurines (Misonne, 1966; Rosevear, 1969); only molar occlusal patterns, which have been interpreted as resembling those of Steatomys (Dieterlen, 1976a; Misonne, 1966; presence of a lingual cusp attached to second row of cusps on M1 and anterior cusp row on M2), have kept Leimacomys in Dendromurinae (Denys, 1993). Phylogenetic analysis of primarily dental traits incorporating dendromurines, deomyines, cricetomyines, petromyscines, gerbillines, Mystromys and Macrotarsomys by Denys et al. (1995) placed Leimacomys in a clade with gerbils and Mystromys that was isolated from the dendromurine clade containing Dendromus, Steatomys, Malacothrix, and Megadendromus, and suggests that the lingual cusp is independently derived in Leimacomys. The affinity with gerbils and Mystromys reflects shared simple molar occlusal patterns, but details of the pattern (lingual cusp present, longitudinal crests absent) differ and external and cranial traits of Leimacomys are unlike either gerbils or Mystromys. Phylogenetically isolated from living dendromurines, murines, gerbillines, and other muroid groups, "Leimacomys pourrait représenter le dernier élément vivant d’une lignée de rongeurs Muroidea isolée depuis longtemps et endémique du bloc forestier de l’Afrique occidentale" (Denys, 1993:617).



GENUS Leimacomys

SPECIES büttneri


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