Petromyscinae Roberts 1951

Wilson, Don E. & Reeder, DeeAnn, 2005, Order Rodentia - Family Nesomyidae, Mammal Species of the World: a Taxonomic and Geographic Reference (3 rd Edition), Volume 2, Baltimore: The Johns Hopkins University Press, pp. 930-955 : 953

Petromyscinae Roberts 1951

Petromyscinae Roberts 1951 , Mammals of South Africa: 434.

Genera: 1 genus with 4 species:

Genus Petromyscus Thomas 1926 (4 species)

Discussion: Emended definition—Small-bodied (76-112 mm), terrestrial muroids with large ears, short limbs, short hind feet and digits, hairy tail (caudal hairs as long as 2-3 scale rows) equal to or moderately longer than head and body, and two pairs inguinal mammae; front feet with stubby thumb and four clawed digits (two outer nearly as long as the two inner); hind foot with five clawed digits (first very short, next three subequal in length, fifth slightly shorter) and full complement of plantar pads (hypothenar much smaller than thenar); pelage long, soft and silky; rostrum long and slender, interorbit broad and smooth, braincase wide and flat without temporal ridging; zygomatic plate wide with prominent projecting anterior spine (deep zygomatic notch) and inconspicuous masseteric tubercle; incisive foramina narrow and reaching anterior margins of M1s or extending beyond them, posterior palatine foramina at middle of M2s; bony palate wide and projecting past posterior margin of M3s to form a prominent shelf confluent with long, very wide, and slightly excavated parapterygoid fossae; mesopterygoid fossa very narrow, breached by spacious sphenopalatine vacuities; alisphenoid strut wide, robust, and appressed against braincase; subsquamosal foramen small in young animals, closed in adults, its former position marked by prominent hamular process; carotid circulatory partially derived (large stapedial foramen, no sphenofrontal foramen or squamosal-alisphenoid groove; pattern 2 as per Carleton, 1980, and Voss, 1988); bulla moderately inflated; mandible with delicate coronoid processes below which incisor capsule forms low mound; upper incisors strongly ophisthodont, enamel faces smooth; lower incisors ungrooved; molars brachydont with uppers three-rooted and lowers two-rooted; anterocone(id) of M1 and m1 large and entire; cusps longitudinally connected by short crests; large cingular lingual cusp adjacent to protocone on M1 and M2 and coalesces with wear, anteroloph and mesoloph absent, anterolophid absent, short mesolophid connecting large mesostylid with entoconid on m1 and m2; wide posterior cingulum (posteroloph) connects posterior margins of metacone and hypocone on M1 and M2, prominent posterior cingulum on m1 and m2; M2 two-thirds size of M1, M3 very small, half the size of M2 with simple C-shaped occlusal pattern unlike that of M2; (drawn from study of specimens in AMNH and USNM, along with information from F. Petter, 1967 b, and Carleton and Musser, 1984; see dental terminology in Carleton and Musser, 1989). Contents— Petromyscus Thomas, 1926 .

Based on the lingual cusps on their upper molars, Hayman (1962 a) regarded Delanymys and Petromyscus as dendromurines. Lavocat (1964) considered their cusp patterns as structural links between Mystromys and the dendromurines and allied them with cricetids, a view shared by F. Petter (1966 c), W. Verheyen (1965 b), and earlier by Ellerman (1941). Whereas these authors regarded the accessory lingual cusp to be an elaboration of the cingulum, Petter (1967 b) considered it to represent the protocone, the new cusp having developed from the longitudinal crest (mure). Petter therefore united Delanymys and Petromyscus in Roberts’ (1951) Petromyscinae and stressed their distant relationship to true dendromurines. Aside from the shared lingual cusps, Delanymys and Petromyscus have little in common and their union as sister taxa in the same subfamily has been challenged ( Carleton and Musser, 1984; Denys, 1994 c). Here we disassociate the two and treat Petromyscus as the sole known member of Petromyscinae (see account of Delanymyinae ). According to phyletic interpretation of cytochrome b data ( Jansa et al., 1999), the genus is closely related to Mystromys and both form a clade that is distantly removed from the single dendromurine sampled ( Steatomys ).

Petromyscus has not yet been convincingly linked by fossils to a possible ancestral group, although both Tong and Jaeger (1993) and Mein et al. (2000 b) believed that it represents a lineage derived from Miocene myocricetodontines. Isolated molars identified as " Petromyscinae " have been uncovered from middle Miocene sediments of Namibia and as Petromyscus from late Miocene beds in the same region ( Senut et al., 1992). The latter teeth have been recently reidentified as Harimyscus hoali , a form regarded as the earliest known petromyscine ( Mein et al., 2000 b). Namibia today comprises the greater part of the distribution of three extant species of Petromyscus .