form stiff keels of margin rhinarium imparting a broad
wedge shape to the head. The dental formula is 1/1, 0/0,
0/0, 3/3 16. The incisors are long and procumbent, and
are used in chisel-tooth digging (fig. 25.2a); their enamel
thickness varies with soil type. The cheek teeth are rooted
(not ever-growing) with Z- or S-shaped enamel patterns,
which are species- and soil-specific (Butler et al. 1993).
Spalacids are distinguished from all other rodents (in-
cluding other subterranean rodents) by the absence of any
external eye opening (figs. 25.1a,b; 25.2a – c). The sub-
cutaneous, vestigial eyes are not used in vision but rather
in photoperiodic perception; they have become essentially
circadian eyes (Sanyal et al. 1990; De Jong et al. 1990; Coo-
per et al. 1993a, 1993b; Nevo 1998, 1999). The pinnae
are rudimentary (figs. 25.1b, 25.2c), but the middle ear os-
sicles (Burda et al. 1989, 1990), particularly the cochlea
(Bruns et al. 1988), are uniquely structured among mam-
mals. As such, they are adapted to underground low fre-
quency and rich-repertoire, short-distance vocal commu-
nication (Heth et al. 1986; Nevo et al. 1987; Heth, Frank-
enberg et al. 1988b). Seismic (vibrational) communication
by head thumping on the burrow ceiling (Heth et al. 1987;
Rado et al. 1987; Nevo et al. 1991) is a major underground
communication modality among these solitary territorial
animals (Nevo 1961; Nevo et al. 1991), and varies among
species (Heth et al. 1991). Adaptive morphological differ-
entiations exist in the body and head skin (hairy skin, vib-
rissal fields, buccal ridge, and rhinarium [Klauer et al.
1997]). Olfaction is an important communication modal-
ity (Nevo and Heth 1976) in reproduction through sexual
pheromones (Nevo et al. 1987; Menzies et al. 1992; Tod-
rank and Heth 1996) and in food identification (Heth et al.
1992, 1996; Heth and Todrank 1995). Tactile cues are im-
portant, but as yet unquantifiable (Burda et al. 1990).
Mole-rats are confined most of their lifetime to sealed
underground tunnels (Nevo 1961). They are chisel-tooth
diggers, using fore and hind feet to push the earth out ahead
of or behind them, thus packing and bulldozing excavated
earth with their broad and flat heads to form the external
mounds (fig. 25.3a – e). Specialized jaws and strong muscles
aid the teeth in loosening the soil. Incisor (Flynn et al. 1987)
and molar (Butler et al. 1993) structures vary with species,
soil, and food.Population BiologySpalacids are solitary, territorial, and aggressive (Nevo
1991, 1999; Nevo et al. 1975, 1986; Guttman et al. 1975).
Aggression is polymorphic within sexes, populations, and
species, each involving militant, intermediate, and pacifist
behavioral phenotypes (Nevo et al. 1986, see the follow-
ing; fig 25.2a – c). Pacifism increases toward the Negev Des-
ert in Israel and culminates in total fixation in a pacifis-
tic species bordering the Sahara Desert in Egypt and North
Africa (Nevo et al. 1991; Nevo, Simson, Heth, Redi, and
Filippucci 1991; Nevo et al. 1992; fig 25.1c, see the fol-
lowing). This animal was identified as a new animal based
on morphological, behavioral, chromosomal, and allo-
zyme evidence (Nevo, Simson, Heth, Redi, and Filippucci
1991).
Territory size (range: 60 –200 m^2 ) varies with the spe-
cies, population, habitat, sex, and age (see Nevo 1979;
Savic ́ and Nevo 1990 and references therein). Population
density varies with habitat productivity, from 0.1 to 23/ha
(Nevo 1979). Populations abound with adults; the propor-
tion of subadults and juveniles is low and variable between
and within species. Sex ratio is skewed to different degrees292 Chapter Twenty-Five
Figure 25.2 Aggressive behavior in Spalax ehrenbergi:(a) frontal view and
exposed incisors, (c) head-on combat with biting, (b) combat with a dominant
militant (left) and a submissive pacifist (right).