Clyomys laticeps ( Thomas, 1909 )

Bezerra, Alexandra M. R., de Oliveira, João A. & Bonvicino, Cibele R., 2016, Clyomys laticeps (Rodentia: Echimyidae), Mammalian Species 48 (938), pp. 83-90 : 83-87

Clyomys laticeps ( Thomas, 1909)

Broad-headed Spiny Rat

L [oncheres]. laticeps Lund, 1839: 226 , 233. Nomen nudum (see Thomas 1909:240, Paula-Couto 1950). Mesomys spinosus: Winge, 1887:92 . Name combination, not spinosus Desmarest, 1817 (see “Nomenclatural Notes”).

Echimys laticeps Thomas, 1909:240 . Type locality “Lagoa Santa, on the Rio São Francisco, Minas Geraes,” in Minas Gerais State, Brazil (see “Nomenclatural Notes”).

Clyomys laticeps: Thomas, 1916:300 . First use of current name combination.

Clyomys laticeps whartoni Moojen, 1952:102 . Type locality “ 1 km north of Aca-Poi, long. 56 o 7’ W., lat. 23 o 5’ S., Department of San Pedro, Partido de Tacuatí, Paraguay; approximately 60 km east-northeast of Puerto Ybapobo and 10 km south of the Rio Ypané.”

Clyomys bishopi Avila-Pires and Wutke, 1981:529 . Type locality “Itapetininga, São Paulo, Brasil.”

CONTEXT AND CONTENT. Order Rodentia , suborder Hystricomorpha , infraorder Hystricognathi , family Echimyidae , subfamily Eumysopinae . No subspecies are currently recognized (Bezerra and Bonvicino 2015).

NOMENCLATURAL NOTES. The synonymies were modified from Bezerra and Bonvicino (2015). Winge (1887) equated Loncheres laticeps Lund, 1839 with Mesomys spinosus Desmarest, 1817 ( Thomas 1909) . Burmeister (1854) assigned Desmarest’s spinosus to Mesomys Wagner, 1845 , but spinosus is recognized as a species of the genus Euryzygomatomys (e.g., Thomas 1916; Bezerra and Bonvicino 2015).

Several taxonomic surveys, including Cabrera (1961) and Woods and Kilpatrick (2005) followed Tate’s (1935:406) incorrect listing of the type locality of Clyomys laticeps as “Joinville, Santa Catherina, Brazil,” despite objections by other authors ( Bishop 1974; Avila-Pires and Wutke 1981). Thomas (1909), in his description of Echimys laticeps , was unambiguous in listing the type locality as “Lagoa Santa, Minas Geraes.” The Joinville locality was only mentioned by Thomas (1909) when referring to specimens of Echimys spinosus (= Euryzygomatomys spinosus ), to which the C. laticeps holotype was compared (AvilaPires and Wutke 1981; Bezerra and Oliveira 2010).

A fossil species, Clyomys riograndensis , was recently described from Holocene deposits of Garivaldino, Rio Grande do Sul State, Brazil ( Hadler et al. 2008). This species was described based on a single skull fragment (holotype) and several maxillar and mandibular fragments, which were compared to 12 recent specimens from 2 localities (Itapetininga, São Paulo State and Camapuã, Mato Grosso do Sul State, Brazil). Other common names for the broad-headed spiny rat are spiny rat, rato-de-espinho (Portuguese), and rata espinosa (Spanish).

DIAGNOSIS

Clyomys laticeps differs from the other South American semifossorial echimyid rodents ( Carterodon sulcidens [Owl’s spiny rat] and Euryzygomatomys spinosus [Fischer’s guiara]) by its grizzled, yellowish and black or rufous and black dorsal pelage contrasting with the uniformly colored, brownish to chestnut-brown dorsal pelage of the other 2 species, and by its very conspicuous typanic bullae ( Thomas 1916), which have breadths of 9.61 to 12.80 mm and lengths of 12.57 to 16.36 mm (measurements from adult specimens from Bezerra and Oliveira 2010). C. laticeps also differs from the sympatric Owl’s spiny rat (endemic to the Cerrado domain— Bishop 1974; Bezerra et al. 2011) by its dorsal spiny pelage and a tail covered with short hairs, the latter species has soft and spineless pelage and a tail sparsely covered with long hairs.

GENERAL CHARACTERS

Clyomys laticeps ( Fig. 1 ) is a medium-sized, semifossorial echimyid rodent with coarse and spinous pelage, short ears, short limbs, long and powerful claws, and short tail (shorter than one-half the head–body length) sparsely covered with short and unbanded hairs that partially cover the scales ( Thomas 1909; Bishop 1974).

Pelage color varies from grizzled rufous and black to grizzled yellow and black on dorsal and lateral surfaces, and whitish or buffy with or without presence of grayish or pale rufous patches on gular and ventral surfaces ( Thomas 1909; Moojen 1952; Bishop 1974; Bezerra 2002). Variation of pelage coloration may be the result of positive selection for cryptic coloration (Bezerra and Oliveira 2010).

Head and body length varies between 150 and 295 mm, length of tail from 48 to 93 mm, hindfoot without claws from 26 to 34 mm and with claws from 26 to 39 mm, internal ear from 13 to 24 mm, and weight ranges from 180 to 334 g ( Bezerra 2002). Craniometric analysis did not reveal significant sexual dimorphism ( Bezerra 2002; Bezerra and Oliveira 2010).

Means and ranges (in parentheses) of cranial measurements (mm) of 44 adult C. laticeps specimens from São Paulo State, Brazil (the largest pooled sample known for this species—Bezerra and Oliveira 2010) were: greatest length of tympanic bulla, 14.99 (13.72–16.31); greatest breadth of tympanic bulla, 11.10 (9.61–12.55); condylobasal length, 46.40 (44.34–48.96); cranial depth at tympanic bulla, 18.63 (16.90–19.51); cranial breadth at external auditory meatus, 24.13 (22.63–26.41); cranial breadth immediately posterior to zygomatic arches, 21.27 (20.00–22.09); diastema length, 11.64 (10.94–12.65); greatest length of skull, 49.91 (47.87–53.08); incisive foramina breadth, 2.83 (2.40–3.37); incisive foramina length, 6.09 (5.15–7.15); interorbital constriction, 11.60 (10.48–12.97); length of lower molar row, 10.88 (10.07–11.75); mandible length, 28.57 (27.30–31.07); mesopterygoid fossa breadth, 3.90 (3.25–4.42); mandibular ramus length, 13.76 (12.60–15.31); palatal breadth measured at dP4–M1, 9.33 (8.43–9.93); nasal length, 14.17 (13.14–15.13); palatal length, 21.89 (20.82–22.87); palatilar length, 18.53 (17.34–19.83); postpalatal length, 25.32 (24.08–26.69); rostral breadth, 7.90 (7.34–8.65); rostral depth, 8.33 (7.70–9.61); rostral length, 16.76 (15.85–19.17); length of upper molar row, 10.08 (8.76–10.76); and greatest zygomatic breadth, 27.85 (25.92–29.48).

Skull ( Fig. 2 ) is broad, with rostrum short and wide. The mesopterygoid fossa occurs in 1 of 3 forms: extending to hypoflexus of M2 (in the majority of the 127 analyzed specimens and in the holotype of C. laticeps ), extending more anteriorly to the Oliveira 2010). Sphenopalatine foramen, sphenopalatine vacuities, and the canal for the infraorbital nerve within the infraorbital foramen well developed.

DISTRIBUTION

Clyomys laticeps inhabits areas of open vegetation and cerrados (a savanna-like vegetation) of the Cerrado domain of central Brazil and enclaves in São Paulo State ( Bishop 1974; Avila-Pires and Wutke 1981), extending to the Paraguayan Chaco ( Moojen 1952; Fig. 3 ), and at elevations ranging from 100 to 1,100 m. Its geographic range in Brazil extends from western São Paulo State (Avila-Pires and Wutke 1981; Vieira 1997; Carmignotto 2005), Minas Gerais State ( Thomas 1909; Amante 1975), western Bahia State ( Bezerra 2002; Bezerra and Oliveira 2010), Federal District and the states of Goiás, Mato Grosso, and Mato Grosso do Sul ( Bishop 1974; Avila-Pires and Wutke 1981; Svartman 1989; Bezerra 2002; Rodrigues et al. 2002; Carmignotto 2005; Bezerra and Oliveira 2010).

level between the hypoflexus and the anterior border of M2 (in 19% of the specimens), and extending to the midlength of M3 (in 6%—Bezerra and Oliveira 2010). This character is polymorphic within populations, except for the samples from Minas Gerais State, which contains only 4 adult specimens, and from Paraguay (a single adult specimen—Bezerra and Oliveira 2010). Anterior projection of premaxillary bone short. Inferior zygomatic root also short, extending laterally at the same level of the palatal surface. Tympanic bullae hypertrophied, highly visible beyond paroccipital process when viewed from behind ( Thomas 1916). Auditory meatus medium-sized, with partial contact between the ectotympanic and squamosal restricted to posterior portion of the dorsal margin of ectotympanic, forming a cleft between these 2 bones. General shape of incisive foramen narrow and elongated ( Thomas 1909), but varying among oval-shaped, elongated, lyriform, amphora-shaped, and lozenge-shaped ( Bezerra 2002; Bezerra and

FOSSIL RECORD

Clyomys laticeps is known from late Pleistocene deposits (ca. 0.3 to 0.01 million years ago) in Lagoa Santa, Minas Gerais State, Brazil ( Lund 1839). Clyomys fossil remains were also recovered in Ensenadan sediments (early–middle Pleistocene—1.2 to 0.8 million years ago) northeast of Mar del Plata and south of Necochea, costal region of Buenos Aires Province, Argentina ( Vucetich et al. 1997), and in Pleistocene sediments from caves in Serra da Bodoquena, Mato Grosso do Sul State, Brazil ( Salles et al. 2006). A fragment identified as “echimyid aff. Clyomys ” was described for the late Miocene (late Huayquerian Age—from 6.02 to 5.3 million years ago) of La Pampa Province, central Argentina ( Montalvo et al. 1998). Clyomys fossil remains from Gerivaldino and Sangão Holocene sites, in the valleys of Taquari and Caí rivers, Rio Grande do Sul State, Brazil, have been described as Clyomys riograndensis by Hadler et al. (2008).

FORM AND FUNCTION

Clyomys laticeps is a semifossorial rodent living in excavated burrows ( Bishop 1974; Bezerra and Oliveira 2010). Its short extremities (tail and limbs) with long, powerful claws ( Bishop 1974) and hypertrophied tympanic bullae ( Thomas 1916) suggest special adaptations for fossorial life.

Clyomys has robust incisors and unilateral hypsodont cheekteeth with 3 roots, with the line of occlusal surfaces of the maxillary teeth nearly on a plane parallel to the palate, similar to Euryzygomatomys ( Carvalho 1999; Carvalho and Salles 2004). Upper molar toothrow with teeth of almost equal size, with M1 sometimes larger and M3 smaller or of same size. Upper molariform teeth with 1 internal and 2 external counterfolds, lower molariform teeth with 2 internal and 1 external counterfolds ( Bezerra 2002; Bezerra and Oliveira 2010).

Dental formula for C. laticeps is 1/1 i, 0/0 c, 1/1 p, 3/ 3 m, total 20. Dental morphology of C. laticeps was described by Carvalho (1999). Upper molariform teeth show a single, large lingual root and 2 almost inconspicuous labial roots. The surface of both upper and lower premolars and molars is semicircular. M3 of upper toothrow is reduced in size, with dP4 and M1 only slightly smaller than M2; with enamel wear, M1 becomes the largest tooth in tooth row ( Fig. 2 ). Maxillary cheekteeth show 3 transversal lophs: the anteroloph, metaloph, and posteroloph. Less worn teeth may exhibit a small protoloph restricted to labial margin. The metaloph is oriented posterolabially from the mure, narrowing and closing the metaflexus; mesoflexus becoming more persistent with tooth wear. The hypoflexus is anterolabially oriented. Worn dP4–M2 teeth show 2 round labial fossettes derived from metaflexus and mesoflexus and a round lingual fossette derived from the hypoflexus ( Bezerra 2002; Bezerra and Oliveira 2010). Mandibular molars show 3 distinct transverse lophs: the anterolophid, hypolophid, and posterolophid. Unworn teeth may show another lophid continuous to the lingual end of the anterolophid. The hypolophid is always in contact with the hypodoconid and ectolophid, and posterolingually oriented as the hypoflexid. The mesoflexid and metaflexid open lingually when unworn. The lower M1 may show a round labial fossette derived from the hypoflexid with increasing wear.

Molar topography allowed the identification of 8 relative age classes based on upper molar eruption and enamel wear, all with functional dP4 and M1 ( Bezerra 2002; Bezerra and Oliveira 2010): (1) M3 still absent and M 2 in the alveolous; (2) M3 absent and M2 erupting; (3) M3 absent and M2 fully erupted; (4) M3 emerging from alveolus; (5) M3 functional, showing light wear; (6) metaflexus on dP4, M1, M2, or a combination of them reduced to a metafossette; (7) mesoflexus on dP4, M1, M2, or a combination of them reduced to a mesofossette; and (8) hypoflexus reduced to hypofossettes.

Major differences in skull morphology among populations are due to multivariate shape, grouping populations into 2 geographic groups along an east–west geographic axis (Bezerra and Oliveira 2010). The relatively larger tympanic bullae groups populations from the states of Goiás, Mato Grosso, and Mato Grosso do Sul, Brazil, whereas populations from Distrito Federal and State of São Paulo, Brazil, show relatively larger and more robust skulls and cranial characters like cranial breadth, palatal length, and the length of lower molar row mostly contributing to group differences (Bezerra and Oliveira 2010).

The phallus of C. laticeps (described and illustrated in Bezerra 2002; Bezerra 2013) is subcylindrical, long, and straight. Some specimens show a slight median constriction on the sides or an extension in the region of the intromittent sac. Longitudinal grooves are present on sides of the phallus, with simple, small spines extending to the inside of the intromittent sac uniformly covering the epidermis. The dorsal side of the glans is longer than the ventral side and distally convergent on the apical mount, the lappet of the glans extends slightly from the crater. The baculum is simple, long, and narrow; a lateral view shows that the ventral surface is slightly concave at its proximal end ( Fig. 4 ).

ONTOGENY AND REPRODUCTION

Births may be seasonal, with usually 1 or 2 young per litter. A pregnant female was captured at Itirapina, São Paulo State, Brazil, at end of the dry period (usually from May to October in this region— Vieira 1997); weaning and growth was completed during wet season ( Vieira 1997). Three pregnant females were captured in Serra do Roncador, Mato Grosso State, Brazil, in June, September (dry season), and December (wet season), all with a single embryo ( Bishop 1974). Juveniles were taken in December (n = 2) and April (n = 1; Bishop 1974).

Figures

Fig. 1.—An adult Clyomys laticeps (sex unknown) from Emas National Park, Goiás State, Brazil. Used with permission of the photographer Paula H. Valdujo.

Fig. 2.—Dorsal, ventral, and lateral views of skull and lateral view of mandible of an adult Clyomys laticeps (MN 63945, deposited in the Museu Nacional, Universidade Federal do Rio de Janeiro) from Corumbá, Mato Grosso do Sul State, Brazil. Condylobasal length is 43.65mm. Photographed by João A. Oliveira.

Fig. 3.—Geographic distribution of Clyomys laticeps. Map redrawn from Bezerra and Oliveira (2010) with modifications.

Fig. 4.—Baculum anatomy of Clyomys laticeps (MN 63871, deposited in the Museu Nacional, Universidade Federal do Rio de Janeiro) in views (from left to right) ventral, right lateral, and dorsal. Bar = 1mm.