A Review of the Pattonomys / Toromys Clade (Rodentia: Echimyidae), with Descriptions of a New Toromys Species and a New Genus Author Emmons, Louise H. Author Fabre, Pierre-henri text American Museum Novitates 2018 2018-03-09 2018 3894 1 52 http://www.bioone.org/doi/10.1206/3894.1 journal article 10.1206/3894.1 0003-0082 5369712 Leiuromys , new genus TYPE SPECIES: Echimys occasius Thomas, 1921: 450 . CONTENTS: Only the type species. ETYMOLOGY: From the Greek leios (“smooth, bald”) and uros (“tail”), thus, “bald-tailed mouse,” in reference to the slick, hairless appearance of the tail, which is more naked than that of any other arboreal echimyine except lowland species of Dactylomys . DIAGNOSIS: Small, arboreally adapted brown rats, heavily spined dorsally with abundant wide, sharp, spines on midback from neck to rump, spines intermixed with fine wavy rust-red underhairs ( fig. 3 ; tables 3–6 ). Tail hairs short, fine, and inconspicuous, so that the tail looks bare and even shiny. Auditory tympanic bullae small, flattened in lateral aspect. Inferior jugal process reduced to nearly absent, but jugal fossa deep and sharply pointed anteriorly. Masticatory and buccinator foramina joined in a single aperture. Incisors bone white; upper incisor root does not extend to within the maxillary base of the zygoma. Lower premolars tetralophodont. Third upper molars trilophodont. The hypoflexids on m1–m3 fall nearly opposite the middle of the mesolophids, such that the teeth viewed from the lingual side are nearly symmetrical, rounded M-shapes. Upper lingual and lower labial hypoflexi short and wide, about a quarter of the width of tooth, but labial meso- and metaflexi long, such that when worn to a mure in M1 and M2, the mure is on the far lingual edge of the tooth. All mandibular cheekteeth have curved posterior borders. TABLE 6. Cranial measurements (mm) of Leiuromys , Pattonomys , and Toromys . Tabulated statistics include the sample mean and (in parentheses) the observed range and the sample size.

L. occasius	P. carrikeri	P. flavidus P. punctatus		P. semivil- losus	T. grandis	T. rhipidurus	T. sp. nov.
Skull greatest length	49.39 (47.9– 50.8, 5)	53.2 (50.6– 58.3, 23)	-	56.9 (55.4– 58.9, 8)	50.9 (50.6– 51.3, 2)	68.3 (64.6– 73.1, 35)	56.53 (52– 59.1, 15)	52.4 (51.6– 54.2, 7)
Zygomatic breadth	23.3 (22.0– 25.2, 5)	24.3 (20.9– 26.2, 22)	26.1	27.1 (25.7– 28.7, 8)	23.9 (23.8– 24.1, 2)	31.2 (25.4– 32.7, 34)	27.4 (25.7– 29.2 15)	23.7 (22.8– 24.5, 7)
Palatal length A	18.3 (16.9– 19.3, 5)	21.3 (19.3– 23.4, 22)	22.1	24.1 (23.2– 24.8, 8)	19.8 (19.5– 20.2, 2)	29.2 (26.6– 30.9, 35)	22.6 (20.5– 24.9, 16)	20.6 (19.0– 21.3, 7)
Palatal length B	8.4 (6.9–9.2, 5)	10.2 (8.8– 11.4, 22)	10.6	11.8 (10.7– 9.9 (9.5–10.3, 12.8, 8) 2)		13.5 (12.4– 14.7, 35)	11.5 (10.2– 12.4, 16)	10.0 (9.2– 10.7, 7)
Mastoid breadth 19.2 (18.2– 20.1, 5)		20.6 (19.3– 22.1, 22)	20.4	21.9 (21.0– 23.0, 8)	20.3 (20.2– 20.4, 2)	25.7 (20.2– 27.4, 35)	22.14 (20.8– 23.5, 14)	20.2 (19.2– 21.7, 7)
Rostral breadth	7.2 (6.2–7.9, 5)	7.9 (7.2–8.5, 22)	8.7	9.2 (8.7–10.1, 7.7 (7.7–7.7, 8) 1)		11.0 (9.9– 11.6, 34)	8.7 (7.8–9.2, 16)	7.7 (7.2–8.0, 7)
Basilar length of Hensel	37.3 (35.6– 39.0, 4)	40.5 (37.8– 43.8, 22)	—	44.3 (43.0– 45.4, 8)	42.4 (39.0– 45.8, 2)	53.9 (50.3– 56.8, 33)	43.15 (38.– 47, 13)	39.6 (38.7– 40.1, 5)
Cranial depth	15.2 (14.7– 15.6, 4)	16.2 (15.0– 18.4, 22)	17	17.0 (15.3– 19.5, 7)	17.0 (17.0– 17.0, 1)	18.4 (17.2– 19.7, 32)	16.69 (15.6– 17.5, 14)	15.6 (14.8– 16.0, 7)
Rostral depth	10.0 (8.4– 10.7, 5)	11.1 (10.1– 11.8, 22)	12	12.4 (11.9– 13.0, 8)	11.0 (11.0– 11.1, 2)	15.3 (13.5– 16.6, 35)	12.7 (11.4– 13.9, 16)	11.2 (10.3– 11.7, 7)
Maxillary 9.7 (7.3–10.8, toothrow 5)		11.4 (10.7– 12.5, 22)	12.7	12.5 (11.8– 13.4, 5)	11.6 (11.4– 11.8, 2)	15.7 (14.4– 16.9, 35)	13.2 (12.2– 14.2, 16)	11.1 (10.1– 11.9, 7)
Nasal length	15.1 (13.2– 16.9, 5)	17.1 (14.7– 19.5, 22)	16.9	17.2 (16.2– 19.1, 8)	16.5 (16.4– 16.7, 2)	22.5 (19.6– 24.8, 35)	17.61 (14.7– 19.3, 15)	17.1 (16.2– 18.9, 6)
Least interor- bital constric- tion	11.4 (10.3– 12.9, 5)	13.1 (11.9– 13.7, 21)	15.3	14.7 (12.5– 16.4, 8)	13.3 (12.7– 13.9, 2)	18.4 (16.5– 20.4, 34)	15.2 (13.6– 17, 16)	13.5 (12.4– 14.6, 6)
Rostral length	16.4 (14.7– 17.6, 5)	19.6 (17.7– 21.9, 22)	19.8	20.4 (19.7– 21.6,, 8)	18.1 (17.6– 18.6, 2)	26.1 (21.0– 28.6, 35)	20.05 (17– 21.5, 15)	18.0 (16.9– 19.7, 6)
Maxillary breadth	6.5 (6.1–7.2, 4, 5)	7.0 (5.6–8.0, 22)	7.3	7.6 (7.0–8.1, 7)	7.2 (7.2–7.2, 1)	10.2 (8.8– 19.4, 35)	8.567 (7.5– 9.3, 15)	7.0 (6.2–7.5, 6)
Diastema length	10.4 (9.6– 11.4, 5)	11.7 (10.8– 12.8, 22)	12	12.9 (12.4– 13.9, 8)	10.9 (10.4– 11.3, 2)	16.3 (14.5– 17.6, 35)	11.8 (10.5– 12.9, 16)	11.0 (10.6– 11.6, 7
Bullar Length 9.7 (8.7–10.5, 5)		12.1 (11.2– 13.0, 22)	10.6	12.7 (11.9– 13.5, 8)	12.0 (12.0– 12.0, 2)	12.7 (11.2– 13.9, 35)	10.5 (9–12.2 16, 16)	10.1 (9.4– 10.7, 7)
Postpalatal Length	23.2 (21.9 23.7, 5)	23.4 (18.2– 27.8, 21)	—	24.4 (23.0– 26.5, 8)	22.6 (22.2– 22.9, 2)	27.8 (23.6– 30.7, 35)	24.71 (24– 25.8, 13)	23.6 (23.3– 23.6, 5)
Molar width	1.4 (0.9–1.8, 5)	2.1 (1.6–2.7, 22)	1.9	2.2 (1.6–3.0, 8)	2.1 (1.9–2.2, 2)	2.7 (2.0–3.8, 35)	—	1.8 (1.6–2.2, 4)

FIG. 4. Pelage of dorsum at rump. A, Leiuromys occasius . FMNH 84529, high density of sharply pointed spines and fine, wavy red underhairs; B, Pattonomys semivillosus USNM 280204, dense, more tapered, white-tipped spines, abundant pale bristles, straight ochraceous underhairs; C, Makalata cf. didelphoides USNM 549593, agouti pelage, sparser narrowly buff-tipped spines, tapered hairlike spine tips; D, Toromys grandis AMNH 94036, thick bristles, no spines; E, T. rhipidurus AMNH 73273, fine-banded agouti bristles; F, T. sp. nov., narrow aristiforms and a few narrow spines with hairlike tips, abundant thin, agouti bristles. The resemblance between Toromys congeners is evident. Spine tips are more sharply tapered in A than in B. DESCRIPTION: Upperparts with abundant, wide, strong spines on midback from neck to rump, spines intermixed with fine, wavy, rust-red underhairs that show through aristiforms, giving back a rusty hue ( fig. 3 ). Spine tips sharp, narrowing abruptly, with short microscopic hairlike processes at tips ( fig. 4A ). Spines tipped with pale buff sparsely speckle the sides of the hindquarters and tail base. Dorsal spines pale gray-brown at base, with a dusky band, a narrow, subterminal pale whitish or buffy band, and dusky, buff, or black-brown tips ( fig. 4A ). Upperparts uniform light ochraceous brown, between Cinnamon and Sayal Brown ( Smithe, 1975 ), lined with dusky, or blackish Dusky Brown (the holotype and AMNH 71897). The spines on the middorsum from neck to rump are the darkest and nearly unbanded ( figs. 3 , 4A ). Head and muzzle brown above, without any red color. Cheeks below the ears, forelimbs, and hindlimbs tinged grayish. Feet pale beige to rusty above; silvery ungual tufts reach to the ends of the claws. Ventral pelage of soft aristiforms, colored strong to pale buff, grading gradually from the sides ( fig. 3 ); inner thighs slightly darker pinkish buff; the chest and lower abdomen and inguinal regions can have self-white patches, including the tail base, or are crossed by a white band between the elbows. Vibrissae black, moderately robust and the longest reaches to the shoulder. Ears short, pigmented, and nearly naked, lined with a few wispy, dusky hairs. Tail slightly longer than head and body length, brown pigmented, with a naked and somewhat shiny appearance. Dorsal hair ends abruptly close to the body at the tail base; distal tail hairs inconspicuous and closely adpressed. Scales on the tail base evenly hexagonal, wider than long, tapered at the lateral ends. Dorsally each scale has one robust, scalelike dark hair about two and a half scale rows long, and one shorter, fine, hair ( fig. 5B ). Ventrally, tail hairs somewhat longer (three scale rows), adpressed, and silvery. An adult female (FMNH 84259) has two used lateral pairs of mammae spaced about evenly between the limbs and 1.5 cm into the dorsal pelage field, and possibly an unused inguinal pair. As far as can be seen on dried specimens, the feet have small digital pads collared with rings of tubercles as in Toromys species ( fig. 6A ), and with numerous plantar tubercles on the bottom and sides of the feet around the pads. Cranium lightly built for the subfamily, inferior jugal process much reduced or essentially absent ( figs. 7D , 8 , 9D , 10D ). Mastoid processes are short, reach to the middle of the auditory meatus, and are adpressed to the cranium; the space above the auditory meatus is nearly as wide as the meatus. Parietal ridges not raised posterior to the postglenoid fossa. Masticator and buccinator foramina joined in a narrow, horizontal slit or a large oval foramen (MCZ 37964) ( fig. 8B ). Posterior opening of the alisphenoid canal thin walled and opens in a tube beneath the strut (pterygoid plate) between the pterygoid canal and the foramen ovale ( fig. 8A ); it sometimes lacks the dorsal wall and appears absent. There are no sphenopalatine vacuities. Auditory bullae not inflated, nearly flat in lateral profile, and markedly smaller than those of most other echimyines ( figs. 7D , 8B ); meatus rim pointed outward. Postglenoid foramen slitlike and enclosed below by a crest of petrosal. The ridges and grooves posterior to the end of the incisive foramina terminate anterior to the premolars, with shallow or absent extensions onto the palate between the toothrows ( fig. 8A, B ). Viewed dorsally, the interparietal is an evenwidth, narrow strip bowed smoothly posteriorly at the parietal suture ( fig. 9D ). Coronoid process of the mandible slender and recurved, above a shallow sigmoid notch ( fig. 7D ). Masseteric crest strongly developed and curved upward anteriorly for about half the width of the mandible; spine of the condyloid ridge on the interior of the mandible does not extend much more than halfway up the condyloid process, except on a specimen from southern Peru . Maxillary toothrows short, 7.3–10.75 mm ( table 6 ); incisors bone white; roots of the upper incisors lie outside the maxillary base of the zygoma. Lower premolar quadralophodont, comprised of a curved anteroloph and a straight metolophid that join with wear into a D-shape around a central fossettid, which joins with wear by a central mure to the lingually opening V-shaped posterior lophid pair ( fig. 11B ). Hypoflexids on m1 to m3 fall nearly opposite the middle of the mesolophids, such that the teeth viewed from the lingual side are nearly symmetrical, rounded M-shapes. Upper lingual and lower labial reentrant folds (hypoflexi) short and wide, about 1/4 of the width of tooth, when worn they form subcircular fossettes; labial reentrant folds are long, and of equal length (meso- and metaflexi), such that when worn to a mure in M1 and M2, the mure is on the far lingual edge of the tooth ( fig. 11B ). Mandibular cheekteeth all with curved posterior borders. M3 trilophodont in all specimens examined, with the third loph much reduced ( fig. 11C ). Worn lower molars nearly circular, somewhat resembling those of Isothrix ( fig. 11C ). FIG. 5. Scales and hairs on dorsal tail base. A, Pattonomys carrikeri USNM 496483, irregular scales nearly square or slightly hexagonal, hairs unicolored, long, and curled outward; B, Leiuromys occasius FMNH 84259, short, wide hexagonal scales in spiral rows, short, adpressed, scalelike hairs in pairs; C, Toromys rhipidurus AMNH 276710, scales rounded posteriorly, about as long as wide, hairs robust, unicolor, black or rusty; D, Makalata macrura USNM 496480, short, rectangular scales in even rows, fine, salient hairs that are often banded dark at base, pale at tips. White scale bars 5 mm, fluid-fixed specimens except B. FIG. 6. Variation among genera in plantar surfaces of hindfeet, fluid-preserved specimens. A, Toromys rhipidurus AMNH 276710; B, Pattonomys carrikeri USNM 496501; C, Phyllomys pattoni , UFES 121; D, Makalata cf. didelphoides USNM 581981 (Bolivia); E, M. cf. macrura USNM 496480 (Venezuela); F, Echimys chrysurus , USNM 549839 (Rio Xingu). Note small digital pads, especially D3, and collars of small tubercles around pads in (A–C); large digital pads and no collars of tubercles in (D–F); merged D1 and thenar pad in (E–F), leaving three separated digital pads; and differences in digital pad shapes (see text). Abbreviations: D, digital pads; Th, thenar pad; Hy, hypothenar pad. Arrow in A indicates supernumerary separated pad of Pattonomys spp. Figures not to scale. Photo panel C, Yuri Leite. FIG. 7. Crania and mandibles, lateral view. A, Toromys grandis AMNH 93601; B, T. rhipidurus BMNH 28.7.21.89 (holotype); C, T. sp. nov., FMNH 55483 (holotype), D, Leiuromys occasius . AMNH 71897; E, Pattonomys punctatus BMNH 98.12.1.18 (holotype); F, P. flavidus USNM 63218 (holotype); G, P. carrikeri AMNH 130790; H, P. semivillosus USNM 280205. Black arrow in F indicates the deep mandible of P. flavidus relative to its congeners. FIG. 8. Leiuromys occasius basicrania. A, internal position of posterior alisphenoid canal (arrows), MCZ 37964 (Ecuador, left M3 lacking); B, buccinator and masticatory foramina joined in a slit (b+M) FMNH 84427 (Peru). Note absence of inferior jugal process, shallow or absent grooves and ridge on anterior palate between premolars, and small tympanic bulla in B. FIG. 9. Crania, dorsal view. A, Toromys grandis AMNH 93601; B, T. rhipidurus BMNH 28.7.21.89 (holotype); C, T. sp. nov., FMNH 55483 (holotype), D, Leiuromys occasius . AMNH 71897; E, Pattonomys punctatus BMNH 98.12.1.18 (holotype); F, P. flavidus USNM 63218 (holotype); G, P. carrikeri AMNH 130790; H, P. semivillosus USNM 280205. Black arrow in A indicates recurved parietal-interparietal suture, white arrow the expanded squamosal shelf. FIG. 10. Crania, palatal view. A, Toromys grandis AMNH 93601; B, T. rhipidurus BMNH 28.7.21.89 (holotype); C, T. sp. nov., FMNH 55483 (holotype), D, Leiuromys occasius . AMNH 71897; E, Pattonomys punctatus BMNH 98.12.1.18 (holotype); F, P. flavidus USNM 63218 (holotype); G, P. carrikeri AMNH 130790; H, P. semivillosus USNM 280205. FIG. 11. Leiuromys occasius upper (top row) and lower (bottom row) occlusal patterns of cheek teeth at three states of toothwear. A, FMNH 84427; B, FMNH 84259; C, MCZ 37964, reversed. Note the trilophodont M3, the rounded posterior edges of the lower molars, the position of the mure of M1–2 on the lingual edges of the teeth, the quadralophodont lower premolar, and the M-shaped lower molars (viewed lingually). FIG. 12. Occlusal patterns of upper (top row) and lower (bottom row) toothrows of Toromys and Pattonomys species , not to scale. A, Toromys sp. nov. FMNH 55483 holotype; B, T. sp. nov. LSUMZ 8904, an old individual; C, Toromys grandis AMNH 93604; D, Toromys rhipidurus AMNH 98667; E, Pattonomys carrikeri AMNH 31530; F, P. semivillosus USNM 280205; G, P. punctatus BMNH 9812118 (holotype). In Toromys maxillary teeth (A–D) note laminar appearance of narrow, nearly parallel molar flexi, lophs of nearly uniform width, and mures lingually (left) of center of teeth. In Pattonomys (E–G) note short, offset flexi, short, wide protoloph (arrow) especially pronounced on M2, mures about in midtooth; unequal loph sizes give irregular appearance. On mandibular teeth, note the straight (flat) posterior molar edges; the square (flat) lingual edge of central lophid (entoconid) in Toromys (A–D, also compare with fig. 17). FIG. 13. Head colors of specimens. A, Toromys , sp. nov. LSUMZ 8904; B, Toromys rhipidurus FMNH 87248; C, Makalata cf. macrura LSUMZ 14408. Specimens in panels A and C were collected at Yarinacocha (type locality of Toromys , sp. nov. ). The tip of the muzzle is variably buff to rusty in Toromys sp. nov. (fig. 16), while Makalata from some distant populations are not as bright rusty as A. On Makalata , the rust color extends well behind the eye above and below. Also note the coarser, more robust vibrissae of both Toromys , the more developed fringe of salient wispy hair on rim of the Makalata ear (also typical of Pattonomys spp. ), and the less robust claws of T. sp. nov. compared to those of T. rhipidurus . COMPARISONS WITH OTHER GENERA: Leiuromys is most easily confused externally with the distantly related taxa Mesomys species and Phyllomys pattoni . Species of Mesomys all have conspicuously hairy tails with brown, outward-curling hairs and a slight-to-prominent pencillike tapering at tip ( Patton et al., 2000 ). In Mesomys the buff or whitish ventral pelage field is sharply demarcated from the spiny dorsal pelage. The molar occlusal pattern has flexi/flexids compressed into narrow parallel lines that do not open on sides of the teeth. Phyllomys pattoni have rusty-tipped spines and rusty sides, and an occlusal pattern of separate laminae ( Emmons et al., 2002 ). Pattonomys species are larger, with grizzled gray heads, sides, and feet, white lower cheeks and throat, a fuzzy tail, and a distinct molar occlusal pattern, including straight posterior edges of the lower cheekteeth ( fig. 12E–G ). The spines of Pattonomys species taper more sharply at the tips ( fig. 4B ). Makalata species have tails slightly but distinctly hairy, with banded tail hairs, and short, rectangular tail scales in even rings ( fig. 5D ); a uniformly ochraceous- or reddish-agouti pelage of dusky and yellowish; multibanded, spinous aristiform hairs with short, pale, hairlike tips that are not as wide or sharp as in Leiuromys ( fig. 4C ); rostra that are reddish anteriorly to above and behind the eyes ( fig. 13C ), and rusty pelage around the tail base. Phyllomys species and Echimys chrysurus have one inguinal and three lateral pairs of mammae, whereas the other genera have two lateral pairs, and if present, inguinal mammae seem obsolete (unused in parous females). All other Echimyini usually have a quadralophodont M3, but P. semivillosus can lack the fourth loph. In Makalata the lower premolars are pentalophodont (illustrated in Emmons, 2005 ). The lower premolar hypoconid is a rounded point in genera of the Echimys clade, while it is flat in Pattonomys and Toromys ; in the latter often slightly indented (Iack-Ximenez et al., 2005: fig. 11 ).