Thomasomys burneoi, Lee Jr. & Tinoco & Brito, 2022

Lee Jr., Thomas E., Tinoco, Nicolas & Brito, Jorge, 2022, A new species of Andean mouse of the genus Thomasomys (Cricetidae, Sigmodontinae) from the eastern Andes of Ecuador, Vertebrate Zoology 72, pp. 219-233 : 219

Thomasomys burneoi sp. nov.

Thomasomys praetor : Lee et al. 2011:9; part no Thomasomys praetor (Thomas, 1900) Thomasomys princeps : Lee et al. 2015:10; part no Thomasomys princeps (Thomas, 1895)

Thomasomys aureus : Brito et al. 2019:9; par not Thomasomys aureus Tomes, 1860

Holotype.

MECN 5662 (field number JBM [Jorge Brito Molina] 1812), an adult female captured on August 18, 2017, by Jorge Brito, Jenny Curay, Rocío Vargas and Erika Beltrán, preserved as dry skin, skull, postcranial skeleton, and muscle and liver biopsies in 95% ethanol.

Paratopotype.

MECN 5666 (JBM 1822), an adult female collected next to the holotype, on August 18, 2017, by J. Brito, J. Curay, R. Vargas and E. Beltrán.

Paratype.

ACUNHC 1548 (field number TEL 2394); 1560 (TEL 2378); QCAZ 11937, adult male captured on July 20, 2010, by Thomas Lee, Carlos Boada, and Amy Scott; QCAZ 11938 (TEL 2295), and adult male captured on July 29, 2010, by TEL at Provincia de Chimborazo, canton Guamote, Parque Nacional Sangay, Lagunas de Atillo - 2.17714° S, - 78.5075° W, elevation 3,400 m. MECN 5259 (JBM 1409), an adult female collected on October 06, 2016, by J. Brito, R. Vargas, G. Encarnación and J. Velastegui at canton Chambo, Parque Nacional Sangay, Cubillines - 1.760633° S, - 78.477092° W, elevation 3,900 m.

Type locality.

Ecuador, Provincia de Morona Santiago, cantón Morona, parroquia Zúñac, Parque Nacional Sangay (Sangay National Park), Laguna Negra - 2.179672° S, - 78.502919° W (coordinates taken by GPS at the site of collection), elevation 3,553 m).

Diagnosis.

A species of Thomasomys from the Thomasomys aureus group described by the following character combinations: large size (combined head and body length 167-184 mm); postauricular patch present; wide metatarsal patch; hind foot large> 40 mm; M1 with broad and deep anteroflexus; additional anterior edge on procingulum of M1 present; M3 with metaflexus large and mesoloph distinctive; m1 with small and distinctive anterolophid; m1 with ectolophid; m2-m3 with hypoflexid wide; m3 size equals m2.

Measurements of the holotype (in mm).

Head and body length = 172, Tail length = 232, Hind foot length = 43, Ear length = 27, Body mass = 105, Condylo-incisive length = 38.28, Zygomatic breadth = 22.04, Least interorbital breadth = 5.16, Length of rostrum = 13.14, Length of nasals = 14.53, Breadth of rostrum = 7.91, Orbital fossa length = 13.87, Length of upper diastema = 10.87, Crown length of maxillary toothrow = 7.8, Length of incisive foramina = 8.95, Breadth of incisive foramina = 3.13, Breadth of first maxillary molar = 2.84, Length of palatal bridge = 6.96, Breadth of bony palate = 3.34, Bullar breadth = 5.43, Depth of upper incisor = 2.05, Breadth of zygomatic plate = 3.98, Braincase breadth = 17.26, Length of mandible = 22.7, Crown length of mandibular toothrow = 8.2, Length of lower diastema = 5.17. External and craniodental of additional specimens are presented in Table 3 .

Morphological description of the holotype and variation.

Large body size (head and body length combined with a range between 128 and 184 mm). Cinnamon-brown dorsal fur (Fig. 4 , 5 ), with a faint dark dorsal band; long hairs (medium length on the back = 18-20 mm) dark gray at the base. Light tan dark ventral coat, hairs with (medium length = 10-12 mm) dark gray base, and pale yellowish tips (Fig. 5 ). Black periocular ring. Postauricular patch present. Mystacial vibrissae long, thick at the base and remain thin towards the tip, exceeding the ear when they are tilted back; 1 superciliary vibrissae present and 1 genal vibrissae present. Ears (between 24-28 mm from notch to margin) externally covered by short orangebrown hairs, pale pink inner surface, dark pale brown margin. Large and wide foot (Fig. 6 ) with 5 digits ending in thin semi-curved claws. Long white ungueal tufts that slightly exceed the claws. Wide and brown metatarsal patch, that extends to the base of the phalanges. Plantar surface with 6 pads, including 4 interdigitals of similar size to each other (Fig. 6 ), slightly larger than hypothenar and with very small space between them. Digit I exceeds the base of digit II; digit II and III are the same size and slightly shorter than digit IV; digit V (apparently opposable) reaches the beyond the middle of digit IV. Long tail (207-232 mm; ~127% of HB), ground cinnamon (color 270) and unicolor; square flow scales with three hairs each, which extend over 2.5 to 3 rows of scales in the dorsal basal sector; with 12-13 scales per cm on the shaft. Hirsute tail, even to the rear, hair increasing in length to the apex of the tail. Protuberant anus prominent. Females present six mammary pairs in pectoral, abdominal and inguinal position (sensu Pacheco 2003). The details of soft and genitalia anatomy are unknown.

The cranium is large for the genus (38.2-40.13 mm of CIL). The rostrum is long, somewhat acuminate and narrow, with the nasal bones exceeding the anterior face of the incisors; poorly developed gnathic process (Fig. 7 ). Posterior margin of the nasal bone slightly exceeds the plane of the lachrymal bone. Moderately deep zygomatic notch (Fig. 8 ). Small and rounded lacrimal bones. Narrow interorbital region with poorly developed supraorbital ridges, the alveolar maxillary processes well exposed in dorsal view. Supraorbital region with divergent posterior borders (sensu Steppan 1995). Frontoparietal suture V-shaped. Broad and rounded braincase, slightly flattened at the outer edges. Large and concave exoccipital. In the lateral view, small nasolacrimal fissures can be seen in the rostral region and internally, no further development in the ethmoturbinals is distinguishable. Developed and oblique lambdoidal crest. Zygomatic arches sturdy and robust with jugals spanning a short segment of each mid-arch but distinctly separating zygomatic processes of the maxillary and squamosal bones. Alisphenoid strut wide and robust. Carotid circulatory pattern type 2, derived (sensu Voss 1988); carotid canal large (Fig. 9 ), stapedial foramen and anterior alar fissure small. Postglenoid foramen narrower as the subsquamosal fenestra (Fig. 10 ); hamular process of squamosal thin, long, but without going beyond the edge on the mastoid capsule. Lightly square tegmen tympanic is superimposed over the suspensory process of the squamous. Lateral expressions of parietals present (Fig. 10 ); bullae small and inflated; pars flaccida of tympanic membrane present, large; orbicular apophysis of malleus well developed, the manubrium of malleus is blade like with a cup at the distal end. Paraoccipital process large. Hill foramen small; long and narrow incisive foramen with curved edges that subsequently exceed the plane defined by the anterior face of M1 (Fig. 7 ). Premaxillary capsule slightly widened in the middle and narrow at the ends, maxillary septum of incisive foramen robust and long. Short and narrow palate (sensu Hershkovitz 1962), with the narrow mesopterygoid fossa that enters between the molars reaching the hypoflexus of M3 or 50% of M3, without a medium process. Posterolateral palatal pit small and inconspicuous. Thin and inconspicuous sphenopalatine vacuities covered by the roof of the palate. The basisphenoid is wide, with a small ovale foramen and the middle lacerate foramen is narrow. Auditory bullae small and inflated with short and wide Eustachian tube. Petrosal little exposed (Fig. 9 ).

Dentary moderately short, robust, with long and wide coronoid process that exceeds the upper edge of the condylar process, (Fig. 9 ); deep sigmoid notch. Semilunar recess is symmetrical, whose lower edge is wide. Capsular projection of the root of the incisor small.

Opistodont incisors with orange front enamel; brachydont and pentalophodont molars (sensu Hershkovitz 1962). Maxillary molar rows parallel and hypsodont; coronal surfaces crested; main cusps slightly opposite and sloping backwards when viewed from side. The outline of M1 is rectangular with procingulum divided by anteromedian flexus deep into subequal anterolabial and anterolingual conules; additional anterior edge on procingulum; narrow anteroloph; narrow mesoloph (Fig. 11 ). M2 is square in outline; mesoloph and posteroloph showing the same condition as in M1. M3 rounded in outline with narrow anteroloph; deep paraflexus; metaflexus large; mesoloph distinctive. Lower molars with main cusps alternated and sloping forward when viewed from side. First lower molar (m1) with anteromedian flexid that divides the procingulum into subequal anterolabial and anterolingual conules; anterolophid distinctive; mesolophid narrow; ectolophid and ectostylid present (Fig. 11 ). Mesolophid of m2 short and narrow; ectolophid absent and ectostylid present; hypoflexid wide (Fig. 11 ); m3 equals m2 in size; ectostylid present; hypoflexid wide.

Tuberculum of first rib articulates with transverse processes of seventh cervical and first thoracic vertebrae; second and third thoracic vertebra with differentially elongated neural spine; thoracicolumbar vertebrae 19-20, the 16-17th with moderately developed anapophyses; sacrals 4; caudals 42, with complete hemal arches; 13 ribs present.

Comparisons.

Thomasomys burneoi sp. nov., apart from being large (Fig. 11 ; Table 2 ), differs from T. pardignasi Brito et al. (2021) (traits in parentheses) by dorsal uniform color (presenting a dim dark band on the back); back hairs of 18-20 mm (15.53); ventral hairs long, 10-12 mm (9.92 mm); long tail ~127% of HB (~152%); genal vibrissae 2 absent (genal vibrissa 2 absent). Craniodentally, qualitative differences between both species are conspicuous. M1 presents deep anteromedian flexus in T. burneoi (shallow); M1-M2 with narrow mesoloph (wide); M3 with distintive mesoloph (indistinct); m1 with ectolophid (present in m1 and m2); m1-m2 with ectostylid (lack ectostylid); m3 equals m2 (m3 is slightly shorter than m2).

Thomasomys burneoi sp. nov., differs from T. aureus (based on sensu stricto material, Brito et al. 2021) (traits in parentheses) by tail with 12-13 rows of scales per cm on the axis (16 scales); postauricular patch present (absent). Craniodentally, qualitative differences between both species are conspicuous. Additional anterior edge on procingulum of M1 present in T. burneoi (absent); M1 with narrow anteroloph (wide); M3 with distintive mesoloph (indistinct); m1 with distintive anterolophid (indistinct); m1 with ectolophid (absent); m3 equals m2 (m3 is longer than m2). Further comparisons among all the recognized species of Thomasomys from the Thomasomys aureus group present in Ecuador are provided in Table 2 .

Etymology.

Named for Santiago F. Burneo, of the Pontificia Universidad Católica del Ecuador, Quito, Ecuador in recognition of his teaching and support of mammalogists both in Ecuador and the United States of America. The specific epithet is a noun in the genitive case formed by the addition of an “i” to the stem of the name.

Distribution.

Known only from Sangay National Park, Chimborazo Province and Morona Santiago Province, Ecuador, 3,400-3,900 m in elevation (Fig. 12 ).

Natural history.

Thomasomys burneoi sp. nov., has been recorded in the Altoandino floor ( Albuja et al. 2012), in the montane evergreen forest plant formation in the southern Cordillera Oriental of the Andes ( Ministerio Del Ambiente Del Ecuador 2013). According to the capture data, it is associated with primary elfin forests and páramo (Fig. 13 ), where the trees are covered by mosses and epiphytes. The specimens were generally collected on thick trunks or branches. In October (dry season), a pregnant female with an embryo was discovered. Thomasomys burneoi was found in sympathy with other small mammals Akodon mollis , Caenolestes sangay , Cavia patzelti , Cryptotis montivagus , Microyzomys altissimus , M. minutus , T. baeops , T. cinnameus , T. hudsoni , T. paramorum and T. taczanowskii .

Figures

Figure 4. Thomasomys burneoi sp. nov. (MECN 5259, paratype), external appearance of an adult female alive in its natural habitat in the Cubillines, Sangay National Park, Ecuador.

Figure 5. Dry skin in dorsal, ventral, and lateral views of Thomasomys burneoi, sp. nov. (MECN 5662, holotype). Scale bar = 10 cm.

Figure 6. Morphology of the dorsal and plantar surface of the right hind foot of: A, C Thomasomys burneoi (MECN 5666, paratype) and Thomasomys pardignasi (MECN 5852, holotype) and B, D Acronyms: I-V = digits, 1 - 4 = pads, h = hypothenar pad, t = thenar pad. Scales = 10 mm.

Figure 7. Dorsal, ventral and lateral view of the cranium, lateral view of the jaw, occlusal view of the right upper and left lower toothrow of Thomasomys burneoi sp. nov. (MECN 5662, holotype) from Sangay National Park, Ecuador. Scale = 10 mm.

Figure 8. Composed figure illustrating selected differences in the cranial anatomy of Thomasomys burneoi, sp. nov. (MECN 5662, holotype; left half cranium), T. pardignasi (MECN 5852, holotype; right half cranium A, C, and T. aureus sensu stricto (MEPN 6144; right half cranium B, D. Acronyms: if = incisive foramen, nl = nasolacrimal capsule, m = molars, mf = mesopterygoid fossa, zn = zygomatic notches.

Figure 9. Detail of the bulla in ventral view. A Thomasomys burneoi, sp. nov. (MECN 5662, holotype), B T. pardignasi (MECN 5852, holotype), and C T. aureus sensu stricto (MEPN 6144). Acronyms: ab = auditory bulla, bet = eustachian tube, cc = carotid canal, me = mastoid exposure, pt = petrosal, sts = stapedial process of bulla.

Figure 10. Lateral views of the skulls of: A Thomasomys burneoi sp. nov. (MECN 5662, holotype), B Thomasomys pardignasi (MECN 5852, holotype) and C T. aureus sensu stricto (MEPN 6144).

Figure 11. Occlusal view of the right upper (A-C) and right lower (D-F) tooth row of: A, D Thomasomys burneoi sp. nov. (MECN 5662, holotype), B, E Thomasomys pardignasi (MECN 5852, holotype) and C, F Thomasomys aureus (MEPN 6144). Acronyms: anf = anteroflexus, al = anteroloph / id, am = anterior mure, ec = ectostylid, hy = hypoflexid, mf = metaflexus, ml = mesoloph / id, ecl = ectolophid. Scale = 2.5 mm.

Figure 12. Geographical distribution of Thomasomys burneoi sp. nov., and other species of the Thomasomys aureus group in Ecuador. Localities are listed in Appendix 1.

Figure 13. The habitat of a high Andean forest in Cubillines, Sangay National Park where specimens of Thomasomys burneoi sp. nov. were found.