Olallamys albicaudus ( Günther, 1879 )

Ramírez-Chaves, Héctor E., Velazco, Paúl M., Liévano Latorre, Luisa F. & Torres-Martínez, María M., 2017, Olallamys albicaudus (Rodentia: Echimyidae), Mammalian Species 49 (943), pp. 18-22 : 18-21

Olallamys albicaudus ( Günther, 1879)

White-tailed Olalla Rat

Thrinacodus albicauda Günther, 1879:145 . Type locality “the vicinity of Medellin, Columbian Confederation.”

Thrinacodus apolinari Allen, 1914:387 . Type locality “Tomeque [= Fómeque] (altitude 6500 feet), Bogota district, Colombia.”

Thrinacodus albicauda albicauda: Cabrera, 1961:545 . Name combination.

Thrinacodus albicauda apolinari: Cabrera, 1961:545 . Name combination.

Olallamys albicauda: Woods, 1993:790 . First use of current name combination, but incorrect gender of specific epithet.

Olallamys (= Thrinacodus) albicauda: Pérez-Torres and Correa, 1997:44 . Name combination.

Olallamys albicaudus: Emmons, Patton and Leite, 2015:887 . Emendation of the specific epithet albicauda .

CONTEXT AND CONTENT. Context as for genus. Two subspecies have been described ( Cabrera 1961) based on morphological characters that are sometimes variable, like tail color, tooth size, and skull size ( Emmons 2015). To date a lack of a suitable number of specimens has prevented a rigorous analysis of geographic variation and 2 subspecies are currently recognized ( Emmons 2015):

O. a. albicaudus ( Günther, 1879:145) . See above.

O. a. apolinari ( Allen, 1914:387) . See above.

NOMENCLATURAL NOTES. The generic name Olallamys was created to replace Thrinacodus Günther, 1879 , the original generic name, which is preoccupied by Thrinacodus St. John and Worthen, 1875 (a fossil shark—Emmons 1988). English common names are white-tailed Olalla rat, and Colombian soft-furred spiny rat; vernacular names used in South America include rata de los chusques, and conocono de los chuscales (Rodríguez-Mahecha et al. 1995; Pérez-Torres and Correa 1997; Delgado-V. and Zurc 2005; Woods and Kilpatrick 2005).

The genus name, Olallamys , is a combination of “Ollala” from the last name of the professional collector Carlos Olalla and his sons (Alfonso, Manuel, Ramón, and Rosalino), and mys (Greek), meaning mouse; the specific epithet, albicaudus , is derived from albi [albus] (Latin), meaning white, and caudus (Latin), meaning tail.

DIAGNOSIS

Olallamys differs from the other 2 representatives ( Dactylomys and Kannabateomys ) of the subfamily Dactylomyinae by a combination of characters. In Ollallamys, the toes present a normal shape (middle digits elongated in Dactylomys and Kannabateomys ), except for the 2nd pair (d2) on the hind foot which present an oblique asymmetrical nail (Thomas 1916; Emmons et al. 2015). The tail is sparsely haired and intermediate in the degree of hairiness between the tails observed in the Bolivian bamboo rat ( Dactylomys boliviensis ) and Amazon bamboo rat ( D. dactylinus —less haired), and Montane bamboo rat ( D. peruanus ) and Atlantic bamboo rat ( Kannabateomys amblyonyx —more haired—Thomas 1916; Emmons et al. 2015). Cranially, the palate is narrow in Olallamys and Dactylomys (wider in Kannabateomys ) and the zygomatic arches are widest posteriorly in Olallamys and Dactylomys (widest anteriorly in Kannabateomys ). The hypoflexids and metaflexids are united to form an anterior V-shaped loph and a single posterior loph in Olallamys and Dactylomys ; these remain separate in Kannabateomys ( Emmons et al. 2015) .

Olallamys albicaudus can be distinguished from the greedy Olalla rat O. edax by its smaller size (zygomatic breadth <27 mm; maxillary toothrow <15 mm—Emmons et al. 2015). It is possible that O. albicaudus and O. edax are conspecific; however, the reduced number of specimens available in museums limits proper analysis ( Emmons et al. 2015).

GENERAL CHARACTERS

Olallamys albicaudus ( Fig. 1 ) is a medium-sized rat with soft, dense, and long dorsal fur (about 25–30 mm in length). The dorsal fur is a bright reddish-brown ( Fig. 1 ), with the longest hairs being black towards the tips. Ventral fur is whitish ( Günther 1879; Allen 1914). Tail is long with the terminal onehalf white, with gray-tinged hairs towards the tip ( Allen 1914; Emmons et al. 2015).

The rostrum is short (> 2/3 of the total cranium length— Günther 1879). The interorbital border is straight ( Allen 1914). Overall, the skull ( Fig. 2 ) is narrow with the rostrum extending anteriorly approximately the same or less than the upper toothrow length ( Allen 1914).

The incisive foramina are short; however, they extend into the maxillaries ( Günther 1879). Molars are broad and almost in contact in the midline, interrupting the continuity of the bony palate ( Günther 1879). Cheek teeth are low (brachyodont), heavy and broad, with the hypoflexids and mesoflexids coalescing forming, with the 4 lophs, 2 independent V- or Y-shaped pair of lophs. Lower molars with 2 lingual and 1 labial flexids. The hypoflexids and metaflexids are united to form an anterior V-shaped loph and a single posterior loph ( Allen 1914; Emmons et al. 2015).

Mean external measurements (mm; with parenthetical ranges) of 2 females (Instituto de Investigaciones Biológicas Alexander von Humboldt [IAvH 1218] and Instituto de Ciencias Naturales, Universidad Nacional de Colombia [ICN 17047]), and one male (IAvH 3857) were: total length, 558 (535–580); length of tail, 327.3 (319–343); length of hind foot (without claws), 39.4 (38.4–41.0); length of hind foot (with claws), 42.6 (41.4–44.0); length of ear, 21 (20–22). Craniodental measurements (mm) of the same 2 female specimens (skull of male specimen missing) were: greatest length of skull, 51.7, –; condylobasal length, 48.3, –; zygomatic breadth, 22.0, 24.8; mastoid width, 19.4, –; least interorbital breadth, 11.7, 11.5; length of nasals, 17.0, 17.1; width of nasals at middle, 5.9, 5.1; length of upper toothrow, 14.1, 14.2; length of lower toothrow, 14.0, 14.6.

External measurements (mm) of the holotype of O. albicaudus albicaudus (Natural History Museum, London [BMNH 1878.8.31.10]), and the holotype of O. a. apolinari (American Museum of Natural History [AMNH 36245]), respectively, were: total length, –, 340; length of tail, 255, 260; length of hind foot, –, 40; length of ear, –, 13 ( Günther 1879; Allen 1914). Craniodental measurements (mm) of the holotype of O. a. apolinari were: greatest length of skull, 57.0; condylobasal length, 50.8; zygomatic breadth, 26.6; mastoid width, 20.3; least interorbital breadth, 11.5; length of nasals, 18.4; width of nasals at middle, 5.3; breadth of braincase, 19.8; length of upper toothrow, 14.3; length of lower toothrow, 14.5.

DISTRIBUTION

Olallamys albicaudus is known from localities in the Central Cordillera in the Department of Antioquia – Reserva San Sebastián-La Castellana (06°06 ′ N, 75°33 ′ W; 2,800 m), Páramo de Belmira (06°38 ′ N, 75°40 ′ W; 3,145 m), and vicinities of Medellín (without precise locality—Günther 1879; Delgado-V. and Zurc 2005), the Department of Valle del Cauca (without precise locality—Rojas-Díaz et al. 2012), and the municipality of

Salento (04°38 ′ N, 75°34 ′ W; 2,740 m), Department of Quindío (Universidad del Valle [UV 3368]— Alberico et al. 2000). In the Eastern Cordillera from the Department of Cundinamarca – Carpanta, Junín (04°36 ′ 07.09 ″ N, 73°39 ′ 29.64 ″ W; 2,400 m [ICN 17047]—Muñoz et al. 2000), Chingaza Natural National Park (Pérez-Torres and Correa 1997; Muñoz et al. 2000), Choachí (04°32 ′ N, 73°56 ′ W; 1,924 m; National Museum of Natural History, Smithsonian Institution [USNM 091820]), San Cristobal, Bogotá (04°34 ′ 0.00 ″ N, 74°04 ′ 59.99 ″ W; 2,600 m; Field Museum of Natural History, Chicago [FMNH 71128–71129]), Fómeque (about 04°29 ′ N, 73°53 ′ W; 1,980 m [AMNH 36245]— Allen 1914; María 1914), Soacha, Finca El Soche, 15 km W of Soacha (04°34 ′ 59.88 ″ N, 74°13 ′ 00.12 ″ W; 3,000 m [IAvH 1218, IAvH 3857]—Muñoz et al. 2000), and Tabio, Reserva Passiflora (04°55 ′ 420.20 ″ N, 74°6 ′ 53.30 ″ W; 1,912 m—Liévano-Latorre and López-Arévalo 2015). Southernmost records are represented by specimens collected in La Cocha, Nudo de Los Pastos in the Department of Nariño (UV 9710—Ramírez-Chaves and Noguera-Urbano 2011). Although it has been suggested that the genus Olallamys is endemic to the Chocó rainforest ( Fabre et al. 2013), O. albicaudus is only known from the Andes region of Colombia ( Fig. 3 ). No fossils are known.

FORM AND FUNCTION

The baculum of Olallamys albicaudus ranges between 6 and 9.5 mm in length (n = 2). It is barely convex, narrow, swollen, slightly raised at the proximal end (1.5–1.6 mm, n = 2), and the ventral surface is flat and incised with small lateral edge marks. The distal end (1.0– 1.1 mm, n = 2) forms a small cup, which bears a long extension of cartilage; the proximal extremity increases in size forming a marked and large angulation, which is slightly narrow at the proximal end, but larger than the distal end ( Didier 1962). The dental formula of O. albicaudus is i 1/1, p 1/1, m 3/3, total 20.

ECOLOGY

Little is known of the habitat preferences and the natural history of Olallamys albicaudus other than the information from the localities where the reported specimens have been found (see Emmons et al. 2015), mainly because the species is arboreal ( Emmons 2005), inconspicuous, and inhabits high-elevation bamboo tickets which makes it difficult to capture (Delgado-V. and Zurc 2005). It is known from mountain ecosystems (2,000 –3,200 m), including Páramos, in Central and Eastern Cordillera, and the Nudo de Los Pastos ( Alberico et al. 2000; Delgado-V. and Zurc 2005; Ramírez- Chaves and Noguera-Urbano 2011). It has a preference for dense bamboo thickets in montane forests ( Eisenberg 1989). In Cundinamarca, O. albicaudus has been found in Andean forest with predominance of Chusquea tessellata . A nest with 3 individuals was found in May 1914 in high-elevation bamboo thickets ( Chusquea ) in Fómeque, Cundinamarca (María 1914). Additional dental remains have been found in scats of crab-eating fox ( Cerdocyon thous ) in 2 localities of the Central Cordillera in the Department of Antioquia (Delgado-V. and Zurc 2005). Although it has been suggested that O. albicaudus inhabits the Chocó rainforest ( Fabre et al. 2013), the data available for this species indicate that this is unlikely. One specimen from Nariño (UV 9710) tested negative for the Pichindé virus (Trapido and Sanmartín 1971), and 3 specimens from Cundinamarca (IAvH 1218, IAvH 3857, UV unknown number) tested negative for Echinococcus ( D’Alessandro et al. 1981) .

GENETICS

Two studies have evaluated the phylogenetic position of Olallamys albicaudus . Upham et al. (2013, 2015) used sequences of 1 mitochondrial (cyt- b) and 2 nuclear markers (GHR and vWF) of O. albicaudus and additional markers (e.g., 12S, RAG1) from other species (e.g., bamboo rats— Kannabateomys amblyonyx and Dactylomys ) to study the evolution of caviomorph rodents. The genetic material of O. albicaudus was obtained from 2 historic specimens housed at the Field Museum of Natural History (FMNH 71128 and 71129), collected in Bogotá, San Cristobal. The analyses placed O. albicaudus as part of a clade formed by Kannabateomys , Olallamys , and Dactylomys , these 3 groups shared a most recent common ancestor of about 10.3 million

years ago (Upham et al. 2013, 2015). The Amazon is suggested as the ancestral geographic range of all bamboo rats, with a post- Pliocene dispersal of Olallamys to its current endemic range in the Andes (Upham et al. 2013).

CONSERVATION

Olallamys albicaudus is only known from a total of 17 records from 12 localities: 14 museum specimens, 2 cranial fragments and molars found in scats (e.g., Delgado-V. and Zurc 2005), and 1 video and photographic record (Liévano-Latorre and López-Arévalo 2015). Two specimens deposited in the collection of the Universidad de La Salle, Bogota, collected with the holotype of Thrinacodus apolinari (María 1914) are lost and probably were destroyed in a fire that affected the collection in 1948 (Mantilla-Meluk et al. 2014).

Globally, O. albicaudus is considered “Data Deficient” by the International Union for Conservation of Nature because of the known patchy distribution and insufficient records (Delgado and Gómez-Laverde 2008). However, Olallamys might be at a high risk of extinction because it is endemic to a small peripheral Andean ecosystem in comparison with other representatives of the family ( Emmons 2005). O. albicaudus has been reported in some protected areas: Chingaza National Natural Park, Reserva Carpanta, and Reserva Passiflora (Department of Cundinamarca), and Reserva San Sebastián-La Castellana (Department of Antioquia). A major threat to O. albicaudus is the deforestation of the Colombian Andean ecosystems (Delgado and Gómez-Laverde 2008).

Figures

Fig. 1.—Dorsal, ventral, and lateral views of a study skin of Olallamys albicaudus (AMNH [American Museum of Natural History] 36245; holotype of Thrinacodus apolinari) from Fómeque, Department of Cundinamarca, Colombia.

Fig. 2.—Dorsal, ventral, and lateral (inverted) views of skull and lateral view of mandible of an adult (sex unknown) Olallamys albicaudus (AMNH [American Museum of Natural History] 36245; holotype of Thrinacodus apolinari) from Fómeque, Department of Cundinamarca, Colombia; collected by Apolinar María on 7 March 1914. Condylobasal length is 50.75 mm.

Fig. 3.—Geographic distribution of Olallamys albicaudus. Localities of sampled specimens obtained from collections records and literature are indicated by triangles.