Transandinomys talamancae is a rodent in the family Cricetidae that occurs from Costa Rica to southwestern Ecuador and northern Venezuela. Its habitat consists of lowland forests up to above sea level. With a body mass of , it is a medium-sized rice rat. The fur is soft and is reddish to brownish on the upperparts and white to buff on the underparts. The tail is dark brown above and lighter below and the ears and feet are long. The vibrissae (whiskers) are very long. In the skull, the rostrum (front part) is long and the braincase is low. The number of chromosomes varies from 34 to 54.
The species was first described in 1891 by Joel Asaph Allen and thereafter a variety of names, now considered synonyms, were applied to local populations. It was lumped into a widespread species "Oryzomys capito" (now Hylaeamys megacephalus) from the 1960s until the 1980s and the current allocation of synonyms dates from 1998. It was placed in the genus Oryzomys until 2006, as Oryzomys talamancae, but it is not closely related to the type species of that genus and was therefore moved to a separate genus Transandinomys in 2006. It shares this genus with Transandinomys bolivaris, which has even longer vibrissae; the two overlap broadly in distribution and are morphologically similar.
Active during the night, Transandinomys talamancae lives on the ground and eats plants and insects. Males move more and have larger home ranges than most females. It breeds throughout the year, although few individuals survive for more than a year. After a gestation period of about 28 days, two to five young are born, which reach sexual maturity within two months. A variety of parasites occur on this species. Widespread and common, it is of no conservation concern.
Taxonomy In 1891, Joel Asaph Allen was the first to scientifically describe Transandinomys talamancae, when he named Oryzomys talamancae from a specimen from Talamanca, Costa Rica. He placed it in the genus Oryzomys, then more broadly defined than it is now, and compared it to both the marsh rice rat (O. palustris) and to O. laticeps.Allen, 1891, pp. 193–194 Several other names that are now recognized as synonyms of Transandinomys talamancae were introduced in the following years. In 1899, Allen described Oryzomys mollipilosus, O. magdalenae, and O. villosus from Magdalena Department, Colombia.Allen, 1899, pp. 208–210; Musser et al., 1998, pp. 273–274 Oldfield Thomas added O. sylvaticus from Santa Rosa, Ecuador in 1900Thomas, 1900, pp. 272–273 and O. panamensis from Panama City, Panama, in 1901.Thomas, 1901, pp. 252–253 In the same year, Wirt Robinson and Markus Lyon named Oryzomys medius from near La Guaira, Venezuela.Robinson and Lyon, 1901, pp. 142–143 Allen added O. carrikeri from Talamanca, Costa Rica, in 1908.Allen, 1908, pp. 656–657
Edward Alphonso Goldman revised North American Oryzomys in 1918. He placed both panamensis and carrikeri as synonyms of Oryzomys talamancae and mentioned O. mollipilosus and O. medius as closely related species. O. talamancae was the only member of its own species group, which Goldman regarded as closest to Oryzomys bombycinus (=Transandinomys bolivaris).Goldman, 1918, pp. 71–74 In 1960, Philip Hershkovitz listed talamancae, medius, magdalenae, sylvaticus, and mollipilosus among the many synonyms of "Oryzomys laticeps", a name later replaced by "Oryzomys capito".Hershkovitz, 1960, p. 544; Musser et al., 1998, p. 179 The species remained lumped under Oryzomys capito until 1983, when Alfred Gardner again listed it as a valid species, an action more fully documented by Guy Musser and Marina Williams in 1985.Musser and Williams, 1985, p. 9 Musser and Williams also found that the holotype of Oryzomys villosus, the affinities of which had been disputed, in fact consisted of a skin of O. talamancae and a skull of the Oryzomys albigularis group (equivalent to the current genus Nephelomys). They restricted the name to the skin, making villosus a synonym of O. talamancae.Musser and Williams, 1985, p. 7 They also examined the holotypes of panamensis, carrikeri, mollipilosus, medius, and magdalenae and identified them as examples of Oryzomys talamancae. Additionally, they included sylvaticus and Oryzomys castaneus J.A. Allen, 1901, from Ecuador as synonyms, but without examining the holotypes.Musser and Williams, 1985, pp. 13–14 Musser and colleagues reviewed the group again in 1998 and confirmed that sylvaticus represents Oryzomys talamancae; however, they found that castaneus was in fact an example of Oryzomys bolivaris (the current Transandinomys bolivaris).Musser et al., 1998, pp. 275–276
In 2006, Marcelo Weksler published a phylogenetic analysis of Oryzomyini ("rice rats"), the tribe to which Oryzomys is allocated, using morphological data and DNA sequences from the IRBP gene. His results showed species of Oryzomys dispersed across Oryzomyini and suggested that most species in the genus should be allocated to new genera.Weksler, 2006, pp. 75–77 Oryzomys talamancae was also included; it appeared within "clade B", together with other species formerly associated with Oryzomys capito. Some analyses placed it closest to species now placed in Euryoryzomys or Nephelomys, but with low support.Weksler, 2006, figs. 34–39 Later in the same year, he, together with Alexandre Percequillo and Robert Voss, named ten new genera for species previously placed in Oryzomys, including Transandinomys, which has Oryzomys talamancae (now Transandinomys talamancae) as its type species. They also included Oryzomys bolivaris, which was not included in Weksler's phylogenetic study, in this new genus. The two species are morphologically similar, but Weksler and colleagues could identify only one synapomorphy (shared-derived trait) for them: very long superciliary vibrissae (vibrissae, or whiskers, above the eyes).Weksler et al., 2006, p. 26 Transandinomys is one of about 30 genera in Oryzomyini, a diverse assemblage of American rodents of over a hundred species,Weksler, 2006, p. 3 and on higher taxonomic levels in the subfamily Sigmodontinae of family Cricetidae, along with hundreds of other species of mainly small rodents.Musser and Carleton, 2005
Several common names have been proposed for Transandinomys talamancae, including "Talamanca Rice Rat",Goldman, 1918, p. 73 "Transandean Oryzomys", and "Talamancan Rice Rat".
Description Transandinomys talamancae is a medium-sized, brightly colored rice rat.Musser and Williams, 1985, p. 14; Musser et al., 1998, p. 173 It is similar to T. bolivaris and the two are often confused.Musser et al., 1998, p. 125 They are about as large, but in T. talamancae the tail is longer and the hindfeet shorter.Musser et al., 1998, p. 127 Both species share uniquely long vibrissae, with both the mystacial (above the mouth) and superciliary vibrissae extending to or beyond the back margin of the ears when laid back against the head, but those in T. bolivaris are substantially longer. H. alfaroi, a widespread species ranging from Mexico to Ecuador, is also similar.Musser et al., 1998, pp. 167, 169 It is smaller and darker, but young adult T. talamancae are similar in color to adult H. alfaroi and often misidentified.Musser et al., 1998, p. 169 Hylaeamys megacephalus, with which T. talamancae was synonymized for some decades, is similar in body size, but is not known to overlap with T. talamancae in range.Musser and Williams, 1985, p. 18; Musser et al., 1998, p. 169
The fur is short, dense and soft in Transandinomys talamancae;Musser and Williams, 1985, p. 14 in T. bolivaris, it is longer and even more soft and dense.Musser et al., 1998, pp. 127–128 The color of the upperparts varies from reddish to brownish, becoming lighter towards the sides and the cheeks. The underparts are white to buff, with the bases of the hairs plumbeous (lead-colored). The fur of T. bolivaris is darker: dark brown above and dark gray below. H. megacephalus also has darker fur.Musser et al., 1998, p. 173 Juveniles have thin, gray fur, which is molted into the dark brown subadult fur when the animal is about 35 to 40 days old. This fur is replaced by the bright adult fur at age 49 to 56 days.Fleming, 1970, p. 479 Juveniles are never blackish as in T. bolivaris.Musser et al., 1998, pp. 128–129 The ears are dark brown, large, and densely covered with very small hairs. + Measurements of Transandinomys talamancaeMusser and Williams, 1985, table 2 Country nNumber of specimens measured. Head and body Tail Hindfoot Ear Panama 22 124.4 (101–136) 124.7 (110–143) 29.2 (27–32) 21.1 (16–25) Colombia 13 135.2 (120–151) 125.2 (114–140) 29.5 (27–32) 19.0 (18–22) Ecuador 2019 for tail length. 124 (118–136) 128.5 (118–137) 29.1 (28–31) – Measurements are in millimeters and in the form "average (minimum–maximum)". The sparsely haired tail is approximately as long as the head and body.Goldman, 1918, p. 71 It is dark brown above and lighter below. In contrast, the tail of H. megacephalus has little to no difference in color between the upper and lower surface. In 2006, Weksler and colleagues noted tail coloration as a difference between the two species of Transandinomys (bicolored in T. talamancae and unicolored in T. bolivaris), but in their 1998 study, Musser and colleagues could not find differences in tail coloration between their Panamanian samples of the two species.Musser et al., 1998, p. 129
The hindfeet are long and have the three central digits longer than the two outer ones. They are white to pale yellow above, where the foot is covered with hairs, which are longer than in T. bolivaris.Musser et al., 1998, p. 131 The digits of the hindfeet are surrounded by ungual tufts of silvery hair that are longer than the claws themselves.Goldman, 1918, pp. 71–72 The claws are short and sharp.Goldman, 1918, p. 72 Parts of the sole are covered by indistinct scales (squamae), which are usually entirely absent in T. bolivaris.Weksler et al., 2006, p. 25; Musser et al., 1998, p. 124 The pads are moderately large.
The length of the head and body is , tail length , hindfoot length , ear length , and body mass .Linares, 1998, p. 287; Tirira, 2007, p. 200; Reid, 2009, p. 208 As in most oryzomyines, females have eight mammae.Weksler, 2006, pp. 17, 19 There are 12 thoracic vertebra with associated ribs, 7 lumbars, and 29 caudals; a pair of supernumerary (additional) ribs is occasionally present.Steppan, 1995, table 5
Skull and teeth
The skull has a long rostrum (front part), a broad interorbital region (between the eyes), and a low braincase.Goldman, 1918, p. 73; Musser and Williams, 1985, p. 14 It differs from that of T. bolivaris in various proportions, which are more apparent in adults than in juveniles; the skull of H. megacephalus is distinctly larger. The zygomatic plate is broad and includes a well-developed zygomatic notch at its front. Its back margin is level with the front of the first upper molar.Weksler, 2006, pp. 31–32 The zygomatic arch (cheekbone) is heavy. The nasal and premaxillary bones extend about as far backward. The interorbital region is narrowest toward the front and shows weak beading at its margins;Weksler, 2006, p. 29, table 5 T. bolivaris is similar, but has stronger beading and H. megacephalus entirely lacks the beading.Musser et al., 1998, p. 174 The parietal bone is usually limited to the roof of the braincase and does not extend to its side, as it does in most T. bolivaris.Musser et al., 1998, p. 135 The interparietal bone, part of the roof of the braincase, is large.