Marmosa isthmica Goldman, 1912

Part, Tate’, The Species In, Mexicana’, And, Closely, Mitis’ Sections And Other & Forms, Related, 2010, A Revision Of The Didelphid Marsupial Genus Marmosa, Bulletin of the American Museum of Natural History 2010 (334), pp. 1-83 : 42-48

Marmosa isthmica Goldman, 1912 Figures 19, 20

Didelphys murina: Thomas, 1880: 403 .

? Didelphys murina: Thomas, 1882b: 111 .? Didelphys murina: Alston, 1880: 200 . Part, not Didelphis murina Linnaeus, 1758 .

Didelphys [(Micoureus)] murina: Thomas, 1888: 343 . Part, not Didelphis murina Linnaeus, 1758 .

? Marmosa murina zeledoni: Allen, 1912: 73 . Part, not Marmosa zeledoni Goldman, 1911 .

Marmosa isthmica Goldman, 1912: 1 . Type locality ‘‘Rio Indio, near Gatun, Canal Zone, Panama.’’

Marmosa isthmica: Anthony, 1916: 363 .

[ Didelphis (Marmosa) ] isthmica: Matschie, 1916: 270 . Name combination.

Marmosa isthmica: Elliot, 1917: 2 .

Marmosa mexicana isthmica: Goldman, 1917: 108 . Name combination.

[ Marmosa (Marmosa) ] mexicana isthmica: Cabrera, 1919: 37 .

Marmosa mimetra Thomas, 1921: 521 . Type locality ‘‘W. Ecuador … Santo Domingo, 0 ° 13 9 S., 79 ° 6 9 W. Alt. 1600 9.’’

Marmosa ruatanica isthmica: Tate, 1933: 125 . Name combination.

Marmosa ruatanica mimetra: Tate, 1933: 126 . Name combination.

Marmosa mitis mimetra: Hershkovitz, 1951: 552 . Name combination.

Marmosa mitis isthmica: Hershkovitz, 1951: 552 . Name combination.

Marmosa [( Marmosa )] robinsoni isthmica: Cabrera, 1958: 24 . Name combination.

Marmosa [( Marmosa )] robinsoni mimetra: Cabrera, 1958: 24 . Name combination.

Marmosa robinsoni: Handley, 1966: 755 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni isthmica: Hall, 1981: 15 .

Marmosa mexicana zeledoni: Hall, 1981: 16 . Part, not Marmosa zeledoni Goldman, 1911 .

Marmosa robinsoni: Honacki et al., 1982: 23 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: O’Connell, 1983: 1 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Eisenberg, 1989: 39 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Gardner, 1993: 18 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Reid, 1997: 48 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Emmons, 1997: 26 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Eisenberg and Redford, 1999: 62 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Nowak, 1999: 21 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Voss and Jansa, 2003: 75 . Part, not Marmosa robinsoni Bangs, 1898 .

Marmosa robinsoni: Brown, 2004: 65 . Part, not Marmosa robinsoni Bangs, 1898 .

[ Marmosa robinsoni ] isthmica: Gardner, 2005: 9 .

[ Marmosa robinsoni ] simonsi: Gardner, 2005: 9 . Part, not Marmosa simonsi Thomas, 1899 .

M [armosa]. r [obinsoni]. isthmica: Creighton and Gardner, 2008: 59 .

M [armosa]. r [obinsoni]. simonsi: Creighton and Gardner, 2008: 59 . Part, not Marmosa simonsi Thomas, 1899 .

TYPE MATERIAL: The holotype (by original designation, USNM 170969) is a mature adult (age class 7) male specimen preserved as a skin and skull, both of which are in good condition.

TYPE LOCALITY: The holotype was collected by E.A. Goldman on 16 February 1911 on the Río Indio (gazetteer entry 103; appendix), a small tidal tributary of the lower Río Chagres, near the town of Gatun, Provincia Colón, Panama. According to Goldman (1912: 2), the type ‘‘was trapped in an old banana plantation only a few feet above sea level.’’ A photograph of the type locality was subsequently published by Goldman (1920: pl. 3, fig. 1).

MORPHOLOGICAL DIAGNOSIS: Midrostral fur usually pale and contrasting sharply with darker fur of crown; dark median rostral stripe absent or inconspicuous; dark facial mask not extending posteriorly to contact base of ear; dorsal body pelage pale to dark orangish brown; dorsal cover hairs 8–12 mm in length, dorsal guard hairs 10–15 mm in length; gray-based ventral pelage conspicuous but usually restricted to the sides of the abdomen, with yellowish or orangish hair tips; self-colored ventral pelage (extending as a continuous median streak from chin to anus) yellowish or orangish. Exposed skin of tail brown, indistinctly bicolored (paler ventrally) in most large specimens, without any clear pattern of scale arrangement (both spiral and annular patterns coexisting); 16– 18 scales/cm on dorsal surface at caudal midlength; caudal scale hairs light brown, usually detectable without magnification; central hair of each caudal-scale triplet usually about 1.5 (sometimes two) scales long. Gular gland present. Mammae 6–1–6 5 13 ( Enders, 1935: 408). Lateral and medial carpal tubercles present in mature adult males; medial carpal tubercle long (reaching the base of the pollex), with subequal but recognizable proximal and distal segments separated by a shallow sulcus.

Length of rostral process of premaxillae similar to I1 height. Orbitosphenoid-alisphe- noid suture usually about twice as long as height of sphenorbital fissure in lateral view. Supraorbital ridges slightly to moderately divergent posteriorly, slender and only slightly produced laterally in younger specimens and females (which usually have indistinct postorbital processes) but becoming much thicker and dorsolaterally produced in mature adult males (which usually have distinct postorbital processes); temporal ridges conspicuous and tending to become strongly convergent posteriorly (behind the postorbital constriction) in mature adult males. Palatine fenestrae absent (but tiny asymmetrical perforations are occasionally present); posterolateral foramina usually longer than M4 (measured across paracone-metacone). Tympanic wing of alisphenoid laterally compressed, with ventral surface globular or slightly pointed; medial process of ectotympanic usually indistinct or absent. I1 hypsodont, normally present in adults; crown of I2 sharply defined in relation to root; preparacrista connected to stylar cusp B on M1-M3; stylar cusps D and E confluent, not separated by a distinct notch on M2.

COMPARISONS: Qualitative and morphometric comparisons among Marmosa isthmica , M. mexicana , and M. zeledoni , all of which have overlapping geographic ranges, are provided in the preceding accounts. The geographic range of M. isthmica also overlaps with that of M. robinsoni in Panama, and it overlaps with that of M. simonsi in western Ecuador. Morphological comparisons with these and other species are provided below.

Marmosa isthmica is larger (on average) and has a relatively longer tail than M. robinsoni , but the two species overlap broadly in all external dimensions (tables 4, 5) and cannot be identified by measurement data alone. In side-by-side comparisons of skins, the two species are most readily distinguished by the more saturated, orangish-brown color of the dorsal pelage in isthmica , by contrast with the usually paler and more yellowishbrown pigmentation of the dorsal fur in robinsoni . Also, the tail appears more sparsely haired in isthmica (in which the central hair of each caudal-scale triplet is only about 1.5 scales long) than in robinsoni (in which the central hair is. 2 scales long). Additionally, the medial carpal tubercle of mature adult male isthmica is long (reaching the base of the pollex) and divided by a shallow sulcus into subequal and morphologically similar proximal and distal segments, whereas the medial carpal tubercle of adult male robinsoni is either short (not reaching the base of the pollex) or (if long) consists of a bulbous proximal knob and a narrower, commashaped distal process.

Cranially, Marmosa isthmica and M. robinsoni differ in the length of the rostral process of the premaxillae (about equal in length to the height of I 1 in isthmica , about half as long as I1 is tall in robinsoni ), in the development of postorbital processes (usually distinct in large specimens of isthmica , usually indistinct in robinsoni ), in the occurrence of palatine fenestrae (consistently absent in isthmica , consistently present in robinsoni ), and in auditory morphology. Auditory differences between these species consist in the size and shape of the alisphenoid tympanic process, which is small, laterally compressed, and usually somewhat pointed ventrally in isthmica versus larger and globular (smoothly rounded ventrally) in robinsoni . Another auditory character is the medial process of the ectotympanic, which is indistinct or altogether absent in isthmica , but which is usually rather well developed in robinsoni .

Marmosa isthmica differs from M. xerophila in all the same characters by which it differs from M. robinsoni , but the contrast in rostral morphology is even more pronounced: the rostral process of the premaxillae (long in isthmica , short in robinsoni ) is completely absent in M. xerophila .

Marmosa isthmica and M. simonsi are easily distinguished by visually obvious morphological differences. Although the two species overlap in all external dimensions (tables 4, 5), isthmica is much the larger species, on average, and it has a relatively longer tail than simonsi . In side-by-side comparisons of skins, the orangish-brown dorsal pelage of isthmica contrasts conspicuously with the grayish-brown fur of simonsi . Ventral pelage differences are also striking: there is always a continuous streak of selfcolored fur that extends from chin to anus in isthmica , whereas almost the entire ventral surface of simonsi is covered by gray-based fur (usually only the fur of the chin, throat, and groin is self-colored). Whereas the medial carpal tubercle of adult male isthmica is long (reaching the base of the pollex), the medial carpal tubercle of simonsi is shorter and does not extend distally to the base of the pollex. The tail, which is entirely dark on its dorsal surface in isthmica , is completely unpigmented (whitish) distally in simonsi . Points of craniodental difference include the rostral process of the premaxillae (long in isthmica , short in simonsi ), palatine fenestrae (absent in isthmica , present in simonsi ), auditory bullae (small and compressed in isthmica , larger and globular in simonsi ), and a notch between stylar cusps D and E (absent in isthmica , present in simonsi ).

Marmosa isthmica is externally similar to M. rubra , but it usually lacks the dark midrostral streak that is usually present in rubra . Other external differences are apparent on close inspection: (1) the gular gland is consistently present in isthmica but absent in rubra ; (2) the medial carpal tubercle of mature adult male specimens is long (extending distally to the base of the pollex) in isthmica , but this tubercle is much shorter and does not extend to the base of the pollex in rubra ; (3) whereas the caudal scales of isthmica are arranged in both spiral and annular series, the caudal scales of rubra are consistently arranged in spiral series. Craniodental differences include the postorbital processes, which are often well developed in large specimens of isthmica , but which are absent or indistinct in all examined specimens of rubra ; and the preparacrista of M1–M3, which is connected to stylar cusp B in isthmica , but which is usually connected to stylar cusp A in rubra .

GEOGRAPHIC DISTRIBUTION AND SYM- PATRY: The known distribution of Marmosa isthmica extends from Ñuri (locality 89; fig. 22) in the Panamanian province of Bocas del Toro eastward across the isthmus and then southward along the Pacific coast of western Colombia to Santa Rosa (locality 188) in the Ecuadorean province of El Oro; M. isthmica also occurs in the Caribbean lowlands of northwestern Colombia, and it extends southward into the inter-Andean valleys of the Río Cauca and the Río Magdalena. Most collection localities are moist lowland and premontane forests below 1700 m elevation, but a few specimens have been collected in dry forests and mangroves, and one specimen has been recorded in the Guajira /Barranquilla Xeric Scrub of Olson et al. (2001).

The range of Marmosa isthmica partially overlaps the distributions of M. mexicana and M. zeledoni , with which it is known to occur sympatrically as described above. The range of M. isthmica also overlaps the distribution of M. robinsoni in Panama, where they have been collected sympatrically at Balboa (locality 91). Lastly, the range of M. isthmica overlaps the distribution of M. simonsi in western Ecuador, where the two species have been collected sympatrically at Santa Rosa (locality 188), Vinces (locality 205), and Río Briceño (locality 210).

GEOGRAPHIC VARIATION: Among the specimens we examined, geographic variation in morphological characters is apparent in pelage color and in the development of supraorbital and temporal ridges. In particular, specimens from Ecuador tend to have less developed supraorbital and temporal ridges by comparison with specimens from Colombia and Panama. Additionally, some specimens from the southern Ecuadorean provinces of Los Ríos and El Oro have intensely yellow-washed pelage in contrast to the darker orangish-brown or yellowishbrown pelage of specimens from northern Ecuador, Colombia, and Panama. As a result, every specimen with yellow-washed pelage has delicate supraorbital and temporal ridges, but not all specimens with delicate supraorbital and temporal ridges have yellowish fur. Neither of the cranial nor coatcolor phenotypes we observed appears to be consistently associated with any of the several ecoregions ( Olson et al., 2001) in which the species has been collected. Because coat color and cranial ornamentation are only partially correlated, and in the absence of other phenotypic evidence of genetic divergence, we provisionally consider M. isthmica to be a monotypic species.

TAXONOMIC HISTORY: The first literature reference to a specimen of Marmosa isthmica is in Thomas (1880), who identified his material as Didelphys murina . Other specimens were subsequently identified by authors as either murina or zeledoni (e.g., by Alston, 1880; Thomas, 1882b, 1888; Allen, 1912). Shortly after Goldman (1912) described Marmosa isthmica based on a single specimen from the Canal Zone of central Panama, Anthony (1916) reported a large series from the eastern Panamanian province of Darién. Just one year later, however, Goldman (1917) treated isthmica as a subspecies of M. mexicana , as did Cabrera (1919).

In his monographic revision of Marmosa, Tate (1933) treated isthmica as a subspecies of M. ruatanica (a member of his Mitis Section, which also included M. chapmani , M. mitis , and M. simonsi as valid species). Hershkovitz (1951), however, regarded all of the nominal taxa in Tate’s Mitis Section as conspecific, listing M. mitis ruatanica and M. mitis isthmica as separate subspecies. Cabrera (1958) accepted Hershkovitz’s taxonomic conclusions, but he correctly pointed out that robinsoni was the oldest available name in Tate’s Mitis Section, and he listed M. robinsoni isthmica as one of several valid South American forms. Most subsequent authors (e.g., Honacki et al., 1982; O’Connell, 1983; Eisenberg, 1989; Emmons, 1997; Nowak, 1999; Brown, 2004) have effectively treated M. robinsoni as monotypic, but Gardner (2005) listed M. r. isthmica as a valid subspecies.

REMARKS: Thomas (1921) described Marmosa mimetra based on four specimens from ‘‘Santo Domingo’’ (5 Santo Domingo de los Colorados, Ecuador; locality 221). Although his description of mimetra strikingly resembles Goldman’s description of isthmica, Thomas considered mimetra to be most similar to Allen’s chapmani from Trinidad. Apparently, Tate (1933: 126) was the first to recognize the essential similarity between isthmica and mimetra —both of which he treated as subspecies of M. ruatanica — remarking that they are separable ‘‘only in certain cases by the stronger cinnamon color of the ventral pelage and the smoother, more shiny tail scales of the latter’’ and adding that ‘‘[s]pecimens from southwestern Colombia are probably transitional.’’ Curiously, however, mimetra was recently included in the synonymy of simonsi by Gardner (2005) and Creighton and Gardner (2008).

We examined the holotypes of isthmica and mimetra , both of which are mature adult males. These specimens are remarkably similar in external and craniodental morphology, except for the slightly more yellowwashed fur of mimetra . Because the pelage color difference is not accompanied by other evidence of genetic divergence, we treat mimetra as a junior synonym of isthmica .

SPECIMENS EXAMINED (N 5 408): PAN- AMA— Bocas del Toro, Ñuri (USNM 575395, 575397–575400). Canal Zone, Balboa (USNM 456810, 456811, 456816, 456819, 456823, 456824, 456827–456832, 456834– 456841), Camp Piña (USNM 301377, 301378, 301546, 302631, 302635, 302636, 303048, 304634, 304636), Chiva Chiva (USNM 302326), Cristóbal (USNM 456842– 456847, 456849–456866), Fort Davis (USNM 297874, 303044), Frijoles (USNM 503421), Gatún (AMNH 36724–36730), Madden Road (USNM 300331–300334, 301135– 301140), Río Indio (USNM 170969 [holotype of Marmosa isthmica Goldman, 1912 ]). Coclé, no other locality data (USNM 303407), El Valle (USNM 304710–304714). Colón, Cuipo Point (5 La Uyama: FMNH 124153), Piña (USNM 318315). Darién, Boca de Río Paya (5 Mouth of Río Paya: USNM 306406–306422; 5 Camp Mack: USNM 314553), Cana (FMNH 53996, 53997; USNM 178614–178616, 178620, 178703– 178707, 178711, 178712, 178971), El Real (AMNH 37576–37579), Jaqué (5 Junction of Ríos Jaque and Imamado: USNM 362318– 362327), Paya Camp (USNM 314554, 314555), Río Chucunaque (USNM 306404, 306405), Río Setegantí (USNM 318120– 318123), Tacarcuna Laguna Camp (USNM 309319–309327), Tacarcuna Village (USNM 309268–309318, 309328, 309329; 5 Mt. Tacarcuna: AMNH 37859; 5 Near G.M.L. Camp: USNM 512870, 512871; 5 Tacarcuna: AMNH 37859–37871, 37873, 37875– 37888, 37891–37893), Tapalisa (AMNH 37889, 37890). Panamá, Cerro Azul (USNM 302414–302416, 302418–302423, 302425– 302428, 302630, 302632–302634, 302637, 302638, 303043, 303045–303047, 303050, 303052–303057, 303232, 303279, 303280, 304637, 306387–306392, 306397–306403, 314552), Cerro Campana (USNM 303406), Cerro Jefe (USNM 306393–306396), Río Pequeni (USNM 318336), Río Trinidad (AMNH 36731, 36732), Tocumen (USNM 304635). San Blas, Armila (5 Quebrada Venado: USNM 335031–335038), Mandinga (USNM 305147–305153). COLOMBIA — Antioquia, Caucasia (USNM 499263), La Tirana (5 25 km S and 22 km W Zaragoza: USNM 499256–499262), Purí (FMNH 69858, 69859), Río Currulao (FMNH 69856, 69857), San Jerónimo (FMNH 69829–69832, 69836, 69852), Valdivia (5 Quebrada Valdivia: FMNH 69828, 69851, 69861, 69862; 5 Quebrada de Oro: FMNH 69860), Villa Arteaga (FMNH 69833–69835, 69839, 69840, 69853, 69854). Caldas, Samaná (FMNH 70978). Chocó, Condoto (BMNH 13.8.10.15, 13.8. 10.16, 14.5.28.29), Unguía (FMNH 69841– 69848, 69855). Córdoba, Socorré (FMNH 69316–69318). Cundinamarca, W of Bogotá (BMNH 95.8.1.34). Nariño, Guayacana (USNM 309046). Sucre, Colosó (5 Las Campañas: FMNH 69319). Valle del Cauca, Lomitas (AMNH 32177), San José (AMNH 31682, 31718), Río Raposo (USNM 334679– 334685). ECUADOR —No other locality data (BMNH 59.11.28.4). Chimborazo, Puente de Chimbo (AMNH 62124, 62125). El Oro, Santa Rosa (AMNH 61392). Esmeraldas, Corondelet (5 Carondelet: BMNH 1.6.5.20), San Javier (BMNH 1.3.19.48, 1.3.19.49; USNM 113319). Guayas, Cerros de Colonche (5 Cerro de Manglaralto: AMNH 64524), Huerta Negra (USNM 534287). Imbabura, Hacienda Paramba (BMNH 1.6.5.19, 99. 12.5.11, 99.12.5.12). Los Ríos, Lima Pareja (USNM 534289), Vinces (5 Near Puerto Nuevo: AMNH 63347–63349; USNM 534288, 534290). Manabí, Cordillera de Balzar (5 Balzar Mts: BMNH 80.5.6.89), Cuaque (5 Coaque: AMNH 64534; FMNH 41248), Río Briceño (5 Bahia de Caraquéz: AMNH 64527–64529), San José (FMNH 53354, 53355). Pichincha, Mindo (BMNH 74.779, 13.10.24.67–13.10.24.69), Nanegal (BMNH 98.5.1.20), Santo Domingo de Los Colorados (BMNH 15.1.1.53, 15.1.1.54 [holotype of Marmosa mimetra Thomas, 1921 ], 15.1.1.55, 15.1.1.57, 15.1.1.59, 15.1.1.60).

OTHER SPECIMENS: In addition to specimens positively identified as Marmosa isthmica , we examined 11 juvenile specimens that we provisionally refer to M. isthmica because they have not developed all of the diagnostic traits that distinguish this species from M. zeledoni .

PANAMA — Canal Zone, Camp Piña ( USNM 301642, 301643, 304631), Fort Sherman ( USNM 296190). Coclé, El Valle ( USNM 304695). Panamá, Cerro Azul ( USNM 302413, 302417, 302424, 303231, 304632), Tocumen ( USNM 304630).