LONG-TAILED FAT-TAILED OPOSSUM Thylamys macrurus FAUNA PARAGUAY

Thylamys macrurus (Olfers, 1818)
TAX: Class Mammalia; Subclass Theria; Infraclass Metatheria; Order Didelphimorphia; Family Didelphidae; Subfamily Didelphinae, Tribe Monodelphini (Myers et al 2006, Gardner 2007). The genus Thylamys was defined by Gray, 1843 and Palma et al (2002) concluded that the genus was differentiated during the Pleistocene. The species currently recognised as Thylamys correspond roughly to the "elegans-group" as defined in the monography by Tate (1933). There are nine known species according to the latest revision (Gardner 2007) two of which are present in Paraguay. The genus Thylamys is from the Greek meaning "pouched mouse". The species name macrurus is Greek meaning "long-tailed". The species is monotypic. The species was described by Olfers (1818) as Didelphys macrura, based on de Azara´s (1801: 290) "Micouré à longue queue" with restricted type locality as Tapuá, Departamento Presidente Hayes, Paraguay". No holotype was designated (Brown 2004). Some authors (Redford & Eisenberg 1992) recognise the descriptor as (Desmarest 1827) whose Didelphis grisea was also based on de Azara´s description. The earliest official description based on de Azara´s "Micouré à longue queue" was by Oken (1816) but his name was non-Linnean and hence unavailable. In fact Azara´s original description lacked precision, was apparently based on an immature specimen (Hershkovitz 1959) and could refer to any small, greyish mouse opossum (Gardner 2007). In recent literature the species has frequently been referred to as Marmosa marmota marmota (Tate 1933) and Marmosa grisea (Cabrera 1958). Following an analysis of nucelotide sequence data from the mitochondrial cytochrome-b gene, Braun et al (2005) concluded that the species was strongly differentiated from other species in the genus and Palma et al (2002) concluded in an earlier molecular analysis that it was in fact the most primitive taxon and that migration of this species across the Rio Paraguay may have given rise to the evolution of Thylamys pusillus. Synonyms adapted from Gardner (2007):
[Didelphys] macroura Illiger 1815:107. Nomen nudum.
[Didelphys] marmota Oken 1816:1140. Name unavailable.
[D]idelphys. macrura Olfers 1818:205. Based on de Azara (1801:290). Type locality "Tapoua" =Tapuá, Departamento Presidente Hayes, Paraguay.
Didelphis grisea Desmarest 1827:398. Based on de Azara (1801:290). Type locality "Tapoua" =Tapuá, Departamento Presidente Hayes, Paraguay.
[Didelphys (]Grymaeomys[(] griseus Burmeister 1856:83. Name combination.
T[hylamys]. marmota Allen & Chapman 1897:28. Name combination but not Marmosa marmota Thomas (1896).
[Didelphys (Marmosa)] grisea Trouessart 1898:1241. Name correction.
Marmosa grisea Bertoni 1914:69. Name combination.
[Didelphis (Thylamys)] grisea Matschie 1916:271. Name combination.
Marmosa marmota marmota Tate 1933:218. Name combination but not Marmosa marmota Thomas (1896).
Marmosa pusilla Hershkovitz 1959:338. In part. Not Didelphis pusilla Desmarest (1804).
Marmosa (Thylamys) grisea Kirsch & Calaby 1977:14. Name combination.
[Thylamys] griseus Reig, Kirsch & Marshall 1987:7. Name combination.
T[hylamys].macrura Gardner & Creighton 1989:4. First use of modern name and incorrect gender.
Thylamys grisea Contreras & Contreras 1992:1. Name combination and incorrect gender.
ENG: Long-tailed Fat-tailed Opossum (Canevari & Vaccaro 2007), Paraguayan Thylamys (Gardner 2007), Paraguayan Fat-tailed Mouse Opossum (IUCN 2009).
ESP: No known names.
GUA: No known names.
DES: A medium-sized, corpulent mouse opossum with short, dense, smooth fur. Dorsally they are darkest, being greyish-brown, fading to light grey on the flanks and with a slight reddish tone on the shoulders. Darker dorsal colouration extends down the centre of the head as a medial line, the hairs being grey-based and white with dark tips except for the area above the eye and in front of the ears where they are white-based with dark tips. Dorsal pelage is composed of long guard hairs (10-12mm) which are grey for the basal third, darker distally and occasionally white-tipped; and shorter cover hairs (9-10mm) which are four-banded, grey basally and distally, changing to dark brown and creamy with dark tips. Ventrally they are creamy-white or pure white, with guard hairs 7-8mm long and cover hairs 5-6mm long and a very narrow 3mm wide line of greyish hairs along the flanks. A highly-developed gular gland may stain the surrounding pelage yellowish. Eyes large, surrounded by narrow black patch that extends only slightly in front of the eye and onto the cheeks. Ears large, naked and reddish-brown in colour. A tuft of white fur is present behind the ears. Tail is furred for the basal 1cm, prehensile and c1.3x head and body length. It appears essentially naked without magnification. Colour brownish-grey on the dorsal side basally, greyish distally and pale greyish on the ventral side for its entire length except for a whitish tip. Tail scales are tiny rounded or square in shape and arranged in rings with three hairs pair scale. The central hair of each caudal scale triplet is longer (4–5 scales long vs. 2–3 scales long) and thicker than the lateral hairs. The prehensile tip lacks hairs and is approximately 20mm long. Though it is often stated that there is no evidence of tail incrassination in this species, Carmignotto & Monfort (2006) found evidence of slight incrassination in all the specimens that they examined. Limbs are grey dorsally and whitish ventrally, those of the forelimbs paler dorsally. Feet are small and white with ungual tufts and short digits. The toes are long with short claws that do not extend beyond the apical pads of the forefeet, but are slightly longer on the hindfeet. Six separate pads are present on each foot, with large granules and dermatoglyphs on the palmar and plantar surfaces. Females lack a marsupium and have bilaterally symmetrical rows of teats including inguinal, abdominal and pectoral teats. The area around the teats may be stained pinkish-cinnamon in some individuals. The scrotum of males is darkly-pigmented and covered with self-pigmented hairs (Tate 1933, Canevari & Vaccaro 2007, Gardner 2007, Carmignotto & Monfort 2006, Solari 2003). CR - Skull robust, with broad zygomatic arch and slender rostrum. Brain case moderately broad. Nasals long and rounded posteriorly. They show slight expansion at the maxillo-frontal suture, narrowing slightly behind it and the lateral margins are subparallel. Supraorbital crests well-developed and pronounced postorbital constriction. Anterior part of interorbital region broader in males than females, but interorbital constriction not greatly constricted in either sex. Small temporal ridges may converge on the parietal. In the male the temporal ridges form an incipient crest on the interparietal but in the female are separated by 2-3mm. Petrosals are laterally exposed in a fenestra between the squamosal and parietal bones. Zygomatic arches slightly expanded and and the external surface of the jugals exhibits a conspicuous concavity along the anterior margin of the zygomata. Lambdoidal crests moderately-developed. Lacrimal foramina large and laterally-exposed in orbital margins. Palate broad and highly fenestrated with maxillopalatine, palatine, and maxillary openings. Posterolateral palatal foramina are large and reach the lingual apices of the protocones of M4. Incisive foramina extend posteriorly to the midline of the canines and are widest anteriorly, narrowing in the middle to posterior portion. Tympanic bullae well-developed but proportionately smaller than in other members of the genus. Carmignotto & Monfort (2006) give the following measurements for 8 specimens (3 male, 4 female and one of indeterminate sex) from Matto Grosso do Sul, Brazil and Paraguay without distinguishing between the sexes: Basal Length: 31.47mm (+/-1.41); Greatest Cranial Length: 32.02mm (+/-1.46); Greatest Cranial Height: 10.26mm (+/-0.44); Width of Braincase: 12.09mm (+/-0.38); Greatest Zygomatic Width: 17.63mm (+/-1.17); Length of Nasals: 13.6mm (+/-1.06); Width of Nasals: 2.96mm (+/-0.32); Palate Length: 16.61mm (+/-0.68); Palate Width: 10.05mm (+/-0.58); Interorbital Constriction: 5.14mm (+/-0.56); Postorbital Constriction: 5.33mm (+/-0.22); Width of Rostrum: 5.24mm (+/-0.47); Width Across Bullae: 11.47mm (+/-0.56); Width Between Bullae: 5.20mm (+/-0.36); Bullae Width: 3.11mm (+/-0.08); Minimum Pterygoid Bridge Width: 2.71mm (+/-0.14); Mandibular Length: 23.22mm (+/-1.56). Tate (1933) and Contreras & Contreras (1992) published the following skull measurements: Basal Length: male 31.8mm, female 31.3mm; Greatest Cranial Length: male 34.9mm, female 33.5mm; Greatest Zygomatic Width: male 18.6-19.8mm, female 19mm; Mandible Length: male 26-27.2mm, female 25.9mm; Length of Nasals: male 15.1-16.3mm, female 14mm; Palate Length: male 18.6mm, female 17.5mm; Bullae Width: male 3.5mm, female 3.5mm. DF: I5/4 C1/1 P 3/3 M 4/4 = 50. Incisors increase in size from I2 to I5. Canines well-developed with posterior accessory cusps. P3 exceeds P2 in height and anteroposterior length. Molar rows convergent. Molars are compressed antero-posteriorly, especially M4. Stylar cusp C is well developed on the upper molars, and is similar in size to stylar cusps B and D in M1, and smaller than stylar cusps B and D in M2 and M3. The ectoflexus is serrated giving the stylar shelf a serrated profile in lingual view. Carmignotto & Monfort (2006) give the following measurements for 8 specimens (3 male, 4 female and one of indeterminate sex) from Matto Grosso do Sul, Brazil and Paraguay without distinguishing between the sexes: Length of Upper Toothrow: 12.38mm (+/-0.42); Length of Upper M1-M4: 6.14mm (+/-0.21); Length of Mandibular Row of Molars: 6.93mm (+/-0.17); Upper Canine Length: 2.43mm (+/-0.37); Upper Canine Width: 1.48mm (+/-0.11); Upper P3 Length: 1.76mm (+/-0.33). Tate (1933) and Contreras & Contreras (1992) give the following for Paraguayan specimens: Length of Mandibular Row of Molars male 7-7.4mm, female 7.3mm. CN: 2n=14; FN=20. X chromosomes are small acrocentrics (Palma 1995).
TRA: No information.
MMT: The larger of the two Paraguayan Thylamys and second only to Micoureus paraguayanus in size amongst the Paraguayan Mouse Opossums. There is evidence of some sexual size dimorphism with males being larger than females in most measurements (Cáceres et al 2007). The following measurements are taken from Cáceres et al (2007) for specimens in southeastern Brazil: HB: male 12.24cm (+/-1.11, n=31) female 11.13cm (+/-5.3, n=12); TA: male 13.84cm (+/-0.79, n=31) female 13.39cm (+/-0.55, n=12) approximately 1.2x head and body length; FT: male 1.69cm (+/-0.14, n=30) female 1.58cm (+/-0.1, n=12); EA: male 2.14cm (+/-0.28, n=30) female 1.92cm (+/-0.24, n=12); WT: male 52.4g (+/-12.2, n=37) female 41g (+/-10, n=17). Carmignotto & Monfort (2006) give the following measurements for 8 specimens (3 male, 4 female and one of indeterminate sex) from Matto Grosso do Sul, Brazil and Paraguay without distinguishing between the sexes: HB: 11.2cm (+/-1.02); TA: 14.45cm (+/-0.67) approximately 1.3x head and body length; FT: 1.75cm (+/-0.09); EA: 2.35cm (+/-0.23); WT: 38.83g (+/-9.92). Contreras & Contreras (1992) cite the following measurements for two male specimens from Paraguay, the first of unknown provenance and the second from Cordillera de los Altos, Departamento Paraguarí: TL: 28cm, 29.2cm; HB: 14.5cm, 13.1cm; TA: 13.5cm, 16.1cm; FT (including claw): 1.9cm, 2.02cm; EA: 2.3cm, 2.85cm; and the following for a single female specimen from Sapucaí, Departamento Paraguarí: TL: 30.8cm; HB: 14.7cm; TA: 16.1cm; FT (including claw): 1.8cm; EA: 2.5cm.
SSP: Members of the genus Thylamys can be distinguished from other mouse opossums by their noticeably bicoloured pelage, being darker dorsally and paler laterally, and by the densely-granulated soles of the feet. Furthermore female Thylamys have the teats arranged in bilaterally symmetrical rows and not in a circular pattern as in other mouse opossums. The only other member of the genus present in Paraguay is Thylamys pusillus, which is principally distinguished on size, being typically <35g in weight and with a tail typically much less than 135mm in length (compared to >40g and >135mm in this species). Note that this species frequently shows a whitish tip to the tail which is absent in T.pusillus. The two species of Thylamys are apparently allopatric, this species being so far only conclusively recorded in eastern Paraguay, whilst T.pusillus appears to be confined to the Chaco. Cranially the posterolateral foramen does not exceed M4 in this species, though it does in T.pusillus.
DIS: The geographical range of this species is poorly known and it may prove to be more widespread than is currently thought. In Brazil it occurs from near Campo Grande, Mato Grosso do Sul in the north and east, south to north-eastern Paraguay. Anderson (1997) provides details of a single specimen from Santa Cruz, Bolivia, the first record for that country. It may be present in the southern Pantanal of Brazil where suitable habitat is apparently present. (Cáceres et al 2007). In Paraguay specimens are known from Asunción, Departamento Central, Departamento Concepción, Pedro Juan Caballero, Departamento Amambay, Coronel Oviedo, Departamento Caaguazú and Sapucaí and Cordillera de los Altos, Departamento Paraguarí, and there is a literature citation from San Ignacio, Departamento Misiones (Contreras & Contreras 1992). The original description of the species was based on de Azara´s vague description of his "Micouré à longue queue" which failed to conclusively identify this species. The type locality given was Tapuá, Departamento Presidente Hayes (Gardner 2007), but Tate (1933) quotes Schuller (undated) in stating that the location of Tapuá is "a few miles northeast of Asunción" at 25º 10´ 25" latitude and 0º 9´ 11" taking Asunción as a meridian of 0º, which presumably places it on the east bank of the Rio Paraguay in Departamento Central. Given the uncertainty over the identity of de Azara´s specimen, the precise locality of Tupuá and the lack of further specimens from the Chaco we prefer to consider its presence on the western bank of the Río Paraguay as hypothetical pending new information.
HAB: Though traditionally considered a species of semideciduous forest (Cannevari & Vaccaro 2007), Cáceres et al (2007) called that into question and demonstrated that the species occurs in open shrubby savanna and cerrado, including cerradón in southwestern Brazil. In fact they considered that functional adaptations were typical of an open-country species and hypothesised that once its distribution is better known it may prove to be present in humid chaco, transitional dry forests and arboreal savannas. They suggested that the presence of the species in forest could be explained by a scansorial mode of life. Carmignotto & Monfort (2006) state that the species is exclusively found in cerrado in Brazil with specimens collected in dense cerrado sensu stricto.
ALI: Considered primarily an insectivore with omnivorous tendencies (Cannevari & Vaccaro 2007), though no detailled information has ever been published on the diet of the species. Cáceres et al (2007) captured individuals in Rio Grande do Sul, Brazil in traps baited with a mixture of bacon, pumpkin, and cod liver oil.
REP: Cáceres et al (2007) caught only one juvenile in the dry season (July) in Mato Grosso do Sul, Brazil compared to 32 in the wet season (October to March), despite the same trapping effort. More males were caught (35/57 total captures) during the dry season (April to September) and more females (27/40 total captures) during the wet season (October to March). The authors speculated that the differences in trapping success between the sexes (with more males than females captured) coupled with the sexual size dimorphism was possibly indicative of a non-monogamous social system owing to the fact that males are more mobile when in search of mates. The higher trapping rate of males in the dry season and bias of juveniles captured in the wet season was associated with a highly seasonal breeding system beginning in the dry season when males search for mates and culminating in the wet season with the birth and growth of young. Females would thus be expected to be more active in the wet season whilst occupied with lactation and care of young and this was also supported by the greater trapping success of females during that season.
BEH: Activity Levels Considered crepuscular in behaviour (Cannevari & Vaccaro 2007). Cáceres et al (2007) caught this species on the ground and in the understorey using pitfall and baited live traps. Previous authors had considered the species arboreal, but they seem more adapted to a scansorial way of life and 32 of 39 (82%) released individuals opted for a terrestrial escape compared to just 7 (18%) which climbed the nearest tree. However the species does have some adaptations to suggest that they are more arboreal than other members of the genus, including longer, more pointed toes and claws. Parasites Cáceres et al (2007) found the following parasites on six individuals from Matto Grosso do Sul, Brazil: Tick Argas miniatus (17 individuals present on 100% of specimens), Trombiculinae (3 individuals; 17% prevalence) and lice Gyropus lenti lenti (1 individuals; 17% prevalence).
VOC: No information.
HUM: None.
CON: Globally considered to be of Low Risk Near Threatened by the IUCN, click here to see their latest assessment of the species on account of an inferred population decline due to habitat destruction and conversion to agriculture. The limited information available on the biology of this species makes it threat status difficult to assess, though Cáceres et al (2007) found it to be the commonest small marsupial in their study area in Mato Grosso do Sul, Brazil. Few specimens are known from Paraguay, but sampling effort has been sporadic and of low intensity, and the species may theoretically be more widespread than is currently known. However habitat destruction is occurring rapidly in eastern Paraguay and like many mammal species with specialist habitat requirements it is undoubtedly declining. The species occurs in some protected areas in Paraguay but apparently does not in Brazil.
Citable Reference: Smith P (2009) FAUNA Paraguay Online Handbook of Paraguayan Fauna Mammal Species Account 31 Thylamys macrurus.
Last Updated: 16 January 2009.
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ACKNOWLEDGEMENTS
Special thanks to Juan Carlos Chebez for providing important literature and Nilton Cáceres for very kindly reviewing texts and providing a copy of his book Os Marsupiais do Brasil.