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3.3.1 Metachirus aritanai new species 3.3.1.1 Synonymy (Didelphys [Metachirus]) nudicaudata: Trouessart 1989:1236; part, not M. nudicaudatus (Geoffroy St. Hilaire 1803). [Philander] nudicaudatus: Pine 1973:391; part, not M. nudicaudatus (Geoffroy St. Hilaire 1803). M. nudicaudatus: Patton et al. 2000:61–64; not M. nudicaudatus (Geoffroy St. Hilaire 1803); first evidence that Metachirus from Pará represented a new taxon. M [etachirus]. n [udicaudatus]. nudicaudatus: Gardner and Dagosto 2007:37; part, not M. nudicaudatus (Geoffroy St. Hilaire 1803). Holotype: An adult male consisting of skin and skull (INPA 2831, original number CS 83), in addition to tissue sample preserved in ethanol, collected on 8 July 1999 by Maria Nazareth F. da Silva in the Tapirapé-Aquiri National Forest, Marabá, Pará, Brazil (05° 46′ 53.10″ S; 50° 31′ 48.60″ W; Figure 1). MC, male from the Carajás region; FC, females from the Carajás region; MN, male of M. nudicaudatus; FN, females of M. nudicaudatus; MM, males of M.myosuros; FM,females of M.myosuros; MCC,maximal cranial circumference;NAS,nasal bone length;RWJ,rostrum width between the jugal bones;RWF, rostrum width between the frontal bonés;NW, greater nasal width; CI, interorbital constriction; PC,postorbital constriction; WZ,width between zygomatic arches; GCW, greatest cranial width; MAX, length of the maxillary row of teeth; LUM, length of the upper molar series; CAN, width between the lateral margins of the upper canines; WPP, width of the palatal projection; WM, width between the external faces of the third molars; LLM, length of the lower molar series; JL, jaw length. Paratypes ( N = 19): Eight adult females (N = 8) consisting of skins, skulls and tissues preserved in ethanol; two adult males (N = 2) consisting of skins, skulls and tissues preserved in ethanol; and five sub-adult and young individuals (N = 9) consisting of specimens preserved in fluid, skull and tissues. Adult females: two specimens (PSA 06; PSA 200) were collected by Cleuton L. Miranda in the Tapirapé-Aquiri National Forest, municipality of Marabá, Pará, Brazil and will be cataloged in the mammal collection of MPEG. Three specimens were collected by Natalia C. Ardente, two (MN 78307; MN 79953) in the Carajás National Forest, municipality of Marabá, Pará, Brazil, and one (MN 75549) in the Tapirapé-Aquiri National Forest, municipality of Marabá, Pará, Brazil. The three remaining specimens (LBCE 14843, 14845, 14859) were collected by Fabiana Caramaschi, Cibele R. Bonvicino and Paulo Sérgio D’ Andrea in the Vila Santa Cruz, Araguatins municipality, State of Tocantins, Brazil, and will be cataloged in the mammal collection of MN. Adult male specimens: two specimens (MN 73864; MN 78309) were collected by Natalia C. Ardente in the Carajás National Forest, State of Pará, Brazil. Sub-adult and young specimens: nine specimens were collected by Marco Antonio R. Junior and Stepheson Abrantes; five specimens (MAR 890, 1165, 1292, 1407, 1409) were collected in the Caxiuanã National Forest, municipality of Portel, Pará, Brazil, and will be cataloged in the mammal collection of MPEG; Four specimens (CN 78, 83, 91, 240) were collected in Bom Futuro on the left margin of the middle Xingu River, Pará, Brazil, and will be cataloged in MPEG. Type locality: Tapirapé-Aquiri National Forest, municipality of Marabá, state of Pará, Brazil (05° 46′ 53.10″ S; 50° 31′ 48.60″ W; Figure 1). Etymology: The name M. aritanai is given in honor of the great leader Aritana Yawalapiti (1949–2020), of the Yawalapiti ethnicity, from the upper Xingu River region and in honour of all indigenous peoples of Brazil. The leader Aritana died in August 2020, a victim of covid-19, representing a great loss for the Xingu people, all indigenous peoples, and all Brazilians. Distribution: M. aritanai new species is restricted to the Xingu-Tocantins interfluve, the endemism center Xingu sensu Silva et al. (2005). As far as we know M. aritanai new species is endemic to this biogeographic region (Figure 1). The species is bounded to the north by the Amazon River, to the west by the Xingu River and to the east by the Tocantins River. The southern boundary cannot yet be clearly defined. According to the consensus topology and times of divergence presented in this study, a sister species of M. aritanai new species, M. nudicaudatus, occurs north of the Amazon River (Figures 2 and 3). Diagnosis: M. aritanai new species is characterized by the combination of the following characters: general colouration light brown with speckles of gold on the back; small amount of rust hair behind the ears; supra-ocular spots of cream colour; cheeks with the same colouration as supra-ocular spots; brown and gold-speckled face; absence of median stripe on the rostrum; the presence of a narrow, blackened dorsal line at the top of the head, usually extending to the nape of the neck; clear ventral surface, usually pure cream, wide interorbital region (average = 12.12 mm) and with incipient ridges; rounded and inflated cranial cavity, with large maxillopalatine (average = 24.68 mm) and fenestrae; small entoconids; absent or incipient temporal crest. Figures 5–7 show the mentioned characters, except for the morphology of the entoconid, which is similar to that of M. nudicaudatus and may be seen in Figure 15, page 46 in Voss et al. (2019). 3.4 Description 3.4.1 External morphology Combined length of adult head and body ca. 230 mm on average (ranging 243–275 mm); adult weight ca. 380 g. Midrostral fur cream coloured with apical portion dark brown (most of the cream-coloured hairs have black tips, but there are also completely blackened or cream hairs in lesser quantities, somewhat like the dorsal coat). Dark median rostral stripe absent or inconspicuous. Dark circumocular mask present (blackened), extending posteriorly to the base of the ear, continuous with the coronal fur. Narrow dark brown dorsal line starting at the coronal spot and extending to the end of the nape. Throat gland present in adult males. Small pure cream supraocular spots present, usually in the shape of an inverted triangle, varying in size. Pure cream-coloured cheeks, of the same colour as the supraocular spots. Completely brown ears. Presence of small amounts of rust hair behind the base of the ears. General colouration light brown speckled with gold. Dorsal colour pale brown, with grey-based hairs, cream stripe over most of its length and short blackish apex, giving the back a golden speckled appearance. Dorsal hairs usually do not exceed 10 mm in length. Dorsal guard hairs short, dark, and inconspicuous. Lateral portions of the body brown and lighter than the back. Ventral pelage usually pure cream, similar in colour to the supra-ocular spots and cheeks. Mammae 4–1–4 = 9, all abdominal inguinal. Pouch absent. Tail is light brown to dark brown, dorsal discolouring gradually towards the distal portion; ventral surface of the tail not pigmented. Scales without a consistent arrangement (both spiral and annular patterns coexisting). Tail longer than the length of the head and body, covered with 5–10 mm long hairs on all sides at the base. Hands and feet covered with cream-coloured hair, like the ventral coat; Manus mesaxonic (d III> d IV); Carpal tubercles absent in mature adult males. 3.4.2 Cranium-dental morphology Cranium wide and robust. Relatively elongated face. Nasal branch of the premaxilla developed. Rostral process of the premaxilla absent. Long nasal bone, widely enlarged in the region of the maxillary/frontal suture. Mandible developed, with elongated and deep infraorbital foramen at the height of the Pm2. Interorbital region-wide (average = 12.12 mm) with incipient ridges. Lacrimal bone extends in the rostrum to the anterior margin of the orbital cavity, surpassing the two exposed lacrimal foramina. Zygomatic arch well developed, composed by the jugal and squamosal. Postorbital process of the jugal absent. Postorbital process of the frontal absent. Palatine articulates ventrally with mandible and dorsally with frontal. Frontal quite developed extending from the posterior region of the nasal branch of the mandible to the posterior region of the cranium, where it articulates with the parietal. Supraorbital crest imperceptible. Absent or incipient temporal crest. When incipient, the crest most often extends from the frontal to the parietal, where it can be joined to the midline of the cranium and extend to the lambdoidal crest. Lamboidal crest not developed. Sagittal crests absent in the anterior part of the occiput. Parietal articulates anteriorly with the frontal, but they are separated by median sutures on the right and on the left. Parietal articulates posteriorly with the supra-occipital and mastoid. Squamosal in contact with the frontal on the side of the cranium. Parietal and alisphenoid not in contact. Petrosal not exposed laterally. Squamosal parietal fenestra absent. Parietal and mastoid normally in contact. Interparietal not in contact with squamosal. Palate long, wide and composed mostly by the mandible, which articulates with the palatal branch of the pre-mandible at the height of the well-developed incisor foramen. Mandible articulates anteriorly with the palate. Maxillopalatine large (average = 24.68 mm) and fenestrated. Mandible and alisphenoid not connected at the bottom of the orbital region, separated by the palatine. Foramen of transverse canal absent. Tympanic process of alisphenoid laterally compressed and non-globular, slightly pointed or rounded. Anterior member of ectotympanic suspended directly from the basicranium. Paraoccipital process broad, erect, and ventrally projected. Dorsal margin of the foramen magnum in contact with exoccipital. Well-developed mandible. Dental formula i5/4, c1/1, pm3/3, m4/4. First upper premolar smaller than the second, well developed and non-vestigial. Second and third upper premolars equivalent in height. Post-metacrist bigger than post-protocrist in molars. The lower third premolar, when deciduous, has three cusps. Entoconids small. 3.4.3 Morphological variation We did not observe differences in the external morphology of males and females within any of the considered age groups (young, sub-adult or adult). However, there were significant age-related morphological differences. Young and sub-adult individuals had a general greyish and darker colour than adult individuals. Yet, sub-adults also exhibit some diagnostic characters of M. aritanai new species, such as cream supra-ocular spots and cheeks of the same colour, absence of median stripe on the rostrum and cream-pure ventral surface (Table 5). 3.4.4 Comparisons M. aritanai new species differs from the nominal form, M. nudicaudatus (sensu Voss et al. 2019 and present study) and from M. myosuros from the Atlantic Forest (sensu present study) by their dorsal colouring (light brown speckled with gold in M. aritanai vs. brown speckled with black and light orange in M. nudicaudatus, vs. brown-orange to light brown in M. myosuros); ventral surface colouring (purecream in M. aritanai vs. yellow-cream in M. nudicaudatus, vs. yellowish hues in M. myosuros); colouring of the sides of the body (similar to the dorsum but slightly lighter in M. aritanai vs. orange-brown, visibly lighter than the dorsum with conspicuous blackish and orange hairs in M. nudicaudatus vs. yellow with a variety of light greyish and even golden hues of grey and golden in M. myosuros); colouring of the supra-ocular spots (cream in M. aritanai vs. cream and slightly orange, especially at the edges in M. nudicaudatus, vs. yellow to cream in M. myosuros); lighter hair behind the ears (yellowish and in small amounts in M. aritanai vs. rust and in large quantities in M. nudicaudatus, vs. yellowish hues in M. myosuros); hair colour on the tarsus (cream in M. aritanai vs. brownish-orange in M. nudicaudatus, vs. varying hues from blackish to brownish-grey with golden fur in M. myosuros); width and robustness of the skull (wider and more robust in M. aritanai vs. narrower and more delicate in both M. nudicaudatus and M. myosuros); nasal width in relation to the maxillary (much narrower than the pre-maxillary in the initial portion and similar width in the end portion with a rounder end near frontal bone in M. aritanai vs. much narrower than the pre-maxillary in the initial portion and similar width in the end portion with a tapered end near frontal in both M. nudicaudatus and M. myosuros); contour of the pre-maxillary (wider, short and pointed in M. aritanai vs. narrower, long and rounded in M. nudicaudatus, vs. narrower, long and pointed in M. myosuros); frontal edges (irregular in the posterior portion with the presence of a protuberance in the median region in M. aritanai vs. more regular and rounded limit, without the presence of a median protuberance in M. nudicaudatus, vs. usually developed and pointed in M. myosuros); average differences in mitochondrial sequences of the Cytb gene (between M. aritanai and M. nudicaudatus = 8.2%; between M. aritanai and M. myosuros = 14.4%; Table 5; Figures 5–7)., Published as part of Miranda, Cleuton Lima, Nunes, Mario da Silva, Fabrício Machado, Arielli, Farias, Izeni Pires, Menezes, Fernando Heberson, Ardente, Natalia Carneiro, Dos Santos-Filho, Manoel, Bredin, Yennie Katarina & da Silva, Maria Nazareth F., 2023, A new species of jupati, genus Metachirus Burmeister 1854 (Didelphimorphia, Didelphidae) for the Brazilian Amazon, pp. 172-189 in Mammalia (Warsaw, Poland) (Warsaw, Poland) 87 (2) on pages 178-184, DOI: 10.1515/mammalia-2021-0176, http://zenodo.org/record/7837851, {"references":["Trouessart, E. - L. (1989). Catalogus mammalium tam viventium quam fossilium. Fasciculus V. Sirenia, Cetacea, Edentata, Marsupialia, Allotheria, Monotremata., 2. R. Friedlander & Sohn, Berolini, pp. 999 - 1264.","Pine, R. H. (1973). Anatomical and nomenclatural notes on opossums. Proc. Biol. Soc. Washington 86: 391 - 402.","Patton, J. L., da Silva, M. N. F., and Malcolm, J. R. (2000). Mammals of the Rio Jurua and the evolutionary and ecological diversification of Amazonia. Bull. Am. Mus. Nat. Hist. 244: 1 - 306.","Gardner, A. L. and Dagosto, M. (2007). Tribe Metachirini. In: Gardner, A. L. (Ed.). Mammals of South America. Volume 1: marsupials, xenarthrans, shrews, and bats. University of Chicago Press, Chicago, pp. 35 - 39.","Silva, J. M. C., Rylands, A. B., and da Fonseca, G. A. B. (2005). The fate of the Amazonian areas of rndemism. Conserv. Biol. 19: 689 - 694.","Voss, R. S., Fleck, D. W., and Jansa, S. A. (2019). Mammalian diversity and Matses ethnomammalogy in Amazonian Peru. Part 3. Marsupials (Didelphimorphia). Bull. Am. Mus. Nat. Hist. 432: 1 - 87."]}

3.3.1 Metachirus aritanai new species 3.3.1.1 Synonymy (Didelphys [Metachirus]) nudicaudata: Trouessart 1989:1236; part, not M. nudicaudatus (Geoffroy St. Hilaire 1803). [Philander] nudicaudatus: Pine 1973:391; part, not M. nudicaudatus (Geoffroy St. Hilaire 1803). M. nudicaudatus: Patton et al. 2000:61–64; not M. nudicaudatus (Geoffroy St. Hilaire 1803); first evidence that Metachirus from Pará represented a new taxon. M [etachirus]. n [udicaudatus]. nudicaudatus: Gardner and Dagosto 2007:37; part, not M. nudicaudatus (Geoffroy St. Hilaire 1803). Holotype: An adult male consisting of skin and skull (INPA 2831, original number CS 83), in addition to tissue sample preserved in ethanol, collected on 8 July 1999 by Maria Nazareth F. da Silva in the Tapirapé-Aquiri National Forest, Marabá, Pará, Brazil (05° 46′ 53.10″ S; 50° 31′ 48.60″ W; Figure 1). MC, male from the Carajás region; FC, females from the Carajás region; MN, male of M. nudicaudatus; FN, females of M. nudicaudatus; MM, males of M.myosuros; FM,females of M.myosuros; MCC,maximal cranial circumference;NAS,nasal bone length;RWJ,rostrum width between the jugal bones;RWF, rostrum width between the frontal bonés;NW, greater nasal width; CI, interorbital constriction; PC,postorbital constriction; WZ,width between zygomatic arches; GCW, greatest cranial width; MAX, length of the maxillary row of teeth; LUM, length of the upper molar series; CAN, width between the lateral margins of the upper canines; WPP, width of the palatal projection; WM, width between the external faces of the third molars; LLM, length of the lower molar series; JL, jaw length. Paratypes ( N = 19): Eight adult females (N = 8) consisting of skins, skulls and tissues preserved in ethanol; two adult males (N = 2) consisting of skins, skulls and tissues preserved in ethanol; and five sub-adult and young individuals (N = 9) consisting of specimens preserved in fluid, skull and tissues. Adult females: two specimens (PSA 06; PSA 200) were collected by Cleuton L. Miranda in the Tapirapé-Aquiri National Forest, municipality of Marabá, Pará, Brazil and will be cataloged in the mammal collection of MPEG. Three specimens were collected by Natalia C. Ardente, two (MN 78307; MN 79953) in the Carajás National Forest, municipality of Marabá, Pará, Brazil, and one (MN 75549) in the Tapirapé-Aquiri National Forest, municipality of Marabá, Pará, Brazil. The three remaining specimens (LBCE 14843, 14845, 14859) were collected by Fabiana Caramaschi, Cibele R. Bonvicino and Paulo Sérgio D’ Andrea in the Vila Santa Cruz, Araguatins municipality, State of Tocantins, Brazil, and will be cataloged in the mammal collection of MN. Adult male specimens: two specimens (MN 73864; MN 78309) were collected by Natalia C. Ardente in the Carajás National Forest, State of Pará, Brazil. Sub-adult and young specimens: nine specimens were collected by Marco Antonio R. Junior and Stepheson Abrantes; five specimens (MAR 890, 1165, 1292, 1407, 1409) were collected in the Caxiuanã National Forest, municipality of Portel, Pará, Brazil, and will be cataloged in the mammal collection of MPEG; Four specimens (CN 78, 83, 91, 240) were collected in Bom Futuro on the left margin of the middle Xingu River, Pará, Brazil, and will be cataloged in MPEG. Type locality: Tapirapé-Aquiri National Forest, municipality of Marabá, state of Pará, Brazil (05° 46′ 53.10″ S; 50° 31′ 48.60″ W; Figure 1). Etymology: The name M. aritanai is given in honor of the great leader Aritana Yawalapiti (1949–2020), of the Yawalapiti ethnicity, from the upper Xingu River region and in honour of all indigenous peoples of Brazil. The leader Aritana died in August 2020, a victim of covid-19, representing a great loss for the Xingu people, all indigenous peoples, and all Brazilians. Distribution: M. aritanai new species is restricted to the Xingu-Tocantins interfluve, the endemism center Xingu sensu Silva et al. (2005). As far as we know M. aritanai new species is endemic to this biogeographic region (Figure 1). The species is bounded to the north by the Amazon River, to the west by the Xingu River and to the east by the Tocantins River. The southern boundary cannot yet be clearly defined. According to the consensus topology and times of divergence presented in this study, a sister species of M. aritanai new species, M. nudicaudatus, occurs north of the Amazon River (Figures 2 and 3). Diagnosis: M. aritanai new species is characterized by the combination of the following characters: general colouration light brown with speckles of gold on the back; small amount of rust hair behind the ears; supra-ocular spots of cream colour; cheeks with the same colouration as supra-ocular spots; brown and gold-speckled face; absence of median stripe on the rostrum; the presence of a narrow, blackened dorsal line at the top of the head, usually extending to the nape of the neck; clear ventral surface, usually pure cream, wide interorbital region (average = 12.12 mm) and with incipient ridges; rounded and inflated cranial cavity, with large maxillopalatine (average = 24.68 mm) and fenestrae; small entoconids; absent or incipient temporal crest. Figures 5–7 show the mentioned characters, except for the morphology of the entoconid, which is similar to that of M. nudicaudatus and may be seen in Figure 15, page 46 in Voss et al. (2019). 3.4 Description 3.4.1 External morphology Combined length of adult head and body ca. 230 mm on average (ranging 243–275 mm); adult weight ca. 380 g. Midrostral fur cream coloured with apical portion dark brown (most of the cream-coloured hairs have black tips, but there are also completely blackened or cream hairs in lesser quantities, somewhat like the dorsal coat). Dark median rostral stripe absent or inconspicuous. Dark circumocular mask present (blackened), extending posteriorly to the base of the ear, continuous with the coronal fur. Narrow dark brown dorsal line starting at the coronal spot and extending to the end of the nape. Throat gland present in adult males. Small pure cream supraocular spots present, usually in the shape of an inverted triangle, varying in size. Pure cream-coloured cheeks, of the same colour as the supraocular spots. Completely brown ears. Presence of small amounts of rust hair behind the base of the ears. General colouration light brown speckled with gold. Dorsal colour pale brown, with grey-based hairs, cream stripe over most of its length and short blackish apex, giving the back a golden speckled appearance. Dorsal hairs usually do not exceed 10 mm in length. Dorsal guard hairs short, dark, and inconspicuous. Lateral portions of the body brown and lighter than the back. Ventral pelage usually pure cream, similar in colour to the supra-ocular spots and cheeks. Mammae 4–1–4 = 9, all abdominal inguinal. Pouch absent. Tail is light brown to dark brown, dorsal discolouring gradually towards the distal portion; ventral surface of the tail not pigmented. Scales without a consistent arrangement (both spiral and annular patterns coexisting). Tail longer than the length of the head and body, covered with 5–10 mm long hairs on all sides at the base. Hands and feet covered with cream-coloured hair, like the ventral coat; Manus mesaxonic (d III> d IV); Carpal tubercles absent in mature adult males. 3.4.2 Cranium-dental morphology Cranium wide and robust. Relatively elongated face. Nasal branch of the premaxilla developed. Rostral process of the premaxilla absent. Long nasal bone, widely enlarged in the region of the maxillary/frontal suture. Mandible developed, with elongated and deep infraorbital foramen at the height of the Pm2. Interorbital region-wide (average = 12.12 mm) with incipient ridges. Lacrimal bone extends in the rostrum to the anterior margin of the orbital cavity, surpassing the two exposed lacrimal foramina. Zygomatic arch well developed, composed by the jugal and squamosal. Postorbital process of the jugal absent. Postorbital process of the frontal absent. Palatine articulates ventrally with mandible and dorsally with frontal. Frontal quite developed extending from the posterior region of the nasal branch of the mandible to the posterior region of the cranium, where it articulates with the parietal. Supraorbital crest imperceptible. Absent or incipient temporal crest. When incipient, the crest most often extends from the frontal to the parietal, where it can be joined to the midline of the cranium and extend to the lambdoidal crest. Lamboidal crest not developed. Sagittal crests absent in the anterior part of the occiput. Parietal articulates anteriorly with the frontal, but they are separated by median sutures on the right and on the left. Parietal articulates posteriorly with the supra-occipital and mastoid. Squamosal in contact with the frontal on the side of the cranium. Parietal and alisphenoid not in contact. Petrosal not exposed laterally. Squamosal parietal fenestra absent. Parietal and mastoid normally in contact. Interparietal not in contact with squamosal. Palate long, wide and composed mostly by the mandible, which articulates with the palatal branch of the pre-mandible at the height of the well-developed incisor foramen. Mandible articulates anteriorly with the palate. Maxillopalatine large (average = 24.68 mm) and fenestrated. Mandible and alisphenoid not connected at the bottom of the orbital region, separated by the palatine. Foramen of transverse canal absent. Tympanic process of alisphenoid laterally compressed and non-globular, slightly pointed or rounded. Anterior member of ectotympanic suspended directly from the basicranium. Paraoccipital process broad, erect, and ventrally projected. Dorsal margin of the foramen magnum in contact with exoccipital. Well-developed mandible. Dental formula i5/4, c1/1, pm3/3, m4/4. First upper premolar smaller than the second, well developed and non-vestigial. Second and third upper premolars equivalent in height. Post-metacrist bigger than post-protocrist in molars. The lower third premolar, when deciduous, has three cusps. Entoconids small. 3.4.3 Morphological variation We did not observe differences in the external morphology of males and females within any of the considered age groups (young, sub-adult or adult). However, there were significant age-related morphological differences. Young and sub-adult individuals had a general greyish and darker colour than adult individuals. Yet, sub-adults also exhibit some diagnostic characters of M. aritanai new species, such as cream supra-ocular spots and cheeks of the same colour, absence of median stripe on the rostrum and cream-pure ventral surface (Table 5). 3.4.4 Comparisons M. aritanai new species differs from the nominal form, M. nudicaudatus (sensu Voss et al. 2019 and present study) and from M. myosuros from the Atlantic Forest (sensu present study) by their dorsal colouring (light brown speckled with gold in M. aritanai vs. brown speckled with black and light orange in M. nudicaudatus, vs. brown-orange to light brown in M. myosuros); ventral surface colouring (purecream in M. aritanai vs. yellow-cream in M. nudicaudatus, vs. yellowish hues in M. myosuros); colouring of the sides of the body (similar to the dorsum but slightly lighter in M. aritanai vs. orange-brown, visibly lighter than the dorsum with conspicuous blackish and orange hairs in M. nudicaudatus vs. yellow with a variety of light greyish and even golden hues of grey and golden in M. myosuros); colouring of the supra-ocular spots (cream in M. aritanai vs. cream and slightly orange, especially at the edges in M. nudicaudatus, vs. yellow to cream in M. myosuros); lighter hair behind the ears (yellowish and in small amounts in M. aritanai vs. rust and in large quantities in M. nudicaudatus, vs. yellowish hues in M. myosuros); hair colour on the tarsus (cream in M. aritanai vs. brownish-orange in M. nudicaudatus, vs. varying hues from blackish to brownish-grey with golden fur in M. myosuros); width and robustness of the skull (wider and more robust in M. aritanai vs. narrower and more delicate in both M. nudicaudatus and M. myosuros); nasal width in relation to the maxillary (much narrower than the pre-maxillary in the initial portion and similar width in the end portion with a rounder end near frontal bone in M. aritanai vs. much narrower than the pre-maxillary in the initial portion and similar width in the end portion with a tapered end near frontal in both M. nudicaudatus and M. myosuros); contour of the pre-maxillary (wider, short and pointed in M. aritanai vs. narrower, long and rounded in M. nudicaudatus, vs. narrower, long and pointed in M. myosuros); frontal edges (irregular in the posterior portion with the presence of a protuberance in the median region in M. aritanai vs. more regular and rounded limit, without the presence of a median protuberance in M. nudicaudatus, vs. usually developed and pointed in M. myosuros); average differences in mitochondrial sequences of the Cytb gene (between M. aritanai and M. nudicaudatus = 8.2%; between M. aritanai and M. myosuros = 14.4%; Table 5; Figures 5–7).