Melomys burtoni (Ramsay, 1887)
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publication ID |
https://doi.org/ 10.1515/mammalia-2016-0137 |
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DOI |
https://doi.org/10.5281/zenodo.7859566 |
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persistent identifier |
https://treatment.plazi.org/id/03D45355-FFD0-FF90-7378-F93C1CEDF97A |
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treatment provided by |
Felipe |
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scientific name |
Melomys burtoni |
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Melomys burtoni View in CoL View at ENA from Halmahera
Referred specimens
Ten specimens of Melomys burtoni from Halmahera were caught near the Gemaf and Sagea villages on June 2010 and September 2013 ( MZB 33533 View Materials , 33537 View Materials , 33539 View Materials , 33540 View Materials , GoogleMaps
33225, 36359, 36360, 36361, 36362, 36363), and eight specimens were collected on the South ( MZB 33538 View Materials ) and North Ake Jira ( Sake River ; MZB 33223 View Materials , 33224 View Materials , 33226 View Materials , 33534 View Materials , 33536 View Materials , 33541 View Materials , 33552 View Materials ) in January 2010, 19 km NW of Gemaf and 26 km NW of Sagea at the GPS coordinates 00°37′23.8″N, 127°55′12.6″E ( South Ake Jira ) and 00°38′49.9″N, 127°56′01.2″E ( North Ake Jira ); GoogleMaps Ake Sake ( Sake River ), 5 km NW of the village of Gemaf and 12 km NW of the village of Sagea , Central Halmahera , Halmahera Island , Indonesia, at an altitude of 22 m, at the GPS coordinates 00°29′14.6″N, 127°59′15.7″E (see Figure 1 View Figure 1 ). Their current altitudinal range is 0 from 250 m. Seventeen specimens are prepared as study skins with accompanying skulls. GoogleMaps
Distribution
Currently, Melomys burtoni from Halmahera is known only from the south-central region of the North Moluccan
island of Halmahera ( Figure 1 View Figure 1 ). The species has been collected in lowland forest and forest edge habitats, at elevations between 0 and 250 m. We suspect that it may occur more broadly in other regions in the tropical lowland evergreen rain forest ( Whitmore et al. 1984) in Halmahera, and on neighbouring islands such as Morotai and perhaps Bacan, but little is yet known of its biology and distribution. Previous efforts to survey the rodent fauna of Halmahera and adjacent islands (specimens deposited at AM, AMNH, MZB, USNM), which have documented two native rodent species ( Rattus morotaiensis and Halmaheramys bokimekot ) and several non-native rodents ( Rattus exulans , R. tanezumi / R. rattus , and Mus ), have not yet documented Melomys in other areas of Halmahera or on Morotai or Bacan. However, rodent collecting efforts in the North Moluccas have been very limited to date. Sampling was done at higher elevation in Halmahera by us (900– 1000 m, cf. boki mekot locality Fabre et al. 2013) and also other mammalogists ( Flannery 1995a,b), but M. burtoni were never collected above 250 m.
Measurements
See Tables 4–6 View Table 4 .
Diagnosis
Melomys burtoni from Halmahera can be distinguished from congeners by the following external characters: (1) relatively small body size, e.g. as compared to M. aerosus and M. fulgens of Seram ( Helgen 2003) ( Tate 1951, Menzies
1996, see also Figures 6 View Figure 6 and 7 View Figure 7 ; Tables 5 and 6 View Table 6 ); (2) head-body length is nearly equal to the tail length (103 % of the body length, but see also Figures 6 View Figure 6 and 7 View Figure 7 ) compared to the long-tailed M. obiensis (127 % of the body length); (3) dorsal fur dark brown or red-brown with dark gray bases; (4) ventral fur pure white along mid-ventral region of underparts and grayish on the sides; (5) dorsal surfaces of the forefeet and hindfeet pale brown with scattered rufous hairs; (6) tail usually dark above and below (some specimens have a paler underside), with three hairs per tail scale; (7) brown ears relatively long and large.
Craniodental features diagnostic in combination include (1) a long rostrum, topped by broad nasals and slightly convex at the premaxillary tips ( Figures 5 View Figure 5 , 8 View Figure 8 and 9 View Figure 9 ); (2) a narrow interorbital region with concave borders ( Figure 8 View Figure 8 ); (3) large palatine foramina ( Figure 10 View Figure 10 ), (4) long incisive foramina that extend posteriorly to the start of the molar rows ( Figures 4 View Figure 4 , 5 View Figure 5 and 10 View Figure 10 ), (5) relatively longer incisive foramina and shorter tympanic bullae compared with all other species sampled here ( Figures 4 View Figure 4 , 5 View Figure 5 and 10 View Figure 10 ). Following Menzies (1996), Melomys burtoni from Halmahera belongs within the “ cervinipes division” and more
specifically is a member of the M. burtoni species group that includes M. burtoni of Australia, M. lutillus and M. frigicola of New Guinea, and four insular taxa distributed both west and east of New Guinea ( M. bannisteri , M. cooperae , M. howi , M. paveli ). Six species ( M. aerosus , M. caurinus , M. fulgens , M. obiensis , M. fraterculus , M. talaudium ) from the Moluccan region should not be included in this group due to lack of data as well as their relative morphological divergence.
Description
Melomys burtoni from Halmahera ( Figures 6 View Figure 6 , 7 View Figure 7 , and 11) is relatively small in body size (head-body length 110–141 mm) with short, dense, and soft pelage. Dorsal fur ranges from dark-brown to red-brown; the hairs are bicolored, uniformly gray to blackish at the bases (the proximal 1/4 of the length) and brightly rufous distally. Dorsal guard hairs are soft, short, and pliable, project up to 7 mm beyond the overfur, and are glistening black for most of their length with some reddish tips. The ventral coat is pure white the length of the midventral region and grayish towards the flanks. We detect major chromatic differences between the pelage of an old adult (n = 1), and other adults (n = 15). The old individual MZB 53533 has an overall darker coat and large body size, but is molecularly identical to all other M. burtoni specimens from Halmahera. The studied juvenile (n = 1) display a finer and duller colour tone and a more greyish fur compared to the adults.
The snout of Melomys burtoni from Halmahera is reddish-brown to yellowish above, and white on the sides and underside. The rhinarium and lips are unpigmented. The eyes are small (diameter about 5 mm). Vibrissae are dark gray. Mystacial and superciliary vibrissae are moderately long, extending slightly beyond the ears. The pinnae are relatively small and brown, with a sparse covering of reddish brown hairs on both the inner and outer surfaces.
The tail is nearly equal in length to the combined head and body length (only exceeding HBL in the specimen MZB 33533) ( Tables 4 View Table 4 and 6 View Table 6 ). The tail is dark brown to blackish on the entire surface, except for the proximal portion (10–25 mm), which is unpigmented in some specimens (MZB 33533, 33552). Tail scales are smooth and less raised compared to those in species of the M. rufescens Division ( Menzies 1996), and moderately large (14–15 rows/cm). There are three hairs per tail scale (each 1–2 mm long), which is characteristic of the M. cervinipes Division, as described by Menzies (1996). Tail hairs are dark brown.
Dorsal surfaces of the forefeet and hindfeet are pale brown or unpigmented ( Figures 6 View Figure 6 ) and sparsely covered with short reddish or brownish hairs on top of the metapodials and laterally on the digits. At the base of each claw, long white hairs form ungual tufts. The pollex is very short and bears a flat nail. The other front digits are longer and broader with curved, sharp, white claws. Each palmar surface is hairless, unpigmented, and displays three interdigital pads and two large metacarpal pads. The hindfeet
of Melomys burtoni from Halmahera are shorter than those of M. obiensis and those of M. frigicola ( Tables 4 View Table 4 and 5). Digits are elongated and broad, and each bears a
pale claw that is short, sharp, and recurved. The hallux extends past the middle part of the medial digits. The 5th digit is slightly shorter than the medial digits and has a large associated interdigital pad. The plantar surface is naked and unpigmented, with four large interdigital pads, an elongate thenar pad, and a very small hypothenar pad.
As in all Melomys species, it has only two pairs of inguinal teats (0 + 2 = 4).
The skull of Melomys burtoni from Halmahera ( Figure 11 View Figure 11 ) is smaller than most Moluccan species of Melomys and similar to M. burtoni and allies in most dimensions ( Figures 4 View Figure 4 , 8–10 View Figure 8 View Figure 9 View Figure 10 ). In dorsal view, the rostrum is narrow and short ( Figure 11 View Figure 11 ). The interorbital region is moderately narrow and defined by concave borders. The postorbital region is elongate and the inflated braincase has a rounded outline. The temporal ridges that extend from the supraorbital region to the dorsolateral surfaces of the braincase are slightly developed. Robust zygomatic arches bow out from rostrum and braincase.
In lateral view ( Figures 9 View Figure 9 and 11 View Figure 11 ), the dorsal profile of the skull is broadly convex from the slightly depressed nasal tips to the top of the frontals, straight over the frontals and parietals to the apex of the domed braincase, and sloping abruptly downward over the length of the interparietal. Nasal bones are short with sloping sides that give an angular shape to the tip of the rostrum. The posterior portion of the nasals are flat with nearly no concavity at the junction with the proximal end of the frontal. The zygomatic plate is narrower and the zygomatic notch shallower than in other Moluccan Melomys . The dorsal root and anterior portion of the zygomatic arch are slightly broadened. The squamosal root of the arch is positioned at the medial portion of the braincase. A subsquamosal fenestra is not present. Each auditory bulla is small ( Figures 4 View Figure 4 , 5 View Figure 5 , 10 View Figure 10 , and 11) and separated from the squamosal by a small postglenoid vacuity and from the alisphenoid by a narrow middle lacerate foramen. The lambdoid crest is poorly developed.
The ventral view of the skull ( Figures 10 View Figure 10 and 11 View Figure 11 ) shows long incisive foramina ( Figures 4 View Figure 4 and 5 View Figure 5 ) that project posteriorly beyond the anterior margins of the first molars. The palate is narrow (BPPM1 and BPPM3) and short (LBP). Each palatine foramen is large, positioned between the anterior and posterior roots of the M2, and opens anteriorly into a well-defined palatal sulcus that runs forward to the posterolateral margin of the incisive foramina. The mesopterygoid fossa is moderately broad. The lateral pterygoid fossae are shallow and contain large sphenopterygoid vacuities. The skull exhibits bony landmarks consistent with the primitive pattern of cephalic arterial circulation found in most murine rodents ( Musser and Heaney 1992), as in other Melomys ( Menzies 1996) .
The upper and lower molars of Melomys burtoni from Halmahera are brachydont and broader compared to M. lutillus from Papua and M. burtoni from Australia ( Figures 12 View Figure 12 and 13 View Figure 13 ; Tables 6 View Table 6 and 7 View Table 7 ). Each molar overlaps with its neighbour. The first upper and lower molars form nearly half of the entire toothrow, the second about onethird of the row, with the last molar much smaller than the others ( Figures 12 View Figure 12 and 13 View Figure 13 ). The transverse laminae of the upper molars (rows 1 and 2 of M1 and row 2 of M2) display a posteriorly oriented, angular U-shape with a typically acuspidate chevron pattern (characteristic of Melomys , Paramelomys and Uromys ). The first row is formed by a medium-sized cusp t1 slightly separated from a wide central cusp t2, which in turn is broadly fused with a smaller cusp t3. The second row is composed of a large backward-directed lingual cusp t4 that is attached to a wide and narrow central cusp t5 and a large labial cusp t6, which is smaller than t4. The third row is formed by a large, angular cusp t8 joined to a cusp t9 that projects straight to the labial side. The second molar consists of two laminae with a medium-sized cusp t1. The first lower molar has an oblong outline and three rows of cusps ( Figure 13 View Figure 13 ). The anterior 2/3 of the molar is formed by small anterolingual and anterolabial cusps that are slightly separated in unworn teeth from the second cusp row (metaconid, protoconid). The metaconid and protoconid are large, with a triangular shape, and fused in specimens displaying worn teeth (e.g. MZB 33533; Figure 13 View Figure 13 ). A large entoconid and hypoconid comprise the third cusp row, behind which is a broad but anteroposteriorly narrow posterior cingulum. The subsquare second lower molar has two cusp rows and a posterior cingulum. The pattern and shape of the lamina are similar in cusp shape and pattern to first lower molar. There is a small anterolabial cusplet on the anterolabial margin of the second lower molar close to the protoconid. The small third lower molar displays a rounded shape and a simple occlusal surface with two laminar cusp rows and a posterior cingulum. The molars of Melomys burtoni from Halmahera have multiple roots, which were identified by a µCT scanner. Below each first upper molar, we found one large anterior root, two smaller lingual anchors, one labial root and one large posterior root. Four roots anchor each second molar, there are two anterior roots and two posterior anchor. Three roots anchor each third molar, there are two anterior roots and one posterior anchor. One anterior and posterior roots coupled with smaller labial and lingual anchors attach to each first lower molar. The second lower molars are anchored by two anterior and two posterior roots. The third lower molars are anchored by two anterior and one posterior roots. The alveoli patterns of upper and lower molar roots seen in Melomys burtoni from Halmahera are similar to the patterns found for M. lutillus from Papua and M. burtoni from Australia.
Each dentary of Melomys burtoni from Halmahera is moderately long and stocky ( Figure 11 View Figure 11 ), with a short but stout coronoid process, robust condylar process and strong angular process. There is a concave curvature of the posterior margin of the dentary. The capsular process forms a prominent ridge parallel to the coronoid and anterior part of the condylar process. A prominent masseteric crest extends between the ventral margin and the labial part of the dentary just before the mental foramen. The mandibular foramen is located above a narrow ridge that runs caudally from the molar platform to the base of the condylar process.
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